NASA ASTRONAUT LENTICULAR 3D PUZZLE 50pc Last Man on Moon Apollo 17 Cernan space

$35.32 Buy It Now or Best Offer, Click to see shipping cost, eBay Money Back Guarantee
Seller: sidewaysstairsco ✉️ (1,180) 100%, Location: Santa Ana, California, US, Ships to: US & many other countries, Item: 204318890893 NASA ASTRONAUT LENTICULAR 3D PUZZLE 50pc Last Man on Moon Apollo 17 Cernan space. Check out our other new and used items>>>>>HERE! (click me) FOR SALE: An awesome, NASA astronaut-themed lenticular 3D jigsaw puzzle 2020 DISCOVERY "ASTRONAUT" PUZZLE BY PRIME 3D (9" x 6") DETAILS: It's the "Last Man on the Moon" in puzzle form! The Discovery "Astronaut" 50-piece lenticular jigsaw puzzle features a graphic that utilizes an official photograph of a NASA astronuat on the moon during the Apollo 17 mission. Discovery took some artistic liberty by altering the layout and adding more more mesmerizing color and shape to the background. And what makes the puzzle image even more awesome is that Prime 3D Global utilized their high-quality lenticular printing technology to make it "3D" art. The brave NASA moonwalker in the graphic is American astronaut, naval aviator, electrical engineer, aeronautical engineer, and fighter pilot, Gene Cernan. During the last mission of NASA's Apollo program (AKA Project Apollo) Gene Cernan acted as commander and became one of only 12 astronauts ever to walk the moon and he happens to be the last to step off it - earning him the title "The Last Human on the Moon". Prime 3D Global also printed the beautiful graphic on a separate lenticular card and attached it to the front of the box to showcase the puzzle's main feature. This small "3D" art jigsaw puzzle would look great framed! Hang on a deserving wall or display on a shelf or mantel. Perfect for a space-themed bar or man cave. A must have for the lenticular art and space fanatic especially those who collect all things NASA! Brand: Discovery Title: "Astronaut" Year: 2020 Piece Count: 50 Completed Size: 9 x 6 in. (22.9 x 15.2 cm) Manufacturer: Prime 3D Global Country: China CONDITION: New in box. Box may have shelf wear. Please see photos. To ensure safe delivery all items are carefully packaged before shipping out. THANK YOU FOR LOOKING. QUESTIONS? JUST ASK. *ALL PHOTOS AND TEXT ARE INTELLECTUAL PROPERTY OF SIDEWAYS STAIRS CO. ALL RIGHTS RESERVED.* "Eugene Andrew Cernan (/ˈsɜːrnən/; March 14, 1934 – January 16, 2017) was an American astronaut, naval aviator, electrical engineer, aeronautical engineer, and fighter pilot. During the Apollo 17 mission, Cernan became the eleventh human being to walk on the Moon. As he re-entered the Apollo Lunar Module after Harrison Schmitt on their third and final lunar excursion, he remains as of 2023, famously: "The last human on the Moon". Before becoming an astronaut, Cernan graduated with a Bachelor of Science degree in electrical engineering from Purdue University and joined the U.S. Navy through the Naval Reserve Officers Training Corps (NROTC). After flight training, he received his naval aviator wings and served as a fighter pilot. In 1963, he received a Master of Science degree in aeronautical engineering from the U.S. Naval Postgraduate School. Achieving the rank of captain, he retired from the Navy in 1976. Cernan traveled into space three times and to the Moon twice: as pilot of Gemini 9A in June 1966, as lunar module pilot of Apollo 10 in May 1969, and as commander of Apollo 17 in December 1972, the final Apollo lunar landing. Cernan was also a backup crew member of the Gemini 12, Apollo 7 and Apollo 14 space missions. Biography Early years Cernan was born on March 14, 1934, in Chicago, Illinois;[1] he was the son of Andrew George Cernan (1904–1967) and Rose Cernan (née Cihlar; 1898–1991). His father was of Slovak descent and his mother was of Czech ancestry. He had one older sister, Dolores Ann (1929–2019).[2][3] Cernan grew up in the Illinois towns of Bellwood and Maywood. He was a Boy Scout and earned the rank of Second Class.[4] After attending McKinley Elementary School in Bellwood, and graduating from Proviso Township High School in Maywood in 1952, he studied at Purdue University where he became a member of the Phi Gamma Delta fraternity, serving as a treasurer. At Purdue, Cernan was also president of the Quarterdeck Society and the Scabbard and Blade, and a member of the Phi Eta Sigma honor society and Tau Beta Pi engineering honor society. He was on the military ball committee and was a member of the Skull and Crescent leadership honor society.[5] After his sophomore year, he accepted a partial Navy ROTC scholarship that required him to serve aboard USS Roanoke between his junior and senior years. In 1956, Cernan received a Bachelor of Science degree in electrical engineering; his final GPA was 5.1 out of 6.0.[6] Navy service Cernan was commissioned a U.S. Navy Ensign through the Naval Reserve Officers Training Corps (NROTC) at Purdue, and was initially stationed on the USS Saipan. Cernan changed to active duty and attended flying training at Whiting Field, Florida, Barron Field, Texas, NAS Corpus Christi, Texas, and NAS Memphis, Tennessee.[7]: 29–31  Following flight training on the T-28 Trojan, T-33 Shooting Star, and F9F Panther, Cernan became a Naval Aviator, flying FJ-4 Fury and A-4 Skyhawk jets in Attack Squadrons 126 and 113.[7]: 31–33, 38–39  Upon completion of his assignment in NAS Miramar, California, he finished his education in 1963 at the U.S. Naval Postgraduate School with a Master of Science degree in aeronautical engineering.[8] During his naval career, Cernan logged more than 5,000 hours of flying time, including 4,800 hours in jet aircraft. Cernan also made at least 200 successful landings on aircraft carriers.[8] NASA career In October 1963, NASA selected Cernan as one of the third group of astronauts to participate in the Gemini and Apollo space programs.[8] Gemini program Main article: Gemini 9A Cernan aboard Gemini 9A Cernan was originally selected with Thomas Stafford as backup pilot for Gemini 9. When the prime crew of Elliot See and Charles Bassett was killed in the crash of NASA T-38A "901" (USAF serial 63–8181) at Lambert Field, Missouri, on February 28, 1966, the backup crew became the prime crew—the first time in NASA history this happened.[9] Gemini 9A encountered a number of problems; the original target vehicle exploded during launch and the planned docking with a substitute target vehicle was made impossible by the failure of a protective shroud to separate after launch.[9] The crew, however, performed a rendezvous that simulated procedures that would be used in the Apollo 10 mission; the first optical rendezvous and a lunar-orbit-abort rendezvous. Cernan performed the second American EVA, the third-ever spacewalk, but overexertion caused by a lack of limb restraints prevented testing of the Astronaut Maneuvering Unit and forced the early termination of the spacewalk.[9] Cernan was also a backup pilot for the Gemini 12 mission.[10] Apollo program Main articles: Apollo 10 and Apollo 17 Cernan and Snoopy during Apollo 10 press conference Cernan in the LM after EVA 3 on Apollo 17 0:30 Astronauts Cernan and Schmitt singing "The Fountain in the Park" on the Moon during the Apollo 17 mission Cernan at the beginning of EVA 3 The Blue Marble, an iconic photograph of Earth, is credited to the three crewmen of Apollo 17. Apollo 10 Cernan was selected for the lunar module pilot position on the backup crew for Apollo 7—although that flight carried no lunar module.[11] Standard crew rotation put him in place as the Lunar Module Pilot on Apollo 10—the final dress rehearsal mission for the first Apollo lunar landing—on May 18–26, 1969. During the Apollo 10 mission, Cernan and his commander, Tom Stafford, piloted the Lunar Module Snoopy in lunar orbit to within 8.5 nautical miles (15.7 km) of the lunar surface, and successfully executed every phase of a lunar landing up to final powered descent. This provided NASA planners with critical knowledge of technical systems and lunar gravitational conditions to enable Apollo 11 to land on the Moon two months later. Apollo 10 holds the record for the highest speed attained by any crewed vehicle at 39,897 km/h (24,791 mph) – more than 11km per second — during its return from the Moon on May 26, 1969.[10] Apollo 17 Cernan turned down the opportunity to walk on the Moon as Lunar Module Pilot of Apollo 16, preferring to risk missing a flight for the opportunity to command his own mission.[12] Cernan moved back into the Apollo rotation as commander of the backup crew of Cernan, Ronald E. Evans, and Joe Engle for Apollo 14, putting him in position through normal crew rotation to command his own crew on Apollo 17. Escalating budget cutbacks for NASA, however, brought the number of future lunar missions into question. After the cancellation of Apollo 15 in its original H class profile and Apollo 19 in September 1970, pressure from the scientific community to shift Harrison Schmitt, the sole professional geologist in the active Apollo roster of astronauts, to the crew of Apollo 17, the final scheduled Apollo mission, mounted. In August 1971, NASA named Schmitt as the lunar module pilot for Apollo 17, which meant the original LM pilot Joe Engle never had the opportunity to walk on the Moon. Cernan fought to keep his crew together; given the choice of flying with Schmitt as LMP or seeing his entire crew removed from Apollo 17, Cernan chose to fly with Schmitt. Cernan eventually came to have a positive evaluation of Schmitt's abilities; he concluded that Schmitt was an outstanding LM pilot while Engle—notwithstanding his outstanding record as an aircraft test pilot—was merely an adequate one.[13] Cernan's role as commander of Apollo 17 closed out the Apollo program's lunar exploration mission with a number of record-setting achievements. During the three days of Apollo 17's surface activity (Dec. 11–14, 1972), Cernan and Schmitt performed three EVAs for a total of about 22 hours of exploration of the Taurus–Littrow valley. Their first EVA alone was more than three times the length astronauts Neil Armstrong and Buzz Aldrin spent outside the LM on Apollo 11. During this time Cernan and Schmitt covered more than 35 km (22 mi) using the Lunar Roving Vehicle and spent a great deal of time collecting geologic samples (including a record 34 kilograms (75 lb) of samples, the most of any Apollo mission) that would shed light on the Moon's early history. Cernan piloted the rover on its final sortie, recording a maximum speed of 11.2 mph (18.0 km/h), giving him the unofficial lunar land speed record.[14] As Cernan prepared to climb the ladder for the final time, he spoke these words, currently the last spoken by a human being standing on the lunar surface:     Bob, this is Gene, and I'm on the surface; and, as I take man's last step from the surface, back home for some time to come—but we believe not too long into the future—I'd like to just (say) what I believe history will record: that America's challenge of today has forged man's destiny of tomorrow. And, as we leave the Moon at Taurus–Littrow, we leave as we came and, God willing, as we shall return, with peace and hope for all mankind. Godspeed the crew of Apollo 17.     — Cernan, [15] Cernan's status as the last person to walk on the Moon means Purdue University is the alma mater of both the first person to walk on the Moon—Neil Armstrong—and the most recent. Cernan is one of only three astronauts to travel to the Moon on two occasions; the others being Jim Lovell and John Young. He is also one of only twelve people to have walked on the Moon. Post-NASA activities Eugene Cernan at a memorial service for Neil Armstrong September 13, 2012 In 1976, Cernan retired from the Navy with the rank of captain and went from NASA into private business, becoming Executive Vice President of Coral Petroleum Inc. before starting his own company, The Cernan Corporation, in 1981.[8] In 1981 and 1982, Cernan joined Frank Reynolds and Jules Bergman on the extensive ABC coverage of the first 3 Space Shuttle launches. Many hours of these ABC broadcasts have been uploaded to YouTube in recent years. From 1987 he was a contributor to ABC News and the weekly segment of its Good Morning America program titled "Breakthrough", which covered health, science, and medicine.[16] In 1999, with co-author Donald A. Davis, he published his memoir The Last Man on the Moon, which is about his naval and NASA career. He is featured in the space exploration documentary In the Shadow of the Moon in which he said, "truth needs no defense" and "nobody can take those footsteps I made on the surface of the Moon away from me".[17] Cernan also contributed to the book of the same name. Cernan and Neil Armstrong testified before U.S. Congress in 2010 in opposition to the cancellation of the Constellation program, which had been initiated during the George W. Bush administration as part of the Vision for Space Exploration with the aim of returning humans to the Moon and eventually Mars, but was deemed underfunded and unsustainable by the Augustine Commission in 2009.[18] Cernan paired his criticism of the cancellation of Constellation with expressions of skepticism about Commercial Resupply Services (CRS) and Commercial Crew Development (CCDev), NASA's planned replacements for that program's role in supplying cargo and crew to the International Space Station. Such companies, Cernan warned, "do not yet know what they don't know." Cernan's view of commercial space companies—in particular SpaceX, which participates in both programs—underwent a positive shift after being debriefed by SpaceX venture capitalist Steve Jurvetson as part of his effort to obtain the signatures of nine Apollo astronauts on a photograph meant as a gift to SpaceX founder Elon Musk to commemorate the first successful SpaceX cargo mission to the ISS in 2012. Eventually, Cernan was won over and signed the photograph; "As I told him these stories of heroic entrepreneurship, I could see his mind turning." Jurvetson wrote; "He found a reconciliation: 'I never read any of this in the news. Why doesn't the press report on this?'" [19] Cernan gave a eulogy at Armstrong's funeral in 2012.[20][21] In 2014, Cernan appeared in the documentary The Last Man on the Moon, made by British filmmaker Mark Craig and based on Cernan's 1999 memoir of the same title.[22] The film received the Texas Independent Film Award from Houston Film Critics Society and the Movies for Grownups Award from AARP The Magazine.[23][24] Personal life Cernan was married twice and had one daughter. His first wife was Barbara Jean Atchley, a flight attendant for Continental Airlines, whom he married in 1961. They had one daughter, Tracy (born in 1963). The couple separated in 1980 and divorced in 1981. They remained friends.[25] His second marriage was to Janis Ellen "Nanna" Cernan (née Jones; 1939–2021), which lasted for nearly 30 years from 1987 until his death. Cernan gained two step-daughters, Kelly and Danielle.[26] Death Cernan died in a hospital in Houston on January 16, 2017, at the age of 82.[27] His funeral was held at St. Martin's Episcopal Church in Houston.[28] He was buried with full military honors at Texas State Cemetery, the first astronaut to be buried there, in a private service on January 25, 2017.[29][30] Organizations Cernan was a member of several organizations, including Fellow, American Astronautical Society; member, Society of Experimental Test Pilots; member, Tau Beta Pi (National Engineering Society), Sigma Xi (National Science Research Society), Phi Gamma Delta (National Social Fraternity), and The Explorers Club.[8] Awards and honors     Naval Aviator Astronaut Insignia[8]     Navy Distinguished Service Medal, Gold star device in lieu of second award[8]     Distinguished Flying Cross[8]     National Defense Service Medal     NASA Distinguished Service Medal[8]     NASA Exceptional Service Medal[8]     Wright Brothers Memorial Trophy, 2007[31]     U.S. Astronaut Hall of Fame[32][33]      Slovakia: Grand Officer (or 2nd Class) of the Order of the White Double Cross (September 25, 1994).[34]     Great American Award, The All-American Boys Chorus, 2014.[35]     Cernan was inducted into the International Air & Space Hall of Fame at the San Diego Air & Space Museum in 2007.[36]     Orbital ATK announced the naming of its Cygnus CRS OA-8E Cargo Delivery Spacecraft the S.S. Gene Cernan in honor of Cernan in October 2017.[37] The S.S. Gene Cernan successfully launched to the International Space Station on November 12, 2017.[38]     In 2000, Eugene Cernan was inducted into the National Aviation Hall of Fame.[39] Cernan, along with nine of his Gemini astronaut colleagues, was inducted into the International Space Hall of Fame in 1982.[10][40] In popular culture Cernan's lunar space suit on display at the National Air and Space Museum in Washington, D.C. On July 2, 1974, Cernan was a roaster of Don Rickles on The Dean Martin Celebrity Roast. At the end of the roast, Rickles—who attended the Apollo 17 launch—paid tribute to Cernan as a "delightful, wonderful, great hero".[41] In the 1998 Primetime Emmy Award-winning HBO miniseries From the Earth to the Moon, Cernan was portrayed by Daniel Hugh Kelly.[42] Cernan was featured in the Discovery Channel's 2008 documentary miniseries When We Left Earth: The NASA Missions, talking about his involvement and missions as an astronaut.[43] A popular belief is that Cernan wrote his daughter's initials on a rock on the Moon, Tracy's Rock. The story, and Cernan's relationship with his daughter, was later adapted into "Tracy's Song" by pop-rock band No More Kings. The story is inaccurate, as Cernan wrote her initials in the dust, not on a rock. He states in the 2014 documentary The Last Man on the Moon[44] that he wrote them in the lunar dust as he left the rover to return to the LEM and Earth.[45] The true story of leaving the initials on the lunar surface was prominently mentioned in "The Last Walt", a 2012 episode of Modern Family.[46] A recording of Cernan's voice during the Apollo 17 mission was sampled by Daft Punk for "Contact", the last track on their 2013 album Random Access Memories.[47] Cernan's last words from the lunar surface, along with Lunar Module Pilot Harrison Schmitt's recollections, were used by the band Public Service Broadcasting for the song "Tomorrow", the final track of their 2015 album The Race for Space.[48] The Apple TV+ show For All Mankind dramatizes the Moon landings. The fictional main character draws comparisons to and shares similarity with the commander of the Apollo 17 mission, Gene Cernan.[" (wikipedia.org) "The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet,[f] with a diameter about one-quarter that of Earth (comparable to the width of Australia).[16] The Moon is a planetary-mass object with a differentiated rocky body, making it a satellite planet under the geophysical definitions of the term and larger than all known dwarf planets of the Solar System.[17] It lacks any significant atmosphere, hydrosphere, or magnetic field. Its surface gravity is about one-sixth of Earth's at 0.1654 g, with Jupiter's moon Io being the only satellite in the Solar System known to have a higher surface gravity and density. The Moon orbits Earth at an average distance of 384,400 km (238,900 mi), or about 30 times Earth's diameter. Its gravitational influence is the main driver of Earth's tides and very slowly lengthens Earth's day. The Moon's orbit around Earth has a sidereal period of 27.3 days. During each synodic period of 29.5 days, the amount of visible surface illuminated by the Sun varies from none up to 100%, resulting in lunar phases that form the basis for the months of a lunar calendar. The Moon is tidally locked to Earth, which means that the length of a full rotation of the Moon on its own axis causes its same side (the near side) to always face Earth, and the somewhat longer lunar day is the same as the synodic period. However, 59% of the total lunar surface can be seen from Earth through cyclical shifts in perspective known as libration. The most widely accepted origin explanation posits that the Moon formed 4.51 billion years ago, not long after Earth, out of the debris from a giant impact between the planet and a hypothesized Mars-sized body called Theia. It then receded to a wider orbit because of tidal interaction with the Earth. The near side of the Moon is marked by dark volcanic maria ("seas"), which fill the spaces between bright ancient crustal highlands and prominent impact craters. Most of the large impact basins and mare surfaces were in place by the end of the Imbrian period, some three billion years ago. The lunar surface is fairly non-reflective, with the reflectance of lunar soil being comparable to that of asphalt. However, due to its large angular diameter, the full moon is the brightest celestial object in the night sky. The Moon's apparent size is nearly the same as that of the Sun, allowing it to cover the Sun almost completely during a total solar eclipse. Both the Moon's prominence in Earth's sky and its regular cycle of phases have provided cultural references and influences for human societies throughout history. Such influences can be found in language, calendar systems, art, and mythology. The first artificial object to reach the Moon was the Soviet Union's uncrewed Luna 2 spacecraft in 1959; this was followed by the first successful soft landing by Luna 9 in 1966. The only human lunar missions to date have been those of the United States' Apollo program, which landed twelve men on the surface between 1969 and 1972. These and later uncrewed missions returned lunar rocks that have been used to develop a detailed geological understanding of the Moon's origins, internal structure, and subsequent history. The Moon is the only celestial body visited by humans. Names and etymology See also: Moon § Mythology and art The usual English proper name for Earth's natural satellite is simply Moon, with a capital M.[18][19] The noun moon is derived from Old English mōna, which (like all its Germanic cognates) stems from Proto-Germanic *mēnōn,[20] which in turn comes from Proto-Indo-European *mēnsis "month"[21] (from earlier *mēnōt, genitive *mēneses) which may be related to the verb "measure" (of time).[22] Occasionally, the name Luna /ˈluːnə/ is used in scientific writing[23] and especially in science fiction to distinguish the Earth's moon from others, while in poetry "Luna" has been used to denote personification of the Moon.[24] Cynthia /ˈsɪnθiə/ is another poetic name, though rare, for the Moon personified as a goddess,[25] while Selene /səˈliːniː/ (literally "Moon") is the Greek goddess of the Moon. The usual English adjective pertaining to the Moon is "lunar", derived from the Latin word for the Moon, lūna. The adjective selenian /səliːniən/,[26] derived from the Greek word for the Moon, σελήνη selēnē, and used to describe the Moon as a world rather than as an object in the sky, is rare,[27] while its cognate selenic was originally a rare synonym[28] but now nearly always refers to the chemical element selenium.[29] The Greek word for the Moon does however provide us with the prefix seleno-, as in selenography, the study of the physical features of the Moon, as well as the element name selenium.[30][31] The Greek goddess of the wilderness and the hunt, Artemis, equated with the Roman Diana, one of whose symbols was the Moon and who was often regarded as the goddess of the Moon, was also called Cynthia, from her legendary birthplace on Mount Cynthus.[32] These names – Luna, Cynthia and Selene – are reflected in technical terms for lunar orbits such as apolune, pericynthion and selenocentric. The astronomical symbol for the Moon is a crescent, ☾, for example in M☾ 'lunar mass' (also ML).... Atmosphere Main article: Atmosphere of the Moon The thin lunar atmosphere is visible on the Moon's surface at sunrise and sunset with the Lunar Horizon Glow[76] and lunar twilight rays, like Earth's crepuscular rays. This Apollo 17 sketch depicts the glow and rays[77] among the general zodiacal light.[78][79] The Moon has an atmosphere so tenuous as to be nearly vacuum, with a total mass of less than 10 tonnes (9.8 long tons; 11 short tons).[80] The surface pressure of this small mass is around 3 × 10−15 atm (0.3 nPa); it varies with the lunar day. Its sources include outgassing and sputtering, a product of the bombardment of lunar soil by solar wind ions.[15][81] Elements that have been detected include sodium and potassium, produced by sputtering (also found in the atmospheres of Mercury and Io); helium-4 and neon[82] from the solar wind; and argon-40, radon-222, and polonium-210, outgassed after their creation by radioactive decay within the crust and mantle.[83][84] The absence of such neutral species (atoms or molecules) as oxygen, nitrogen, carbon, hydrogen and magnesium, which are present in the regolith, is not understood.[83] Water vapor has been detected by Chandrayaan-1 and found to vary with latitude, with a maximum at ~60–70 degrees; it is possibly generated from the sublimation of water ice in the regolith.[85] These gases either return into the regolith because of the Moon's gravity or are lost to space, either through solar radiation pressure or, if they are ionized, by being swept away by the solar wind's magnetic field.[83] Studies of Moon magma samples retrieved by the Apollo missions demonstrate that the Moon had once possessed a relatively thick atmosphere for a period of 70 million years between 3 and 4 billion years ago. This atmosphere, sourced from gases ejected from lunar volcanic eruptions, was twice the thickness of that of present-day Mars. The ancient lunar atmosphere was eventually stripped away by solar winds and dissipated into space.[86] A permanent Moon dust cloud exists around the Moon, generated by small particles from comets. Estimates are 5 tons of comet particles strike the Moon's surface every 24 hours, resulting in the ejection of dust particles. The dust stays above the Moon approximately 10 minutes, taking 5 minutes to rise, and 5 minutes to fall. On average, 120 kilograms of dust are present above the Moon, rising up to 100 kilometers above the surface. Dust counts made by LADEE's Lunar Dust EXperiment (LDEX) found particle counts peaked during the Geminid, Quadrantid, Northern Taurid, and Omicron Centaurid meteor showers, when the Earth, and Moon pass through comet debris. The lunar dust cloud is asymmetric, being more dense near the boundary between the Moon's dayside and nightside.[87][88] Surface conditions Gene Cernan with lunar dust stuck on his suit. Lunar dust is highly abrasive and can cause damage to human lungs, nervous, and cardiovascular systems.[89] Ionizing radiation from cosmic rays, the Sun and the resulting neutron radiation[90] produce radiation levels on average of 1.369 millisieverts per day during lunar daytime,[14] which is about 2.6 times more than on the International Space Station with 0.53 millisieverts per day at about 400 km above Earth in orbit, 5-10 times more than during a trans-Atlantic flight, 200 times more than on Earth's surface.[91] For further comparison radiation on a flight to Mars is about 1.84 millisieverts per day and on Mars on average 0.342, with some locations on Mars possibly having levels as low as 0.64 millisieverts per day.[92][93] The Moon's axial tilt with respect to the ecliptic is only 1.5427°,[8][94] much less than the 23.44° of Earth. Because of this small tilt, the Moon's solar illumination varies much less with season than on Earth and it allows for the existence of some peaks of eternal light at the Moon's north pole, at the rim of the crater Peary. The surface is exposed to drastic temperature differences ranging from 140 °C to −171 °C depending on the solar irradiance. Because of the lack of atmosphere, temperatures of different areas vary particularly upon whether they are in sunlight or shadow,[95] making topographical details play a decisive role on local surface temperatures.[96] Parts of many craters, particularly the bottoms of many polar craters,[97] are permanently shadowed, these "craters of eternal darkness" have extremely low temperatures. The Lunar Reconnaissance Orbiter measured the lowest summer temperatures in craters at the southern pole at 35 K (−238 °C; −397 °F)[98] and just 26 K (−247 °C; −413 °F) close to the winter solstice in the north polar crater Hermite. This is the coldest temperature in the Solar System ever measured by a spacecraft, colder even than the surface of Pluto.[96] Blanketed on top of the Moon's crust is a highly comminuted (broken into ever smaller particles) and impact gardened mostly gray surface layer called regolith, formed by impact processes. The finer regolith, the lunar soil of silicon dioxide glass, has a texture resembling snow and a scent resembling spent gunpowder.[99] The regolith of older surfaces is generally thicker than for younger surfaces: it varies in thickness from 10–15 m (33–49 ft) in the highlands and 4–5 m (13–16 ft) in the maria.[100] Beneath the finely comminuted regolith layer is the megaregolith, a layer of highly fractured bedrock many kilometers thick.[101] These extreme conditions for example are considered to make it unlikely for spacecraft to harbor bacterial spores at the Moon longer than just one lunar orbit.[102] Surface features Main articles: Selenography, Lunar terrane, List of lunar features, and List of quadrangles on the Moon Astronaut Harrison H. Schmitt next to a large Moon boulder The topography of the Moon has been measured with laser altimetry and stereo image analysis.[103] Its most extensive topographic feature is the giant far-side South Pole–Aitken basin, some 2,240 km (1,390 mi) in diameter, the largest crater on the Moon and the second-largest confirmed impact crater in the Solar System.[104][105] At 13 km (8.1 mi) deep, its floor is the lowest point on the surface of the Moon.[104][106] The highest elevations of the Moon's surface are located directly to the northeast, which might have been thickened by the oblique formation impact of the South Pole–Aitken basin.[107] Other large impact basins such as Imbrium, Serenitatis, Crisium, Smythii, and Orientale possess regionally low elevations and elevated rims.[104] The far side of the lunar surface is on average about 1.9 km (1.2 mi) higher than that of the near side.[1] The discovery of fault scarp cliffs suggest that the Moon has shrunk by about 90 metres (300 ft) within the past billion years.[108] Similar shrinkage features exist on Mercury. Mare Frigoris, a basin near the north pole long assumed to be geologically dead, has cracked and shifted. Since the Moon doesn't have tectonic plates, its tectonic activity is slow and cracks develop as it loses heat.[109] Volcanic features Main article: Volcanism on the Moon The names of the main maria (blue) and some crater (brown) features of the near side of the Moon The main features visible from Earth by the naked eye are dark and relatively featureless lunar plains called maria (singular mare; Latin for "seas", as they were once believed to be filled with water)[110] are vast solidified pools of ancient basaltic lava. Although similar to terrestrial basalts, lunar basalts have more iron and no minerals altered by water.[111] The majority of these lava deposits erupted or flowed into the depressions associated with impact basins. Several geologic provinces containing shield volcanoes and volcanic domes are found within the near side "maria".[112] Almost all maria are on the near side of the Moon, and cover 31% of the surface of the near side[60] compared with 2% of the far side.[113] This is likely due to a concentration of heat-producing elements under the crust on the near side, which would have caused the underlying mantle to heat up, partially melt, rise to the surface and erupt.[65][114][115] Most of the Moon's mare basalts erupted during the Imbrian period, 3.3–3.7 billion years ago, though some being as young as 1.2 billion years[55] and as old as 4.2 billion years.[56] In 2006, a study of Ina, a tiny depression in Lacus Felicitatis, found jagged, relatively dust-free features that, because of the lack of erosion by infalling debris, appeared to be only 2 million years old.[116] Moonquakes and releases of gas indicate continued lunar activity.[116] Evidence of recent lunar volcanism has been identified at 70 irregular mare patches, some less than 50 million years old. This raises the possibility of a much warmer lunar mantle than previously believed, at least on the near side where the deep crust is substantially warmer because of the greater concentration of radioactive elements.[117][118][119][120] Evidence has been found for 2–10 million years old basaltic volcanism within the crater Lowell,[121][122] inside the Orientale basin. Some combination of an initially hotter mantle and local enrichment of heat-producing elements in the mantle could be responsible for prolonged activities on the far side in the Orientale basin.[123][124] The lighter-colored regions of the Moon are called terrae, or more commonly highlands, because they are higher than most maria. They have been radiometrically dated to having formed 4.4 billion years ago, and may represent plagioclase cumulates of the lunar magma ocean.[56][55] In contrast to Earth, no major lunar mountains are believed to have formed as a result of tectonic events.[125] The concentration of maria on the near side likely reflects the substantially thicker crust of the highlands of the Far Side, which may have formed in a slow-velocity impact of a second moon of Earth a few tens of millions of years after the Moon's formation.[126][127] Alternatively, it may be a consequence of asymmetrical tidal heating when the Moon was much closer to the Earth.[128] Impact craters Further information: List of craters on the Moon A gray, many-ridged surface from high above. The largest feature is a circular ringed structure with high walled sides and a lower central peak: the entire surface out to the horizon is filled with similar structures that are smaller and overlapping. A view of a three kilometer deep larger crater Daedalus on the Moon's far side A major geologic process that has affected the Moon's surface is impact cratering,[129] with craters formed when asteroids and comets collide with the lunar surface. There are estimated to be roughly 300,000 craters wider than 1 km (0.6 mi) on the Moon's near side.[130] The lunar geologic timescale is based on the most prominent impact events, including Nectaris, Imbrium, and Orientale; structures characterized by multiple rings of uplifted material, between hundreds and thousands of kilometers in diameter and associated with a broad apron of ejecta deposits that form a regional stratigraphic horizon.[131] The lack of an atmosphere, weather, and recent geological processes mean that many of these craters are well-preserved. Although only a few multi-ring basins have been definitively dated, they are useful for assigning relative ages. Because impact craters accumulate at a nearly constant rate, counting the number of craters per unit area can be used to estimate the age of the surface.[131] The radiometric ages of impact-melted rocks collected during the Apollo missions cluster between 3.8 and 4.1 billion years old: this has been used to propose a Late Heavy Bombardment period of increased impacts.[132] High-resolution images from the Lunar Reconnaissance Orbiter in the 2010s show a contemporary crater-production rate significantly higher than was previously estimated. A secondary cratering process caused by distal ejecta is thought to churn the top two centimeters of regolith on a timescale of 81,000 years.[133][134] This rate is 100 times faster than the rate computed from models based solely on direct micrometeorite impacts.[135] Lunar swirls Main article: Lunar swirls Wide angle image of a lunar swirl, the 70 kilometer long Reiner Gamma Lunar swirls are enigmatic features found across the Moon's surface. They are characterized by a high albedo, appear optically immature (i.e. the optical characteristics of a relatively young regolith), and often have a sinuous shape. Their shape is often accentuated by low albedo regions that wind between the bright swirls. They are located in places with enhanced surface magnetic fields and many are located at the antipodal point of major impacts. Well known swirls include the Reiner Gamma feature and Mare Ingenii. They are hypothesized to be areas that have been partially shielded from the solar wind, resulting in slower space weathering.[136] Presence of water Main article: Lunar water In 2008, NASA's Moon Mineralogy Mapper equipment on India's Chandrayaan-1 discovered, for the first time, water-rich minerals (shown in blue around a small crater from which they were ejected). Liquid water cannot persist on the lunar surface. When exposed to solar radiation, water quickly decomposes through a process known as photodissociation and is lost to space. However, since the 1960s, scientists have hypothesized that water ice may be deposited by impacting comets or possibly produced by the reaction of oxygen-rich lunar rocks, and hydrogen from solar wind, leaving traces of water which could possibly persist in cold, permanently shadowed craters at either pole on the Moon.[137][138] Computer simulations suggest that up to 14,000 km2 (5,400 sq mi) of the surface may be in permanent shadow.[97] The presence of usable quantities of water on the Moon is an important factor in rendering lunar habitation as a cost-effective plan; the alternative of transporting water from Earth would be prohibitively expensive.[139] In years since, signatures of water have been found to exist on the lunar surface.[140] In 1994, the bistatic radar experiment located on the Clementine spacecraft, indicated the existence of small, frozen pockets of water close to the surface. However, later radar observations by Arecibo, suggest these findings may rather be rocks ejected from young impact craters.[141] In 1998, the neutron spectrometer on the Lunar Prospector spacecraft showed that high concentrations of hydrogen are present in the first meter of depth in the regolith near the polar regions.[142] Volcanic lava beads, brought back to Earth aboard Apollo 15, showed small amounts of water in their interior.[143] The 2008 Chandrayaan-1 spacecraft has since confirmed the existence of surface water ice, using the on-board Moon Mineralogy Mapper. The spectrometer observed absorption lines common to hydroxyl, in reflected sunlight, providing evidence of large quantities of water ice, on the lunar surface. The spacecraft showed that concentrations may possibly be as high as 1,000 ppm.[144] Using the mapper's reflectance spectra, indirect lighting of areas in shadow confirmed water ice within 20° latitude of both poles in 2018.[145] In 2009, LCROSS sent a 2,300 kg (5,100 lb) impactor into a permanently shadowed polar crater, and detected at least 100 kg (220 lb) of water in a plume of ejected material.[146][147] Another examination of the LCROSS data showed the amount of detected water to be closer to 155 ± 12 kg (342 ± 26 lb).[148] In May 2011, 615–1410 ppm water in melt inclusions in lunar sample 74220 was reported,[149] the famous high-titanium "orange glass soil" of volcanic origin collected during the Apollo 17 mission in 1972. The inclusions were formed during explosive eruptions on the Moon approximately 3.7 billion years ago. This concentration is comparable with that of magma in Earth's upper mantle. Although of considerable selenological interest, this insight does not mean that water is easily available since the sample originated many kilometers below the surface, and the inclusions are so difficult to access that it took 39 years to find them with a state-of-the-art ion microprobe instrument. Analysis of the findings of the Moon Mineralogy Mapper (M3) revealed in August 2018 for the first time "definitive evidence" for water-ice on the lunar surface.[150][151] The data revealed the distinct reflective signatures of water-ice, as opposed to dust and other reflective substances.[152] The ice deposits were found on the North and South poles, although it is more abundant in the South, where water is trapped in permanently shadowed craters and crevices, allowing it to persist as ice on the surface since they are shielded from the sun.[150][152] In October 2020, astronomers reported detecting molecular water on the sunlit surface of the Moon by several independent spacecraft, including the Stratospheric Observatory for Infrared Astronomy (SOFIA).[153][154][155][156] Earth–Moon system See also: Satellite system (astronomy), Claimed moons of Earth, and Double planet Orbit Main articles: Orbit of the Moon and Lunar theory A view of the rotating Earth and the far side of the Moon as the Moon passes on its orbit in between the observing DSCOVR satellite and Earth The Earth and the Moon form the Earth-Moon satellite system with a shared center of mass, or barycenter. This barycenter stays located at all times 1,700 km (1,100 mi) (about a quarter of Earth's radius) beneath the Earth's surface, making the Moon seemingly orbit the Earth. The orbital eccentricity is 0.055, indicating a slightly elliptical orbit.[1] The Lunar distance, or the semi-major axis of the geocentric lunar orbit, is approximately 400,000 km, which is a quarter of a million miles or 1.28 light-seconds, and a unit of measure in astronomy. This is not to be confused with the instantaneous Earth–Moon distance, or distance to the Moon, the momentanous distance from the center of Earth to the center of the Moon. The Moon makes a complete orbit around Earth with respect to the fixed stars, its sidereal period, about once every 27.3 days[h] However, because the Earth-Moon system moves at the same time in its orbit around the Sun, it takes slightly longer, 29.5 days,[i][60] to return at the same lunar phase, completing a full cycle, as seen from Earth. This synodic period or synodic month is commonly known as the lunar month and is equal to the length of the solar day on the Moon.[157] Due to tidal locking, the Moon has a 1:1 spin–orbit resonance. This rotation–orbit ratio makes the Moon's orbital periods around Earth equal to its corresponding rotation periods. This is the reason for only one side of the Moon, its so-called near side, being visible from Earth. That said, while the movement of the Moon is in resonance, it still is not without nuances such as libration, resulting in slightly changing perspectives, making over time and location on Earth about 59% of the Moon's surface visible from Earth.[158] Unlike most satellites of other planets, the Moon's orbital plane is closer to the ecliptic plane than to the planet's equatorial plane. The Moon's orbit is subtly perturbed by the Sun and Earth in many small, complex and interacting ways. For example, the plane of the Moon's orbit gradually rotates once every 18.61 years,[159] which affects other aspects of lunar motion. These follow-on effects are mathematically described by Cassini's laws.[160] Minimum, mean and maximum distances of the Moon from Earth with its angular diameter as seen from Earth's surface, to scale Tidal effects Main articles: Tidal force, Tidal acceleration, Tide, and Theory of tides Simplified diagram of the Moon's gravity tidal effect on the Earth The gravitational attraction that Earth and the Moon (as well as the Sun) exert on each other manifests in a slightly greater attraction on the sides of closest to each other, resulting in tidal forces. Ocean tides are the most widely experienced result of this, but tidal forces considerably affect also other mechanics of Earth, as well as the Moon and their system. The lunar solid crust experiences tides of around 10 cm (4 in) amplitude over 27 days, with three components: a fixed one due to Earth, because they are in synchronous rotation, a variable tide due to orbital eccentricity and inclination, and a small varying component from the Sun.[161] The Earth-induced variable component arises from changing distance and libration, a result of the Moon's orbital eccentricity and inclination (if the Moon's orbit were perfectly circular and un-inclined, there would only be solar tides).[161] According to recent research, scientists suggest that the Moon's influence on the Earth may contribute to maintaining Earth's magnetic field.[162] The cumulative effects of stress built up by these tidal forces produces moonquakes. Moonquakes are much less common and weaker than are earthquakes, although moonquakes can last for up to an hour – significantly longer than terrestrial quakes – because of scattering of the seismic vibrations in the dry fragmented upper crust. The existence of moonquakes was an unexpected discovery from seismometers placed on the Moon by Apollo astronauts from 1969 through 1972.[163] The most commonly known effect of tidal forces are elevated sea levels called ocean tides.[164] While the Moon exerts most of the tidal forces, the Sun also exerts tidal forces and therefore contributes to the tides as much as 40% of the Moon's tidal force; producing in interplay the spring and neap tides.[164] The tides are two bulges in the Earth's oceans, one on the side facing the Moon and the other on the side opposite. As the Earth rotates on its axis, one of the ocean bulges (high tide) is held in place "under" the Moon, while another such tide is opposite. As a result, there are two high tides, and two low tides in about 24 hours.[164] Since the Moon is orbiting the Earth in the same direction of the Earth's rotation, the high tides occur about every 12 hours and 25 minutes; the 25 minutes is due to the Moon's time to orbit the Earth. If the Earth were a water world (one with no continents) it would produce a tide of only one meter, and that tide would be very predictable, but the ocean tides are greatly modified by other effects:     the frictional coupling of water to Earth's rotation through the ocean floors     the inertia of water's movement     ocean basins that grow shallower near land     the sloshing of water between different ocean basins[165] As a result, the timing of the tides at most points on the Earth is a product of observations that are explained, incidentally, by theory. Delays in the tidal peaks of both ocean and solid-body tides cause torque in opposition to the Earth's rotation. This "drains" angular momentum and rotational kinetic energy from Earth's rotation, slowing the Earth's rotation.[164][161] That angular momentum, lost from the Earth, is transferred to the Moon in a process known as tidal acceleration, which lifts the Moon into a higher orbit while lowering orbital speed around the Earth. Thus the distance between Earth and Moon is increasing, and the Earth's rotation is slowing in reaction.[161] Measurements from laser reflectors left during the Apollo missions (lunar ranging experiments) have found that the Moon's distance increases by 38 mm (1.5 in) per year (roughly the rate at which human fingernails grow).[166][167][168] Atomic clocks show that Earth's day lengthens by about 17 microseconds every year,[169][170][171] slowly increasing the rate at which UTC is adjusted by leap seconds. This tidal drag makes the rotation of the Earth and the orbital period of the Moon very slowly match. This matching first results in tidally locking the lighter body of the orbital system, as is already the case with the Moon. Theoretically, in 50 billion years,[172] the Earth's rotation will have slowed to the point of matching the Moon's orbital period, causing the Earth to always present the same side to the Moon. However, the Sun will become a red giant, engulfing the Earth-Moon system, long before then.[173][174] Position and appearance See also: Lunar observation Over one lunar month more than half of the Moon's surface can be seen from Earth's surface. Libration, the slight variation in the Moon's apparent size and viewing angle over a single lunar month as viewed from Earth's north The Moon's highest altitude at culmination varies by its lunar phase, or more correctly its orbital position, and time of the year, or more correctly the position of the Earth's axis. The full moon is highest in the sky during winter and lowest during summer (for each hemisphere respectively), with its altitude changing towards dark moon to the opposite. At the North and South Poles the Moon is 24 hours above the horizon for two weeks every tropical month (about 27.3 days), comparable to the polar day of the tropical year. Zooplankton in the Arctic use moonlight when the Sun is below the horizon for months on end.[175] The apparent orientation of the Moon depends on its position in the sky and the hemisphere of the Earth from which it is being viewed. In the northern hemisphere it is seen upside down compared to the view in the southern hemisphere.[176] Sometimes the "horns" of a crescent moon appear to be pointing more upwards than sideways. This phenomenon is called a wet moon and occurs more frequently in the tropics.[177] The distance between the Moon and Earth varies from around 356,400 km (221,500 mi) to 406,700 km (252,700 mi) at perigee (closest) and apogee (farthest), respectively, making the Moon's apparent size fluctuate. On average the Moon's angular diameter is about 0.52° (on average) in the sky, roughly the same apparent size as the Sun (see § Eclipses). Additionally when close to the horizon a purely psychological effect, known as the Moon illusion, makes the Moon appear larger.[178] Despite the Moon's tidal locking, the effect of libration makes about 59% of the Moon's surface visible from Earth over the course of one month.[158][60] Rotation Comparison between the Moon on the left, rotating tidally locked (correct), and with the Moon on the right, without rotation (incorrect) The tidally locked synchronous rotation of the Moon as it orbits the Earth results in it always keeping nearly the same face turned towards the planet. The side of the Moon that faces Earth is called the near side, and the opposite the far side. The far side is often inaccurately called the "dark side", but it is in fact illuminated as often as the near side: once every 29.5 Earth days. During dark moon to new moon, the near side is dark.[179] The Moon originally rotated at a faster rate, but early in its history its rotation slowed and became tidally locked in this orientation as a result of frictional effects associated with tidal deformations caused by Earth.[180] With time, the energy of rotation of the Moon on its axis was dissipated as heat, until there was no rotation of the Moon relative to Earth. In 2016, planetary scientists using data collected on the 1998-99 NASA Lunar Prospector mission, found two hydrogen-rich areas (most likely former water ice) on opposite sides of the Moon. It is speculated that these patches were the poles of the Moon billions of years ago before it was tidally locked to Earth.[181] Illumination and phases See also: Moonlight and Halo (optical phenomenon) Half of the Moon's surface is always illuminated by the Sun (except during a lunar eclipse). Earth also reflects light onto the Moon, observable at times as Earthlight when it is again reflected back to Earth from areas of the near side of the Moon that are not illuminated by the Sun. With the different positions of the Moon, different areas of it are illuminated by the Sun. This illumination of different lunar areas, as viewed from Earth, produces the different lunar phases during the synodic month. A phase is equal to the area of the visible lunar sphere that is illuminated by the Sun. This area or degree of illumination is given by ( 1 − cos ⁡ e ) / 2 = sin 2 ⁡ ( e / 2 ) {\displaystyle (1-\cos e)/2=\sin ^{2}(e/2)} {\displaystyle (1-\cos e)/2=\sin ^{2}(e/2)}, where e {\displaystyle e} e is the elongation (i.e., the angle between Moon, the observer on Earth, and the Sun). The monthly changes in the angle between the direction of sunlight and view from Earth, and the phases of the Moon that result, as viewed from the Northern Hemisphere. The Earth–Moon distance is not to scale. On 14 November 2016, the Moon was at full phase closer to Earth than it had been since 1948. It was 14% closer and larger than its farthest position in apogee.[182] This closest point coincided within an hour of a full moon, and it was 30% more luminous than when at its greatest distance because of its increased apparent diameter, which made it a particularly notable example of a "supermoon".[183][184][185] At lower levels, the human perception of reduced brightness as a percentage is provided by the following formula:[186][187]     perceived reduction % = 100 × actual reduction % 100 {\displaystyle {\text{perceived reduction}}\%=100\times {\sqrt {{\text{actual reduction}}\% \over 100}}} {\displaystyle {\text{perceived reduction}}\%=100\times {\sqrt {{\text{actual reduction}}\% \over 100}}} When the actual reduction is 1.00 / 1.30, or about 0.770, the perceived reduction is about 0.877, or 1.00 / 1.14. This gives a maximum perceived increase of 14% between apogee and perigee moons of the same phase.... First missions to the Moon (1959–1990) See also: Space Race and Moon landing After World War II the first launch systems were developed and by the end of the 1950s they reached capabilities that allowed the Soviet Union and the United States to launch spacecrafts into space. The Cold War fueled a closely followed development of launch systems by the two states, resulting in the so-called Space Race and its later phase the Moon Race, accelerating efforts and interest in exploration of the Moon. First view of the far side of the Moon, taken by Luna 3, 7 October 1959 After the first spaceflight of Sputnik 1 in 1957 during International Geophysical Year the spacecrafts of the Soviet Union's Luna program were the first to accomplish a number of goals. Following three unnamed failed missions in 1958,[216] the first human-made object Luna 1 escaped Earth's gravity and passed near the Moon in 1959. Later that year the first human-made object Luna 2 reached the Moon's surface by intentionally impacting. By the end of the year Luna 3 reached as the first human-made object the normally occluded far side of the Moon, taking the first photographs of it. The first spacecraft to perform a successful lunar soft landing was Luna 9 and the first vehicle to orbit the Moon was Luna 10, both in 1966.[60] The small blue-white semicircle of Earth, almost glowing with color in the blackness of space, rising over the limb of the desolate, cratered surface of the Moon. Earthrise, the first color image of Earth taken by a human from the Moon, during Apollo 8 (1968) the first time a crewed spacecraft left Earth orbit and reached another astronomical body Following President John F. Kennedy's 1961 commitment to a crewed Moon landing before the end of the decade, the United States, under NASA leadership, launched a series of uncrewed probes to develop an understanding of the lunar surface in preparation for human missions: the Jet Propulsion Laboratory's Ranger program, the Lunar Orbiter program and the Surveyor program. The crewed Apollo program was developed in parallel; after a series of uncrewed and crewed tests of the Apollo spacecraft in Earth orbit, and spurred on by a potential Soviet lunar human landing, in 1968 Apollo 8 made the first human mission to lunar orbit. The subsequent landing of the first humans on the Moon in 1969 is seen by many as the culmination of the Space Race.[217] Neil Armstrong became the first person to walk on the Moon as the commander of the American mission Apollo 11 by first setting foot on the Moon at 02:56 UTC on 21 July 1969.[218] An estimated 500 million people worldwide watched the transmission by the Apollo TV camera, the largest television audience for a live broadcast at that time.[219][220] The Apollo missions 11 to 17 (except Apollo 13, which aborted its planned lunar landing) removed 380.05 kilograms (837.87 lb) of lunar rock and soil in 2,196 separate samples.[221] Scientific instrument packages were installed on the lunar surface during all the Apollo landings. Long-lived instrument stations, including heat flow probes, seismometers, and magnetometers, were installed at the Apollo 12, 14, 15, 16, and 17 landing sites. Direct transmission of data to Earth concluded in late 1977 because of budgetary considerations,[222][223] but as the stations' lunar laser ranging corner-cube retroreflector arrays are passive instruments, they are still being used.[224] Apollo 17 in 1972 remains the last crewed mission to the Moon. Explorer 49 in 1973 was the last dedicated U.S. probe to the Moon until the 1990s. The Soviet Union continued sending robotic missions to the Moon until 1976, deploying in 1970 with Luna 17 the first remote controlled rover Lunokhod 1 on an extraterrestrial surface, and collecting and returning 0.3 kg of rock and soil samples with three Luna sample return missions (Luna 16 in 1970, Luna 20 in 1972, and Luna 24 in 1976).[225] Moon Treaty and explorational absence (1976–1990) Main article: Moon Treaty A near lunar quietude of fourteen years followed the last Soviet mission to the Moon of 1976. Astronautics had shifted its focus towards the exploration of the inner (e.g. Venera program) and outer (e.g. Pioneer 10, 1972) Solar System planets, but also towards Earth orbit, developing and continuously operating, beside communication satellites, Earth observation satellites (e.g. Landsat program, 1972) space telescopes and particularly space stations (e.g. Salyut program, 1971). The until 1979 negotiated Moon treaty, with its ratification in 1984 by its few signatories was about the only major activity regarding the Moon until 1990. Renewed exploration (1990-present) Map of all soft landing sites on the near side of the Moon In 1990 Hiten-Hagoromo,[226] the first dedicated lunar mission since 1976, reached the Moon. Sent by Japan, it became the first mission that was not a Soviet Union or U.S. mission to the Moon. In 1994, the U.S. dedicated a mission to fly a spacecraft (Clementine) to the Moon again for the first time since 1973. This mission obtained the first near-global topographic map of the Moon, and the first global multispectral images of the lunar surface.[227] In 1998, this was followed by the Lunar Prospector mission, whose instruments indicated the presence of excess hydrogen at the lunar poles, which is likely to have been caused by the presence of water ice in the upper few meters of the regolith within permanently shadowed craters.[228] The next years saw a row of first missions to the Moon by a new group of states actively exploring the Moon. Between 2004 and 2006 the first spacecraft by the European Space Agency (ESA) (SMART-1) reached the Moon, recording the first detailed survey of chemical elements on the lunar surface.[229] The Chinese Lunar Exploration Program began with Chang'e 1 between 2007 and 2009,[230] obtaining a full image map of the Moon. India reached the Moon in 2008 for the first time with its Chandrayaan-1, creating a high-resolution chemical, mineralogical and photo-geological map of the lunar surface, and confirming the presence of water molecules in lunar soil.[231] The U.S. launched the Lunar Reconnaissance Orbiter (LRO) and the LCROSS impactor on 18 June 2009. LCROSS completed its mission by making a planned and widely observed impact in the crater Cabeus on 9 October 2009,[232] whereas LRO is currently in operation, obtaining precise lunar altimetry and high-resolution imagery. China continued its lunar program in 2010 with Chang'e 2, mapping the surface at a higher resolution over an eight-month period, and in 2013 with Chang'e 3, a lunar lander along with a lunar rover named Yutu (Chinese: 玉兔; lit. 'Jade Rabbit'). This was the first lunar rover mission since Lunokhod 2 in 1973 and the first lunar soft landing since Luna 24 in 1976. In 2014 the first privately funded probe, the Manfred Memorial Moon Mission, reached the Moon. Another Chinese rover mission, Chang'e 4, achieved the first landing on the Moon's far side in early 2019.[233] Also in 2019, India successfully sent its second probe, Chandrayaan-2 to the Moon. In 2020, China carried out its first robotic sample return mission (Chang'e 5), bringing back 1,731 grams of lunar material to Earth.[234] With the signing of the U.S.-led Artemis Accords in 2020, the Artemis program aims to return the astronauts to the Moon in the 2020s.[235] The Accords have been joined by a growing number of countries. The introduction of the Artemis Accords has fueled a renewed discussion about the international framework and cooperation of lunar activity, building on the Moon Treaty and the ESA-led Moon Village concept.[236][237][238] The U.S. developed plans for returning to the Moon beginning in 2004,[239] which resulted in several programs. The Artemis program has advanced the farthest, and includes plans to send the first woman to the Moon[240] as well as build an international lunar space station called Lunar Gateway. Future See also: List of proposed missions to the Moon Orion spacecraft's flyby of the Moon in the Artemis 1 mission Upcoming lunar missions include the Artemis program missions and Russia's first lunar mission, Luna-Glob: an uncrewed lander with a set of seismometers, and an orbiter based on its failed Martian Fobos-Grunt mission.[241] In 2021, China announced a plan with Russia to develop and construct an International Lunar Research Station in the 2030s. Human presence See also: Human presence in space Humans last landed on the Moon during the Apollo Program, a series of crewed exploration missions carried out from 1969 to 1972. Lunar orbit has seen uninterrupted presence of orbiters since 2006, performing mainly lunar observation and providing relayed communication for robotic missions on the lunar surface. Lunar orbits and orbits around Earth–Moon Lagrange points are used to establish a near-lunar infrastructure to enable increasing human activity in cislunar space as well as on the Moon's surface. Missions at the far side of the Moon or the lunar north and south polar regions need spacecraft with special orbits, such as the Queqiao relay satellite or the planned first extraterrestrial space station, the Lunar Gateway.[242][243] Human impact See also: Space debris, Space sustainability, List of artificial objects on the Moon, Space art § Art in space, Moonbase, Lunar resources § Mining, Tourism on the Moon, and Space archaeology Artifacts of human activity, Apollo 17's Lunar Surface Experiments Package[244] While the Moon has the lowest planetary protection target-categorization, its degradation as a pristine body and scientific place has been discussed.[245] If there is astronomy performed from the Moon, it will need to be free from any physical and radio pollution. While the Moon has no significant atmosphere, traffic and impacts on the Moon causes clouds of dust that can spread far and possibly contaminate the original state of the Moon and its special scientific content.[246] Scholar Alice Gorman asserts that, although the Moon is inhospitable, it is not dead, and that sustainable human activity would require treating the Moon's ecology as a co-participant.[247] The so-called "Tardigrade affair" of the 2019 crashed Beresheet lander and its carrying of tardigrades has been discussed as an example for lacking measures and lacking international regulation for planetary protection.[248] Space debris beyond Earth around the Moon has been considered as a future challenge with increasing numbers of missions to the Moon, particularly as a danger for such missions.[249][250] As such lunar waste management has been raised as an issue which future lunar missions, particularly on the surface, need to tackle.[251][252] Beside the remains of human activity on the Moon, there have been some intended permanent installations like the Moon Museum art piece, Apollo 11 goodwill messages, six lunar plaques, the Fallen Astronaut memorial, and other artifacts.[244] Longterm missions continuing to be active are some orbiters such as the 2009-launched Lunar Reconnaissance Orbiter surveilling the Moon for future missions, as well as some Landers such as the 2013-launched Chang'e 3 with its Lunar Ultraviolet Telescope still operational.[253] Five retroreflectors have been installed on the Moon since the 1970s and since used for accurate measurements of the physical librations through laser ranging to the Moon. There are several missions by different agencies and companies planned to establish a longterm human presence on the Moon, with the Lunar Gateway as the currently most advanced project as part of the Artemis program. Astronomy from the Moon Further information: Extraterrestrial sky § The Moon The LCRT concept for a radio telescope on the Moon For many years, the Moon has been recognized as an excellent site for telescopes.[254] It is relatively nearby; astronomical seeing is not a concern; certain craters near the poles are permanently dark and cold, and thus especially useful for infrared telescopes; and radio telescopes on the far side would be shielded from the radio chatter of Earth.[255] The lunar soil, although it poses a problem for any moving parts of telescopes, can be mixed with carbon nanotubes and epoxies and employed in the construction of mirrors up to 50 meters in diameter.[256] A lunar zenith telescope can be made cheaply with an ionic liquid.[257] In April 1972, the Apollo 16 mission recorded various astronomical photos and spectra in ultraviolet with the Far Ultraviolet Camera/Spectrograph.[258] The Moon has been also a site of Earth observation, particularly culturally as in the imagery called Earthrise. Living on the Moon Main article: Lunar habitation Astronaut Buzz Aldrin in life-supporting suit looking back at the first lunar habitat and base, the Lunar Module Eagle of Tranquility Base, during Apollo 11 (1969), the first crewed Moon landing The only instances of humans living on the Moon have taken place in an Apollo Lunar Module for several days at a time (for example, during the Apollo 17 mission).[259] One challenge to astronauts during their stay on the surface is that lunar dust sticks to their suits and is carried into their quarters. Astronauts could taste and smell the dust, calling it the "Apollo aroma".[260] This fine lunar dust can cause health issues.[260] In 2019, at least one plant seed sprouted in an experiment on the Chang'e 4 lander. It was carried from Earth along with other small life in its Lunar Micro Ecosystem.... In culture and life Calendar Further information: Lunar calendar, Lunisolar calendar, and Metonic cycle The Venus of Laussel (c. 25,000 BP) holding a crescent shaped horn, the 13 notches on the horn may symbolize the number of days from menstruation to ovulation, or of menstrual cycles or moons per year.[277][278] Since pre-historic times people have taken note of the Moon's phases, its waxing and waning, and used it to keep record of time. Tally sticks, notched bones dating as far back as 20–30,000 years ago, are believed by some to mark the phases of the Moon.[200][279][280] The counting of the days between the Moon's phases gave eventually rise to generalized time periods of the full lunar cycle as months, and possibly of its phases as weeks.[281] The words for the month in a range of different languages carry this relation between the period of the month and the Moon etymologically. The English month as well as moon, and its cognates in other Indo-European languages (e.g. the Latin mensis and Ancient Greek μείς (meis) or μήν (mēn), meaning "month")[282][283][284][285] stem from the Proto-Indo-European (PIE) root of moon, *méh1nōt, derived from the PIE verbal root *meh1-, "to measure", "indicat[ing] a functional conception of the Moon, i.e. marker of the month" (cf. the English words measure and menstrual).[286][287][288] To give another example from a different language family, the Chinese language uses the same word (月) for moon as well as for month, which furthermore can be found in the symbols for the word week (星期). This lunar timekeeping gave rise to the historically dominant, but varied, lunisolar calendars. The 7th-century Islamic calendar is an example of a purely lunar calendar, where months are traditionally determined by the visual sighting of the hilal, or earliest crescent moon, over the horizon.[289] Of particular significance has been the occasion of full moon, highlighted and celebrated in a range of calendars and cultures. Around autumnal equinox, the Full Moon is called the Harvest Moon and is celebrated with festivities such as the Harvest Moon Festival of the Chinese Lunar Calendar, its second most important celebration after Chinese New Year.[290] Furthermore, association of time with the Moon can also be found in religion, such as the ancient Egyptian temporal and lunar deity Khonsu. Cultural representation Further information: Cultural astronomy, Archaeoastronomy, Lunar deity, Selene, Luna (goddess), Crescent, and Man in the Moon See also: Nocturne (painting) and Moon magic Recurring lunar aspects of lunar deities Sumerian cylinder seal and impression, dated c. 2100 BC, of Ḫašḫamer, ensi (governor) of Iškun-Sin c. 2100 BC. The seated figure is probably king Ur-Nammu, bestowing the governorship on Ḫašḫamer, who is led before him by Lamma (protective goddess).[291] The crescent (Nanna/Sîn, c. 2100 BC Luna on the Parabiago plate (2nd–5th century), featuring the crescent crown and chariot lunar aspect found in different cultures. Crescent headgear and chariot (Luna, 2nd–5th century) Rabbits are in a range of cultures identified with the Moon, from China to the Indigenous peoples of the Americas, as with the rabbit (on the left) of the Maya moon goddess (6th–9th century). A Moon rabbit (Mayan moon goddess, 6th–9th century) Since prehistoric and ancient times humans have drawn the Moon and have described a range of understandings of it, having prominent importance in different cosmologies, often exhibiting a spirit, being a deity or an aspect, particularly in astrology. For the representation of the Moon, especially its lunar phases, the crescent symbol (🌙) has been particularly used by many cultures. In writing systems such as Chinese the crescent has developed into the symbol 月, the word for Moon, and in ancient Egyptian it was the symbol 𓇹, which is spelled like the ancient Egyptian lunar deity Iah, meaning Moon.[292] Iconographically the crescent was used in Mesopotamia as the primary symbol of Nanna/Sîn,[293] the ancient Sumerian lunar deity,[294][293] who was the father of Innana/Ishtar, the goddess of the planet Venus (symbolized as the eight pointed Star of Ishtar),[294][293] and Utu/Shamash, the god of the Sun (symbolized as a disc, optionally with eight rays),[294][293] all three often depicted next to each other. Nanna was later known as Sîn,[293][294] and was particularly associated with magic and sorcery.[294] The crescent was further used as an element of lunar deities wearing headgears or crowns in an arrangement reminiscent of horns, as in the case of the ancient Greek Selene[295][296] or the ancient Egyptian Khonsu. Selene is associated with Artemis and paralleled by the Roman Luna, which both are occasionally depicted driving a chariot, like the Hindu lunar deity Chandra. The different or sharing aspects of deities within pantheons has been observed in many cultures, especially by later or contemporary culture, particularly forming triple deities. The Moon in Roman mythology for example has been associated with Juno and Diana, while Luna being identified as their byname and as part of a triplet (diva triformis) with Diana and Proserpina, Hecate being identified as their binding manifestation as trimorphos. The star and crescent (☪️) arrangement goes back to the Bronze Age, representing either the Sun and Moon, or the Moon and planet Venus, in combination. It came to represent the goddess Artemis or Hecate, and via the patronage of Hecate came to be used as a symbol of Byzantium, possibly influencing the development of the Ottoman flag, specifically the combination of the Turkish crescent with a star.[297] Since then the heraldric use of the star and crescent proliferated becoming a popular symbol for Islam (as the hilal of the Islamic calendar) and for a range of nations.[298] In Roman Catholic Marian veneration, the Virgin Mary (Queen of Heaven) has been depicted since the late Middle Ages on a crescent and adorned with stars. In Islam Muhammad is particularly attributed with the Moon through the so-called splitting of the Moon (Arabic: انشقاق القمر) miracle.[299] The contrast between the brighter highlands and the darker maria have been seen by different cultures forming abstract shapes, which are among others the Man in the Moon or the Moon Rabbit (e.g. the Chinese Tu'er Ye or in Indigenous American mythologies, as with the aspect of the Mayan Moon goddess).[291] In Western alchemy silver is associated with the Moon, and gold with the Sun.[300] Modern culture representation See also: Moon in science fiction and List of appearances of the Moon in fiction The Moon is prominently featured in Vincent van Gogh's 1889 painting, The Starry Night (left). An iconic image of the Man in the Moon from the first science-fiction film set in space, A Trip to the Moon (1902), inspired by a history of literature about going to the Moon (right). The perception of the Moon in modern times has been informed by telescope enabled modern astronomy and later by spaceflight enabled actual human activity at the Moon, particularly the culturally impactful lunar landings. These new insights inspired cultural references, connecting romantic reflections about the Moon[301] and speculative fiction such as science-fiction dealing with the Moon.[302][303] Contemporarily the Moon has been seen as a place for economic expansion into space, with missions prospecting for lunar resources. This has been accompanied with renewed public and critical reflection on humanity's cultural and legal relation to the celestial body, especially regarding colonialism,[248] as in the 1970 poem "Whitey on the Moon". In this light the Moon's nature has been invoked,[274] particularly for lunar conservation[250] and as a common.[304][268][276] Lunar effect Main article: Lunar effect The lunar effect is a purported unproven correlation between specific stages of the roughly 29.5-day lunar cycle and behavior and physiological changes in living beings on Earth, including humans. The Moon has long been associated with insanity and irrationality; the words lunacy and lunatic are derived from the Latin name for the Moon, Luna. Philosophers Aristotle and Pliny the Elder argued that the full moon induced insanity in susceptible individuals, believing that the brain, which is mostly water, must be affected by the Moon and its power over the tides, but the Moon's gravity is too slight to affect any single person.[305] Even today, people who believe in a lunar effect claim that admissions to psychiatric hospitals, traffic accidents, homicides or suicides increase during a full moon, but dozens of studies invalidate these claims." (wikipedia.org) "The Solar System[c] is the gravitationally bound system of the Sun and the objects that orbit it. It formed 4.6 billion years ago from the gravitational collapse of a giant interstellar molecular cloud. The vast majority (99.86%) of the system's mass is in the Sun, with most of the remaining mass contained in the planet Jupiter. The planetary system around the Sun contains eight planets. The four inner system planets—Mercury, Venus, Earth and Mars—are terrestrial planets, being composed primarily of rock and metal. The four giant planets of the outer system are substantially larger and more massive than the terrestrials. The two largest, Jupiter and Saturn, are gas giants, being composed mainly of hydrogen and helium; the next two, Uranus and Neptune, are ice giants, being composed mostly of volatile substances with relatively high melting points compared with hydrogen and helium, such as water, ammonia, and methane. All eight planets have nearly circular orbits that lie near the plane of Earth's orbit, called the ecliptic. There are an unknown number of smaller dwarf planets and innumerable small Solar System bodies orbiting the Sun.[d] Six of the major planets, the six largest possible dwarf planets, and many of the smaller bodies are orbited by natural satellites, commonly called "moons" after Earth's Moon. Two natural satellites, Jupiter's moon Ganymede and Saturn's moon Titan, are larger than Mercury, the smallest terrestrial planet, though less massive, and Jupiter's moon Callisto is nearly as large. Each of the giant planets and some smaller bodies are encircled by planetary rings of ice, dust and moonlets. The asteroid belt, which lies between the orbits of Mars and Jupiter, contains objects composed of rock, metal and ice. Beyond Neptune's orbit lie the Kuiper belt and scattered disc, which are populations of objects composed mostly of ice and rock. In the outer reaches of the Solar System lies a class of minor planets called detached objects. There is considerable debate as to how many such objects there will prove to be.[9] Some of these objects are large enough to have rounded under their own gravity and thus to be categorized as dwarf planets. Astronomers generally accept about nine objects as dwarf planets: the asteroid Ceres, the Kuiper-belt objects Pluto, Orcus, Haumea, Quaoar, and Makemake, and the scattered-disc objects Gonggong, Eris, and Sedna.[d] Various small-body populations, including comets, centaurs and interplanetary dust clouds, freely travel between the regions of the Solar System. The solar wind, a stream of charged particles flowing outwards from the Sun, creates a bubble-like region of interplanetary medium in the interstellar medium known as the heliosphere. The heliopause is the point at which pressure from the solar wind is equal to the opposing pressure of the interstellar medium; it extends out to the edge of the scattered disc. The Oort cloud, which is thought to be the source for long-period comets, may also exist at a distance roughly a thousand times further than the heliosphere. The Solar System is located 26,000 light-years from the center of the Milky Way galaxy in the Orion Arm, which contains most of the visible stars in the night sky. The nearest stars are within the so-called Local Bubble, with the closest, Proxima Centauri, at 4.2441 light-years.... Inner Solar System Overview of the Inner Solar System up to the Jovian System The inner Solar System is the region comprising the terrestrial planets and the asteroid belt.[87] Composed mainly of silicates and metals,[88] the objects of the inner Solar System are relatively close to the Sun; the radius of this entire region is less than the distance between the orbits of Jupiter and Saturn. This region is also within the frost line, which is a little less than 5 AU (750 million km; 460 million mi) from the Sun.[28] Inner planets Main article: Terrestrial planet The four terrestrial planets Mercury, Venus, Earth and Mars The four terrestrial or inner planets have dense, rocky compositions, few or no moons, and no ring systems. They are composed largely of refractory minerals such as the silicates—which form their crusts and mantles—and metals such as iron and nickel which form their cores. Three of the four inner planets (Venus, Earth and Mars) have atmospheres substantial enough to generate weather; all have impact craters and tectonic surface features, such as rift valleys and volcanoes. The term inner planet should not be confused with inferior planet, which designates those planets that are closer to the Sun than Earth is (i.e. Mercury and Venus).[89] Mercury Main article: Mercury (planet) Mercury (0.307–0.588 AU (45.9–88.0 million km; 28.5–54.7 million mi) from the Sun[90]) is the closest planet to the Sun. The smallest planet in the Solar System (0.055 MEarth), Mercury has no natural satellites. The dominant geological features are impact craters or basins with ejecta blankets, the remains of early volcanic activity including magma flows, and lobed ridges or rupes that were probably produced by a period of contraction early in the planet's history.[91] Mercury's very tenuous atmosphere consists of solar-wind particles trapped by Mercury's magnetic field, as well as atoms blasted off its surface by the solar wind.[92][93] Its relatively large iron core and thin mantle have not yet been adequately explained. Hypotheses include that its outer layers were stripped off by a giant impact, or that it was prevented from fully accreting by the young Sun's energy.[94][95] There have been searches for "Vulcanoids", asteroids in stable orbits between Mercury and the Sun, but none have been discovered.[96][97] Venus Main article: Venus Venus (0.718–0.728 AU (107.4–108.9 million km; 66.7–67.7 million mi) from the Sun[90]) is close in size to Earth (0.815 MEarth) and, like Earth, has a thick silicate mantle around an iron core, a substantial atmosphere, and evidence of internal geological activity. It is much drier than Earth, and its atmosphere is ninety times as dense. Venus has no natural satellites. It is the hottest planet, with surface temperatures over 400 °C (752 °F), mainly due to the amount of greenhouse gases in the atmosphere.[98] The planet has no magnetic field that would prevent depletion of its substantial atmosphere, which suggests that its atmosphere is being replenished by volcanic eruptions.[99] A relatively young planetary surface displays extensive evidence of volcanic activity, but is devoid of plate tectonics. It may undergo resurfacing episodes on a time scale of 700 million years.[100] Earth Main article: Earth Earth (0.983–1.017 AU (147.1–152.1 million km; 91.4–94.5 million mi) from the Sun) is the largest and densest of the inner planets, the only one known to have current geological activity, and the only place where life is known to exist.[101] Its liquid hydrosphere is unique among the terrestrial planets, and it is the only planet where plate tectonics has been observed.[102] Earth's atmosphere is radically different from those of the other planets, having been altered by the presence of life to contain 21% free oxygen.[103][104] The planetary magnetosphere shields the surface from solar and cosmic radiation, limiting atmospheric stripping and maintaining habitability.[105] It has one natural satellite, the Moon, the only large satellite of a terrestrial planet in the Solar System. Mars Main article: Mars Mars (1.382–1.666 AU (206.7–249.2 million km; 128.5–154.9 million mi) from the Sun) is smaller than Earth and Venus (0.107 MEarth). It has an atmosphere of mostly carbon dioxide with a surface pressure of 6.1 millibars (0.088 psi; 0.18 inHg); roughly 0.6% of that of Earth but sufficient to support weather phenomena.[106] Its surface, peppered with volcanoes, such as Olympus Mons, and rift valleys, such as Valles Marineris, shows geological activity that may have persisted until as recently as 2 million years ago.[107] Its red color comes from iron oxide (rust) in its soil.[108] Mars has two tiny natural satellites (Deimos and Phobos) thought to be either captured asteroids,[109] or ejected debris from a massive impact early in Mars's history.[110] Asteroid belt Main articles: Asteroid belt and Asteroid Linear map of the inner Solar System, showing many asteroid populations Asteroids except for the largest, Ceres, are classified as small Solar System bodies[d] and are composed mainly of refractory rocky and metallic minerals, with some ice.[111][112] They range from a few metres to hundreds of kilometres in size. Asteroids smaller than one meter are usually called meteoroids and micrometeoroids (grain-sized), with the exact division between the two categories being debated over the years.[113] As of 2017, the IAU designates asteroids having diameter between about 30 micrometres and 1 metre as micrometeroids, and terms smaller particles "dust".[114] The asteroid belt occupies the orbit between Mars and Jupiter, between 2.3 and 3.3 AU (340 and 490 million km; 210 and 310 million mi) from the Sun. It is thought to be remnants from the Solar System's formation that failed to coalesce because of the gravitational interference of Jupiter.[115] The asteroid belt contains tens of thousands, possibly millions, of objects over one kilometre in diameter.[116] Despite this, the total mass of the asteroid belt is unlikely to be more than a thousandth of that of Earth.[46] The asteroid belt is very sparsely populated; spacecraft routinely pass through without incident.[117] Ceres Main article: Ceres (dwarf planet) Ceres (2.77 AU (414 million km; 257 million mi) from the Sun) is the largest asteroid, a protoplanet, and a dwarf planet.[d] It has a diameter of slightly under 1,000 km (620 mi) and a mass large enough for its own gravity to pull it into a spherical shape. Ceres was considered a planet when it was discovered in 1801, but as further observations revealed additional asteroids, it became common to consider it as one of the minor rather than major planets.[118] It was then reclassified again as a dwarf planet in 2006 when the IAU definition of planet was established.[119]: 218  Pallas and Vesta Main articles: 2 Pallas and 4 Vesta Pallas (2.77 AU from the Sun) and Vesta (2.36 AU from the Sun) are the largest asteroids in the asteroid belt, after Ceres. They are the other two protoplanets that survive more or less intact. At about 520 km (320 mi) in diameter, they were large enough to have developed planetary geology in the past, but both have suffered large impacts and been battered out of being round.[120][121][122] Fragments from impacts upon these two bodies survive elsewhere in the asteroid belt, as the Pallas family and Vesta family. Both were considered planets upon their discoveries in 1802 and 1807 respectively, and then like Ceres generally considered as minor planets with the discovery of more asteroids. Some authors today have begun to consider Pallas and Vesta as planets again, along with Ceres, under geophysical definitions of the term.[5] Asteroid groups Asteroids in the asteroid belt are divided into asteroid groups and families based on their orbital characteristics. Kirkwood gaps are sharp dips in the distribution of asteroid orbits that correspond to orbital resonances with Jupiter.[123] Asteroid moons are asteroids that orbit larger asteroids. They are not as clearly distinguished as planetary moons, sometimes being almost as large as their partners (e.g. that of 90 Antiope). The asteroid belt includes main-belt comets, which may have been the source of Earth's water.[124] Jupiter trojans are located in either of Jupiter's L4 or L5 points (gravitationally stable regions leading and trailing a planet in its orbit); the term trojan is also used for small bodies in any other planetary or satellite Lagrange point. Hilda asteroids are in a 2:3 resonance with Jupiter; that is, they go around the Sun three times for every two Jupiter orbits.[125] The inner Solar System contains near-Earth asteroids, many of which cross the orbits of the inner planets.[126] Some of them are potentially hazardous objects.[127] Outer Solar System Plot of objects around the Kuiper belt and other asteroid populations, the J, S, U and N denotes Jupiter, Saturn, Uranus and Neptune The outer region of the Solar System is home to the giant planets and their large moons. The centaurs and many short-period comets also orbit in this region. Due to their greater distance from the Sun, the solid objects in the outer Solar System contain a higher proportion of volatiles, such as water, ammonia, and methane than those of the inner Solar System because the lower temperatures allow these compounds to remain solid.[16] Outer planets Main article: Giant planet The outer planets Jupiter, Saturn, Uranus and Neptune, compared to the inner planets Earth, Venus, Mars, and Mercury at the bottom right The four outer planets, also called giant planets or Jovian planets, collectively make up 99% of the mass known to orbit the Sun.[f] Jupiter and Saturn are together more than 400 times the mass of Earth and consist overwhelmingly of the gases hydrogen and helium, hence their designation as gas giants.[128] Uranus and Neptune are far less massive—less than 20 Earth masses (MEarth) each—and are composed primarily of ices. For these reasons, some astronomers suggest they belong in their own category, ice giants.[129] All four giant planets have rings, although only Saturn's ring system is easily observed from Earth. The term superior planet designates planets outside Earth's orbit and thus includes both the outer planets and Mars.[89] The ring–moon systems of Jupiter, Saturn, and Uranus are like miniature versions of the Solar System; that of Neptune is significantly different, having been disrupted by the capture of its largest moon Triton.[130] Jupiter Main article: Jupiter Jupiter (4.951–5.457 AU (740.7–816.4 million km; 460.2–507.3 million mi) from the Sun[90]), at 318 MEarth, is 2.5 times the mass of all the other planets put together. It is composed largely of hydrogen and helium. Jupiter's strong internal heat creates semi-permanent features in its atmosphere, such as cloud bands and the Great Red Spot. The planet possesses a 4.2–14 Gauss strength magnetosphere that spans 22–29 million km, making it, in certain respects, the largest object in the Solar System.[131] Jupiter has 95 known satellites. The four largest, Ganymede, Callisto, Io, and Europa, are called the Galilean moons: they show similarities to the terrestrial planets, such as volcanism and internal heating.[132] Ganymede, the largest satellite in the Solar System, is larger than Mercury; Callisto is almost as large.[133] Saturn Main article: Saturn Saturn (9.075–10.07 AU (1.3576–1.5065 billion km; 843.6–936.1 million mi) from the Sun[90]), distinguished by its extensive ring system, has several similarities to Jupiter, such as its atmospheric composition and magnetosphere. Although Saturn has 60% of Jupiter's volume, it is less than a third as massive, at 95 MEarth. Saturn is the only planet of the Solar System that is less dense than water. The rings of Saturn are made up of small ice and rock particles.[134] Saturn has 83 confirmed satellites composed largely of ice. Two of these, Titan and Enceladus, show signs of geological activity;[135] they, as well as five other Saturnian moons (Iapetus, Rhea, Dione, Tethys, and Mimas), are large enough to be round. Titan, the second-largest moon in the Solar System, is bigger than Mercury and the only satellite in the Solar System to have a substantial atmosphere.[136][137] Uranus Main article: Uranus Uranus (18.27–20.06 AU (2.733–3.001 billion km; 1.698–1.865 billion mi) from the Sun[90]), at 14 MEarth, has the lowest mass of the outer planets. Uniquely among the planets, it orbits the Sun on its side; its axial tilt is over ninety degrees to the ecliptic. This gives the planet extreme seasonal variation as each pole points toward and then away from the Sun.[138] It has a much colder core than the other giant planets and radiates very little heat into space.[139] As a consequence, it has the coldest planetary atmosphere in the Solar System.[140] Uranus has 27 known satellites, the largest ones being Titania, Oberon, Umbriel, Ariel, and Miranda.[141] Like the other giant planets, it possesses a ring system and magnetosphere.[142] Neptune Main article: Neptune Neptune (29.89–30.47 AU (4.471–4.558 billion km; 2.778–2.832 billion mi) from the Sun[90]), though slightly smaller than Uranus, is more massive (17 MEarth) and hence more dense. It radiates more internal heat than Uranus, but not as much as Jupiter or Saturn.[143] Neptune has 14 known satellites. The largest, Triton, is geologically active, with geysers of liquid nitrogen.[144] Triton is the only large satellite with a retrograde orbit, which indicates that it did not form with Neptune, but was probably captured from the Kuiper belt.[145] Neptune is accompanied in its orbit by several minor planets, termed Neptune trojans, that either lead or trail the planet by about one-sixth of the way around the Sun, positions known as Lagrange points.[146] Centaurs Main article: Centaur (small Solar System body) The centaurs are icy comet-like bodies whose orbits have semi-major axes greater than Jupiter's (5.5 AU (820 million km; 510 million mi)) and less than Neptune's (30 AU (4.5 billion km; 2.8 billion mi)). These are former Kuiper belt and scattered disc objects that were gravitationally perturbed closer to the Sun by the outer planets, and are expected to become comets or get ejected out of the Solar System.[45] While most centaurs are inactive and asteroid-like, some exhibit clear cometary activity, such as the first centaur discovered, 2060 Chiron, which has been classified as a comet (95P) because it develops a coma just as comets do when they approach the Sun.[147] The largest known centaur, 10199 Chariklo, has a diameter of about 250 km (160 mi) and is one of the only few minor planets known to possess a ring system." (wikipedia.org) "Outer space, commonly shortened to space, is an infinite expanse that exists beyond Earth and its atmosphere and between celestial bodies. Outer space is not completely empty; it is a near-perfect vacuum[1] containing a low density of particles, predominantly a plasma of hydrogen and helium, as well as electromagnetic radiation, magnetic fields, neutrinos, dust, and cosmic rays. The baseline temperature of outer space, as set by the background radiation from the Big Bang, is 2.7 kelvins (−270 °C; −455 °F).[2] The plasma between galaxies is thought to account for about half of the baryonic (ordinary) matter in the universe, having a number density of less than one hydrogen atom per cubic metre and a kinetic temperature of millions of kelvins.[3] Local concentrations of matter have condensed into stars and galaxies. Intergalactic space takes up most of the volume of the universe, but even galaxies and star systems consist almost entirely of empty space. Most of the remaining mass-energy in the observable universe is made up of an unknown form, dubbed dark matter and dark energy.[4][5][6][7] Outer space does not begin at a definite altitude above Earth's surface. The Kármán line, an altitude of 100 km (62 mi) above sea level,[8][9] is conventionally used as the start of outer space in space treaties and for aerospace records keeping. Certain portions of the upper stratosphere and the mesosphere are sometimes referred to as "near space". The framework for international space law was established by the Outer Space Treaty, which entered into force on 10 October 1967. This treaty precludes any claims of national sovereignty and permits all states to freely explore outer space. Despite the drafting of UN resolutions for the peaceful uses of outer space, anti-satellite weapons have been tested in Earth orbit. Humans began the physical exploration of space during the 20th century with the advent of high-altitude balloon flights. This was followed by crewed rocket flights and, then, crewed Earth orbit, first achieved by Yuri Gagarin of the Soviet Union in 1961. The economic cost of putting objects, including humans, into space is very high, limiting human spaceflight to low Earth orbit and the Moon. On the other hand, uncrewed spacecraft have reached all of the known planets in the Solar System. Outer space represents a challenging environment for human exploration because of the hazards of vacuum and radiation. Microgravity has a negative effect on human physiology that causes both muscle atrophy and bone loss. Formation and state Main article: Big Bang This is an artist's concept of the metric expansion of space, where a volume of the Universe is represented at each time interval by the circular sections. At left is depicted the rapid inflation from the initial state, followed thereafter by steadier expansion to the present day, shown at right. A black background with luminous shapes of various sizes scattered randomly about. They typically have white, red or blue hues. Part of the Hubble Ultra-Deep Field image showing a typical section of space containing galaxies interspersed by deep vacuum. Given the finite speed of light, this view covers the past 13 billion years of the history of outer space. The size of the whole universe is unknown, and it might be infinite in extent.[10] According to the Big Bang theory, the very early Universe was an extremely hot and dense state about 13.8 billion years ago[11] which rapidly expanded. About 380,000 years later the Universe had cooled sufficiently to allow protons and electrons to combine and form hydrogen—the so-called recombination epoch. When this happened, matter and energy became decoupled, allowing photons to travel freely through the continually expanding space.[12] Matter that remained following the initial expansion has since undergone gravitational collapse to create stars, galaxies and other astronomical objects, leaving behind a deep vacuum that forms what is now called outer space.[13] As light has a finite velocity, this theory also constrains the size of the directly observable universe.[12] The present day shape of the universe has been determined from measurements of the cosmic microwave background using satellites like the Wilkinson Microwave Anisotropy Probe. These observations indicate that the spatial geometry of the observable universe is "flat", meaning that photons on parallel paths at one point remain parallel as they travel through space to the limit of the observable universe, except for local gravity.[14] The flat Universe, combined with the measured mass density of the Universe and the accelerating expansion of the Universe, indicates that space has a non-zero vacuum energy, which is called dark energy.[15] Estimates put the average energy density of the present day Universe at the equivalent of 5.9 protons per cubic meter, including dark energy, dark matter, and baryonic matter (ordinary matter composed of atoms). The atoms account for only 4.6% of the total energy density, or a density of one proton per four cubic meters.[16] The density of the Universe is clearly not uniform; it ranges from relatively high density in galaxies—including very high density in structures within galaxies, such as planets, stars, and black holes—to conditions in vast voids that have much lower density, at least in terms of visible matter.[17] Unlike matter and dark matter, dark energy seems not to be concentrated in galaxies: although dark energy may account for a majority of the mass-energy in the Universe, dark energy's influence is 5 orders of magnitude smaller than the influence of gravity from matter and dark matter within the Milky Way.[18] Environment The interplanetary dust cloud illuminated and visible as zodiacal light, with its parts the false dawn,[19] gegenschein and the rest of its band, which is visually crossed by the Milky Way Outer space is the closest known approximation to a perfect vacuum. It has effectively no friction, allowing stars, planets, and moons to move freely along their ideal orbits, following the initial formation stage. The deep vacuum of intergalactic space is not devoid of matter, as it contains a few hydrogen atoms per cubic meter.[20] By comparison, the air humans breathe contains about 1025 molecules per cubic meter.[21][22] The low density of matter in outer space means that electromagnetic radiation can travel great distances without being scattered: the mean free path of a photon in intergalactic space is about 1023 km, or 10 billion light years.[23] In spite of this, extinction, which is the absorption and scattering of photons by dust and gas, is an important factor in galactic and intergalactic astronomy.[24] Stars, planets, and moons retain their atmospheres by gravitational attraction. Atmospheres have no clearly delineated upper boundary: the density of atmospheric gas gradually decreases with distance from the object until it becomes indistinguishable from outer space.[25] The Earth's atmospheric pressure drops to about 0.032 Pa at 100 kilometres (62 miles) of altitude,[26] compared to 100,000 Pa for the International Union of Pure and Applied Chemistry (IUPAC) definition of standard pressure. Above this altitude, isotropic gas pressure rapidly becomes insignificant when compared to radiation pressure from the Sun and the dynamic pressure of the solar wind. The thermosphere in this range has large gradients of pressure, temperature and composition, and varies greatly due to space weather.[27] The temperature of outer space is measured in terms of the kinetic activity of the gas,[28] as it is on Earth. The radiation of outer space has a different temperature than the kinetic temperature of the gas, meaning that the gas and radiation are not in thermodynamic equilibrium.[29][30] All of the observable universe is filled with photons that were created during the Big Bang, which is known as the cosmic microwave background radiation (CMB). (There is quite likely a correspondingly large number of neutrinos called the cosmic neutrino background.[31]) The current black body temperature of the background radiation is about 3 K (−270 °C; −454 °F).[32] The gas temperatures in outer space can vary widely. For example, the temperature in the Boomerang Nebula is 1 K,[33] while the solar corona reaches temperatures over 1.2–2.6 million K.[34] Magnetic fields have been detected in the space around just about every class of celestial object. Star formation in spiral galaxies can generate small-scale dynamos, creating turbulent magnetic field strengths of around 5–10 μG. The Davis–Greenstein effect causes elongated dust grains to align themselves with a galaxy's magnetic field, resulting in weak optical polarization. This has been used to show ordered magnetic fields exist in several nearby galaxies. Magneto-hydrodynamic processes in active elliptical galaxies produce their characteristic jets and radio lobes. Non-thermal radio sources have been detected even among the most distant, high-z sources, indicating the presence of magnetic fields.[35] Outside a protective atmosphere and magnetic field, there are few obstacles to the passage through space of energetic subatomic particles known as cosmic rays. These particles have energies ranging from about 106 eV up to an extreme 1020 eV of ultra-high-energy cosmic rays.[36] The peak flux of cosmic rays occurs at energies of about 109 eV, with approximately 87% protons, 12% helium nuclei and 1% heavier nuclei. In the high energy range, the flux of electrons is only about 1% of that of protons.[37] Cosmic rays can damage electronic components and pose a health threat to space travelers.[38] According to astronauts, like Don Pettit, space has a burned/metallic odor that clings to their suits and equipment, similar to the scent of an arc welding torch.[39][40] Effect on biology and human bodies Main articles: Effect of spaceflight on the human body, Bioastronautics, Uncontrolled decompression, and Weightlessness See also: Astrobiology, Astrobotany, Plants in space, and Animals in space The lower half shows a blue planet with patchy white clouds. The upper half has a man in a white spacesuit and maneuvering unit against a black background. Because of the hazards of a vacuum, astronauts must wear a pressurized space suit while off-Earth and outside their spacecraft. Despite the harsh environment, several life forms have been found that can withstand extreme space conditions for extended periods. Species of lichen carried on the ESA BIOPAN facility survived exposure for ten days in 2007.[41] Seeds of Arabidopsis thaliana and Nicotiana tabacum germinated after being exposed to space for 1.5 years.[42] A strain of Bacillus subtilis has survived 559 days when exposed to low Earth orbit or a simulated martian environment.[43] The lithopanspermia hypothesis suggests that rocks ejected into outer space from life-harboring planets may successfully transport life forms to another habitable world. A conjecture is that just such a scenario occurred early in the history of the Solar System, with potentially microorganism-bearing rocks being exchanged between Venus, Earth, and Mars.[44] Even at relatively low altitudes in the Earth's atmosphere, conditions are hostile to the human body. The altitude where atmospheric pressure matches the vapor pressure of water at the temperature of the human body is called the Armstrong line, named after American physician Harry G. Armstrong. It is located at an altitude of around 19.14 km (11.89 mi). At or above the Armstrong line, fluids in the throat and lungs boil away. More specifically, exposed bodily liquids such as saliva, tears, and liquids in the lungs boil away. Hence, at this altitude, human survival requires a pressure suit, or a pressurized capsule.[45] Out in space, sudden exposure of an unprotected human to very low pressure, such as during a rapid decompression, can cause pulmonary barotrauma—a rupture of the lungs, due to the large pressure differential between inside and outside the chest.[46] Even if the subject's airway is fully open, the flow of air through the windpipe may be too slow to prevent the rupture.[47] Rapid decompression can rupture eardrums and sinuses, bruising and blood seep can occur in soft tissues, and shock can cause an increase in oxygen consumption that leads to hypoxia.[48] As a consequence of rapid decompression, oxygen dissolved in the blood empties into the lungs to try to equalize the partial pressure gradient. Once the deoxygenated blood arrives at the brain, humans lose consciousness after a few seconds and die of hypoxia within minutes.[49] Blood and other body fluids boil when the pressure drops below 6.3 kPa, and this condition is called ebullism.[50] The steam may bloat the body to twice its normal size and slow circulation, but tissues are elastic and porous enough to prevent rupture. Ebullism is slowed by the pressure containment of blood vessels, so some blood remains liquid.[51][52] Swelling and ebullism can be reduced by containment in a pressure suit. The Crew Altitude Protection Suit (CAPS), a fitted elastic garment designed in the 1960s for astronauts, prevents ebullism at pressures as low as 2 kPa.[53] Supplemental oxygen is needed at 8 km (5 mi) to provide enough oxygen for breathing and to prevent water loss, while above 20 km (12 mi) pressure suits are essential to prevent ebullism.[54] Most space suits use around 30–39 kPa of pure oxygen, about the same as on the Earth's surface. This pressure is high enough to prevent ebullism, but evaporation of nitrogen dissolved in the blood could still cause decompression sickness and gas embolisms if not managed.[55] Humans evolved for life in Earth gravity, and exposure to weightlessness has been shown to have deleterious effects on human health. Initially, more than 50% of astronauts experience space motion sickness. This can cause nausea and vomiting, vertigo, headaches, lethargy, and overall malaise. The duration of space sickness varies, but it typically lasts for 1–3 days, after which the body adjusts to the new environment. Longer-term exposure to weightlessness results in muscle atrophy and deterioration of the skeleton, or spaceflight osteopenia. These effects can be minimized through a regimen of exercise.[56] Other effects include fluid redistribution, slowing of the cardiovascular system, decreased production of red blood cells, balance disorders, and a weakening of the immune system. Lesser symptoms include loss of body mass, nasal congestion, sleep disturbance, and puffiness of the face.[57] During long-duration space travel, radiation can pose an acute health hazard. Exposure to high-energy, ionizing cosmic rays can result in fatigue, nausea, vomiting, as well as damage to the immune system and changes to the white blood cell count. Over longer durations, symptoms include an increased risk of cancer, plus damage to the eyes, nervous system, lungs and the gastrointestinal tract.[58] On a round-trip Mars mission lasting three years, a large fraction of the cells in an astronaut's body would be traversed and potentially damaged by high energy nuclei.[59] The energy of such particles is significantly diminished by the shielding provided by the walls of a spacecraft and can be further diminished by water containers and other barriers. The impact of the cosmic rays upon the shielding produces additional radiation that can affect the crew. Further research is needed to assess the radiation hazards and determine suitable countermeasures.... Interplanetary space Main article: Interplanetary medium At lower left, a white coma stands out against a black background. Nebulous material streams away to the top and left, slowly fading with distance. The sparse plasma (blue) and dust (white) in the tail of comet Hale–Bopp are being shaped by pressure from solar radiation and the solar wind, respectively. Interplanetary space is defined by the solar wind, a continuous stream of charged particles emanating from the Sun that creates a very tenuous atmosphere (the heliosphere) for billions of kilometers into space. This wind has a particle density of 5–10 protons/cm3 and is moving at a velocity of 350–400 km/s (780,000–890,000 mph).[105] Interplanetary space extends out to the heliopause where the influence of the galactic environment starts to dominate over the magnetic field and particle flux from the Sun.[83] The distance and strength of the heliopause varies depending on the activity level of the solar wind.[106] The heliopause in turn deflects away low-energy galactic cosmic rays, with this modulation effect peaking during solar maximum.[107] The volume of interplanetary space is a nearly total vacuum, with a mean free path of about one astronomical unit at the orbital distance of the Earth. This space is not completely empty, and is sparsely filled with cosmic rays, which include ionized atomic nuclei and various subatomic particles. There is also gas, plasma and dust,[108] small meteors, and several dozen types of organic molecules discovered to date by microwave spectroscopy.[109] A cloud of interplanetary dust is visible at night as a faint band called the zodiacal light.[110] Interplanetary space contains the magnetic field generated by the Sun.[105] There are also magnetospheres generated by planets such as Jupiter, Saturn, Mercury and the Earth that have their own magnetic fields. These are shaped by the influence of the solar wind into the approximation of a teardrop shape, with the long tail extending outward behind the planet. These magnetic fields can trap particles from the solar wind and other sources, creating belts of charged particles such as the Van Allen radiation belts. Planets without magnetic fields, such as Mars, have their atmospheres gradually eroded by the solar wind.[111] Interstellar space Main article: Interstellar medium "Interstellar space" redirects here. For the album, see Interstellar Space. Patchy orange and blue nebulosity against a black background, with a curved orange arc wrapping around a star at the center. Bow shock formed by the magnetosphere of the young star LL Orionis (center) as it collides with the Orion Nebula flow Interstellar space is the physical space within a galaxy beyond the influence each star has upon the encompassed plasma.[84] The contents of interstellar space are called the interstellar medium. Approximately 70% of the mass of the interstellar medium consists of lone hydrogen atoms; most of the remainder consists of helium atoms. This is enriched with trace amounts of heavier atoms formed through stellar nucleosynthesis. These atoms are ejected into the interstellar medium by stellar winds or when evolved stars begin to shed their outer envelopes such as during the formation of a planetary nebula.[112] The cataclysmic explosion of a supernova generates an expanding shock wave consisting of ejected materials that further enrich the medium.[113] The density of matter in the interstellar medium can vary considerably: the average is around 106 particles per m3,[114] but cold molecular clouds can hold 108–1012 per m3.[29][112] A number of molecules exist in interstellar space, as can tiny 0.1 μm dust particles.[115] The tally of molecules discovered through radio astronomy is steadily increasing at the rate of about four new species per year. Large regions of higher density matter known as molecular clouds allow chemical reactions to occur, including the formation of organic polyatomic species. Much of this chemistry is driven by collisions. Energetic cosmic rays penetrate the cold, dense clouds and ionize hydrogen and helium, resulting, for example, in the trihydrogen cation. An ionized helium atom can then split relatively abundant carbon monoxide to produce ionized carbon, which in turn can lead to organic chemical reactions.[116] The local interstellar medium is a region of space within 100 parsecs (pc) of the Sun, which is of interest both for its proximity and for its interaction with the Solar System. This volume nearly coincides with a region of space known as the Local Bubble, which is characterized by a lack of dense, cold clouds. It forms a cavity in the Orion Arm of the Milky Way galaxy, with dense molecular clouds lying along the borders, such as those in the constellations of Ophiuchus and Taurus. (The actual distance to the border of this cavity varies from 60 to 250 pc or more.) This volume contains about 104–105 stars and the local interstellar gas counterbalances the astrospheres that surround these stars, with the volume of each sphere varying depending on the local density of the interstellar medium. The Local Bubble contains dozens of warm interstellar clouds with temperatures of up to 7,000 K and radii of 0.5–5 pc.[117] When stars are moving at sufficiently high peculiar velocities, their astrospheres can generate bow shocks as they collide with the interstellar medium. For decades it was assumed that the Sun had a bow shock. In 2012, data from Interstellar Boundary Explorer (IBEX) and NASA's Voyager probes showed that the Sun's bow shock does not exist. Instead, these authors argue that a subsonic bow wave defines the transition from the solar wind flow to the interstellar medium.[118][119] A bow shock is the third boundary of an astrosphere after the termination shock and the astropause (called the heliopause in the Solar System).[119] Intergalactic space Structure of the Universe Large-scale matter distribution in a cubic section of the universe. The blue fiber structures represent the matter and the empty regions in between represent the cosmic voids of the intergalactic medium. Main articles: Warm–hot intergalactic medium, Intracluster medium, and Intergalactic dust Intergalactic space is the physical space between galaxies. Studies of the large-scale distribution of galaxies show that the Universe has a foam-like structure, with groups and clusters of galaxies lying along filaments that occupy about a tenth of the total space. The remainder forms huge voids that are mostly empty of galaxies. Typically, a void spans a distance of 7–30 megaparsecs.[120] Surrounding and stretching between galaxies, there is a rarefied plasma[121] that is organized in a galactic filamentary structure.[122] This material is called the intergalactic medium (IGM). The density of the IGM is 5–200 times the average density of the Universe.[123] It consists mostly of ionized hydrogen; i.e. a plasma consisting of equal numbers of electrons and protons. As gas falls into the intergalactic medium from the voids, it heats up to temperatures of 105 K to 107 K,[3] which is high enough so that collisions between atoms have enough energy to cause the bound electrons to escape from the hydrogen nuclei; this is why the IGM is ionized. At these temperatures, it is called the warm–hot intergalactic medium (WHIM). (Although the plasma is very hot by terrestrial standards, 105 K is often called "warm" in astrophysics.) Computer simulations and observations indicate that up to half of the atomic matter in the Universe might exist in this warm–hot, rarefied state.[123][124][125] When gas falls from the filamentary structures of the WHIM into the galaxy clusters at the intersections of the cosmic filaments, it can heat up even more, reaching temperatures of 108 K and above in the so-called intracluster medium (ICM)." (wikipedia.org) "The Apollo/Skylab space suit (sometimes called the Apollo 11 Spacesuit due to the fact that it was most known for being used in the Apollo 11 Mission) is a class of space suits used in Apollo and Skylab missions. The names for both the Apollo and Skylab space suits were Extravehicular Mobility Unit (EMU).[2] The Apollo EMUs consisted of a Pressure Suit Assembly (PSA) aka "suit" and a Portable Life Support System (PLSS) that was more commonly called the "backpack".[3] The A7L was the PSA model used on the Apollo 7 through 14 missions.[4] The subsequent Apollo 15-17 lunar missions,[5] Skylab,[6] and Apollo–Soyuz used A7LB pressure suits.[7] Additionally, these pressure suits varied by program usage. For the Skylab EMU, NASA elected to use an umbilical life support system named the Astronaut Life Support Assembly. Basic design A7L suit without outer-layer and visor assembly Apollo 11 EMU worn by Buzz Aldrin on lunar surface The base Apollo EMU design took over three years to produce. At the beginning of the Apollo program, the Apollo spacesuit had not yet received its final EMU. NASA held a competition for the Apollo SSA contract in March 1962. Each competition proposal had to demonstrate all the abilities needed to develop and produce the entire SSA. Many contractor-teams submitted proposals. Two gained NASA interest. The Hamilton Standard Division of United Aircraft Corporation proposal offered Hamilton providing the SSA program management and PLSS with David Clark Company as the PGA provider. The International Latex Corporation (ILC) proposal planned International Latex as the SSA program manager and PGA manufacturer, Republic Aviation providing additional suit experience and Westinghouse providing the PLSS. After evaluation of the proposals, NASA preferred the Hamilton PLSS concept and program experience but the ILC PGA design. NASA elected to split the Hamilton and ILC teams, issuing the contract to Hamilton with the stipulation that ILC provide the PGA. By March 1964, Hamilton and NASA had found three successive ILC Apollo PGA designs to not meet requirements. In comparative testing, only the David Clark Gemini suit was acceptable for Apollo Command Module use. While the Hamilton PLSS met all requirements, crewed testing proved the life support requirements were inadequate, forcing the Apollo SSA program to start over. In October 1964, NASA elected to split the spacesuit program into three parts. David Clark would provide the suits for the "Block I" early missions without extra-vehicular activity (EVA). The Hamilton/ILC program would continue as "Block II" to support the early EVA missions. The pressure suit design for Block II was to be selected in a June 1965 re-competition. To assure Block II backpack success, AiResearch was funded for a parallel backpack effort. The later, longer-duration Apollo missions would be Block III and have more advanced pressure suits and a longer duration backpack to be provided by suppliers selected in future competitions. To reflect this new start in the program, the PGA was renamed the Pressure Suit Assembly (PSA) across the programs and the Block II and III SSAs were renamed Extravehicular Mobility Unit (EMU). Hamilton and International Latex were never able to form an effective working relationship. In March 1965, Hamilton switched to B. F. Goodrich as suit supplier.[8] International Latex, in July 1965, won the Block II suit competition with its A5L design. This forced NASA to assume management of the Block II EMU program directly.[9] Before the end of 1965, Hamilton Standard completed certification of its new backpack.[10] NASA subsequently terminated the Block II AiResearch backpack, thus completing the selection of the suit/backpack designs and suppliers to support man's first walking on the Moon. However, this was not to be without improvements. The Apollo 11 EMU featured an A7L suit with a -6 (dash six) backpack reflecting seven suit and six backpack design iterations.[4] The A7L was a rear entry suit made in two versions. The Extra-vehicular (EV), which would be used on the Moon and the Command Module Pilot (CMP) that was a simpler garment.[2] The A7L pressure suits reached space flight in October 1968 aboard Apollo 7.[11] These were used as launch and reentry emergency suits. Also in 1968, NASA recognized that with modifications, the Block II EMU could additionally support the later EVA missions that involved a Lunar Rover Vehicle (LRV). This resulted in the termination of Apollo Block III in favor of an Apollo 15 through 17 EMU using an A7LB suit and a "-7" long duration backpack.[2] The complete Apollo EMU made its space debut with Apollo 9 launched into space on March 3, 1969.[12] On the fourth day of the mission, Lunar Module Pilot Russell Schweickart and Commander James McDivitt went into the Lunar Module. The astronauts then depressurized both the Command and Lunar Modules. Schweickart emerged from the Lunar Module to test the backpack and conduct experiments. David Scott partially emerged from the Command Module's hatch supported by an umbilical system connected to the Command Module to observe. The EVA lasted only 46 minutes but allowed a verification of both EVA configurations of the EMU. This was the only Apollo spacewalk prior to the Apollo 11 lunar landing mission. Apollo 11 made the A7L the most iconic suit of the program. It proved to be the primary pressure suit worn by NASA astronauts for Project Apollo. Starting in 1969, the A7L suits were designed and produced by ILC Dover (a division of Playtex at the time). The A7L is an evolution of ILC's initial A5L, which won a 1965 pressure suit competition, and A6L, which introduced the integrated thermal and micrometeroid cover layer. After the deadly Apollo 1 fire, the suit was upgraded to be fire-resistant and designated A7L.[13][14] On July 20, 1969, the Apollo 11 EMUs were prominent in television coverage of the first lunar landing. Also in 1969, International Latex elected to spin-off its pressure suit business to form ILC Dover. The basic design of the A7L suit was a one piece, five-layer "torso-limb" suit with convoluted joints made of synthetic and natural rubber at the shoulders, elbows, wrist, hips, ankle, and knee joints. A shoulder "cable/conduit" assembly allowed the suit's shoulder to move forward, backwards, up, or down with user movements. Quick disconnects at the neck and forearms allowed for the connection of the pressure gloves and the famous Apollo "fishbowl helmet" (adopted by NASA as it allowed an unrestricted view, as well as eliminating the need for a visor seal required in the Mercury and Gemini and Apollo Block I spacesuit helmets). A cover layer, which was designed to be fireproof after the deadly Apollo 1 fire, was attached to the pressure garment assembly and was removable for repairs and inspection. All A7L suits featured a vertical zipper from the helmet disconnect (neck ring), down the back, and around the crotch. Specifications, Apollo 7 - 14 EMU     Name: Extravehicular Mobility Unit (EMU)     Manufacturer: ILC Dover (Pressure Suit Assembly) and Hamilton Standard (Portable Life Support System)[2]     Missions: Apollo 7-14[2]     Function: Intra-vehicular activity (IVA), orbital Extra-vehicular activity (EVA), and terrestrial EVA[2]     Operating Pressure: 3.7 psi (25.5 kPa)[2]     IVA Suit Mass: 62 lb (28.1 kg)[2]     EVA Suit Mass: 76 lb (34.5 kg)[2]     Total EVA Suit Mass: 200 lb (91 kg)[2]     Primary Life Support: 6 hours[2]     Backup Life Support: 30 minutes[2] Extravehicular Pressure Suit Assembly IV-A7L.png EV-A7L.png Torso Limb Suit Assembly Between Apollos 7 and 14, the Commander (CDR) and Lunar Module pilot (LMP), had Torso Limb Suit Assemblies (TSLA) with six life support connections placed in two parallel columns on the chest. The 4 lower connectors passed oxygen, an electrical headset/biomed connector was on the upper right, and a bidirectional cooling water connector was on the upper left. Integrated Thermal Micrometeoroid Garment Covering the Torso Limb Suit Assembly was an Integrated Thermal Micrometeoroid Garment (ITMG). This garment protected the suit from abrasion and protected the astronaut from thermal solar radiation and micrometeoroids which could puncture the suit. The garment was made from thirteen layers of material which were (from inside to outside): rubber coated nylon, 5 layers of aluminized Mylar, 4 layers of nonwoven Dacron, 2 layers of aluminized Kapton film/Beta marquisette laminate, and Teflon coated Beta filament cloth. Additionally, the ITMG also used a patch of 'Chromel-R' woven nickel-chrome (the familiar silver-colored patch seen especially on the suits worn by the Apollo 11 crew) for abrasion protection from the Portable Life Support System (PLSS) backpack. Chromel-R was also used on the uppers of the lunar boots and on the EVA gloves. Finally, patches of Teflon were used for additional abrasion protection on the knees, waist and shoulders of the ITMG. Starting with Apollo 13, a red band of Beta cloth was added to the commander's ITMG on each arm and leg, as well as a red stripe on the newly added EVA central visor assembly. The stripes, initially known as "Public Affairs stripes" but quickly renamed "commander's stripes", made it easy to distinguish the two astronauts on the lunar surface and were added by Brian Duff, head of Public Affairs at the Manned Spacecraft Center, to resolve the problem for the media as well as NASA of identifying astronauts in photographs.[15] Liquid Cooling Garment Lunar crews also wore a three-layer Liquid Cooling and Ventilation Garment (LCG) or "union suit" with plastic tubing which circulated water to cool the astronaut down, minimizing sweating and fogging of the suit helmet. Water was supplied to the LCG from the PLSS backpack, where the circulating water was cooled to a constant comfortable temperature by a sublimator. Portable Life Support System At the beginning of the Apollo spacesuit competition, no one knew how the life support would attach to the suit, how the controls needed to be arranged, or what amount of life support was needed. What was known was that in ten months, the Portable Life Support System, aka "backpack", needed to be completed to support complete suit-system testing before the end of the twelfth month. Before the spacesuit contract was awarded, the requirement for normal life support per hour almost doubled. At this point, a maximum hourly metabolic energy expenditure requirement was added, which was over three times the original requirement.[16] In late 1962, testing of an early training suit raised concerns about life support requirements. The concerns were dismissed because the forthcoming Apollo new-designs were expected to have lower effort mobility and improved ventilation systems. However, Hamilton took this as a strong indication that Apollo spacesuit life support requirements might significantly increase and initiated internally funded research and development in "backpack" technologies. In the tenth month, the first backpack was completed. Manned testing found the backpack to meet requirements. This would have been a great success but for the crewed testing confirming that the 1963 life support requirements were not sufficient to meet lunar mission needs. Early in 1964, the final Apollo spacesuit specifications were established that increased normal operations by 29% and increased maximum use support 25%. Again, the volume and weight constraints did not change. These final increases required operational efficiencies that spawned the invention of the porous plate sublimator[17] and the Apollo liquid cooling garment.[18] The porous plate sublimator had a metal plate with microscopic pores sized just right so that if the water flowing under the plate warmed to more than a user-comfortable level, frozen water in the plate would thaw, flow through the plate, and boil to the vacuum of space, taking away heat in the process. Once the water under the plate cooled to a user-comfortable temperature, the water in the plate would re-freeze, sealing the plate and stopping the cooling process. Thus, heat rejection with automatic temperature control was accomplished with no sensors or moving parts to malfunction. The Apollo liquid cooling garment was an open mesh garment with attached tubes to allow cooling water to circulate around the body to remove excess body heat when needed. The garment held the tubes against the body for highly efficient heat removal. The open mesh allowed air circulation over the body to remove humidity and additionally remove body heat. In 1966, NASA bought the rights to the liquid cooling garment to allow all organizations access to this technology. Before the first Apollo spacewalk, the backpack gained a front-mounted display and control unit named the remote control unit. This was revised for Apollo 11 to additionally provide camera attachment to provide high quality lunar pictures. Intravehicular (CMP) Pressure Suit Assembly CMP-A7L.png Torso Limb Suit Assembly The Command Module pilot (CMP) had a TSLA similar to the commander and lunar module pilot, but with unnecessary hardware deleted since the CMP would not be performing any extravehicular activities. For example, the CMP's TSLA had only one set of gas connectors instead of two, and had no water cooling connector. Also deleted was the pressure relief valve in the sleeve of the suit and the tether mounting attachments which were used in the lunar module. The TSLA for the CMP also deleted an arm bearing that allowed the arm to rotate above the elbow. Intravehicular Cover Layer Over the TSLA, command module pilots wore only a three-layer Intravehicular Cover Layer (IVCL) of nomex and beta cloth for fire and abrasion protection. Constant Wear Garment The CMP wore a simpler cotton fabric union suit called the Constant Wear Garment (CWG) underneath the TSLA instead of the water cooled Liquid Cooling Garment. His cooling came directly from the flow of oxygen into his suit via an umbilical from the spacecraft environmental control system. When not performing lunar EVA's, the LMP and CDR also wore a CWG instead of the LCG. Apollo 15-17, Skylab and ASTP Spacesuits Apollo 15-17 EMU A7LB without outer-layer and visor assembly Apollo 17 A7LB space suit worn by Gene Cernan on lunar surface EV-A7LB.png For the last three Apollo lunar flights Apollos 15, 16, and 17, the spacesuits were extensively revised. The pressure suits were called A7LB, which came in two versions. The Extra-vehicular (EV) version was a new mid-entry suit that allowed greater mobility and easier operations with the lunar rover. The A7LB EV suits were designed for longer duration J-series missions, in which three EVAs would be conducted and the Lunar Roving Vehicle (LRV) would be used for the first time. Originally developed by ILC-Dover as the "A9L," but given the designation "A7LB" by NASA,[19] the new suit incorporated two new joints at the neck and waist. The waist joint was added to allow the astronaut to sit on the LRV and the neck joint was to provide additional visibility while driving the LRV. Because of the waist joint, the six life-support connectors were rearranged from the parallel pattern to a set of two "triangles," and the up-and-down back zipper was revised and relocated.[14] The "zipper" is actually a misnomer in that the A7L entry was through two zippers sewn over each other. The inner zipper had rubber teeth and provided sealing. The outer (externally visible) zipper was a conventional metal toothed slider for mechanical restraint. The A7LB had two pairs of such zipper sets that intersected on the right side of the suit above the waist joint. Opening the suit required undoing a clasp that held the zipper sets together.[20] In addition, the EVA backpacks were modified to carry more oxygen, lithium hydroxide (LiOH), more power, and cooling water for the longer EVAs.[14] While NASA wished these revisions to be accomplished without a volume increase, that was not possible. NASA allowed a minor protrusion on one side for an auxiliary water tank resulting in the last configuration of backpack. To maximize the return of lunar samples, the main module of both the Apollo 11,12,14 and 15-17 backpacks were left on the Moon. To facilitate these longer EVAs, small energy bars were carried in special pouches beneath the interior of the suit helmet ring, and the astronauts wore collar-like drinking water bags beneath the outer suit. Because the Vietnam War had taken toll on the federal budget, NASA's budget was in decline. The Command Module Pilot did not get a new mid-entry suit. NASA elected to modify existing A7L EV units by simply removing the liquid cooling features to create a "new" A7LB CMP suit. Once the existing inventory was consumed, a few new A7LB CMP suits were made to support Apollo 17. Because the J-series CSMs incorporated the Scientific Instrument Module (SIM) Bay, which used special film cameras similar to those used on Air Force spy satellites, and required a "deep space" EVA for retrieval, the CMP for each of the three J-series missions wore a five-connector A7LB-based H-series A7L suits, with the liquid cooling connections eliminated as the CMP would be attached to a life-support umbilical (like that used on Gemini EVAs) and only an "oxygen purge system" (OPS) would be used for emergency backup in the case of the failure of the umbilical. The CMP wore the commander's red-striped EVA visor assembly, while the LMP, who performed a "stand-up EVA" (to prevent the umbilical from getting "fouled up" and to store the film into the CSM) in the spacecraft hatch and connected to his normal life-support connections, wore the plain white EVA visor assembly. Specifications     Name: Apollo 15-17 EMU     Manufacturer: ILC Dover (Pressure Suit Assembly) Hamilton Standard (Primary Life Support System)[2]     Missions: Apollo 15-17[2]     Function: Intra-vehicular activity (IVA), orbital Extra-vehicular activity and terrestrial Extra-vehicular activity (EVA)     Operating Pressure: 3.7 psi (25.5 kPa)[2]     IVA Suit Mass: 64.6 lb (29.3 kg)[2]     EVA Suit Mass: 78 lb (35.4 kg)[2]     Total EVA Suit Mass: 212 lb (96.2 kg)[2]     Primary Life Support: 7 hours (420 minutes)[2]     Backup Life Support: 30 minutes[2] Skylab EMU Alan Bean wearing a Skylab A7L during a Skylab 3 EVA The American space station Skylab had three crewed flights. To minimize program costs, NASA elected to fund ILC Dover for modifications to the mid-entry Apollo A7LB EV PSA design to reduce costs and use an umbilical system named the Astronaut Life Support Assembly (ALSA) to allow extra-vehicular activities. AiResearch won the competition for the ALSA. The result was the Skylab EMU. During launch, the space station was damaged. The Skylab EMUs enabled emergency repair and outfitting tasks that permitted the program to conduct its long duration crewed missions and experiments. Skylab returned to all the crew members having the same configuration suits. With the exception of the Orbital Workshop (OWS) repairs carried out by Skylab 2 and Skylab 3, all of the Skylab EVAs were conducted in connection to the routine maintenance carried out on the Apollo Telescope Mount, which housed the station's solar telescopes. Because of the short duration of those EVAs, and as a need to protect the delicate instruments, the Apollo lunar EVA backpack was replaced with an umbilical assembly designed to incorporate both breathing air (Skylab's atmosphere was 74% oxygen and 26% nitrogen at 5 psi) and liquid water for cooling. The assembly was worn on the astronaut's waist and served as the interface between the umbilical and the suit. An emergency oxygen pack was strapped to the wearer's right thigh and was able to supply a 30-minute emergency supply of pure oxygen in the case of umbilical failure. Another unique feature of the Skylab EMU was its simplified EVA visor assembly that did not include an insulated thermal cover over the outer visor shell. There were three crewed Skylab flights. All three missions included "space walks." Specifications     Name: Skylab EMU     Manufacturer: ILC Dover (Pressure Suit Assembly) and AiResearch (bought by AlliedSignal Corporation)(Astronaut Life Support Assembly) [2]     Missions: Skylab 2-4[2]     Function: Intra-vehicular activity (IVA) and orbital Extra-vehicular activity (EVA)[2]     Operating Pressure: 3.7 psi (25.5 kPa)[2]     IVA Suit Mass: 64.6 lb (29.3 kg)[2]     EVA Suit Mass: 72 lb (32.7 kg)[2]     Total EVA Suit Mass: 143 lb (64.9 kg)[2]     Primary Life Support: Vehicle Provided via ALSA[2]     Backup Life Support: 30 minutes[2] ASTP Spacesuit The ASTP crew, entering the transfer van For the Apollo–Soyuz Test Project, NASA decided to use the A7LB CMP pressure suit assembly worn on the J-missions with a few changes to save cost and weight since an EVA was not planned during the mission. The changes included a simplified cover layer which was cheaper, lighter and more durable as well as the removal of the pressure relief valve and unused gas connectors. No EVA visor assemblies or EVA gloves were carried on the mission.[21] The ASTP A7LB suit was the only Apollo suit to use the NASA "worm" logo, which was introduced in 1975 and used extensively by NASA until 1992. Specifications     Name: Apollo A7LB Pressure Suit Assembly     Manufacturer: ILC Dover[2]     Missions: ASTP[2]     Function: Intra-vehicular activity (IVA)[2]     Operating Pressure: 3.7 psi (25.5 kPa)[2]     IVA Suit Mass: 64.6 lb (29.3 kg)[2]     Primary Life Support: Vehicle Provided" (wikipedia.org) "Apollo 17 (December 7–19, 1972) was the final mission of NASA's Apollo program, the most recent time humans have set foot on the Moon or traveled beyond low Earth orbit. Commander Gene Cernan and Lunar Module Pilot Harrison Schmitt walked on the Moon, while Command Module Pilot Ronald Evans orbited above. Schmitt was the only professional geologist to land on the Moon; he was selected in place of Joe Engle, as NASA had been under pressure to send a scientist to the Moon. The mission's heavy emphasis on science meant the inclusion of a number of new experiments, including a biological experiment containing five mice that was carried in the command module. Mission planners had two primary goals in deciding on the landing site: to sample lunar highland material older than that at Mare Imbrium and to investigate the possibility of relatively recent volcanic activity. They therefore selected Taurus–Littrow, where formations that had been viewed and pictured from orbit were thought to be volcanic in nature. Since all three crew members had backed up previous Apollo lunar missions, they were familiar with the Apollo spacecraft and had more time for geology training. Launched at 12:33 a.m. Eastern Standard Time (EST) on December 7, 1972, following the only launch-pad delay in the course of the whole Apollo program that was caused by a hardware problem, Apollo 17 was a "J-type" mission that included three days on the lunar surface, expanded scientific capability, and the use of the third Lunar Roving Vehicle (LRV). Cernan and Schmitt landed in the Taurus–Littrow valley, completed three moonwalks, took lunar samples and deployed scientific instruments. Orange soil was discovered at Shorty crater; it proved to be volcanic in origin, although from early in the Moon's history. Evans remained in lunar orbit in the command and service module (CSM), taking scientific measurements and photographs. The spacecraft returned to Earth on December 19. The mission broke several records for crewed spaceflight, including the longest crewed lunar landing mission (12 days, 14 hours),[7] greatest distance from a spacecraft during an extravehicular activity of any type (7.6 kilometers or 4.7 miles), longest total duration of lunar-surface extravehicular activities (22 hours, 4 minutes),[8] largest lunar-sample return (approximately 115 kg or 254 lb), longest time in lunar orbit (6 days, 4 hours),[7] and greatest number of lunar orbits (75).[9] Crew and key Mission Control personnel Position[10]     Astronaut Commander     Eugene A. Cernan Third and last spaceflight Command Module Pilot (CMP)     Ronald E. Evans Only spaceflight Lunar Module Pilot (LMP)     Harrison H. Schmitt Only spaceflight In 1969, NASA announced[11] that the backup crew of Apollo 14 would be Gene Cernan, Ronald Evans, and former X-15 pilot Joe Engle.[12][13] This put them in line to be the prime crew of Apollo 17, because the Apollo program's crew rotation generally meant that a backup crew would fly as prime crew three missions later. Harrison Schmitt, who was a professional geologist as well as an astronaut, had served on the backup crew of Apollo 15, and thus, because of the rotation, would have been due to fly as lunar module pilot on Apollo 18.[14] In September 1970, the plan to launch Apollo 18 was cancelled. The scientific community pressed NASA to assign a geologist, rather than a pilot with non-professional geological training, to an Apollo landing. NASA subsequently assigned Schmitt to Apollo 17 as the lunar module pilot. After that, NASA’s director of flight crew operations, Deke Slayton, was left with the question of who would fill the two other Apollo 17 slots: the rest of the Apollo 15 backup crew (Dick Gordon and Vance Brand), or Cernan and Evans from the Apollo 14 backup crew. Slayton ultimately chose Cernan and Evans.[11] Support at NASA for assigning Cernan was not unanimous. Cernan had crashed a Bell 47G helicopter into the Indian River near Cape Kennedy during a training exercise in January 1971; the accident was later attributed to pilot error, as Cernan had misjudged his altitude before crashing into the water. Jim McDivitt, who was manager of the Apollo Spacecraft Program Office at the time, objected to Cernan's selection because of this accident, but Slayton dismissed the concern. After Cernan was offered command of the mission, he advocated for Engle to fly with him on the mission, but it was made clear to him that Schmitt would be assigned instead, with or without Cernan, so he acquiesced.[15][16] The prime crew of Apollo 17 was publicly announced on August 13, 1971.[17] When assigned to Apollo 17, Cernan was a 38-year-old captain in the United States Navy; he had been selected in the third group of astronauts in 1963, and flown as pilot of Gemini 9A in 1966 and as lunar module pilot of Apollo 10 in 1969 before he served on Apollo 14's backup crew. Evans, 39 years old when assigned to Apollo 17, had been selected as part of the fifth group of astronauts in 1966, and had been a lieutenant commander in the United States Navy. Schmitt, a civilian, was 37 years old when assigned Apollo 17, had a doctorate in geology from Harvard University, and had been selected in the fourth group of astronauts in 1965. Both Evans and Schmitt were making their first spaceflights.[18] For the backup crews of Apollo 16 and 17, the final Apollo lunar missions, NASA selected astronauts who had already flown Apollo lunar missions, to take advantage of their experience, and avoid investing time and money in training rookies who would be unlikely to ever fly an Apollo mission.[19][20] The original backup crew for Apollo 17, announced at the same time as the prime crew,[17] was the crew of Apollo 15: David Scott as commander, Alfred Worden as CMP and James Irwin as LMP, but in May 1972 they were removed from the backup crew because of their roles in an incident known as the Apollo 15 postal covers incident.[21] They were replaced with the landing crew of Apollo 16: John W. Young as backup crew commander, Charles Duke as LMP, and Apollo 14's CMP, Stuart Roosa.[18][22][23] Originally, Apollo 16's CMP, Ken Mattingly, was to be assigned along with his crewmates, but he declined so he could spend more time with his family, his son having just been born, and instead took an assignment to the Space Shuttle program.[24] Roosa had also served as backup CMP for Apollo 16.[25] For the Apollo program, in addition to the prime and backup crews that had been used in the Mercury and Gemini programs, NASA assigned a third crew of astronauts, known as the support crew. Their role was to provide any assistance in preparing for the missions that the missions director assigned then. Preparations took place in meetings at facilities across the US and sometimes needed a member of the flight crew to attend them. Because McDivitt was concerned that problems could be created if a prime or backup crew member was unable to attend a meeting, Slayton created the support crews to ensure that someone would be able to attend in their stead.[26] Usually low in seniority, they also assembled the mission's rules, flight plan and checklists, and kept them updated;[27][28] For Apollo 17, they were Robert F. Overmyer, Robert A. Parker and C. Gordon Fullerton.[29] Flight directors were Gerry Griffin, first shift, Gene Kranz and Neil B. Hutchinson, second shift, and Pete Frank and Charles R. Lewis, third shift.[30] According to Kranz, flight directors during the program Apollo had a one-sentence job description, "The flight director may take any actions necessary for crew safety and mission success."[31] Capsule communicators (CAPCOMs) were Fullerton, Parker, Young, Duke, Mattingly, Roosa, Alan Shepard and Joseph P. Allen.[32] Mission insignia and call signs The insignia's most prominent feature is an image of the Greek sun god Apollo backdropped by a rendering of an American eagle, the red bars on the eagle mirroring those on the U.S. flag. Three white stars above the red bars represent the three crewmembers of the mission. The background includes the Moon, the planet Saturn, and a galaxy or nebula. The wing of the eagle partially overlays the Moon, suggesting humanity's established presence there.[33] The Apollo seventeen emblem containing Apollo, an eagle made of lines, the Moon, and Saturn; around the outside of the emblem the text Apollo XVII, and then the names Cernan, Evans, and Schmitt. Apollo 17 space-flown silver Robbins medallion The insignia includes, along with the colors of the U.S. flag (red, white, and blue), the color gold, representative of a "golden age" of spaceflight that was to begin with Apollo 17.[33] The image of Apollo in the mission insignia is a rendering of the Apollo Belvedere sculpture in the Vatican Museums. It looks forward into the future, towards the celestial objects shown in the insignia beyond the Moon. These represent humanity's goals, and the image symbolizes human intelligence, wisdom and ambition. The insignia was designed by artist Robert McCall, based on ideas from the crew.[34] In deciding the call signs for the command module (CM) and lunar module (LM), the crew wished to pay tribute to the American public for their support of the Apollo program, and to the mission, and wanted names with a tradition within American history. The CM was given the call sign "America". According to Cernan, this evoked the 19th century sailing ships which were given that name, and was a thank-you to the people of the United States. The crew selected the name "Challenger" for the LM in lieu of an alternative, "Heritage". Cernan stated that the selected name "just seemed to describe more of what the future for America really held, and that was a challenge".[35] After Schmitt stepped onto the Moon from Challenger, he stated, "I think the next generation ought to accept this as a challenge. Let's see them leave footprints like these."[36] Planning and training Scheduling and landing site selection Prior to the cancellation of Apollo 18 through 20, Apollo 17 was slated to launch in September 1971 as part of NASA's tentative launch schedule set forth in 1969.[4] The in-flight abort of Apollo 13 and the resulting modifications to the Apollo spacecraft delayed subsequent missions.[37] Following the cancellation of Apollo 20 in early 1970, NASA decided there would be no more than two Apollo missions per year.[38] Part of the reason Apollo 17 was scheduled for December 1972 was to make it fall after the presidential election in November, ensuring that if there was a disaster, it would have no effect on President Richard Nixon's re-election campaign.[39] Nixon had been deeply concerned about the Apollo 13 astronauts, and, fearing another mission in crisis as he ran for re-election, initially decided to omit the funds for Apollo 17 from the budget; he was persuaded to accept a December 1972 date for the mission.[40] Like Apollo 15 and 16, Apollo 17 was slated to be a "J-mission", an Apollo mission type that featured lunar surface stays of three days, higher scientific capability, and the usage of the Lunar Roving Vehicle. Since Apollo 17 was to be the final lunar landing of the Apollo program, high-priority landing sites that had not been visited previously were given consideration for potential exploration. Some sites were rejected at earlier stages. For instance, a landing in the crater Copernicus was rejected because Apollo 12 had already obtained samples from that impact, and three other Apollo expeditions had already visited the vicinity of Mare Imbrium, near the rim of which Copernicus is located. The lunar highlands near the crater Tycho were rejected because of the rough terrain that the astronauts would encounter there. A site on the lunar far side in the crater Tsiolkovskiy was rejected due to technical considerations and the operational costs of maintaining communication with Earth during surface operations. Lastly, a landing in a region southwest of Mare Crisium was rejected on the grounds that a Soviet spacecraft could easily access the site and retrieve samples; Luna 20 ultimately did so shortly after the Apollo 17 site selection was made.[41] Schmitt advocated for a landing on the far side of the Moon until told by Director of Flight Operations Christopher C. Kraft that it would not happen as NASA lacked the funds for the necessary communications satellites.[42] Black and white photo of a created surface of the Moon showing the landing site and surrounding area for Apollo 17 as taken from Apollo 17. Landing site and surrounding area, as imaged from the Apollo 17 command module, 1972 The three sites that made the final consideration for Apollo 17 were Alphonsus crater, Gassendi crater, and the Taurus–Littrow valley. In making the final landing site decision, mission planners considered the primary objectives for Apollo 17: obtaining old highlands material a substantial distance from Mare Imbrium, sampling material from young volcanic activity (i.e., less than three billion years), and having minimal ground overlap with the orbital ground tracks of Apollo 15 and Apollo 16 to maximize the amount of new data obtained.[41] A significant reason for the selection of Taurus–Littrow was that Apollo 15's CMP, Al Worden, had overflown the site and observed features he described as likely volcanic in nature.[43] Gassendi was eliminated because NASA felt that its central peak would be difficult to reach due to the roughness of the local terrain, and, though Alphonsus might be easier operationally than Taurus–Littrow, it was of lesser scientific interest.[44] At Taurus–Littrow, it was believed that the crew would be able to obtain samples of old highland material from the remnants of a landslide event that occurred on the south wall of the valley and the possibility of relatively young, explosive volcanic activity in the area. Although the valley is similar to the landing site of Apollo 15 in that it is on the border of a lunar mare, the advantages of Taurus–Littrow were believed to outweigh the drawbacks.[41] The Apollo Site Selection Board, a committee of NASA personnel and scientists charged with setting out scientific objectives of the Apollo landing missions and selecting landing sites for them,[45] unanimously recommended Taurus–Littrow at its final meeting in February 1972. Upon that recommendation, NASA selected Taurus–Littrow as the landing site for Apollo 17.[44] Training A photo of Gene Cernan standing on a rock with holding a stick while participating in geology training. Gene Cernan participates in geology training in Sudbury, Ontario, in May 1972 As with previous lunar landings, the Apollo 17 astronauts undertook an extensive training program that included learning to collect samples on the surface, usage of the spacesuits, navigation in the Lunar Roving Vehicle, field geology training, survival training, splashdown and recovery training, and equipment training.[46] The geology field trips were conducted as much as possible as if the astronauts were on the Moon: they would be provided with aerial images and maps, and briefed on features of the site and a suggested routing. The following day, they would follow the route, and have tasks and observations to be done at each of the stops.[47] The geology field trips began with one to Big Bend National Park in Texas in October 1971. The early ones were not specifically tailored to prepare the astronauts for Taurus–Littrow, which was not selected until February 1972, but by June, the astronauts were going on field trips to sites specifically selected to prepare for Apollo 17's landing site.[48] Both Cernan and Schmitt had served on backup crews for Apollo landing missions, and were familiar with many of the procedures. Their trainers, such as Gordon Swann, feared that Cernan would defer to Schmitt as a professional geologist on matters within his field. Cernan also had to adjust for the loss of Engle, with whom he had trained for Apollo 14. In spite of these issues, Cernan and Schmitt worked well together as a team, and Cernan became adept at describing what he was seeing on geology field trips, and working independently of Schmitt when necessary.[49] The landing crew aimed for a division of labor so that, when they arrived in a new area, Cernan would perform tasks such as adjusting the antenna on the Lunar Roving Vehicle so as to transmit to Earth while Schmitt gave a report on the geological aspects of the site. The scientists in the geology "backroom" relied on Schmitt's reports to adjust the tasks planned for that site, which would be transmitted to the CapCom and then to Cernan and Schmitt. According to William R. Muehlberger, one of the scientists who trained the astronauts, "In effect [Schmitt] was running the mission from the Moon. But we set it up this way. All of those within the geological world certainly knew it, and I had a sneaking hunch that the top brass knew it too, but this is a practical way out, and they didn't object."[50] Also participating in some of the geology field trips were the commander and lunar module pilot of the backup crew. The initial field trips took place before the Apollo 15 astronauts were assigned as the backup crew for Apollo 17 in February 1972. Either one or both of Scott and Irwin of Apollo 15 took part in four field trips, though both were present together for only two of them. After they were removed from the backup crew, the new backup commander and LMP, Young and Duke, took part in the final four field trips.[21] On field trips, the backup crew would follow half an hour after the prime crew, performing identical tasks, and have their own simulated CapCom and Mission Control guiding them.[47] The Apollo 17 astronauts had fourteen field trips—the Apollo 11 crew had only one.[51] Evans did not go on the geology field trips, having his own set of trainers—by this time, geology training for the CMP was well-established. He would fly with a NASA geologist/pilot, Dick Laidley, over geologic features, with part of the exercise conducted at 40,000 feet (12,000 m), and part at 1,000 feet (300 m) to 5,000 feet (1,500 m). The higher altitude was equivalent to what could be seen from the planned lunar orbit of about 60 nmi with binoculars. Evans would be briefed for several hours before each exercise, and given study guides; afterwards, there would be debriefing and evaluation. Evans was trained in lunar geology by Farouk El-Baz late in the training cycle; this continued until close to launch. The CMP was given information regarding the lunar features he would overfly in the CSM and which he was expected to photograph.[52] Mission hardware and experiments Saturn five rocket on a launch pat at dusk while cloudy outside. SA-512, Apollo 17's Saturn V rocket, on the launch pad awaiting liftoff, November 1972 Spacecraft and launch vehicle The Apollo 17 spacecraft comprised CSM-114 (consisting of Command Module 114 (CM-114) and Service Module 114 (SM-114)); Lunar Module 12 (LM-12);[53] a Spacecraft-Lunar Module Adapter (SLA) numbered SLA-21; and a Launch Escape System (LES).[54][55] The LES contained a rocket motor that would propel the CM to safety in the event of an aborted mission in the moments after launch, while the SLA housed the LM during the launch and early part of the flight. The LES was jettisoned after the launch vehicle ascended to the point that it was not needed, while the SLA was left atop the S-IVB third stage of the rocket after the CSM and LM separated from it.[56][57] The launch vehicle, SA-512,[53] was one of fifteen Saturn V rockets built,[58] and was the twelfth to fly.[59] With a weight at launch of 6,529,784 pounds (2,961,860 kg) (116,269 pounds (52,739 kg) of which was attributable to the spacecraft), Apollo 17's vehicle was slightly lighter than Apollo 16, but heavier than every other crewed Apollo mission.[60] Preparation and assembly The first piece of the launch vehicle to arrive at Kennedy Space Center was the S-II second stage, on October 27, 1970; it was followed by the S-IVB on December 21; the S-IC first stage did not arrive until May 11, 1972, followed by the Instrument Unit on June 7. By then, LM-12 had arrived, the ascent stage on June 16, 1971, and the descent stage the following day; they were not mated until May 18, 1972. CM-114, SM-114 and SLA-21 all arrived on March 24, 1972. The rover reached Kennedy Space Center on June 2, 1972.[61] Schmitt, (left), Cernan, (right) in a training LRV, with the Lunar Landing Module in the background. Cernan (seated, right) and Schmitt in the training Lunar Roving Vehicle, with the mockup Lunar Module in the background, August 1972 The CM and the service module (SM) were mated on March 28, 1972,[61] and the testing of the spacecraft began that month.[62] The CSM was placed in a vacuum chamber at Kennedy Space Center, and the testing was conducted under those conditions. The LM was also placed in a vacuum chamber; both the prime and the backup crews participated in testing the CSM and LM.[63] During the testing, it was discovered that the LM's rendezvous radar assembly had received too much voltage during earlier tests; it was replaced by the manufacturer, Grumman. The LM's landing radar also malfunctioned intermittently and was also replaced. The front and rear steering motors of the Lunar Roving Vehicle (LRV) also had to be replaced, and it required several modifications.[62] Following the July 1972 removal from the vacuum chamber, the LM's landing gear was installed, and it, the CSM and the SLA were mated to each other. The combined craft was moved into the Vehicle Assembly Building in August for further testing, after which it was mounted on the launch vehicle.[63] After completing testing, including a simulated mission, the LRV was placed in the LM on August 13.[64] Erection of the stages of the launch vehicle began on May 15, 1972, in High Bay 3 of the Vehicle Assembly Building, and was completed on June 27. Since the launch vehicles for Skylab 1 and Skylab 2 were being processed in that building at the same time, this marked the first time NASA had three launch vehicles there since the height of the Apollo program in 1969. After the spacecraft was mounted on the launch vehicle on August 24,[64] it was rolled out to Pad 39-A on August 28.[61] Although this was not the final time a Saturn V would fly (another would lift Skylab to orbit), area residents reacted as though it was, and 5,000 of them watched the rollout, during which the prime crew joined the operating crew from Bendix atop the crawler.[62] At Pad 39-A, testing continued, and the CSM was electrically mated to the launch vehicle on October 11, 1972. Testing concluded with the countdown demonstration tests, accomplished on November 20 and 21.[61] The countdown to launch began at 7:53 a.m. (12:53 UTC) on December 5, 1972.[65] Lunar surface science ALSEP The Apollo Lunar Surface Experiments Package was a suite of nuclear-powered experiments, flown on each landing mission after Apollo 11. This equipment was to be emplaced by the astronauts to continue functioning after the astronauts returned to Earth.[66] For Apollo 17, the ALSEP experiments were a Heat Flow Experiment (HFE), to measure the rate of heat flow from the interior of the Moon, a Lunar Surface Gravimeter (LSG), to measure alterations in the lunar gravity field at the site,[67] a Lunar Atmospheric Composition Experiment (LACE), to investigate what the lunar atmosphere is made up of,[68] a Lunar Seismic Profiling Experiment (LSPE), to detect nearby seismic activity, and a Lunar Ejecta and Meteorites Experiment (LEME), to measure the velocity and energy of dust particles.[67] Of these, only the HFE had been flown before; the others were new.[66] The HFE had been flown on the aborted Apollo 13 mission, as well as on Apollo 15 and 16, but placed successfully only on Apollo 15, and unexpected results from that device made scientists anxious for a second successful emplacement. It was successfully deployed on Apollo 17.[69] The lunar gravimeter was intended to detect wavers in gravity, which would provide support for Albert Einstein's general theory of relativity;[70] it ultimately failed to function as intended.[71] The LACE was a surface-deployed module that used a mass spectrometer to analyze the Moon's atmosphere.[72] On previous missions, the Code Cathode Gauge experiment had measured the quantity of atmospheric particles, but the LACE determined which gases were present: principally neon, helium and hydrogen.[68] The LSPE was a seismic-detecting device that used geophones, which would detect explosives to be set off by ground command once the astronauts left the Moon.[67] When operating, it could only send useful data to Earth in high bit rate, meaning that no other ALSEP experiment could send data then, and limiting its operating time. It was turned on to detect the liftoff of the ascent stage, as well as use of the explosives packages, and the ascent stage's impact, and thereafter about once a week, as well as for some 100 hour periods.[73] The LEME had a set of detectors to measure the characteristics of the dust particles it sought.[67] It was hoped that the LEME would detect dust impacting the Moon from elsewhere, such as from comets or interstellar space, but analysis showed that it primarily detected dust moving at slow speeds across the lunar surface.[74] All powered ALSEP experiments that remained active were deactivated on September 30, 1977,[66] principally because of budgetary constraints.[75] Other lunar-surface science Black and white photo of a lunar rover with a lunar landing module in the background. Apollo 17's Lunar Roving Vehicle as it was left parked on the Moon at the conclusion of the mission. The Surface Electrical Properties (SEP) experiment receiver is the antenna on the right-rear of the vehicle Like Apollo 15 and 16, Apollo 17 carried a Lunar Roving Vehicle. In addition to being used by the astronauts for transport from station to station on the mission's three moonwalks, the LRV was used to transport the astronauts' tools, communications equipment, and the lunar samples they gathered.[76] The Apollo 17 LRV was also used to carry some of the scientific instruments, such as the Traverse Gravimeter Experiment (TGE) and Surface Electrical Properties (SEP) experiment.[71][77] The Apollo 17 LRV traveled a cumulative distance of approximately 35.7 km (22.2 mi) in a total drive time of about four hours and twenty-six minutes; the greatest distance Cernan and Schmitt traveled from the lunar module was about 7.6 km (4.7 mi).[78] This was the only mission to carry the TGE, which was built by Draper Laboratory at the Massachusetts Institute of Technology. As gravimeters had been useful in studying the Earth's internal structure, the objective of this experiment was to do the same on the Moon. The gravimeter was used to obtain relative gravity measurements at the landing site in the immediate vicinity of the lunar module, as well as various locations on the mission's traverse routes. Scientists would then use this data to help determine the geological substructure of the landing site and the surrounding vicinity. Measurements were taken while the TGE was mounted on the LRV, and also while the device was placed on the lunar surface. A total of 26 measurements were taken with the TGE during the mission's three moonwalks, with productive results.[71] The SEP was also unique to Apollo 17, and included two major components: a transmitting antenna deployed near the lunar module and a receiver mounted on the LRV. At different stops during the mission's traverses, electrical signals traveled from the transmitting device, through the ground, and were received at the LRV. The electrical properties of the lunar regolith could be determined by comparison of the transmitted and received electrical signals. The results of this experiment, which are consistent with lunar rock composition, show that there is almost no water in the area of the Moon in which Apollo 17 landed, to a depth of 2 km (1.2 mi).[77] A 2.4 m (7.9 ft) long, 2 cm (0.79 in) diameter[79] device, the Lunar Neutron Probe was inserted into one of the holes drilled into the surface to collect core samples. It was designed to measure the quantity of neutrons which penetrated to the detectors it bore along its length. This was intended to measure the rate of the "gardening" process on the lunar surface, whereby the regolith on the surface is slowly mixed or buried due to micrometeorites and other events. Placed during the first EVA, it was retrieved during the third and final EVA. The astronauts brought it with them back to Earth, and the measurements from it were compared with the evidence of neutron flux in the core that had been removed from the hole it had been placed in. Results from the probe and from the cores were instrumental in current theories that the top centimeter of lunar regolith turns over every million years, whereas "gardening" to a depth of one meter takes about a billion years.[80] Orbital science Biological experiments Main article: Fe, Fi, Fo, Fum, and Phooey Apollo 17's CM carried a biological cosmic ray experiment (BIOCORE), containing five mice that had been implanted with radiation monitors under their scalps to see whether they suffered damage from cosmic rays. These animals were placed in individual metal tubes inside a sealed container that had its own oxygen supply, and flown on the mission. All five were pocket mice (Perognathus longimembris);[81] this species was chosen because it was well-documented, small, easy to maintain in an isolated state (not requiring drinking water during the mission and with highly concentrated waste), and for its ability to withstand environmental stress.[82] Officially, the mice—four male and one female—were assigned the identification numbers A3326, A3400, A3305, A3356 and A3352. Unofficially, according to Cernan, the Apollo 17 crew dubbed them Fe, Fi, Fo, Fum, and Phooey.[83] Four of the five mice survived the flight, though only two of them appeared healthy and active; the cause of death of the fifth mouse was not determined. Of those that survived, the study found lesions in the scalp itself and, in one case, the liver. The scalp lesions and liver lesions appeared to be unrelated to one another; nothing was found that could be attributed to cosmic rays.[84] The Biostack experiment was similar to one carried on Apollo 16, and was designed to test the effects of the cosmic rays encountered in space travel on microorganisms that were included, on seeds, and on the eggs of simple animals (brine shrimp and beetles), which were carried in a sealed container. After the mission, the microorganisms and seeds showed little effect, but many of the eggs of all species failed to hatch, or to mature normally; many died or displayed abnormalities.[85] Scientific Instrument Module Apollo 17 SIM bay on the service module America, seen from the Lunar Module Challenger in orbit around the Moon The Apollo 17 SM contained the scientific instrument module (SIM) bay. The SIM bay housed three new experiments for use in lunar orbit: a lunar sounder, an infrared scanning radiometer, and a far-ultraviolet spectrometer. A mapping camera, panoramic camera, and a laser altimeter, which had been carried previously, were also included in the SIM bay.[86] The lunar sounder was to beam electromagnetic impulses toward the lunar surface, which were designed with the objective of obtaining data to assist in developing a geological model of the interior of the Moon to an approximate depth of 1.3 km (0.81 mi).[86] The infrared scanning radiometer was designed with the objective of generating a temperature map of the lunar surface to aid in locating surface features such as rock fields, structural differences in the lunar crust, and volcanic activity. The far-ultraviolet spectrometer was to be used to obtain information on the composition, density, and constituency of the lunar atmosphere. The spectrometer was also designed to detect far-UV radiation emitted by the Sun that had been reflected off the lunar surface. The laser altimeter was designed to measure the altitude of the spacecraft above the lunar surface within approximately 2 meters (6.6 feet), providing altitude information to the panoramic and mapping cameras, which were also in the SIM bay.[86][87] Light-flash phenomenon and other experiments Main article: Cosmic ray visual phenomena Beginning with Apollo 11, crew members observed light flashes that penetrated their closed eyelids. These flashes, described by the astronauts as "streaks" or "specks" of light, were usually observed while the spacecraft was darkened during a sleep period. These flashes, while not observed on the lunar surface, would average about two per minute and were observed by the crew members during the trip out to the Moon, back to Earth, and in lunar orbit.[88] The Apollo 17 crew repeated an experiment, also conducted on Apollo 16, with the objective of linking these light flashes with cosmic rays. Evans wore a device over his eyes that recorded the time, strength, and path of high-energy atomic particles that penetrated the device, while the other two wore blindfolds to keep out light. Investigators concluded that the available evidence supports the hypothesis that these flashes occur when charged particles travel through the retina in the eye.[88] Apollo 17 carried a sodium-iodide crystal identical to the ones in the gamma-ray spectrometer flown on Apollo 15 and 16. Data from this, once it was examined on Earth, was to be used to help form a baseline, allowing for subtraction of rays from the CM or from cosmic radiation to gain better data from the earlier results.[89] In addition, the S-band transponders in the CSM and LM were pointed at the Moon to gain data on its gravitational field. Results from the Lunar Orbiter probes had revealed that lunar gravity varies slightly due to the presence of mass concentrations, or "mascons". Data from the missions, and from the lunar subsatellites left by Apollo 15 and 16, were used to map such variations in lunar gravity.[90][91] Mission events Launch and outbound trip Apollo 17 launches on December 7, 1972 Originally planned to launch on December 6, 1972, at 9:53 p.m. EST (2:53 a.m. on December 7 UTC),[65] Apollo 17 was the final crewed Saturn V launch, and the only one to occur at night. The launch was delayed by two hours and forty minutes due to an automatic cutoff in the launch sequencer at the T-30 second mark in the countdown. The cause of the problem was quickly determined to be the launch sequencer's failure to automatically pressurize the liquid oxygen tank in the third stage of the rocket; although launch control noticed this and manually caused the tank to pressurize, the sequencer did not recognize the fix and therefore paused the countdown. The clock was reset and held at the T-22 minute mark while technicians worked around the malfunction in order to continue with the launch. This pause was the only launch delay in the Apollo program caused by a hardware problem. The countdown then resumed, and the liftoff occurred at 12:33 a.m. EST on December 7, 1972.[4][92] The launch window, which had begun at the originally planned launch time of 9:53 p.m. on December 6, remained open until 1:31 a.m., the latest time at which a launch could have occurred during the December 6–7 window.[93] Approximately 500,000 people observed the launch in the immediate vicinity of Kennedy Space Center, despite the early-morning hour. The launch was visible as far away as 800 km (500 mi), and observers in Miami, Florida, reported a "red streak" crossing the northern sky.[92] Among those in attendance at the program's final launch were astronauts Neil Armstrong and Dick Gordon, as well as centenarian Charlie Smith, who alleged he was 130 years old at the time of Apollo 17.[94] The ascent resulted in an orbit with an altitude and velocity almost exactly that which had been planned.[95] In the hours following the launch, Apollo 17 orbited the Earth while the crew spent time monitoring and checking the spacecraft to ensure its readiness to depart Earth orbit. At 3:46 a.m. EST, the S-IVB third stage was reignited for the 351-second trans-lunar injection burn to propel the spacecraft towards the Moon.[11][4] Ground controllers chose a faster trajectory for Apollo 17 than originally planned to allow the vehicle to reach lunar orbit at the planned time, despite the launch delay.[96] The Command and Service Module separated from the S-IVB approximately half an hour following the S-IVB trans-lunar injection burn, after which Evans turned the spacecraft to face the LM, still attached to the S-IVB. The CSM then docked with the LM and extracted it from the S-IVB. Following the LM extraction, Mission Control programmed the S-IVB, no longer needed to propel the spacecraft, to impact the Moon and trip the seismometers left by prior Apollo crews.[11] It struck the Moon just under 87 hours into the mission, triggering the seismometers from Apollo 12, 14, 15 and 16.[97] Approximately nine hours after launch, the crew concluded the mission's first day with a sleep period, until waking up to begin the second day.[11] View of Earth from Apollo 17 while in transit to the Moon, a photo now known as The Blue Marble Mission Control and the crew decided to shorten the mission's second day, the first full day in space, in order to adjust the crew's wake-up times for the subsequent days in preparation for an early morning (EST) wake-up time on the day of the lunar landing, then scheduled for early afternoon (EST). This was done since the first day of the mission had been extended because of the launch delay. Following the second rest period, and on the third day of the mission, the crew executed the first mid-course correction, a two-second burn of the CSM's service propulsion engine to adjust the spacecraft's Moon-bound trajectory. Following the burn, the crew opened the hatch separating the CSM and LM in order to check the LM's systems and concluded that they were nominal.[11] So that events would take place at the time indicated in the flight plan, the mission clocks were moved ahead by 2 hours and 40 minutes, the amount of the launch delay, with one hour of it at 45:00:00 into the mission and the remainder at 65:00:00.[98] Among their other activities during the outbound trip, the crew photographed the Earth from the spacecraft as it travelled towards the Moon. One of these photographs is now known as The Blue Marble.[99] The crew found that one of the latches holding the CSM and LM together was unlatched. While Schmitt and Cernan were engaged in a second period of LM housekeeping beginning just before sixty hours into the Mission, Evans worked on the balky latch. He was successful, and left it in the position it would need to be in for the CSM-LM docking that would occur upon return from the lunar surface.[100] Also during the outward journey, the crew performed a heat flow and convection demonstration, as well as the Apollo light-flash experiment. A few hours before entry into lunar orbit, the SIM door on the SM was jettisoned. At approximately 2:47 p.m. EST on December 10, the service propulsion system engine on the CSM ignited to slow down the CSM/LM stack into lunar orbit. Following orbit insertion and orbital stabilization, the crew began preparations for the landing at Taurus–Littrow.[4] Lunar landing The valley of Taurus-Littrow as seen from the Challenger on the orbit before powered descent there. The CSM America can be seen crossing the base of the 2.3 km high South Massif. Between the South and North Massifs, the valley is 7 km wide. Mare Serenitatis is on the horizon. The day of the landing began with a checkout of the Lunar Module's systems, which revealed no problems preventing continuation of the mission. Cernan, Evans, and Schmitt each donned their spacesuits, and Cernan and Schmitt entered the LM in preparation for separating from the CSM and landing. The LM undocked from the CSM, and the two spacecraft orbited close together for about an hour and a half while the astronauts made visual inspections and conducted their final pre-landing checks.[11] After finally separating from the CSM, the LM Challenger and its crew of two adjusted their orbit, such that its lowest point would pass about 10.5 mi (16.9 km) above the landing site, and began preparations for the descent to Taurus–Littrow. While Cernan and Schmitt prepared for landing, Evans remained in orbit to take observations, perform experiments and await the return of his crewmates a few days later.[4][11][101] Soon after completing their preparations for landing and just over two hours following the LM's undocking from the CSM, Cernan and Schmitt began their descent to the Taurus–Littrow valley on the lunar surface with the ignition of the Lunar Module's descent propulsion system (DPS) engine.[101][102] Approximately ten minutes later, as planned, the LM pitched over, giving Cernan and Schmitt their first look at the landing site during the descent phase and allowing Cernan to guide the spacecraft to a desirable landing target while Schmitt provided data from the flight computer essential for landing. The LM touched down on the lunar surface at 2:55 p.m. EST on December 11, just over twelve minutes after DPS ignition.[102] Challenger landed about 656 feet (200 m) east of the planned landing point.[103] Shortly thereafter, the two astronauts began re-configuring the LM for their stay on the surface and began preparations for the first moonwalk of the mission, or EVA-1.[4][101] Lunar surface First EVA Cernan on the lunar surface, December 13, 1972 During their approximately 75-hour stay[104] on the lunar surface, Cernan and Schmitt performed three moonwalks (EVAs). The astronauts deployed the LRV, then emplaced the ALSEP and the seismic explosive charges. They drove the rover to nine planned geological-survey stations to collect samples and make observations. Additionally, twelve short sampling stops were made at Schmitt's discretion while riding the rover, during which the astronauts used a handled scoop to get a sample, without dismounting.[105] During lunar-surface operations, Commander Cernan always drove the rover, while Lunar Module Pilot Schmitt was a passenger who assisted with navigation. This division of responsibilities between the two crew positions was used consistently throughout Apollo's J-missions.[106][107][108] The first lunar excursion began four hours after landing, at 6:54 p.m. EST on December 11. After exiting through the hatch of the LM and descending the ladder to the footpad, Cernan took the first step on the lunar surface of the mission. Just before doing so, Cernan remarked, "I'm on the footpad. And, Houston, as I step off at the surface at Taurus–Littrow, we'd like to dedicate the first step of Apollo 17 to all those who made it possible."[109] After Cernan surveyed the exterior of the LM and commented on the immediate landing site, Schmitt joined Cernan on the surface.[109] The first task was to offload the rover and other equipment from the LM. While working near the rover, Cernan caught his hammer under the right-rear fender extension, accidentally breaking it off. A similar incident occurred on Apollo 16 as John Young maneuvered around the rover. Although this was not a mission-critical issue, the loss of the part caused Cernan and Schmitt to be covered with dust stirred up when the rover was in motion.[110] The crew made a short-lived fix using duct tape at the beginning of the second EVA, attaching a paper map to the damaged fender. Lunar dust stuck to the tape's surface, however, preventing it from adhering properly. Following deployment and testing the maneuverability of the rover, the crew deployed the ALSEP just west of the landing site. The ALSEP deployment took longer than had been planned, with the drilling of core holes presenting some difficulty, meaning the geological portion of the first EVA would need to be shortened, cancelling a planned visit to Emory crater. Instead, following the deployment of the ALSEP, Cernan and Schmitt drove to Steno crater, to the south of the landing site. The objective at Steno was to sample the subsurface material excavated by the impact that formed the crater. The astronauts gathered 14 kilograms (31 lb) of samples, took seven gravimeter measurements, and deployed two explosive packages. The explosive packages were later detonated remotely; the resulting explosions detected by geophones placed by the astronauts and also by seismometers left during previous missions.[111] The first EVA ended after seven hours and twelve minutes.[4] and the astronauts remained in the pressurized LM for the next 17 hours.[112] Second and third EVAs 0:30 Astronauts Cernan and Schmitt singing "I Was Strolling on the Moon One Day" to the words and tune of the 1884 song "While Strolling Through the Park One Day" On December 12, awakened by a recording of "Ride of the Valkyries" played from Mission Control,[113] Cernan and Schmitt began their second lunar excursion. The first order of business was to provide the rover's fender a better fix. Overnight, the flight controllers devised a procedure communicated by John Young: taping together four stiff paper maps[113] to form a "replacement fender extension" and then clamping it onto the fender.[114] The astronauts carried out the new fix which did its job without failing until near the end of the third excursion.[115][116] Cernan and Schmitt then departed for station 2—Nansen Crater, at the foot of the South Massif. When they arrived, their range from the Challenger was 7.6 kilometers (4.7 miles, 25,029 feet[8]). This remains the furthest distance any spacefarers have ever traveled away from the safety of a pressurizable spacecraft while on a planetary body,[117] and also during an EVA of any type.[a] The astronauts were at the extremity of their "walkback limit", a safety constraint meant to ensure that they could walk back to the LM if the rover failed. They began a return trip, traveling northeast in the rover.[119] At station 3, Schmitt fell to the ground while working, looking so awkward that Parker jokingly told him that NASA's switchboard had lit up seeking Schmitt's services for Houston's ballet group, and the site of station 3 was in 2019 renamed Ballet Crater.[120] Cernan took a sample at Station 3 that was to be maintained in vacuum until better analytical techniques became available, joking with the CAPCOM, Parker, about placing a note inside. The container remained unopened until 2022.[114][121] Stopping at station 4—Shorty crater—the astronauts discovered orange soil, which proved to be very small beads of volcanic glass formed over 3.5 billion years ago.[122] This discovery caused great excitement among the scientists at Mission Control, who felt that the astronauts may have discovered a volcanic vent. However, post-mission sample analysis revealed that Shorty is not a volcanic vent, but rather an impact crater. Analysis also found the orange soil to be a remnant of a fire fountain. This fire fountain sprayed molten lava high into the lunar sky in the Moon's early days, some 3.5 billion years ago and long before Shorty's creation. The orange volcanic beads were droplets of molten lava from the fountain that solidified and were buried by lava deposits until exposed by the impact that formed Shorty, less than 20 million years ago.[119] The final stop before returning to the LM was Camelot crater; throughout the sojourn, the astronauts collected 34 kilograms (75 lb) of samples, took another seven gravimeter measurements, and deployed three more explosive packages.[4] Concluding the EVA at seven hours and thirty-seven minutes, Cernan and Schmitt had completed the longest-duration EVA in history to-date, traveling further away from a spacecraft and covering more ground on a planetary body during a single EVA than any other spacefarers.[8] The improvised fender had remained intact throughout, causing the president of the "Auto Body Association of America" to award them honorary lifetime membership.[123] Composite image of Harrison Schmitt working next to Tracy's Rock during EVA-3 The third moonwalk, the last of the Apollo program, began at 5:25 p.m. EST on December 13. Cernan and Schmitt rode the rover northeast of the landing site, exploring the base of the North Massif and the Sculptured Hills. Stopping at station 6, they examined a house-sized split boulder dubbed Tracy's Rock (or Split Rock), after Cernan's daughter. The ninth and final planned station was conducted at Van Serg crater. The crew collected 66 kilograms (146 lb) of lunar samples and took another nine gravimeter measurements.[4] Schmitt had seen a fine-grained rock, unusual for that vicinity, earlier in the mission and had stood it on its edge; before closing out the EVA, he went and got it. Subsequently, designated Sample 70215, it was, at 17.7 pounds (8.0 kg), the largest rock brought back by Apollo 17. A small piece of it is on exhibit at the Smithsonian Institution, one of the few rocks from the Moon that the public may touch.[124] Schmitt also collected a sample, designated as Sample 76535, at geology station 6 near the base of the North Massif; the sample, a troctolite, was later identified as the oldest known "unshocked" lunar rock, meaning it has not been damaged by high-impact geological events. Scientists have therefore used Sample 76535 in thermochronological studies to determine if the Moon formed a metallic core or, as study results suggest, a core dynamo.[125][126] Before concluding the moonwalk, the crew collected a breccia rock, dedicating it to the nations of Earth, 70 of which were represented by students touring the U.S. and present in Mission Control Center in Houston, Texas, at the time. Portions of this sample, known as the Friendship Rock, were subsequently distributed to the nations represented by the students. A plaque located on the LM, commemorating the achievements made during the Apollo program, was then unveiled. Before reentering the LM for the final time, Cernan remarked,[4][127]     ... I'm on the surface; and, as I take man's last step from the surface, back home for some time to come – but we believe not too long into the future – I'd like to just [say] what I believe history will record. That America's challenge of today has forged man's destiny of tomorrow. And, as we leave the Moon at Taurus–Littrow, we leave as we came and, God willing, as we shall return, with peace and hope for all mankind. "Godspeed the crew of Apollo 17."[128] Cernan then followed Schmitt into the LM; the final lunar excursion had a duration of seven hours and fifteen minutes.[4] Following closing of the LM hatch and repressurization of the LM cabin, Cernan and Schmitt removed their spacesuits and reconfigured the cabin for a final rest period on the lunar surface. As they did following each of the previous two EVAs, Cernan and Schmitt discussed their geological observations from the day's excursion with mission control while preparing to rest.[129] Solo activities While Cernan and Schmitt were on the lunar surface, Evans remained alone in the CSM in lunar orbit and was assigned a number of observational and scientific tasks to perform while awaiting the return of his crewmates. In addition to the operation of the various orbital science equipment contained in the CSM's SIM bay, Evans conducted both visual and photographic observation of surface features from his aerial vantage point.[130] The orbit of the CSM having been modified to an elliptical orbit in preparation for the LM's departure and eventual descent, one of Evans' solo tasks in the CSM was to circularize its orbit such that the CSM would remain at approximately the same distance above the surface throughout its orbit.[131] Evans observed geological features visible to him and used handheld cameras to record certain visual targets.[130] Evans also observed and sketched the solar corona at "sunrise," or the period of time during which the CSM would pass from the darkened portion of the Moon to the illuminated portion when the Moon itself mostly obscured the sun.[132] To photograph portions of the surface that were not illuminated by the sun while Evans passed over them, Evans relied in conjunction on exposure and Earthlight. Evans photographed such features as the craters Eratosthenes and Copernicus, as well as the vicinity of Mare Orientale, using this technique.[133] According to the Apollo 17 Mission Report, Evans was able to capture all scientific photographic targets, as well as some other targets of interest.[134] An oblique, black-and-white view of a portion of Mare Orientale from the CSM, illustrating the illuminating effect of Earthlight on the lunar terrain below during local nighttime; Evans reported seeing a light "flash" apparently originating from the surface in this area Similarly to the crew of Apollo 16, Evans (as well as Schmitt, while in lunar orbit) reported seeing light "flashes" apparently originating from the lunar surface, known as transient lunar phenomena (TLP); Evans reported seeing these "flashes" in the vicinity of Grimaldi crater and Mare Orientale. The causes of TLP are not well-understood and, though inconclusive as an explanation, both of the sites in which Evans reported seeing TLP are the general locations of outgassing from the Moon's interior. Meteorite impacts are another possible explanation.[135][136] The flight plan kept Evans busy, making him so tired he overslept one morning by an hour, despite the efforts of Mission Control to awaken him. Before the LM departed for the lunar surface, Evans had discovered that he had misplaced his pair of scissors, necessary to open food packets. Cernan and Schmitt lent him one of theirs.[137] The instruments in the SIM bay functioned without significant hindrance during the orbital portion of the mission, though the lunar sounder and the mapping camera encountered minor problems.[138] Evans spent approximately 148 total hours in lunar orbit, including solo time and time spent together with Cernan and Schmitt, which is more time than any other individual has spent orbiting the Moon.[104][139] Evans was also responsible for piloting the CSM during the orbital phase of the mission, maneuvering the spacecraft to alter and maintain its orbital trajectory. In addition to the initial orbital recircularization maneuver shortly after the LM's departure, one of the solo activities Evans performed in the CSM in preparation for the return of his crewmates from the lunar surface was the plane change maneuver. This maneuver was meant to align the CSM's trajectory to the eventual trajectory of the LM to facilitate rendezvous in orbit. Evans fired the SPS engine of the CSM for about 20 seconds in successfully adjusting the CSM's orbital plane.[9][138] Return to Earth Apollo 17 post-splashdown recovery operations Cernan and Schmitt successfully lifted off from the lunar surface in the ascent stage of the LM on December 14, at 5:54 p.m. EST. The return to lunar orbit took just over seven minutes.[140] The LM, piloted by Cernan, and the CSM, piloted by Evans, maneuvered, and redocked about two hours after liftoff from the surface. Once the docking had taken place, the crew transferred equipment and lunar samples from the LM to the CSM for return to Earth.[102][141] The crew sealed the hatches between the CSM and the LM ascent stage following completion of the transfer and the LM was jettisoned at 11:51 p.m. EST on December 14. The unoccupied ascent stage was then remotely deorbited, crashing it into the Moon with an impact recorded by the seismometers left by Apollo 17 and previous missions.[4][141] At 6:35 p.m. EST on December 16, the CSM's SPS engine was ignited once more to propel the spacecraft away from the Moon on a trajectory back towards Earth. The successful trans-Earth injection SPS burn lasted just over two minutes.[140] During the return to Earth, Evans performed a 65-minute EVA to retrieve film cassettes from the service module's SIM bay, with assistance from Schmitt who remained at the command module's hatch. At approximately 160,000 nautical miles[142]: 1730  (184,000 mi; 296,000 km) from Earth, it was the third "deep space" EVA in history, performed at great distance from any planetary body. As of 2023, it remains one of only three such EVAs, all performed during Apollo's J-missions under similar circumstances. It was the last EVA of the Apollo program.[4][143] During the trip back to Earth, the crew operated the infrared radiometer in the SM, as well as the ultraviolet spectrometer. One midcourse correction was performed, lasting 9 seconds.[144] On December 19, the crew jettisoned the no-longer-needed SM, leaving only the CM for return to Earth. The Apollo 17 spacecraft reentered Earth's atmosphere and splashed down safely in the Pacific Ocean at 2:25 p.m. EST, 6.4 kilometers (4.0 mi) from the recovery ship, USS Ticonderoga. Cernan, Evans, and Schmitt were then retrieved by a recovery helicopter piloted by Commander Edward E. Dahill, III and were safe aboard the recovery ship 52 minutes after splashdown.[4][141][145] As the final Apollo mission concluded successfully, Mission Control in Houston was filled with many former flight controllers and astronauts, who applauded as America returned to Earth.[146] Aftermath and spacecraft locations Apollo 17 command module America, on display at Space Center Houston Lunar Reconnaissance Orbiter image of the Apollo 17 mission site taken in 2011, the Challenger descent stage is in the center, the Lunar Roving Vehicle appears in the lower right. Following their mission, the crew undertook both domestic and international tours, visiting 29 states and 11 countries. The tour kicked off at Super Bowl VII, with the crew leading the crowd in the Pledge of Allegiance; the CM America was also displayed during the pregame activities.[147] None of the Apollo 17 astronauts flew in space again.[148] Cernan retired from NASA and the Navy in 1976. He died in 2017.[149] Evans retired from the Navy in 1976 and from NASA in 1977, entering the private sector. He died in 1990.[150] Schmitt resigned from NASA in 1975 prior to his successful run for a United States Senate seat from New Mexico in 1976. There, he served one six-year term.[151] The Command Module America is currently on display at Space Center Houston at the Lyndon B. Johnson Space Center in Houston, Texas.[152][153] The ascent stage of Lunar Module Challenger impacted the Moon on December 15, 1972, at 06:50:20.8 UTC (1:50 a.m. EST), at 19.96°N 30.50°E.[152] The descent stage remains on the Moon at the landing site, 20.19080°N 30.77168°E.[9] Eugene Cernan's flown Apollo 17 spacesuit is in the collection of the Smithsonian's National Air and Space Museum (NASM), where it was transferred in 1974,[154] and Harrison Schmitt's is in storage at NASM's Paul E. Garber Facility. Amanda Young of NASM indicated in 2004 that Schmitt's suit is in the best condition of the flown Apollo lunar spacesuits, and therefore is not on public display.[155] Ron Evans' spacesuit was also transferred from NASA in 1974 to the collection of the NASM; it remains in storage.[156] Since Apollo 17's return, there have been attempts to photograph the landing site, where the LM's descent stage, LRV and some other mission hardware, remain. In 2009 and again in 2011, the Lunar Reconnaissance Orbiter photographed the landing site from increasingly low orbits.[157] At least one group has indicated an intention to visit the site as well; in 2018, the German space company PTScientists said that it planned to land two lunar rovers nearby." (wikipedia.org) "An astronaut (from the Ancient Greek ἄστρον (astron), meaning 'star', and ναύτης (nautes), meaning 'sailor') is a person trained, equipped, and deployed by a human spaceflight program to serve as a commander or crew member aboard a spacecraft. Although generally reserved for professional space travelers, the term is sometimes applied to anyone who travels into space, including scientists, politicians, journalists, and tourists.[1][2] "Astronaut" technically applies to all human space travelers regardless of nationality. However, astronauts fielded by Russia or the Soviet Union are typically known instead as cosmonauts (from the Russian "kosmos" (космос), meaning "space", also borrowed from Greek).[3] Comparatively recent developments in crewed spaceflight made by China have led to the rise of the term taikonaut (from the Mandarin "tàikōng" (太空), meaning "space"), although its use is somewhat informal and its origin is unclear. In China, the People's Liberation Army Astronaut Corps astronauts and their foreign counterparts are all officially called hángtiānyuán (航天员, meaning "heaven navigator" or literally "heaven-sailing staff"). Since 1961, 600 astronauts have flown in space.[4] Until 2002, astronauts were sponsored and trained exclusively by governments, either by the military or by civilian space agencies. With the suborbital flight of the privately funded SpaceShipOne in 2004, a new category of astronaut was created: the commercial astronaut. Definition Alan Shepard aboard Freedom 7 (1961) The criteria for what constitutes human spaceflight vary, with some focus on the point where the atmosphere becomes so thin that centrifugal force, rather than aerodynamic force, carries a significant portion of the weight of the flight object. The Fédération Aéronautique Internationale (FAI) Sporting Code for astronautics recognizes only flights that exceed the Kármán line, at an altitude of 100 kilometers (62 mi).[5] In the United States, professional, military, and commercial astronauts who travel above an altitude of 50 miles (80 km)[6] are awarded astronaut wings. As of 17 November 2016, 552 people from 36 countries have reached 100 km (62 mi) or more in altitude, of whom 549 reached low Earth orbit or beyond.[7] Of these, 24 people have traveled beyond low Earth orbit, either to lunar orbit, the lunar surface, or, in one case, a loop around the Moon.[note 1] Three of the 24—Jim Lovell, John Young and Eugene Cernan—did so twice.[8] As of 17 November 2016, under the U.S. definition, 558 people qualify as having reached space, above 50 miles (80 km) altitude. Of eight X-15 pilots who exceeded 50 miles (80 km) in altitude, only one, Joseph A. Walker, exceeded 100 kilometers (about 62.1 miles) and he did it two times, becoming the first person in space twice.[7] Space travelers have spent over 41,790 man-days (114.5 man-years) in space, including over 100 astronaut-days of spacewalks.[9][10] As of 2016, the man with the longest cumulative time in space is Gennady Padalka, who has spent 879 days in space.[11] Peggy A. Whitson holds the record for the most time in space by a woman, 377 days.[12] Terminology See also: Astronaut ranks and positions In 1959, when both the United States and Soviet Union were planning, but had yet to launch humans into space, NASA Administrator T. Keith Glennan and his Deputy Administrator, Hugh Dryden, discussed whether spacecraft crew members should be called astronauts or cosmonauts. Dryden preferred "cosmonaut", on the grounds that flights would occur in and to the broader cosmos, while the "astro" prefix suggested flight specifically to the stars.[13] Most NASA Space Task Group members preferred "astronaut", which survived by common usage as the preferred American term.[14] When the Soviet Union launched the first man into space, Yuri Gagarin in 1961, they chose a term which anglicizes to "cosmonaut".[15][16] Astronaut The first sixteen NASA astronauts, February 1963. Back row: White, McDivitt, Young, See, Conrad, Borman, Armstrong, Stafford, Lovell. Front row: Cooper, Grissom, Carpenter, Schirra, Glenn, Shepard, Slayton. A professional space traveler is called an astronaut.[17] The first known use of the term "astronaut" in the modern sense was by Neil R. Jones in his 1930 short story "The Death's Head Meteor". The word itself had been known earlier; for example, in Percy Greg's 1880 book Across the Zodiac, "astronaut" referred to a spacecraft. In Les Navigateurs de l'infini (1925) by J.-H. Rosny aîné, the word astronautique (astronautics) was used. The word may have been inspired by "aeronaut", an older term for an air traveler first applied in 1784 to balloonists. An early use of "astronaut" in a non-fiction publication is Eric Frank Russell's poem "The Astronaut", appearing in the November 1934 Bulletin of the British Interplanetary Society.[18] The first known formal use of the term astronautics in the scientific community was the establishment of the annual International Astronautical Congress in 1950, and the subsequent founding of the International Astronautical Federation the following year.[19] NASA applies the term astronaut to any crew member aboard NASA spacecraft bound for Earth orbit or beyond. NASA also uses the term as a title for those selected to join its Astronaut Corps.[20] The European Space Agency similarly uses the term astronaut for members of its Astronaut Corps.[21] Cosmonaut The first eleven Soviet cosmonauts, July 1965. Back row, left to right: Leonov, Titov, Bykovsky, Yegorov, Popovich; front row: Komarov, Gagarin, Tereshkova, Nikolayev, Feoktistov, Belyayev. Main article: Soviet space program For a more comprehensive list, see List of cosmonauts. By convention, an astronaut employed by the Russian Federal Space Agency (or its Soviet predecessor) is called a cosmonaut in English texts.[20] The word is an Anglicization of kosmonavt (Russian: космонавт Russian pronunciation: [kəsmɐˈnaft]).[22] Other countries of the former Eastern Bloc use variations of the Russian kosmonavt, such as the Polish: kosmonauta (although Polish also uses astronauta, and the two words are considered synonyms).[23] Coinage of the term космонавт has been credited to Soviet aeronautics (or "cosmonautics") pioneer Mikhail Tikhonravov (1900–1974).[15][16] The first cosmonaut was Soviet Air Force pilot Yuri Gagarin, also the first person in space. He was part of the first six Soviet citizens, with German Titov, Yevgeny Khrunov, Andriyan Nikolayev, Pavel Popovich, and Grigoriy Nelyubov, who were given the title of pilot-cosmonaut in January 1961.[24] Valentina Tereshkova was the first female cosmonaut and the first and youngest woman to have flown in space with a solo mission on the Vostok 6 in 1963.[25] On 14 March 1995,[26] Norman Thagard became the first American to ride to space on board a Russian launch vehicle, and thus became the first "American cosmonaut".[27][28] Taikonaut The first Chinese taikonauts on a 2010 Somalia stamp Main articles: People's Liberation Army Astronaut Corps and China Manned Space Program For a more comprehensive list, see List of Chinese astronauts. In Chinese, the term Yǔ háng yuán (宇航员, "cosmos navigating personnel") is used for astronauts and cosmonauts in general,[29][30] while hángtiān yuán (航天员, "navigating celestial-heaven personnel") is used for Chinese astronauts. Here, hángtiān (航天, literally "heaven-navigating", or spaceflight) is strictly[31] defined as the navigation of outer space within the local star system, i.e. Solar System. The phrase tàikōng rén (太空人, "spaceman") is often used in Hong Kong and Taiwan.[32] The term taikonaut is used by some English-language news media organizations for professional space travelers from China.[33] The word has featured in the Longman and Oxford English dictionaries, and the term became more common in 2003 when China sent its first astronaut Yang Liwei into space aboard the Shenzhou 5 spacecraft.[34] This is the term used by Xinhua News Agency in the English version of the Chinese People's Daily since the advent of the Chinese space program.[35] The origin of the term is unclear; as early as May 1998, Chiew Lee Yih (趙裡昱) from Malaysia, used it in newsgroups.[36][37] Parastronaut For its 2022 Astronaut Group, the European Space Agency envisioned recruiting an astronaut with a physical disability, a category they called "parastronauts", with the intention but not guarantee of spaceflight.[38] The categories of disability considered for the program were individuals with lower limb deficiency (either through amputation or congenital), leg length difference, or a short stature (less than 130 centimetres or 4 feet 3 inches).[39] On 23 November 2022, John McFall was selected to be the first ESA parastronaut.[40] Other terms With the rise of space tourism, NASA and the Russian Federal Space Agency agreed to use the term "spaceflight participant" to distinguish those space travelers from professional astronauts on missions coordinated by those two agencies. Finnish American astronaut Timothy Kopra While no nation other than Russia (and previously the Soviet Union), the United States, and China have launched a crewed spacecraft, several other nations have sent people into space in cooperation with one of these countries, e.g. the Soviet-led Interkosmos program. Inspired partly by these missions, other synonyms for astronaut have entered occasional English usage. For example, the term spationaut (French: spationaute) is sometimes used to describe French space travelers, from the Latin word spatium for "space"; the Malay term angkasawan (deriving from angkasa meaning 'space') was used to describe participants in the Angkasawan program (note its similarity with the Indonesian term antariksawan). Plans of the Indian Space Research Organisation to launch its crewed Gaganyaan spacecraft have spurred at times public discussion if another term than astronaut should be used for the crew members, suggesting vyomanaut (from the Sanskrit word व्योमन्/vyoman meaning 'sky' or 'space') or gagannaut (from the Sanskrit word gagan for 'sky').[41][42] In Finland, the NASA astronaut Timothy Kopra, a Finnish American, has sometimes been referred to as sisunautti, from the Finnish word sisu.[43] Across Germanic languages, the word for "astronaut" typically translates to "space traveler", as it does with German's Raumfahrer, Dutch's ruimtevaarder, Swedish's rymdfarare, and Norwegian's romfarer. As of 2021 in the United States, astronaut status is conferred on a person depending on the authorizing agency:     one who flies in a vehicle above 50 miles (80 km) for NASA or the military is considered an astronaut (with no qualifier)     one who flies in a vehicle to the International Space Station in a mission coordinated by NASA and Roscosmos is a spaceflight participant     one who flies above 50 miles (80 km) in a non-NASA vehicle as a crewmember and demonstrates activities during flight that are essential to public safety, or contribute to human space flight safety, is considered a commercial astronaut by the Federal Aviation Administration[44]     one who flies to the International Space Station as part of a "privately funded, dedicated commercial spaceflight on a commercial launch vehicle dedicated to the mission ... to conduct approved commercial and marketing activities on the space station (or in a commercial segment attached to the station)" is considered a private astronaut by NASA[45] (as of 2020, nobody has yet qualified for this status)     a generally-accepted but unofficial term for a paying non-crew passenger who flies a private non-NASA or military vehicles above 50 miles (80 km) is a space tourist (as of 2020[needs update], nobody has yet qualified for this status) On July 20, 2021, the FAA issued an order redefining the eligibility criteria to be an astronaut in response to the private suborbital spaceflights of Jeff Bezos and Richard Branson.[46][47] The new criteria states that one must have "[d]emonstrated activities during flight that were essential to public safety, or contributed to human space flight safety" in order to qualify as an astronaut. This new definition excludes Bezos and Branson. Space travel milestones See also: Spaceflight records and Timeline of space travel by nationality Yuri Gagarin, first human in space (1961) Valentina Tereshkova, first woman in space (1963) Neil Armstrong, first human to walk on the Moon (1969) Vladimír Remek, a Czechoslovak who became the first non-American and non-Soviet cosmonaut in space (1978) Yang Liwei, first person sent into space by China (2003) Map of countries whose citizens have flown in space The first human in space was Soviet Yuri Gagarin, who was launched on 12 April 1961, aboard Vostok 1 and orbited around the Earth for 108 minutes. The first woman in space was Soviet Valentina Tereshkova, who launched on 16 June 1963, aboard Vostok 6 and orbited Earth for almost three days. Alan Shepard became the first American and second person in space on 5 May 1961, on a 15-minute sub-orbital flight aboard Freedom 7. The first American to orbit the Earth was John Glenn, aboard Friendship 7 on 20 February 1962. The first American woman in space was Sally Ride, during Space Shuttle Challenger's mission STS-7, on 18 June 1983.[48] In 1992, Mae Jemison became the first African American woman to travel in space aboard STS-47. Cosmonaut Alexei Leonov was the first person to conduct an extravehicular activity (EVA), (commonly called a "spacewalk"), on 18 March 1965, on the Soviet Union's Voskhod 2 mission. This was followed two and a half months later by astronaut Ed White who made the first American EVA on NASA's Gemini 4 mission.[49] The first crewed mission to orbit the Moon, Apollo 8, included American William Anders who was born in Hong Kong, making him the first Asian-born astronaut in 1968. The Soviet Union, through its Intercosmos program, allowed people from other "socialist" (i.e. Warsaw Pact and other Soviet-allied) countries to fly on its missions, with the notable exceptions of France and Austria participating in Soyuz TM-7 and Soyuz TM-13, respectively. An example is Czechoslovak Vladimír Remek, the first cosmonaut from a country other than the Soviet Union or the United States, who flew to space in 1978 on a Soyuz-U rocket.[50] Rakesh Sharma became the first Indian citizen to travel to space. He was launched aboard Soyuz T-11, on 2 April 1984. On 23 July 1980, Pham Tuan of Vietnam became the first Asian in space when he flew aboard Soyuz 37.[51] Also in 1980, Cuban Arnaldo Tamayo Méndez became the first person of Hispanic and black African descent to fly in space, and in 1983, Guion Bluford became the first African American to fly into space. In April 1985, Taylor Wang became the first ethnic Chinese person in space.[52][53] The first person born in Africa to fly in space was Patrick Baudry (France), in 1985.[54][55] In 1985, Saudi Arabian Prince Sultan Bin Salman Bin AbdulAziz Al-Saud became the first Arab Muslim astronaut in space.[56] In 1988, Abdul Ahad Mohmand became the first Afghan to reach space, spending nine days aboard the Mir space station.[57] With the increase of seats on the Space Shuttle, the U.S. began taking international astronauts. In 1983, Ulf Merbold of West Germany became the first non-US citizen to fly in a US spacecraft. In 1984, Marc Garneau became the first of eight Canadian astronauts to fly in space (through 2010).[58] In 1985, Rodolfo Neri Vela became the first Mexican-born person in space.[59] In 1991, Helen Sharman became the first Briton to fly in space.[60] In 2002, Mark Shuttleworth became the first citizen of an African country to fly in space, as a paying spaceflight participant.[61] In 2003, Ilan Ramon became the first Israeli to fly in space, although he died during a re-entry accident. On 15 October 2003, Yang Liwei became China's first astronaut on the Shenzhou 5 spacecraft. On 30 May 2020, Doug Hurley and Bob Behnken became the first astronauts to launch on a private crewed spacecraft, Crew Dragon. Age milestones The youngest person to reach space is Oliver Daemen, who was 18 years and 11 months old when he made a suborbital spaceflight on Blue Origin NS-16.[62] Daemen, who was a commercial passenger aboard the New Shepard, broke the record of Soviet cosmonaut Gherman Titov, who was 25 years old when he flew Vostok 2. Titov remains the youngest human to reach orbit; he rounded the planet 17 times. Titov was also the first person to suffer space sickness and the first person to sleep in space, twice.[63][64] The oldest person to reach space is William Shatner, who was 90 years old when he made a suborbital spaceflight on Blue Origin NS-18.[65] The oldest person to reach orbit is John Glenn, one of the Mercury 7, who was 77 when he flew on STS-95.[66] For greater detail on age records, see list of spaceflight records § Age records. Duration and distance milestones 438 days is the longest time spent in space, by Russian Valeri Polyakov.[9] As of 2006, the most spaceflights by an individual astronaut is seven, a record held by both Jerry L. Ross and Franklin Chang-Diaz. The farthest distance from Earth an astronaut has traveled was 401,056 km (249,205 mi), when Jim Lovell, Jack Swigert, and Fred Haise went around the Moon during the Apollo 13 emergency.[9] Civilian and non-government milestones The first civilian in space was Valentina Tereshkova[67] aboard Vostok 6 (she also became the first woman in space on that mission). Tereshkova was only honorarily inducted into the USSR's Air Force, which did not accept female pilots at that time. A month later, Joseph Albert Walker became the first American civilian in space when his X-15 Flight 90 crossed the 100 kilometers (54 nautical miles) line, qualifying him by the international definition of spaceflight.[68][69] Walker had joined the US Army Air Force but was not a member during his flight. The first people in space who had never been a member of any country's armed forces were both Konstantin Feoktistov and Boris Yegorov aboard Voskhod 1. The first non-governmental space traveler was Byron K. Lichtenberg, a researcher from the Massachusetts Institute of Technology who flew on STS-9 in 1983.[70] In December 1990, Toyohiro Akiyama became the first paying space traveler and the first journalist in space for Tokyo Broadcasting System, a visit to Mir as part of an estimated $12 million (USD) deal with a Japanese TV station, although at the time, the term used to refer to Akiyama was "Research Cosmonaut".[71][72][73] Akiyama suffered severe space sickness during his mission, which affected his productivity.[72] The first self-funded space tourist was Dennis Tito on board the Russian spacecraft Soyuz TM-3 on 28 April 2001. Self-funded travelers Further information: Space tourism The first person to fly on an entirely privately funded mission was Mike Melvill, piloting SpaceShipOne flight 15P on a suborbital journey, although he was a test pilot employed by Scaled Composites and not an actual paying space tourist.[74][75] Seven others have paid the Russian Space Agency to fly into space:     Dennis Tito (American): 28 April – 6 May 2001 (ISS)     Mark Shuttleworth (South African): 25 April – 5 May 2002 (ISS)     Gregory Olsen (American): 1–11 October 2005 (ISS)     Anousheh Ansari (Iranian / American): 18–29 September 2006 (ISS)     Charles Simonyi (Hungarian / American): 7–21 April 2007 (ISS), 26 March – 8 April 2009 (ISS)     Richard Garriott (British / American): 12–24 October 2008 (ISS)     Guy Laliberté (Canadian): 30 September 2009 – 11 October 2009 (ISS)     Jared Isaacman (American): 15–18 September 2021 (Free Flier)     Yusaku Maezawa (Japanese): 8 – 24 December 2021 (ISS) Training Elliot See during water egress training with NASA (1965) Main article: Astronaut training See also: Astronaut ranks and positions The first NASA astronauts were selected for training in 1959.[76] Early in the space program, military jet test piloting and engineering training were often cited as prerequisites for selection as an astronaut at NASA, although neither John Glenn nor Scott Carpenter (of the Mercury Seven) had any university degree, in engineering or any other discipline at the time of their selection. Selection was initially limited to military pilots.[77][78] The earliest astronauts for both the US and the USSR tended to be jet fighter pilots, and were often test pilots. Once selected, NASA astronauts go through twenty months of training in a variety of areas, including training for extravehicular activity in a facility such as NASA's Neutral Buoyancy Laboratory.[1][77] Astronauts-in-training (astronaut candidates) may also experience short periods of weightlessness (microgravity) in an aircraft called the "Vomit Comet," the nickname given to a pair of modified KC-135s (retired in 2000 and 2004, respectively, and replaced in 2005 with a C-9) which perform parabolic flights.[76] Astronauts are also required to accumulate a number of flight hours in high-performance jet aircraft. This is mostly done in T-38 jet aircraft out of Ellington Field, due to its proximity to the Johnson Space Center. Ellington Field is also where the Shuttle Training Aircraft is maintained and developed, although most flights of the aircraft are conducted from Edwards Air Force Base. Astronauts in training must learn how to control and fly the Space Shuttle and, it is vital that they are familiar with the International Space Station so they know what they must do when they get there.[79] NASA candidacy requirements Unless otherwise noted, the following data are incorporated from the Astronaut Requirements article by NASA     The candidate must be a citizen of the United States.     The candidate must complete a master's degree in a STEM field, including engineering, biological science, physical science, computer science or mathematics.     The candidate must have at least two years of related professional experience obtained after degree completion or at least 1,000 hours pilot-in-command time on jet aircraft.     The candidate must be able to pass the NASA long-duration flight astronaut physical.     The candidate must also have skills in leadership, teamwork and communications. The master's degree requirement can also be met by:     Two years of work toward a doctoral program in a related science, technology, engineering or math field.     A completed Doctor of Medicine or Doctor of Osteopathic Medicine degree.     Completion of a nationally recognized test pilot school program. Mission Specialist Educator Main article: Educator Astronaut Project     Applicants must have a bachelor's degree with teaching experience, including work at the kindergarten through twelfth grade level. An advanced degree, such as a master's degree or a doctoral degree, is not required, but is strongly desired.[80] Mission Specialist Educators, or "Educator Astronauts", were first selected in 2004, and as of 2007, there are three NASA Educator astronauts: Joseph M. Acaba, Richard R. Arnold, and Dorothy Metcalf-Lindenburger.[81][82] Barbara Morgan, selected as back-up teacher to Christa McAuliffe in 1985, is considered to be the first Educator astronaut by the media, but she trained as a mission specialist.[83] The Educator Astronaut program is a successor to the Teacher in Space program from the 1980s.[84][85] Health risks of space travel See also: Effect of spaceflight on the human body and Space medicine Gennady Padalka performing ultrasound on Michael Fincke during ISS Expedition 9 Astronauts are susceptible to a variety of health risks including decompression sickness, barotrauma, immunodeficiencies, loss of bone and muscle, loss of eyesight, orthostatic intolerance, sleep disturbances, and radiation injury.[86][87][88][89][90][91][92][93][94][95] A variety of large scale medical studies are being conducted in space via the National Space Biomedical Research Institute (NSBRI) to address these issues. Prominent among these is the Advanced Diagnostic Ultrasound in Microgravity Study in which astronauts (including former ISS commanders Leroy Chiao and Gennady Padalka) perform ultrasound scans under the guidance of remote experts to diagnose and potentially treat hundreds of medical conditions in space. This study's techniques are now being applied to cover professional and Olympic sports injuries as well as ultrasound performed by non-expert operators in medical and high school students. It is anticipated that remote guided ultrasound will have application on Earth in emergency and rural care situations, where access to a trained physician is often rare.[96][97][98] A 2006 Space Shuttle experiment found that Salmonella typhimurium, a bacterium that can cause food poisoning, became more virulent when cultivated in space.[99] More recently, in 2017, bacteria were found to be more resistant to antibiotics and to thrive in the near-weightlessness of space.[100] Microorganisms have been observed to survive the vacuum of outer space.[101][102] On 31 December 2012, a NASA-supported study reported that human spaceflight may harm the brain and accelerate the onset of Alzheimer's disease.[103][104][105] In October 2015, the NASA Office of Inspector General issued a health hazards report related to space exploration, including a human mission to Mars.[106][107] Over the last decade, flight surgeons and scientists at NASA have seen a pattern of vision problems in astronauts on long-duration space missions. The syndrome, known as visual impairment intracranial pressure (VIIP), has been reported in nearly two-thirds of space explorers after long periods spent aboard the International Space Station (ISS).[108] On 2 November 2017, scientists reported that significant changes in the position and structure of the brain have been found in astronauts who have taken trips in space, based on MRI studies. Astronauts who took longer space trips were associated with greater brain changes.[109][110] Being in space can be physiologically deconditioning on the body. It can affect the otolith organs and adaptive capabilities of the central nervous system. Zero gravity and cosmic rays can cause many implications for astronauts.[111] In October 2018, NASA-funded researchers found that lengthy journeys into outer space, including travel to the planet Mars, may substantially damage the gastrointestinal tissues of astronauts. The studies support earlier work that found such journeys could significantly damage the brains of astronauts, and age them prematurely.[112] Researchers in 2018 reported, after detecting the presence on the International Space Station (ISS) of five Enterobacter bugandensis bacterial strains, none pathogenic to humans, that microorganisms on ISS should be carefully monitored to continue assuring a medically healthy environment for astronauts.[113][114] A study by Russian scientists published in April 2019 stated that astronauts facing space radiation could face temporary hindrance of their memory centers. While this does not affect their intellectual capabilities, it temporarily hinders formation of new cells in brain's memory centers. The study conducted by Moscow Institute of Physics and Technology (MIPT) concluded this after they observed that mice exposed to neutron and gamma radiation did not impact the rodents' intellectual capabilities.[115] A 2020 study conducted on the brains of eight male Russian cosmonauts after they returned from long stays aboard the International Space Station showed that long-duration spaceflight causes many physiological adaptions, including macro- and microstructural changes. While scientists still know little about the effects of spaceflight on brain structure, this study showed that space travel can lead to new motor skills (dexterity), but also slightly weaker vision, both of which could possibly be long lasting. It was the first study to provide clear evidence of sensorimotor neuroplasticity, which is the brain's ability to change through growth and reorganization.[116][117] Food and drink Main article: Space food Astronauts making and eating hamburgers on board the ISS, 2002[118] An astronaut on the International Space Station requires about 830 g (29 oz) mass of food per meal each day (inclusive of about 120 g or 4.2 oz packaging mass per meal). Space Shuttle astronauts worked with nutritionists to select menus that appealed to their individual tastes. Five months before flight, menus were selected and analyzed for nutritional content by the shuttle dietician. Foods are tested to see how they will react in a reduced gravity environment. Caloric requirements are determined using a basal energy expenditure (BEE) formula. On Earth, the average American uses about 35 US gallons (130 L) of water every day. On board the ISS astronauts limit water use to only about three US gallons (11 L) per day.[119] Insignia NASA Astronaut lapel pin In Russia, cosmonauts are awarded Pilot-Cosmonaut of the Russian Federation upon completion of their missions, often accompanied with the award of Hero of the Russian Federation. This follows the practice established in the USSR where cosmonauts were usually awarded the title Hero of the Soviet Union. At NASA, those who complete astronaut candidate training receive a silver lapel pin. Once they have flown in space, they receive a gold pin. U.S. astronauts who also have active-duty military status receive a special qualification badge, known as the Astronaut Badge, after participation on a spaceflight. The United States Air Force also presents an Astronaut Badge to its pilots who exceed 50 miles (80 km) in altitude. Deaths For a more comprehensive list, see List of spaceflight-related accidents and incidents § Astronaut fatalities. Space Mirror Memorial As of 2020, eighteen astronauts (fourteen men and four women) have died during four space flights. By nationality, thirteen were American, four were Russian (Soviet Union), and one was Israeli. As of 2020, eleven people (all men) have died training for spaceflight: eight Americans and three Russians. Six of these were in crashes of training jet aircraft, one drowned during water recovery training, and four were due to fires in pure oxygen environments. Astronaut David Scott left a memorial consisting of a statuette titled Fallen Astronaut on the surface of the Moon during his 1971 Apollo 15 mission, along with a list of the names of eight of the astronauts and six cosmonauts known at the time to have died in service.[120] The Space Mirror Memorial, which stands on the grounds of the Kennedy Space Center Visitor Complex, is maintained by the Astronauts Memorial Foundation and commemorates the lives of the men and women who have died during spaceflight and during training in the space programs of the United States. In addition to twenty NASA career astronauts, the memorial includes the names of an X-15 test pilot, a U.S. Air Force officer who died while training for a then-classified military space program, and a civilian spaceflight participant." (wikipedia.org) "Science, technology, engineering, and mathematics (STEM) is an umbrella term used to group together the distinct but related technical disciplines of science, technology, engineering, and mathematics. The term is typically used in the context of education policy or curriculum choices in schools. It has implications for workforce development, national security concerns (as a shortage of STEM-educated citizens can reduce effectiveness in this area) and immigration policy, with regards to admitting foreign students and tech workers.[1] There is no universal agreement on which disciplines are included in STEM; in particular whether or not the science in STEM includes social sciences, such as psychology, sociology, economics, and political science. In the United States, these are typically included by organizations such as the National Science Foundation (NSF),[1] the Department of Labor's O*Net online database for job seekers,[2] and the Department of Homeland Security.[3] In the United Kingdom, the social sciences are categorized separately and are instead grouped together with humanities and arts to form another counterpart acronym HASS (Humanities, Arts, and Social Sciences), rebranded in 2020 as SHAPE (Social Sciences, Humanities and the Arts for People and the Economy).[4][5] Some sources also use HEAL (health, education, administration, and literacy) as the counterpart of STEM.[6] Terminology History In the early 1990s, the acronym STEM was used by a variety of educators in preference to SMET, including Charles E. Vela, the founder and director of the Center for the Advancement of Hispanics in Science and Engineering Education (CAHSEE).[7][8][9] Moreover, the CAHSEE started a summer program for talented under-represented students in the Washington, D.C., area called the STEM Institute. Based on the program's recognized success and his expertise in STEM education,[10] Charles Vela was asked to serve on numerous NSF and Congressional panels in science, mathematics and engineering education;[11] it is through this manner that NSF was first introduced to the acronym STEM. One of the first NSF projects to use the acronym was STEMTEC, the Science, Technology, Engineering and Math Teacher Education Collaborative at the University of Massachusetts Amherst, which was founded in 1998.[12] In 2001, at the urging of Dr. Peter Faletra, the Director of Workforce Development for Teachers and Scientists at the Office of Science, the acronym was adopted by Rita Colwell and other science administrators in the National Science Foundation (NSF). The Office of Science was also an early adopter of the STEM acronym.[13] Other variations A-STEM (arts, science, technology, engineering, and mathematics);[14] more focus and based on humanism and arts. eSTEM (environmental STEM)[15][16] GEMS (girls in engineering, math, and science); used for programs to encourage women to enter these fields.[17][18] MINT (mathematics, informatics, natural sciences, and technology)[19] SHTEAM (science, humanities, technology, engineering, arts, and mathematics)[20] SMET (science, mathematics, engineering, and technology); previous name[21] STEAM (science, technology, engineering, arts, and mathematics)[22]     STEAM (science, technology, engineering, agriculture, and mathematics); add agriculture[23]     STEAM (science, technology, engineering, and applied mathematics); more focus on applied mathematics[24] STEEM (science, technology, engineering, economics, and mathematics); adds economics as a field[25] STEMIE (science, technology, engineering, mathematics, invention and entrepreneurship); adds Inventing and Entrepreneurship as means to apply STEM to real world problem solving and markets.[26] STEMM (science, technology, engineering, mathematics, and medicine)[27] STM (scientific, technical, and mathematics[28] or science, technology, and medicine)[29] STREAM (science, technology, robotics, engineering, arts, and mathematics); adds robotics and arts as fields[" (wikipedia.org) "Lenticular printing is a technology in which lenticular lenses (a technology also used for 3D displays) are used to produce printed images with an illusion of depth, or the ability to change or move as they are viewed from different angles. Examples include flip and animation effects such as winking eyes, and modern advertising graphics whose messages change depending on the viewing angle. Colloquial terms for lenticular prints include "flickers", "winkies", "wiggle pictures", and "tilt cards". The trademarks Vari-Vue and Magic Motion are often used for lenticular pictures, without regard to the actual manufacturer. Process How a lenticular lens works Lenticular printing is a multi-step process which consists of creating a lenticular image from at least two images, and placing it behind a lenticular lens. It can be used to create frames of animation, for a motion effect; offsetting the various layers at different increments, for a 3D effect; or simply to show sets of alternative images that appear to transform into each other. Once the images are collected, they are arranged in individual frame files, then digitally combined into a single file in a process called interlacing. The interlaced image may be printed directly on the back (smooth side) of the lens, or on a substrate (ideally a synthetic paper) which is laminated to the lens. When printing on the backside of the lens, the critical registration of the fine "slices" of interlaced images must be absolutely correct during the lithographic or screen printing process to avoid "ghosting" and poor image definition. The combined lenticular print shows two or more images by changing the angle from which the print is viewed. If a sequence of images is used, it can even show a short animation. Though normally produced in sheet form by interlacing simple images or colors throughout the artwork, lenticular images can also be created in roll form with 3D effects or multi-color changes. Alternatively, several images of the same object, taken from slightly different angles, can be used to create a lenticular print with a stereoscopic 3D effect. 3D effects can be achieved only in a lateral (side-by-side) orientation, as each of the viewer's eyes must see them from a slightly different angle to achieve the stereoscopic effect. Other effects, like morphs, motion, and zooms work better (with less ghosting or latent effects) in top-to-bottom orientation, but can be achieved in both orientations. There are many commercial processes in the manufacture of lenticular images, which can be made from PVC, APET, acrylic, and PETG, as well as other materials. While PETG and APET are the most common, other materials are becoming popular to accommodate outdoor use and special forming due to the increasing use of lenticular images on items such as gift cards. Lithographic lenticular printing allows for the flat side of the lenticular sheet to have ink placed directly onto the lens, while high-resolution photographic lenticulars typically have the image laminated to the lens.[citation needed] Lenticular images saw a surge in popularity in the first decade of the 21st century, appearing on the cover of the May 2006 issue of Rolling Stone, trading cards, sports posters, and signs in stores that help to attract buyers.[citation needed] Construction Images are interlaced on the substrate Each image is arranged (slicing) into strips, which are then interlaced with one or more similarly arranged images (splicing). These are printed on the back of a piece of plastic, with a series of thin lenses molded into the opposite side. Alternatively, the images can be printed on paper, which is then bonded to the plastic. With the new technology, lenses are printed in the same printing operation as the interlaced image, either on both sides of a flat sheet of transparent material, or on the same side of a sheet of paper, the image being covered with a transparent sheet of plastic or with a layer of transparent, which in turn is printed with several layers of varnish to create the lenses. The lenses are accurately aligned with the interlaces of the image, so that light reflected off each strip is refracted in a slightly different direction, but the light from all pixels originating from the same original image is sent in the same direction. The end result is that a single eye looking at the print sees a single whole image, but two eyes will see different images, which leads to stereoscopic 3D perception. Types of lenticular prints There are three distinct types of lenticular prints, distinguished by how great a change in angle of view is required to change the image: Transforming prints     Here two or more very different pictures are used, and the lenses are designed to require a relatively large change in angle of view to switch from one image to another. This allows viewers to easily see the original images, since small movements cause no change. Larger movement of the viewer or the print causes the image to flip from one image to another (the "flip effect"). An example of this is the lenticular print of hockey player Mario Tremblay at Centre Mario-Tremblay in Alma, Quebec where he is transformed from a minor hockey playing boy as an Alma Eagle into the professional hockey playing man, four years later, as a Montreal Canadien.[1] Animated prints     Here the distance between different angles of view is "medium", so that while both eyes usually see the same picture, moving a little bit switches to the next picture in the series. Two or more sequential images are used, with only small differences between each image and the next. This can be used to create an image that moves ("motion effect"), or can create a "zoom" or "morph" effect, in which part of the image expands in size or changes shape as the angle of view changes. The movie poster of the film Species II, shown in this article, is an example of this technique. Stereoscopic effects     Here the change in viewing angle needed to change images is small, so that each eye sees a slightly different view. This creates a 3D effect without requiring special glasses, using two or more images. For example, the Dolby-Philips Lenticular 3D display produces 28 different images. Motorized lenticular With static (non-motorized) lenticular, the viewer either moves the piece or moves past the piece in order to see the graphic effects. With motorized lenticular, a motor moves the graphics behind the lens, enabling the graphic effects while both the viewer and the display remain stationary. History Predecessors Tabula scalata Main article: Tabula scalata Corrugated images that change when viewed from different angles predate the development of lenticular printing. A few examples from the paleolithic era exist in French caves.[2][3] Tabula scalata or "turning pictures" were popular in England since the 16th century.[4] Extant double paintings, with two distinct images on a corrugated panel, are known from the 17th century.[5][6] H.C.J. Deeks used a similar technique with minute vertical corrugations pressed into photographic paper and then exposed to two different images from two different angles.[7] Under a 1906 patent H.C.J. Deeks & Co marketed a Puzzle Post Card or Photochange Post Card. In 1907 a Colorchange Post Card followed, featuring identical pictures on each side of the corrugations that were sprayed with different "liquid pigment or coloring matter" on (parts of) each side.[8] Barrier grid autostereograms and animation Main article: Barrier grid animation and stereography Berthier's diagram: A-B=glass plate, with a-b=opaque lines, P=Picture, O=Eyes, c-n=blocked and allowed views (Le Cosmos 05-1896) The oldest known publication about using a line sheet as a parallax barrier to produce an autostereogram is found in an article by Auguste Berthier in the French scientific magazine "Le Cosmos" of May 1896.[9] Berthier's idea was hardly noticed, but American inventor Frederic Eugene Ives had more success with his very similar parallax stereogram since 1901. He also patented the technique for a "Changeable sign, picture, &c." in 1903, which showed different pictures from different angles (instead of one stereoscopic image from the right angle and distance). Léon Gaumont introduced Ives' pictures in France and encouraged Eugène Estanave to work on the technique. Estanave patented a barrier grid technique for animated autostereograms. Animated portrait photographs with line sheets were marketed for a while, mostly in the 1910s and 1920s. In the US "Magic Moving Picture" postcards with simple 3 phase animation or changing pictures were marketed after 1906. Maurice Bonnett improved barrier grid autostereography in the 1930s with his relièphographie technique and scanning cameras. On 11 April 1898 John Jacobson filed an application for US patent No. 624,043 (granted 2 May 1899) for a Stereograph of an interlaced stereoscopic picture and "a transparent mount for said picture having a corrugated or channeled surface".[10] The corrugated lines or channels were not yet really lenticular, but this is the first known autostereogram that used a corrugated transparent surface rather than the opaque lines of most barrier grid stereograms. Gabriel Lippmann's integral photography Main article: Integral imaging French Nobel Prize winning physicist Gabriel Lippmann represented Eugène Estanave at several presentations of Estanave's works at the French Academy of Sciences. On 2 March 1908 Lippmann presented his own ideas for "photographie intégrale", based on insect eyes. He suggested to use a screen of tiny lenses. Spherical segments should be pressed into a sort of film with photographic emulsion on the other side. The screen would be placed inside a lightproof holder and on a tripod for stability. When exposed each tiny lens would function as a camera and record the surroundings from a slightly different angle than neighboring lenses. When developed and lit from behind the lenses should project the life-size image of the recorded subject in space. He could not yet present concrete results in March 1908, but by the end of 1908 he claimed to have exposed some Integral photography plates and to have seen the "resulting single, full-sized image". However, the technique remained experimental since no material or technique seemed to deliver the optical quality desired. At the time of his death in 1921 Lippmann reportedly had a system with only twelve lenses.[11] Early lenticular methods On 11 April 1898, John Jacobson filed an application for US patent No. 624,043 (granted 2 May 1899) for a Stereograph of an interlaced stereoscopic picture and "a transparent mount for said picture having a corrugated or channeled surface".[10] In 1912, Louis Chéron described in his French patent 443,216 a screen with long vertical lenses that would be sufficient for recording "stereoscopic depth and the shifting of the relations of objects to each other as the viewer moved", while he suggested pinholes for integral photography.[11] In June 1912, Swiss Nobel Prize winning physiologist Walter Rudolf Hess applied for a US patent for a Stereoscopic picture with a "celluloid covering having a surface composed of cylindrical lens elements".[12] US patent 1,128,979 (published 16 February 1915) was one of several patents in different countries he would register for this technique. The company Stereo-Photographie A.G., registered in Zürich in 1914 and 1915, would produce pictures on transparencies through Hess' process. Few examples of these pictures are still known to have survived. They are circa 3 1/6 × 4 inches black and white pictures (with discolored or intentional hues) and labeled on their passe-partouts "Stereo-Photo nach W.R. Hess - Stereo-Photographie A.G. Zürich. Patente: "Schweiz / Deutschland / Frankreich / Italien / England / Oesterreich / Vereinigte Staaten angemeldet". The Société française de photographie has three lenticular "Stereo-photo" plates in their collection, three more were on auction in 2017.[13][11][14] Herbert E. Ives, son of Frederic Eugene Ives, was one of several researchers who worked on lenticular sheets in the 1920s. These were basically simpler versions of Lippmann's integral photography and had a linear array of small plano-convex cylindrical lenses (lenticules).[15] The first successful commercial application of the lenticular technique was not used for 3D or motion display but for color movies. Eastman Kodak's 1928 Kodacolor film was based on Keller-Dorian cinematography. It used 16 mm black and white sensitive film embossed with 600 lenses per square inch for use with a filter with RGB stripes.[16] In the 1930s several US patents relating to lenticular techniques were granted, mostly for color film.[17] On 15 December 1936, Douglas F. Winnek Coffey was granted US patent 2,063,985 (application 24 May 1935) for an "Apparatus for making a composite stereograph".[18] The description does not include changing pictures or animation concepts. Further history During World War II, research for military purposes was done into 3D imaging, including lenticular technologies. Mass production of plastics and the technique of injection moulding came about around the same period and enabled commercially viable production of lenticular sheets for novelty toys and advertisements.[19] Victor Anderson and Vari-Vue Victor G. Anderson worked for the Sperry Corporation during World War II where 3D imaging was used for military instructional products, for instance on how to use a bomb sight. After the war Anderson started his company Pictorial Productions Inc. A patent application for a Process in the assembling of changeable picture display devices was filed on 1 March 1952 and granted on 3 December 1957 (US patent 2,815,310. Anderson stated in 1996 that the company's first product was the I Like Ike button.[19] The presidential campaign button's image changed from the slogan "I Like Ike" (in black letters on white) into a black and white picture of Ike Eisenhower when viewed from different angles.[20] It was copyrighted on 14 May 1952.[21] In December 1953 the company registered their trademark Vari-Vue.[22] Vari-Vue further popularized lenticular images during the 1950s and 1960s. By the late sixties, the company marketed about two thousand stock products including twelve-inch-square (30 cm) moving pattern and color sheets, large images (many religious), billboards, and novelty toys.[citation needed] The company went bankrupt in 1986.[23] Xograph Look magazine of 25 February 1964 introduced the publisher's "parallax panoramagram" technology with 8 million copies of a 10x12 cm black and white card with a photographic 3D image of an Edison bust surrounded by some inventions. A 10 x 12 cm full color picture of a model promoting Kodel followed on 7 April. The technique was soon trademarked as "xograph" by Cowles' daughter company Visual Panographics Inc. Magazines like Look and Venture published xographs until the mid 1970s. Some baseball cards were produced as xographs.[24][25] Images produced by the company ranged from just a few millimeters (0.1 inch) to 28 by 19.5 inches (71 by 50 cm).[citation needed] Other early companies In the 1960s, more companies manufactured lenticular products, including Hallmark Cards (registering the Magic Motion trademark in 1964[26]), Reflexa (Nürnberg, Germany), Toppan (Tokyo, Japan) and Dai-Nippon (Japan).[15] OptiGraphics Corporation of Grand Prairie, Texas[27] was formed in 1970 and—under the guidance of Victor Anderson, working well into his 80s. The company trademarked Magic Motion in 1976.[28] Optigraphics produced the lenticular prizes for Cracker Jack in the 1980s, 7-Eleven Slurpee lenticular sports coins from 1983 to 1987,[29] and in 1986 it produced the first set of 3D traditional baseball cards marketed as Sportflics, which ultimately led to the creation of Pinnacle Brands.[30] In 1999 Performance Companies bought OptiGraphics after Pinnacle Trading Card Company went bankrupt in 1998.[27] While lenticular images were very popular in the 1960s and 1970s, by the 1980s OptiGraphics was the only significant manufacturer left in the US.[15] 21st century The techniques for lenticular printing were further improved in the 21st century. Lenticular full motion video effects or "motion print" enabled viewing of up to 60 video frames within a print. Common and notable products Political campaign and pop star "flasher" badges After their first presidential campaign badge I like Ike in 1952, Pictorial Productions Inc. made many more similar political campaign buttons, including presidential campaign badge like Don't blame me! - I voted democratic (1956), John F. Kennedy - The Man for the 60s (1960), I Like Ben (1963) and I'm for Nixon (1968?).[31] Official "flasher" badges for pop stars like Elvis Presley were manufactured by Vari-Vue at least since 1956,[32] including badges for Beatles, Rolling Stones' and other bands in the 1960s. Cheerios and Cracker Jack prizes Pictorial Productions/Vari-Vue produced small animated picture cards for Cheerios in the 1950s, of which founder Victor Anderson claimed to have produced 40 million. He also stated that the cards were originally stuck to the outside of the packaging and were only put inside the boxes after too many cards were stolen before the boxes reached the store shelves.[19] Many different lenticular "tilt cards" were produced as prizes in Cracker Jack boxes. These were first produced by Vari-Vue (1950s-1970s), later by Toppan Printing, Ltd. (1980s), and Optigraphics Corporation (1980s-1990s).[33] Novelty toys In 1958 Victor Anderson patented an Ocular Toy: an eye glass mount with lenticular winking eyes.[34] Lenticular images were used in many small and cheap plastic toys, often as gumball machine prizes. These include: miniature toy televisions with an animated lenticular screen, charms in the shape of animals with lenticular faces, "flicker rings", etcetera. In 1960 Takara's Dakkochan - a little plastic golliwog toy with lenticular eyes - originally intended for toddlers, became very popular with Japanese teenagers as a fashion accessory worn around the arm.[35] Postcards Around 1966 several companies started producing lenticular postcards. Common themes are winking girls, religious scenes, animals, dioramas with dolls, touristic sites and pin-up models wearing clothes when viewed from one angle and nude when viewed from another angle. Covers for books, music albums and movies The lenticular picture on the album cover for the Rolling Stones' 1967 LP Their Satanic Majesties Request was manufactured by Vari-Vue, as well as the postcards and other promotional items that accompanied the release.[36] Other lenticular LP covers include Johnny Cash's The Holy Land (1969)[37] and The Stranglers' The Raven.[38] In the 2010s lenticular covers for LPs became a bit more common, especially for deluxe re-releases.[39] Saturnalia 1973 LP with lenticular label that switches from "Magical love" to a logo. In 1973 the band Saturnalia had lenticular labels on their Magical Love picture disc lp.[40] From around the mid-1990s some lenticular cd covers were produced (mostly for limited editions), including Pet Shop Boys' Alternative (1995) with an image of Chris changing into Neil,[41] The Sacrilicious Sounds of the Supersuckers (1995),[42] Tool's Ænima (1996), Velvet Underground's Loaded 2CD version (1997),[43] Kraftwerk Expo2000 (1999) and David Bowie's Hours (1999).[44] Ministry's 2007 The last sucker had an image of George W. Bush changing into a monstrous, alien-like face.[45] In the 2010s lenticular covers for movies on DVD and Blu-ray became quite common. Lenticular covers have also been used as a collectible cover variant for comic books since the 1990s; Marvel, DC, and other publishers have created such covers with animated or 3-D effects.[46] Lentograph In August 1967 the trademark Lentograph was filed by Victor Anderson 3D Studios, Inc. (registered in October 1968).[47][48] Lentographs were marketed as relatively large lenticular plates (16 x 12 inches / 12 × 8 inches), often found in an illuminated brass frame. Commonly found are 3D pictures of Paul Cunningham's biblical displays with sculpted figurines in dramatic poses based on paintings (Plate 501-508), a family of teddy bears in a domestic scene, Plate No. 106 Evening Flowers, Plate No. 115 Goldilocks and 3 bears, Plate No. 124 Bijou (a white poodle), Plate No. 121 Midday Respite (a taxidermied young deer in a forest setting), Plate No. 213 Red Riding Hood. Also known are a harbor scene (Plate No. 114), Plate No. 118 Japanese Floral, Plate No. 123 Faustus (a yorky dog) and Plate No. 212 of a covered bridge.[49] Lenticular postage stamps In 1967 Bhutan introduced lenticular 3D postage stamps as one of the many unusual stamp designs of the Bhutan Stamp Agency initiated by American businessman Burt Kerr Todd.[50][51] Countries like Ajman, Yemen, Manama, Umm Al Qiwain and North Korea released lenticular stamps in the 1970s. Animated lenticular stamps have been issued since the early 1980s by countries like North Korea.[52] In 2004 full motion lenticular postage stamps were issued in New Zealand. Over the years many other countries have produced stamps with similar lenticular full motion effects, mostly depicting sport events.[52] In 2010 Communications agency KesselsKramer produced the "Smallest Shortest Film" on a Dutch stamp, directed by Anton Corbijn and featuring actress Carice van Houten.[53] In 2012, Design Consultancy GBH.London created the UK's first 'Motion Stamps' for Royal Mail's Special Stamp Issue, The Genius of Gerry Anderson. The minisheet featured four fully lenticular stamps based on Gerry and Sylvia Anderson's Thunderbirds TV series. The Stamps and their background border used 48 frame 'MotionPrint’ technology and were produced by Outer Aspect from New Zealand. In August 2018 the United States Postal Service introduced "The Art of Magic" lenticular stamp, sold in a souvenir sheet of three. The stamp was designed to celebrate the art of magic and "by rotating each stamp, you can see a white rabbit popping out of a black top hat."[54] In August 2019 the United States Postal Service introduced a second stamp with lenticular technology, this time featuring the dinosaur Tyrannosaurus Rex. The USPS explained that "two of the four designs show movement when rotated. See the skeletal remains with and without flesh and watch as an approaching T. rex suddenly lunges forward."[55] Books In 2012, Dan Kainen's first "photicular" book Safari was published, with processed video images animated by having a lens sheet slide by turning the page,[56] much like Rufus Butler Seder's "scanimation" process. It was followed by Ocean (2014), Polar (2015), Jungle (2016), Wild (2017), Dinosaur (2018) and Outback (2019). Related techniques Han-O-Disc manufactured for Light Fantastic with metal flake outside and Dufex process print within. Han-O-Disc record with diffraction grating 'Rainbow' film (outside ring), color shifting Rowlux (middle ring) and "silver balls" Rowlux film (center of record). A related product, produced by a small company in New Jersey, was Rowlux. Unlike the Vari-Vue product, Rowlux used a microprismatic lens structure made by a process they patented in 1972,[57] and no paper print. Instead, the plastic (polycarbonate, flexible PVC and later PETG) was dyed with translucent colors, and the film was usually thin and flexible (from 0.002" or 0.051 mm in thickness). While not a true lenticular process, the Dufex Process (manufactured by F.J. Warren Ltd.)[58] does use a form of lens structure to animate the image. The process consists of imprinting a metallic foil with an image. The foil is then laminated onto a thin sheet of card stock that has been coated with a thick layer of wax. The heated lamination press has the Dufex embossing plate on its upper platen, which has been engraved with 'lenses' at different angles, designed to match the artwork and reflect light at different intensities depending on angle of view. Lenticular cinema and television Since at least the early 1930s many researchers have tried to develop lenticular cinema. Herbert E. Ives presented an apparatus on 31 October 1930 with small autostereoscopic motion pictures viewable by only small groups at a time. Ives would continue to improve his system over the years. However, producing autostereoscopic movies was deemed too costly for commercial purposes. A November 1931 New York Times article entitled New screens gives depth to movies describes a lenticular system by Douglas F. Winnek and also mentions an optical appliance fitted near the screen by South African astronomer R.T.A. Innes.[59] Lenticular arrays have also been used for 3D autostereoscopic television, which produces the illusion of 3D vision without the use of special glasses. At least as early as 1954 patents for lenticular television were filed,[60] but it lasted until 2010 before a range of 3D televisions became available. Some of these systems used cylindrical lenses slanted from the vertical, or spherical lenses arranged in a honeycomb pattern, to provide a better resolution. While over 40 million 3D televisions were sold in 2012 (including systems that required glasses),[61] by 2016 very little 3D content was offered and manufacturers had stopped producing 3D TV sets. While the need to wear glasses for the more affordable systems seemed to have been a letdown for customers, affordable autostereoscopic televisions were seen as a future solution.[62] Further information: 3D television Manufacturing process Printing Lenticular front sheeting and image-processing software are both sold for home computer printing, where the interlaced image backing is inkjet printed in photo resolution and affixed behind the lenticular sheet. [63] Creation of lenticular images on a commercial scale requires printing presses that are adapted to print on sensitive thermoplastic materials. Lithographic offset printing is typically used, to ensure the images are good quality. Printing presses for lenticulars must be capable of adjusting image placement in 10-µm steps, to allow good alignment of the image to the lens array. Typically, ultraviolet-cured inks are used. These dry very quickly by direct conversion of the liquid ink to a solid form, rather than by evaporation of liquid solvents from a mixture. Powerful (400-watt-per-square-inch or 0.083 hp/cm2) ultraviolet (UV) lamps have been used to rapidly cure the ink. This allowed lenticular images to be printed at high speed. In some cases, electron beam lithography has been used instead. The curing of the ink was then initiated directly by an electron beam scanned across the surface. Defects Design defects Double images on the relief and in depth Double images are usually caused by an exaggeration of the 3D effect from some angles of view, or an insufficient number of frames. Poor design can lead to doubling, small jumps, or a fuzzy image, especially on objects in relief or in depth. For some visuals, where the foreground and background are fuzzy or shaded, this exaggeration can prove to be an advantage. In most cases, the detail and precision required do not allow this. Image ghosting Ghosting occurs due to poor treatment of the source images, and also due to transitions where demand for an effect goes beyond the limits and technical possibilities of the system. This causes some of the images to remain visible when they should disappear. These effects can depend on the lighting of the lenticular print. Prepress defects Synchronization of the print (master) with the pitch This effect is also known as "banding". Poor calibration of the material can cause the passage from one image to another to not be simultaneous over the entire print. The image transition progresses from one side of the print to the other, giving the impression of a veil or curtain crossing the visual. This phenomenon is felt less for the 3D effects, but is manifested by a jump of the transverse image. In some cases, the transition starts in several places and progresses from each starting point towards the next, giving the impression of several curtains crossing the visual, as described above. Discordant harmonics This phenomenon is unfortunately very common, and is explained either by incorrect calibration of the support or by incorrect parametrization of the prepress operations. It is manifested in particular by streaks that appear parallel to the lenticules during transitions from one visual to the other. Printing defects Color synchronization One of the main difficulties in lenticular printing is color synchronization. The causes are varied, they may come from a malleable material, incorrect printing conditions and adjustments, or again a dimensional differential of the engraving of the offset plates in each color. This poor marking is shown by doubling of the visual; a lack of clarity; a streak of color or wavy colors (especially for four-color shades) during a change of phase by inclination of the visual. Synchronization of parallelism of the printing to the lenticules The origin of this problem is a fault in the printing and forcibly generates a phase defect. The passage from one visual to another must be simultaneous over the entire format. But when this problem occurs, there is a lag in the effects on the diagonals. At the end of one diagonal of the visual, there is one effect, and at the other end, there is another. Phasing In most cases, the phasing problem comes from imprecise cutting of the material, as explained below. Nevertheless, poor printing and rectification conditions may also be behind it. In theory, for a given angle of observation, one and the same visual must appear, for the entire batch. As a general rule, the angle of vision is around 45°, and this angle must be in agreement with the sequence provided by the master. If the images have a tendency to double perpendicularly (for 3D) or if the images provided for observation to the left appear to the right (top/bottom), then there is a phasing problem. Cutting defects Defects, in the way the lenticular lens has been cut, can lead to phase errors between the lens and the image. Two examples, taken from the same production batch: First image     Second image The first image shows a cut which removed about 150 µm of the first lens, and which shows irregular cutting of the lenticular lenses. The second image shows a cut which removed about 30 µm of the first lens. Defects in cutting such as these lead to a serious phase problem. In the printing press the image being printed is aligned relative to the edges of the sheet of material. If the sheet is not always cut in the same place relative to the first lenticule, a phase error is introduced between the lenses and the image slices. " (wikipedia.org) "A 3D display is a display device capable of conveying depth to the viewer. Many 3D displays are stereoscopic displays, which produce a basic 3D effect by means of stereopsis, but can cause eye strain and visual fatigue. Newer 3D displays such as holographic and light field displays produce a more realistic 3D effect by combining stereopsis and accurate focal length for the displayed content. Newer 3D displays in this manner cause less visual fatigue than classical stereoscopic displays. As of 2021, the most common type of 3D display is a stereoscopic display, which is the type of display used in almost all virtual reality equipment. 3D displays can be near-eye displays like in VR headsets, or they can be in a device further away from the eyes like a 3D-enabled mobile device or 3D movie theater. The term “3D display” can also be used to refer to a volumetric display which may generate content that can be viewed from all angles. History The first 3D display was created by Sir Charles Wheatstone in 1832.[1] It was a stereoscopic display that had rudimentary ability for representing depth. Stereoscopic displays Main article: Stereoscopy Stereoscopic displays are commonly referred to as “stereo displays,” “stereo 3D displays,” “stereoscopic 3D displays,” or sometimes erroneously as just “3D displays.” The basic technique of stereo displays is to present offset images that are displayed separately to the left and right eye. Both of these 2D offset images are then combined in the brain to give the perception of 3D depth. Although the term "3D" is ubiquitously used, it is important to note that the presentation of dual 2D images is distinctly different from displaying a light field, and is also different from displaying an image in three-dimensional space. The most notable difference to real 3D displays is that the observer's head and eyes movements will not increase information about the 3D objects being displayed. For example, holographic displays do not have such limitations. It is an overstatement of capability to refer to dual 2D images as being "3D". The accurate term "stereoscopic" is more cumbersome than the common misnomer "3D", which has been entrenched after many decades of unquestioned misuse. Although most stereoscopic displays do not qualify as real 3D displays, all real 3D displays are often referred to as also stereoscopic displays because they meet the lower criteria of being stereoscopic as well. Based on the principles of stereopsis, described by Sir Charles Wheatstone in the 1830s, stereoscopic technology provides a different image to the viewer's left and right eyes. The following are some of the technical details and methodologies employed in some of the more notable stereoscopic systems that have been developed. Side-by-side images "The early bird catches the worm" Stereograph published in 1900 by North-Western View Co. of Baraboo, Wisconsin, digitally restored. Traditional stereoscopic photography consists of creating a 3D illusion starting from a pair of 2D images, a stereogram. The easiest way to enhance depth perception in the brain is to provide the eyes of the viewer with two different images, representing two perspectives of the same object, with a minor deviation exactly equal to the perspectives that both eyes naturally receive in binocular vision. If eyestrain and distortion are to be avoided, each of the two 2D images preferably should be presented to each eye of the viewer so that any object at infinite distance seen by the viewer should be perceived by that eye while it is oriented straight ahead, the viewer's eyes being neither crossed nor diverging. When the picture contains no object at infinite distance, such as a horizon or a cloud, the pictures should be spaced correspondingly closer together. The side-by-side method is extremely simple to create, but it can be difficult or uncomfortable to view without optical aids. Stereoscope and stereographic cards Main article: Stereoscope A stereoscope is a device for viewing stereographic cards, which are cards that contain two separate images that are printed side by side to create the illusion of a three-dimensional image. Transparency viewers Main article: Slide viewer § Stereo slide viewer A View-Master Model E of the 1950s Pairs of stereo views printed on a transparent base are viewed by transmitted light. One advantage of transparency viewing is the opportunity for a wider, more realistic dynamic range than is practical with prints on an opaque base; another is that a wider field of view may be presented since the images, being illuminated from the rear, may be placed much closer to the lenses. The practice of viewing film-based stereoscopic transparencies dates to at least as early as 1931, when Tru-Vue began to market sets of stereo views on strips of 35 mm film that were fed through a hand-held Bakelite viewer. In 1939, a modified and miniaturized variation of this technology, employing cardboard disks containing seven pairs of small Kodachrome color film transparencies, was introduced as the View-Master. Head-mounted displays Main articles: Head-mounted display and Virtual retinal display The user typically wears a helmet or glasses with two small LCD or OLED displays with magnifying lenses, one for each eye. The technology can be used to show stereo films, images or games. Head-mounted displays may also be coupled with head-tracking devices, allowing the user to "look around" the virtual world by moving their head, eliminating the need for a separate controller. Owing to rapid advancements in computer graphics and the continuing miniaturization of video and other equipment these devices are beginning to become available at more reasonable cost. Head-mounted or wearable glasses may be used to view a see-through image imposed upon the real world view, creating what is called augmented reality. This is done by reflecting the video images through partially reflective mirrors. The real world can be seen through the partial mirror. A recent development in holographic-waveguide or "waveguide-based optics" allows a stereoscopic images to be superimposed on real world without the uses of bulky reflective mirror.[2][3] Head-mounted projection displays Head-mounted projection displays (HMPD) is similar to head-mounted displays but with images projected to and displayed on a retroreflective screen, The advantage of this technology over head-mounted display is that the focusing and vergence issues didn't require fixing with corrective eye lenses. For image generation, Pico-projectors are used instead of LCD or OLED screens.[4][5] Anaglyph Main article: Anaglyph 3D The archetypal 3D glasses, with modern red and cyan color filters, similar to the red/green and red/blue lenses used to view early anaglyph films. In an anaglyph, the two images are superimposed in an additive light setting through two filters, one red and one cyan. In a subtractive light setting, the two images are printed in the same complementary colors on white paper. Glasses with colored filters in each eye separate the appropriate image by canceling the filter color out and rendering the complementary color black. A compensating technique, commonly known as Anachrome, uses a slightly more transparent cyan filter in the patented glasses associated with the technique. Process reconfigures the typical anaglyph image to have less parallax. An alternative to the usual red and cyan filter system of anaglyph is ColorCode 3-D, a patented anaglyph system which was invented in order to present an anaglyph image in conjunction with the NTSC television standard, in which the red channel is often compromised. ColorCode uses the complementary colors of yellow and dark blue on-screen, and the colors of the glasses' lenses are amber and dark blue. Polarization systems Resembling sunglasses, RealD circular polarized glasses are now the standard for theatrical releases and theme park attractions. Main article: Polarized 3D system To present a stereoscopic picture, two images are projected superimposed onto the same screen through different polarizing filters. The viewer wears eyeglasses which also contain a pair of polarizing filters oriented differently (clockwise/counterclockwise with circular polarization or at 90 degree angles, usually 45 and 135 degrees,[6] with linear polarization). As each filter passes only that light which is similarly polarized and blocks the light polarized differently, each eye sees a different image. This is used to produce a three-dimensional effect by projecting the same scene into both eyes, but depicted from slightly different perspectives. Additionally, since both lenses have the same color, people with one dominant eye, where one eye is used more, are able to see the colors properly, previously negated by the separation of the two colors. Circular polarization has an advantage over linear polarization, in that the viewer does not need to have their head upright and aligned with the screen for the polarization to work properly. With linear polarization, turning the glasses sideways causes the filters to go out of alignment with the screen filters causing the image to fade and for each eye to see the opposite frame more easily. For circular polarization, the polarizing effect works regardless of how the viewer's head is aligned with the screen such as tilted sideways, or even upside down. The left eye will still only see the image intended for it, and vice versa, without fading or crosstalk. Polarized light reflected from an ordinary motion picture screen typically loses most of its polarization. So an expensive silver screen or aluminized screen with negligible polarization loss has to be used. All types of polarization will result in a darkening of the displayed image and poorer contrast compared to non-3D images. Light from lamps is normally emitted as a random collection of polarizations, while a polarization filter only passes a fraction of the light. As a result, the screen image is darker. This darkening can be compensated by increasing the brightness of the projector light source. If the initial polarization filter is inserted between the lamp and the image generation element, the light intensity striking the image element is not any higher than normal without the polarizing filter, and overall image contrast transmitted to the screen is not affected. Eclipse method A pair of LCD shutter glasses used to view XpanD 3D films. The thick frames conceal the electronics and batteries. Main article: Active shutter 3D system With the eclipse method, a shutter blocks light from each appropriate eye when the converse eye's image is projected on the screen. The display alternates between left and right images, and opens and closes the shutters in the glasses or viewer in synchronization with the images on the screen. This was the basis of the Teleview system which was used briefly in 1922.[7][8] A variation on the eclipse method is used in LCD shutter glasses. Glasses containing liquid crystal that will let light through in synchronization with the images on the cinema, television or computer screen, using the concept of alternate-frame sequencing. This is the method used by nVidia, XpanD 3D, and earlier IMAX systems. A drawback of this method is the need for each person viewing to wear expensive, electronic glasses that must be synchronized with the display system using a wireless signal or attached wire. The shutter-glasses are heavier than most polarized glasses, though lighter models are no heavier than some sunglasses or deluxe polarized glasses.[9] However these systems do not require a silver screen for projected images. Liquid crystal light valves work by rotating light between two polarizing filters. Due to these internal polarizers, LCD shutter-glasses darken the display image of any LCD, plasma, or projector image source, which has the result that images appear dimmer and contrast is lower than for normal non-3D viewing. This is not necessarily a usage problem; for some types of displays which are already very bright with poor grayish black levels, LCD shutter glasses may actually improve the image quality. Interference filter technology Main article: Anaglyph 3D § Interference filter systems Dolby 3D uses specific wavelengths of red, green, and blue for the right eye, and different wavelengths of red, green, and blue for the left eye. Eyeglasses which filter out the very specific wavelengths allow the wearer to see a 3D image. This technology eliminates the expensive silver screens required for polarized systems such as RealD, which is the most common 3D display system in theaters. It does, however, require much more expensive glasses than the polarized systems. It is also known as spectral comb filtering or wavelength multiplex visualization The recently introduced Omega 3D/Panavision 3D system also uses this technology, though with a wider spectrum and more "teeth" to the "comb" (5 for each eye in the Omega/Panavision system). The use of more spectral bands per eye eliminates the need to color process the image, required by the Dolby system. Evenly dividing the visible spectrum between the eyes gives the viewer a more relaxed "feel" as the light energy and color balance is nearly 50-50. Like the Dolby system, the Omega system can be used with white or silver screens. But it can be used with either film or digital projectors, unlike the Dolby filters that are only used on a digital system with a color correcting processor provided by Dolby. The Omega/Panavision system also claims that their glasses are cheaper to manufacture than those used by Dolby.[10] In June 2012, the Omega 3D/Panavision 3D system was discontinued by DPVO Theatrical, who marketed it on behalf of Panavision, citing "challenging global economic and 3D market conditions".[citation needed] Although DPVO dissolved its business operations, Omega Optical continues promoting and selling 3D systems to non-theatrical markets. Omega Optical’s 3D system contains projection filters and 3D glasses. In addition to the passive stereoscopic 3D system, Omega Optical has produced enhanced anaglyph 3D glasses. The Omega’s red/cyan anaglyph glasses use complex metal oxide thin film coatings and high quality annealed glass optics. Autostereoscopy Main article: Autostereoscopy The Nintendo 3DS uses parallax barrier autostereoscopy to display a 3D image. In this method, glasses are not necessary to see the stereoscopic image. Lenticular lens and parallax barrier technologies involve imposing two (or more) images on the same sheet, in narrow, alternating strips, and using a screen that either blocks one of the two images' strips (in the case of parallax barriers) or uses equally narrow lenses to bend the strips of image and make it appear to fill the entire image (in the case of lenticular prints). To produce the stereoscopic effect, the person must be positioned so that one eye sees one of the two images and the other sees the other. The optical principles of multiview auto-stereoscopy have been known for over a century.[11] Both images are projected onto a high-gain, corrugated screen which reflects light at acute angles. In order to see the stereoscopic image, the viewer must sit within a very narrow angle that is nearly perpendicular to the screen, limiting the size of the audience. Lenticular was used for theatrical presentation of numerous shorts in Russia from 1940 to 1948[12] and in 1946 for the feature-length film Robinzon Kruzo[13] Though its use in theatrical presentations has been rather limited, lenticular has been widely used for a variety of novelty items and has even been used in amateur 3D photography.[14][15] Recent use includes the Fujifilm FinePix Real 3D with an autostereoscopic display that was released in 2009. Other examples for this technology include autostereoscopic LCD displays on monitors, notebooks, TVs, mobile phones and gaming devices, such as the Nintendo 3DS. Other Main article: Stereoscopy The Pulfrich effect is a psychophysical percept wherein lateral motion of an object in the field of view is interpreted by the visual cortex as having a depth component, due to a relative difference in signal timings between the two eyes. Prismatic glasses make cross-viewing easier as well as over/under-viewing possible, examples include the KMQ viewer. Volumetric display Main article: Volumetric display Volumetric 3D display Volumetric displays use some physical mechanism to display points of light within a volume. Such displays use voxels instead of pixels. Volumetric displays include multiplanar displays, which have multiple display planes stacked up, and rotating panel displays, where a rotating panel sweeps out a volume. Other technologies have been developed to project light dots in the air above a device. An infrared laser is focused on the destination in space, generating a small bubble of plasma which emits visible light. Light field / holographic display A light field display tries to recreate a "light field" on the surface of the display. In contrast to a 2D display which shows a distinct color on each pixel, a light field display shows a distinct color on each pixel for each direction that the light ray emits to. This way, eyes from different positions will see different pictures on the display, creating parallax and thus creating a sense of 3D. A light field display is like a glass window, people see 3D objects behind the glass, despite that all light rays they see come from (through) the glass. The light field in front of the display can be created in two ways: 1) by emitting different light rays in different directions at each point on the display; 2) by recreating a wavefront in front of the display. Displays using the first method are called ray-based or light field displays. Displays using the second method are called wavefront-based or holographic displays. Wavefront-based displays work in the same way as holograms. Compared to ray-based displays, a wavefront-based display not only reconstructs the light field, but also reconstructs the curvature of the plane waves, and the phase differences of the waves in different directions.[16] Integral photography is one of the ray-based methods with full-parallax information. However, there are also ray-based techniques developed with horizontal-parallax-only.[16] Holographic displays Main articles: Holographic display and Computer-generated holography Holographic display is a display technology that has the ability to provide all four eye mechanisms: binocular disparity, motion parallax, accommodation and convergence. The 3D objects can be viewed without wearing any special glasses and no visual fatigue will be caused to human eyes. In 2013, a Silicon valley Company LEIA Inc started manufacturing holographic displays well suited for mobile devices (watches, smartphones or tablets) using a multi-directional backlight and allowing a wide full-parallax angle view to see 3D content without the need of glasses.[17] Their first product was part of a mobile phone (Red Hydrogen One) and later on in their own Android tablet.[citation needed] Integral imaging Main article: Integral imaging Integral imaging is an autostereoscopic or multiscopic 3D display, meaning that it displays a 3D image without the use of special glasses on the part of the viewer. It achieves this by placing an array of microlenses (similar to a lenticular lens) in front of the image, where each lens looks different depending on viewing angle. Thus rather than displaying a 2D image that looks the same from every direction, it reproduces a 3D light field, creating stereo images that exhibit parallax when the viewer moves. Compressive light field displays A new display technology called "compressive light field" is being developed. These prototype displays use layered LCD panels and compression algorithms at the time of display. Designs include dual[18] and multilayer[19][20][21] devices that are driven by algorithms such as computed tomography and Non-negative matrix factorization and non-negative tensor factorization." (wikipedia.org) "In geometry, a three-dimensional space (3D space, 3-space or, rarely, tri-dimensional space) is a mathematical space in which three values (coordinates) are required to determine the position of a point. Most commonly, it is the three-dimensional Euclidean space, the Euclidean n-space of dimension n=3 that models physical space. More general three-dimensional spaces are called 3-manifolds. Technically, a tuple of n numbers can be understood as the Cartesian coordinates of a location in a n-dimensional Euclidean space. The set of these n-tuples is commonly denoted R n , {\displaystyle \mathbb {R} ^{n},} {\displaystyle \mathbb {R} ^{n},} and can be identified to the pair formed by a n-dimensional Euclidean space and a Cartesian coordinate system. When n = 3, this space is called the three-dimensional Euclidean space (or simply "Euclidean space" when the context is clear).[1] It serves as a model of the physical universe (when relativity theory is not considered), in which all known matter exists. While this space remains the most compelling and useful way to model the world as it is experienced,[2] it is only one example of a large variety of spaces in three dimensions called 3-manifolds. In this classical example, when the three values refer to measurements in different directions (coordinates), any three directions can be chosen, provided that vectors in these directions do not all lie in the same 2-space (plane). Furthermore, in this case, these three values can be labeled by any combination of three chosen from the terms width/breadth, height/depth, and length. History Books XI to XIII of Euclid's Elements dealt with three-dimensional geometry. Book XI develops notions of orthogonality and parallelism of lines and planes, and defines solids including parallelpipeds, pyramids, prisms, spheres, octahedra, icosahedra and dodecahedra. Book XII develops notions of similarity of solids. Book XIII describes the construction of the five regular Platonic solids in a sphere. In the 17th century, three-dimensional space was described with Cartesian coordinates, with the advent of analytic geometry developed by René Descartes in his work La Géométrie and Pierre de Fermat in the manuscript Ad locos planos et solidos isagoge (Introduction to Plane and Solid Loci), which was unpublished during Fermat's lifetime. However, only Fermat's work dealt with three-dimensional space. In the 19th century, developments of the geometry of three-dimensional space came with William Rowan Hamilton's development of the quaternions. In fact, it was Hamilton who coined the terms scalar and vector, and they were first defined within his geometric framework for quaternions. Three dimensional space could then be described by quaternions q = a + u i + v j + w k {\displaystyle q=a+ui+vj+wk} {\displaystyle q=a+ui+vj+wk} which had vanishing scalar component, that is, a = 0 {\displaystyle a=0} a=0. While not explicitly studied by Hamilton, this indirectly introduced notions of basis, here given by the quaternion elements i , j , k {\displaystyle i,j,k} i,j,k, as well as the dot product and cross product, which correspond to (the negative of) the scalar part and the vector part of the product of two vector quaternions. It was not until Josiah Willard Gibbs that these two products were identified in their own right, and the modern notation for the dot and cross product were introduced in his classroom teaching notes, found also in the 1901 textbook Vector Analysis written by Edwin Bidwell Wilson based on Gibbs' lectures. Also during the 19th century came developments in the abstract formalism of vector spaces, with the work of Hermann Grassmann and Giuseppe Peano, the latter of whom first gave the modern definition of vector spaces as an algebraic structure." (wikipedia.org) "The National Aeronautics and Space Administration (NASA /ˈnæsə/) is an independent agency of the U.S. federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding the National Advisory Committee for Aeronautics (NACA), to give the U.S. space development effort a distinctly civilian orientation, emphasizing peaceful applications in space science.[5][6][7] NASA has since led most American space exploration, including Project Mercury, Project Gemini, the 1968–1972 Apollo Moon landing missions, the Skylab space station, and the Space Shuttle. NASA supports the International Space Station and oversees the development of the Orion spacecraft and the Space Launch System for the crewed lunar Artemis program, Commercial Crew spacecraft, and the planned Lunar Gateway space station. The agency is also responsible for the Launch Services Program, which provides oversight of launch operations and countdown management for uncrewed NASA launches. NASA's science is focused on better understanding Earth through the Earth Observing System;[8] advancing heliophysics through the efforts of the Science Mission Directorate's Heliophysics Research Program;[9] exploring bodies throughout the Solar System with advanced robotic spacecraft such as New Horizons and planetary rovers such as Perseverance;[10] and researching astrophysics topics, such as the Big Bang, through the James Webb Space Telescope, and the Great Observatories and associated programs.[11] Management Leadership Administrator Bill Nelson (2021–present) The agency's administration is located at NASA Headquarters in Washington, DC, and provides overall guidance and direction.[12] Except under exceptional circumstances, NASA civil service employees are required to be US citizens.[13] NASA's administrator is nominated by the President of the United States subject to the approval of the US Senate,[14] and serves at the President's pleasure as a senior space science advisor. The current administrator is Bill Nelson, appointed by President Joe Biden, since May 3, 2021.[15] Strategic plan NASA operates with four FY2022 strategic goals.[16]     Expand human knowledge through new scientific discoveries     Extend human presence to the Moon and on towards Mars for sustainable long-term exploration, development, and utilization     Catalyze economic growth and drive innovation to address national challenges     Enhance capabilities and operations to catalyze current and future mission success Budget Further information: Budget of NASA NASA budget requests are developed by NASA and approved by the administration prior to submission to the U.S. Congress. Authorized budgets are those that have been included in enacted appropriations bills that are approved by both houses of Congress and enacted into law by the U.S. president.[17] Center-wide activities such as the Chief Engineer and Safety and Mission Assurance organizations are aligned to the headquarters function. The MSD budget estimate includes funds for these HQ functions. The administration operates 10 major field centers with several managing additional subordinate facilities across the country. Each is led by a Center Director (data below valid as of September 1, 2022). Field Center     Primary Location     Center Director Ames Research Center     Mountain View, California     Dr. Eugene L. Tu[33] Armstrong Flight Research Center     Palmdale, California     Brad Flick (acting)[34] Glenn Research Center     Cleveland, Ohio     Dr. James A. Kenyon (acting)[35] Goddard Space Flight Center     Greenbelt, Maryland     Dr. Makenzie Lystrup[36] Jet Propulsion Laboratory     La Canada-Flintridge, California     Laurie Leshin[37] Johnson Space Center     Houston, Texas     Vanessa E. Wyche[38] Kennedy Space Center     Merritt Island, Florida     Janet Petro[39] Langley Research Center     Hampton, Virginia     Clayton Turner[40] Marshall Space Flight Center     Huntsville, Alabama     Jody Singer[41] Stennis Space Center     Hancock County, Mississippi     Richard J. Gilbrech[42] History Establishment of NASA Further information: Creation of NASA, NASA's Space Place, and Science Mission Directorate Short 2018 documentary about NASA produced for its 60th anniversary Beginning in 1946, the National Advisory Committee for Aeronautics (NACA) began experimenting with rocket planes such as the supersonic Bell X-1.[43] In the early 1950s, there was challenge to launch an artificial satellite for the International Geophysical Year (1957–1958). An effort for this was the American Project Vanguard. After the Soviet space program's launch of the world's first artificial satellite (Sputnik 1) on October 4, 1957, the attention of the United States turned toward its own fledgling space efforts. The US Congress, alarmed by the perceived threat to national security and technological leadership (known as the "Sputnik crisis"), urged immediate and swift action; President Dwight D. Eisenhower counseled more deliberate measures. The result was a consensus that the White House forged among key interest groups, including scientists committed to basic research; the Pentagon which had to match the Soviet military achievement; corporate America looking for new business; and a strong new trend in public opinion looking up to space exploration.[44] On January 12, 1958, NACA organized a "Special Committee on Space Technology", headed by Guyford Stever.[7] On January 14, 1958, NACA Director Hugh Dryden published "A National Research Program for Space Technology", stating,[45]     It is of great urgency and importance to our country both from consideration of our prestige as a nation as well as military necessity that this challenge [Sputnik] be met by an energetic program of research and development for the conquest of space ... It is accordingly proposed that the scientific research be the responsibility of a national civilian agency ... NACA is capable, by rapid extension and expansion of its effort, of providing leadership in space technology.[45] While this new federal agency would conduct all non-military space activity, the Advanced Research Projects Agency (ARPA) was created in February 1958 to develop space technology for military application.[46] On July 29, 1958, Eisenhower signed the National Aeronautics and Space Act, establishing NASA.[47] When it began operations on October 1, 1958, NASA absorbed the 43-year-old NACA intact; its 8,000 employees, an annual budget of US$100 million, three major research laboratories (Langley Aeronautical Laboratory, Ames Aeronautical Laboratory, and Lewis Flight Propulsion Laboratory) and two small test facilities.[48] Elements of the Army Ballistic Missile Agency and the United States Naval Research Laboratory were incorporated into NASA. A significant contributor to NASA's entry into the Space Race with the Soviet Union was the technology from the German rocket program led by Wernher von Braun, who was now working for the Army Ballistic Missile Agency (ABMA), which in turn incorporated the technology of American scientist Robert Goddard's earlier works.[49] Earlier research efforts within the US Air Force[48] and many of ARPA's early space programs were also transferred to NASA.[50] In December 1958, NASA gained control of the Jet Propulsion Laboratory, a contractor facility operated by the California Institute of Technology.[48] Past administrators Further information: Administrator of NASA NASA's first administrator was Dr. T. Keith Glennan who was appointed by President Dwight D. Eisenhower. During his term (1958–1961) he brought together the disparate projects in American space development research.[51] James Webb led the agency during the development of the Apollo program in the 1960s.[52] James C. Fletcher has held the position twice; first during the Nixon administration in the 1970s and then at the request of Ronald Reagan following the Challenger disaster.[53] Daniel Goldin held the post for nearly 10 years and is the longest serving administrator to date. He is best known for pioneering the "faster, better, cheaper" approach to space programs.[54] Bill Nelson is currently serving as the 14th administrator of NASA. Insignia Further information: NASA insignia The NASA seal was approved by Eisenhower in 1959, and slightly modified by President John F. Kennedy in 1961.[55][56] NASA's first logo was designed by the head of Lewis' Research Reports Division, James Modarelli, as a simplification of the 1959 seal.[57] In 1975, the original logo was first dubbed "the meatball" to distinguish it from the newly designed "worm" logo which replaced it. The "meatball" returned to official use in 1992.[57] The "worm" was brought out of retirement by administrator Jim Bridenstine in 2020.[58] Facilities Further information: NASA facilities NASA Headquarters in Washington, DC provides overall guidance and political leadership to the agency's ten field centers, through which all other facilities are administered.[59] Aerial views of the NASA Ames (left) and NASA Armstrong (right) centers Ames Research Center (ARC) at Moffett Field is located in the Silicon Valley of central California and delivers wind-tunnel research on the aerodynamics of propeller-driven aircraft along with research and technology in aeronautics, spaceflight, and information technology.[60] It provides leadership in astrobiology, small satellites, robotic lunar exploration, intelligent/adaptive systems and thermal protection. Armstrong Flight Research Center (AFRC) is located inside Edwards Air Force Base and is the home of the Shuttle Carrier Aircraft (SCA), a modified Boeing 747 designed to carry a Space Shuttle orbiter back to Kennedy Space Center after a landing at Edwards AFB. The center focuses on flight testing of advanced aerospace systems. Glenn Research Center is based in Cleveland, Ohio and focuses on air-breathing and in-space propulsion and cryogenics, communications, power energy storage and conversion, microgravity sciences, and advanced materials.[61] View of GSFC campus (left) and Kraft Mission Control Center at JSC (right) Goddard Space Flight Center (GSFC), located in Greenbelt, Maryland develops and operates uncrewed scientific spacecraft.[62] GSFC also operates two spaceflight tracking and data acquisition networks (the Space Network and the Near Earth Network), develops and maintains advanced space and Earth science data information systems, and develops satellite systems for the National Oceanic and Atmospheric Administration (NOAA).[62] Johnson Space Center (JSC) is the NASA center for human spaceflight training, research and flight control.[63] It is home to the United States Astronaut Corps and is responsible for training astronauts from the US and its international partners, and includes the Christopher C. Kraft Jr. Mission Control Center.[64] JSC also operates the White Sands Test Facility in Las Cruces, New Mexico to support rocket testing. View of JPL (left) and the Langley Research Center (right) Jet Propulsion Laboratory (JPL), located in the San Gabriel Valley area of Los Angeles County, C and builds and operates robotic planetary spacecraft, though it also conducts Earth-orbit and astronomy missions.[65] It is also responsible for operating NASA's Deep Space Network (DSN). Langley Research Center (LaRC), located in Hampton, Virginia devotes two-thirds of its programs to aeronautics, and the rest to space. LaRC researchers use more than 40 wind tunnels to study improved aircraft and spacecraft safety, performance, and efficiency. The center was also home to early human spaceflight efforts including the team chronicled in the Hidden Figures story.[66] Aerial view of Kennedy Space Center showing VAB and Launch Complex 39 View of the SLS exiting the VAB at KSC (left) and of the MSFC test stands (right) Kennedy Space Center (KSC), located west of Cape Canaveral Space Force Station in Florida, has been the launch site for every United States human space flight since 1968. KSC also manages and operates uncrewed rocket launch facilities for America's civil space program from three pads at Cape Canaveral.[67] Marshall Space Flight Center (MSFC), located on the Redstone Arsenal near Huntsville, Alabama, is one of NASA's largest centers and is leading the development of the Space Launch System in support of the Artemis program. Marshall is NASA's lead center for International Space Station (ISS) design and assembly; payloads and related crew training; and was the lead for Space Shuttle propulsion and its external tank.[68] Stennis Space Center, originally the "Mississippi Test Facility", is located in Hancock County, Mississippi, on the banks of the Pearl River at the Mississippi–Louisiana border.[69] Commissioned in October 1961, it is currently used for rocket testing by over 30 local, state, national, international, private, and public companies and agencies.[70][71] It also contains the NASA Shared Services Center.[72] Past human spaceflight programs X-15 (1954–1968) Further information: North American X-15 X-15 in powered flight NASA inherited NACA's X-15 experimental rocket-powered hypersonic research aircraft, developed in conjunction with the US Air Force and Navy. Three planes were built starting in 1955. The X-15 was drop-launched from the wing of one of two NASA Boeing B-52 Stratofortresses, NB52A tail number 52-003, and NB52B, tail number 52-008 (known as the Balls 8). Release took place at an altitude of about 45,000 feet (14 km) and a speed of about 500 miles per hour (805 km/h).[73] Twelve pilots were selected for the program from the Air Force, Navy, and NACA. A total of 199 flights were made between June 1959 and December 1968, resulting in the official world record for the highest speed ever reached by a crewed powered aircraft (current as of 2014), and a maximum speed of Mach 6.72, 4,519 miles per hour (7,273 km/h).[74] The altitude record for X-15 was 354,200 feet (107.96 km).[75] Eight of the pilots were awarded Air Force astronaut wings for flying above 260,000 feet (80 km), and two flights by Joseph A. Walker exceeded 100 kilometers (330,000 ft), qualifying as spaceflight according to the International Aeronautical Federation. The X-15 program employed mechanical techniques used in the later crewed spaceflight programs, including reaction control system jets for controlling the orientation of a spacecraft, space suits, and horizon definition for navigation.[75] The reentry and landing data collected were valuable to NASA for designing the Space Shuttle.[76] Mercury (1958–1963) Further information: Project Mercury Mercury-patch-g.png L. Gordon Cooper, photographed by a slow-scan television camera aboard Faith 7 (May 16, 1963) In 1958, NASA formed an engineering group, the Space Task Group, to manage their human spaceflight programs under the direction of Robert Gilruth. Their earliest programs were conducted under the pressure of the Cold War competition between the US and the Soviet Union. NASA inherited the US Air Force's Man in Space Soonest program, which considered many crewed spacecraft designs ranging from rocket planes like the X-15, to small ballistic space capsules.[77] By 1958, the space plane concepts were eliminated in favor of the ballistic capsule,[78] and NASA renamed it Project Mercury. The first seven astronauts were selected among candidates from the Navy, Air Force and Marine test pilot programs. On May 5, 1961, astronaut Alan Shepard became the first American in space aboard a capsule he named Freedom 7, launched on a Redstone booster on a 15-minute ballistic (suborbital) flight.[79] John Glenn became the first American to be launched into orbit, on an Atlas launch vehicle on February 20, 1962, aboard Friendship 7.[80] Glenn completed three orbits, after which three more orbital flights were made, culminating in L. Gordon Cooper's 22-orbit flight Faith 7, May 15–16, 1963.[81] Katherine Johnson, Mary Jackson, and Dorothy Vaughan were three of the human computers doing calculations on trajectories during the Space Race.[82][83][84] Johnson was well known for doing trajectory calculations for John Glenn's mission in 1962, where she was running the same equations by hand that were being run on the computer.[82] Mercury's competition from the Soviet Union (USSR) was the single-pilot Vostok spacecraft. They sent the first man in space, cosmonaut Yuri Gagarin, into a single Earth orbit aboard Vostok 1 in April 1961, one month before Shepard's flight.[85] In August 1962, they achieved an almost four-day record flight with Andriyan Nikolayev aboard Vostok 3, and also conducted a concurrent Vostok 4 mission carrying Pavel Popovich.[86] Gemini (1961–1966) Further information: Project Gemini GeminiPatch.png Richard Gordon performs a spacewalk to attach a tether to the Agena Target Vehicle on Gemini 11, 1966. Based on studies to grow the Mercury spacecraft capabilities to long-duration flights, developing space rendezvous techniques, and precision Earth landing, Project Gemini was started as a two-man program in 1961 to overcome the Soviets' lead and to support the planned Apollo crewed lunar landing program, adding extravehicular activity (EVA) and rendezvous and docking to its objectives. The first crewed Gemini flight, Gemini 3, was flown by Gus Grissom and John Young on March 23, 1965.[87] Nine missions followed in 1965 and 1966, demonstrating an endurance mission of nearly fourteen days, rendezvous, docking, and practical EVA, and gathering medical data on the effects of weightlessness on humans.[88][89] Under the direction of Soviet Premier Nikita Khrushchev, the USSR competed with Gemini by converting their Vostok spacecraft into a two- or three-man Voskhod. They succeeded in launching two crewed flights before Gemini's first flight, achieving a three-cosmonaut flight in 1964 and the first EVA in 1965.[90] After this, the program was canceled, and Gemini caught up while spacecraft designer Sergei Korolev developed the Soyuz spacecraft, their answer to Apollo. Apollo (1960–1972) Further information: Apollo program Apollo program.svg Buzz Aldrin on the Moon, 1969 (photograph by Neil Armstrong) The U.S. public's perception of the Soviet lead in the Space Race (by putting the first man into space) motivated President John F. Kennedy[91] to ask the Congress on May 25, 1961, to commit the federal government to a program to land a man on the Moon by the end of the 1960s, which effectively launched the Apollo program.[92] Apollo was one of the most expensive American scientific programs ever. It cost more than $20 billion in 1960s dollars[93] or an estimated $236 billion in present-day US dollars.[94] (In comparison, the Manhattan Project cost roughly $30.1 billion, accounting for inflation.)[94][95] The Apollo program used the newly developed Saturn I and Saturn V rockets, which were far larger than the repurposed ICBMs of the previous Mercury and Gemini programs.[96] They were used to launch the Apollo spacecraft, consisting of the Command and Service Module (CSM) and the Lunar Module (LM). The CSM ferried astronauts from Earth to Moon orbit and back, while the Lunar Module would land them on the Moon itself.[note 1] The planned first crew of 3 astronauts were killed due to a fire during a 1967 preflight test for the Apollo 204 mission (later renamed Apollo 1).[97] The second crewed mission, Apollo 8, brought astronauts for the first time in a flight around the Moon in December 1968.[98] Shortly before, the Soviets had sent an uncrewed spacecraft around the Moon.[99] The next two missions (Apollo 9 and Apollo 10) practiced rendezvous and docking maneuvers required to conduct the Moon landing.[100][101] The Apollo 11 mission, launched in July 1969, landed the first humans on the Moon. Astronauts Neil Armstrong and Buzz Aldrin walked on the lunar surface, conducting experiments and sample collection, while Michael Collins orbited above in the CSM.[102] Six subsequent Apollo missions (12 through 17) were launched; five of them were successful, while one (Apollo 13) was aborted after an in-flight emergency nearly killed the astronauts. Throughout these seven Apollo spaceflights, twelve men walked on the Moon. These missions returned a wealth of scientific data and 381.7 kilograms (842 lb) of lunar samples. Topics covered by experiments performed included soil mechanics, meteoroids, seismology, heat flow, lunar ranging, magnetic fields, and solar wind.[103] The Moon landing marked the end of the space race; and as a gesture, Armstrong mentioned mankind when he stepped down on the Moon.[104] On July 3, 1969, the Soviets suffered a major setback on their Moon program when the rocket known as the N-1 had exploded in a fireball at its launch site at Baikonur in Kazakhstan, destroying one of two launch pads. Each of the first four launches of N-1 resulted in failure before the end of the first stage flight effectively denying the Soviet Union the capacity to deliver the systems required for a crewed lunar landing.[105] Apollo set major milestones in human spaceflight. It stands alone in sending crewed missions beyond low Earth orbit, and landing humans on another celestial body.[106] Apollo 8 was the first crewed spacecraft to orbit another celestial body, while Apollo 17 marked the last moonwalk and the last crewed mission beyond low Earth orbit. The program spurred advances in many areas of technology peripheral to rocketry and crewed spaceflight, including avionics, telecommunications, and computers. Apollo sparked interest in many fields of engineering and left many physical facilities and machines developed for the program as landmarks. Many objects and artifacts from the program are on display at various locations throughout the world, notably at the Smithsonian's Air and Space Museums. Skylab (1965–1979) Further information: Skylab Skylab Program Patch.png Skylab in 1974, seen from the departing Skylab 4 CSM Skylab was the United States' first and only independently built space station.[107] Conceived in 1965 as a workshop to be constructed in space from a spent Saturn IB upper stage, the 169,950 lb (77,088 kg) station was constructed on Earth and launched on May 14, 1973, atop the first two stages of a Saturn V, into a 235-nautical-mile (435 km) orbit inclined at 50° to the equator. Damaged during launch by the loss of its thermal protection and one electricity-generating solar panel, it was repaired to functionality by its first crew. It was occupied for a total of 171 days by 3 successive crews in 1973 and 1974.[107] It included a laboratory for studying the effects of microgravity, and a solar observatory.[107] NASA planned to have the in-development Space Shuttle dock with it, and elevate Skylab to a higher safe altitude, but the Shuttle was not ready for flight before Skylab's re-entry and demise on July 11, 1979.[108] To reduce cost, NASA modified one of the Saturn V rockets originally earmarked for a canceled Apollo mission to launch Skylab, which itself was a modified Saturn V fuel tank. Apollo spacecraft, launched on smaller Saturn IB rockets, were used for transporting astronauts to and from the station. Three crews, consisting of three men each, stayed aboard the station for periods of 28, 59, and 84 days. Skylab's habitable volume was 11,290 cubic feet (320 m3), which was 30.7 times bigger than that of the Apollo Command Module.[108] Space Transportation System (1969–1972) Further information: Space Transportation System In February 1969, President Richard Nixon appointed a space task group headed by Vice President Spiro Agnew to recommend human spaceflight projects beyond Apollo. The group responded in September with the Integrated Program Plan (IPP), intended to support space stations in Earth and lunar orbit, a lunar surface base, and a human Mars landing. These would be supported by replacing NASA's existing expendable launch systems with a reusable infrastructure including Earth orbit shuttles, space tugs, and a nuclear-powered trans-lunar and interplanetary shuttle. Despite the enthusiastic support of Agnew and NASA Administrator Thomas O. Paine, Nixon realized public enthusiasm, which translated into Congressional support, for the space program was waning as Apollo neared its climax, and vetoed most of these plans, except for the Earth orbital shuttle, and a deferred Earth space station.[109] Apollo–Soyuz (1972–1975) Further information: Apollo–Soyuz ASTP patch.png Soviet and American crews with spacecraft model, 1975 On May 24, 1972, US President Richard M. Nixon and Soviet Premier Alexei Kosygin signed an agreement calling for a joint crewed space mission, and declaring intent for all future international crewed spacecraft to be capable of docking with each other.[110] This authorized the Apollo–Soyuz Test Project (ASTP), involving the rendezvous and docking in Earth orbit of a surplus Apollo command and service module with a Soyuz spacecraft. The mission took place in July 1975. This was the last US human spaceflight until the first orbital flight of the Space Shuttle in April 1981.[111] The mission included both joint and separate scientific experiments and provided useful engineering experience for future joint US–Russian space flights, such as the Shuttle–Mir program[112] and the International Space Station. Space Shuttle (1972–2011) Further information: Space Shuttle program Shuttle Patch.svg Launch of Space Shuttle Discovery at the start of STS-120 The Space Shuttle was the only vehicle in the Space Transportation System to be developed, and became the major focus of NASA in the late 1970s and the 1980s. Originally planned as a frequently launchable, fully reusable vehicle, the design was changed to use an expendable external propellant tank to reduce development cost, and four Space Shuttle orbiters were built by 1985. The first to launch, Columbia, did so on April 12, 1981, the 20th anniversary of the first human spaceflight.[113] The Shuttle flew 135 missions and carried 355 astronauts from 16 countries, many on multiple trips. Its major components were a spaceplane orbiter with an external fuel tank and two solid-fuel launch rockets at its side. The external tank, which was bigger than the spacecraft itself, was the only major component that was not reused. The shuttle could orbit in altitudes of 185–643 km (115–400 miles)[114] and carry a maximum payload (to low orbit) of 24,400 kg (54,000 lb).[115] Missions could last from 5 to 17 days and crews could be from 2 to 8 astronauts.[114] On 20 missions (1983–1998) the Space Shuttle carried Spacelab, designed in cooperation with the European Space Agency (ESA). Spacelab was not designed for independent orbital flight, but remained in the Shuttle's cargo bay as the astronauts entered and left it through an airlock.[116] On June 18, 1983, Sally Ride became the first American woman in space, on board the Space Shuttle Challenger STS-7 mission.[117] Another famous series of missions were the launch and later successful repair of the Hubble Space Telescope in 1990 and 1993, respectively.[118] In 1995, Russian-American interaction resumed with the Shuttle–Mir missions (1995–1998). Once more an American vehicle docked with a Russian craft, this time a full-fledged space station. This cooperation has continued with Russia and the United States as two of the biggest partners in the largest space station built: the International Space Station (ISS).[119] The strength of their cooperation on this project was even more evident when NASA began relying on Russian launch vehicles to service the ISS during the two-year grounding of the shuttle fleet following the 2003 Space Shuttle Columbia disaster. The Shuttle fleet lost two orbiters and 14 astronauts in two disasters: Challenger in 1986, and Columbia in 2003.[120] While the 1986 loss was mitigated by building the Space Shuttle Endeavour from replacement parts, NASA did not build another orbiter to replace the second loss.[120] NASA's Space Shuttle program had 135 missions when the program ended with the successful landing of the Space Shuttle Atlantis at the Kennedy Space Center on July 21, 2011. The program spanned 30 years with 355 separate astronauts sent into space, many on multiple missions.[121] Constellation (2005–2010) Further information: Constellation program Constellation logo white.svg Artist's rendering of Altair lander on the Moon While the Space Shuttle program was still suspended after the loss of Columbia, President George W. Bush announced the Vision for Space Exploration including the retirement of the Space Shuttle after completing the International Space Station. The plan was enacted into law by the NASA Authorization Act of 2005 and directs NASA to develop and launch the Crew Exploration Vehicle (later called Orion) by 2010, return Americans to the Moon by 2020, land on Mars as feasible, repair the Hubble Space Telescope, and continue scientific investigation through robotic solar system exploration, human presence on the ISS, Earth observation, and astrophysics research. The crewed exploration goals prompted NASA's Constellation program.[122] On December 4, 2006, NASA announced it was planning a permanent Moon base.[123] The goal was to start building the Moon base by 2020, and by 2024, have a fully functional base that would allow for crew rotations and in-situ resource utilization. However, in 2009, the Augustine Committee found the program to be on an "unsustainable trajectory."[124] In February 2010, President Barack Obama's administration proposed eliminating public funds for it.[125] Journey to Mars (2010–2017) An artist's conception, from NASA, of an astronaut planting a US flag on Mars. A human mission to Mars has been discussed as a possible NASA mission since the 1960s. Concepts for how the first human landing site on Mars might evolve over the course of multiple human expeditions President Obama's plan was to develop American private spaceflight capabilities to get astronauts to the International Space Station, replace Russian Soyuz capsules, and use Orion capsules for ISS emergency escape purposes. During a speech at the Kennedy Space Center on April 15, 2010, Obama proposed a new heavy-lift vehicle (HLV) to replace the formerly planned Ares V.[126] In his speech, Obama called for a crewed mission to an asteroid as soon as 2025, and a crewed mission to Mars orbit by the mid-2030s.[126] The NASA Authorization Act of 2010 was passed by Congress and signed into law on October 11, 2010.[127] The act officially canceled the Constellation program.[127] The NASA Authorization Act of 2010 required a newly designed HLV be chosen within 90 days of its passing; the launch vehicle was given the name Space Launch System. The new law also required the construction of a beyond low earth orbit spacecraft.[128] The Orion spacecraft, which was being developed as part of the Constellation program, was chosen to fulfill this role.[129] The Space Launch System is planned to launch both Orion and other necessary hardware for missions beyond low Earth orbit.[130] The SLS is to be upgraded over time with more powerful versions. The initial capability of SLS is required to be able to lift 70 t (150,000 lb) (later 95 t or 209,000 lb) into LEO. It is then planned to be upgraded to 105 t (231,000 lb) and then eventually to 130 t (290,000 lb).[129][131] The Orion capsule first flew on Exploration Flight Test 1 (EFT-1), an uncrewed test flight that was launched on December 5, 2014, atop a Delta IV Heavy rocket.[131] NASA undertook a feasibility study in 2012 and developed the Asteroid Redirect Mission as an uncrewed mission to move a boulder-sized near-Earth asteroid (or boulder-sized chunk of a larger asteroid) into lunar orbit. The mission would demonstrate ion thruster technology and develop techniques that could be used for planetary defense against an asteroid collision, as well as a cargo transport to Mars in support of a future human mission. The Moon-orbiting boulder might then later be visited by astronauts. The Asteroid Redirect Mission was cancelled in 2017 as part of the FY2018 NASA budget, the first one under President Donald Trump.[132] Past robotic exploration programs Further information: List of uncrewed NASA missions NASA has conducted many uncrewed and robotic spaceflight programs throughout its history. Uncrewed robotic programs launched the first American artificial satellites into Earth orbit for scientific and communications purposes and sent scientific probes to explore the planets of the Solar System, starting with Venus and Mars, and including "grand tours" of the outer planets. More than 1,000 uncrewed missions have been designed to explore the Earth and the Solar System.[133] Early efforts The first US uncrewed satellite was Explorer 1, which started as an ABMA/JPL project during the early part of the Space Race. It was launched in January 1958, two months after Sputnik. At the creation of NASA, the Explorer project was transferred to the agency and still continues. Its missions have been focusing on the Earth and the Sun, measuring magnetic fields and the solar wind, among other aspects.[134] The Ranger missions developed technology to build and deliver robotic probes into orbit and to the vicinity of the Moon. Ranger 7 successfully returned images of the Moon in July 1964, followed by two more successful missions.[135] NASA also played a role in the development and delivery of early communications satellite technology to orbit. Syncom 3 was the first geostationary satellite. It was an experimental geosynchronous communications satellite placed over the equator at 180 degrees longitude in the Pacific Ocean. The satellite provided live television coverage of the 1964 Olympic games in Tokyo, Japan and conducted various communications tests. Operations were turned over to the Department of Defense on January 1, 1965; Syncom 3 was to prove useful in the DoD's Vietnam communications.[136] Programs like Syncom, Telstar, and Applications Technology Satellites (ATS) demonstrated the utility of communications satellites and delivered early telephonic and video satellite transmission.[137] Planetary exploration William H. Pickering, (center) JPL Director, President John F. Kennedy, (right). NASA Administrator James E. Webb (background) discussing the Mariner program, with a model presented. Study of Mercury, Venus, or Mars has been the goal of more than ten uncrewed NASA programs. The first was Mariner in the 1960s and 1970s, which made multiple visits to Venus and Mars and one to Mercury. Probes launched under the Mariner program were also the first to make a planetary flyby (Mariner 2), to take the first pictures from another planet (Mariner 4), the first planetary orbiter (Mariner 9), and the first to make a gravity assist maneuver (Mariner 10). This is a technique where the satellite takes advantage of the gravity and velocity of planets to reach its destination.[138] Magellan orbited Venus for four years in the early 1990s capturing radar images of the planet's surface.[139] MESSENGER orbited Mercury between 2011 and 2015 after a 6.5-year journey involving a complicated series of flybys of Venus and Mercury to reduce velocity sufficiently enough to enter Mercury orbit. MESSENGER became the first spacecraft to orbit Mercury and used its science payload to study Mercury's surface composition, geological history, internal magnetic field, and verified its polar deposits were dominantly water-ice.[140] From 1966 to 1968, the Lunar Orbiter and Surveyor missions provided higher quality photographs and other measurements to pave the way for the crewed Apollo missions to the Moon.[141] Clementine spent a couple of months mapping the Moon in 1994 before moving on to other mission objectives.[142] Lunar Prospector spent 19 months from 1998 mapping the Moon's surface composition and looking for polar ice.[143] The first successful landing on Mars was made by Viking 1 in 1976. Viking 2 followed two months later. Twenty years later the Sojourner rover was landed on Mars by Mars Pathfinder.[144] After Mars, Jupiter was first visited by Pioneer 10 in 1973. More than 20 years later Galileo sent a probe into the planet's atmosphere and became the first spacecraft to orbit the planet.[145] Pioneer 11 became the first spacecraft to visit Saturn in 1979, with Voyager 2 making the first (and so far, only) visits to Uranus and Neptune in 1986 and 1989, respectively. The first spacecraft to leave the Solar System was Pioneer 10 in 1983. For a time, it was the most distant spacecraft, but it has since been surpassed by both Voyager 1 and Voyager 2.[146] Pioneers 10 and 11 and both Voyager probes carry messages from the Earth to extraterrestrial life.[147][148] Communication can be difficult with deep space travel. For instance, it took about three hours for a radio signal to reach the New Horizons spacecraft when it was more than halfway to Pluto.[149] Contact with Pioneer 10 was lost in 2003. Both Voyager probes continue to operate as they explore the outer boundary between the Solar System and interstellar space.[150] NASA continued to support in situ exploration beyond the asteroid belt, including Pioneer and Voyager traverses into the unexplored trans-Pluto region, and gas giant orbiters Galileo (1989–2003) and Cassini (1997–2017) exploring the Jovian and Saturnian systems respectively. Heliophysics The missions below represent the robotic spacecraft that have been delivered and operated by NASA to study the heliosphere. The Helios A and Helios B missions were launched in the 1970s to study the Sun and were the first spacecraft to orbit inside of Mercury's orbit.[151] The Fast Auroral Snapshot Explorer (FAST) mission was launched in August 1996 becoming the second SMEX mission placed in orbit. It studied the auroral zones near each pole during its transits in a highly elliptical orbit.[152] The International Earth-Sun Explorer-3 (ISEE-3) mission was launched in 1978 and is the first spacecraft designed to operate at the Earth-Sun L1 libration point. It studied solar-terrestrial relationships at the outermost boundaries of the Earth's magnetosphere and the structure of the solar wind. The spacecraft was subsequently maneuvered out of the halo orbit and conducted a flyby of the Giacobini-Zinner comet in 1985 as the rechristened International Cometary Explorer (ICE).[153] Ulysses was launched in 1990 and slingshotted around Jupiter to put it in an orbit to travel over the poles of the Sun. It was designed study the space environment above and below the poles and delivered scientific data for about 19 years.[154] Additional spacecraft launched for studies of the heliosphere include: Cluster II, IMAGE, POLAR, Reuven Ramaty High Energy Solar Spectroscopic Imager, and the Van Allen Probes. Earth Science The Earth Sciences Division of the NASA Science Mission Directorate leads efforts to study the planet Earth. Spacecraft have been used to study Earth since the mid-1960s. Efforts included the Television Infrared Observation Satellite (TIROS) and Nimbus satellite systems of which there were many carrying weather research and forecasting from space from 1960 into the 2020s. Artist rendering of ICESat in orbit, 2003 The Combined Release and Radiation Effects Satellite (CRRES) was launched in 1990 on a three-year mission to investigate fields, plasmas, and energetic particles inside the Earth's magnetosphere.[155] The Upper Atmosphere Research Satellite (UARS) was launched in 1991 by STS-48 to study the Earth's atmosphere especially the protective ozone layer.[156] TOPEX/Poseidon was launched in 1992 and was the first significant oceanographic research satellite.[157] The Ice, Cloud, and land Elevation Satellite (ICESat) was launched in 2003, operated for seven years, and measured ice sheet mass balance, cloud and aerosol heights, and well as topography and vegetation characteristics.[158] Over a dozen past robotic missions have focused on the study of the Earth and its environment. Some of these additional missions include Aquarius, Earth Observing-1 (EO-1), Jason-1, Ocean Surface Topography Mission/Jason-2, and Radarsat-1 missions. Active programs Human spaceflight International Space Station (1993–present) Further information: International Space Station ISS emblem.png The International Space Station as seen from Space Shuttle Endeavour during STS-134 The International Space Station (ISS) combines NASA's Space Station Freedom project with the Soviet/Russian Mir-2 station, the European Columbus station, and the Japanese Kibō laboratory module.[159] NASA originally planned in the 1980s to develop Freedom alone, but US budget constraints led to the merger of these projects into a single multi-national program in 1993, managed by NASA, the Russian Federal Space Agency (RKA), the Japan Aerospace Exploration Agency (JAXA), the European Space Agency (ESA), and the Canadian Space Agency (CSA).[160][161] The station consists of pressurized modules, external trusses, solar arrays and other components, which were manufactured in various factories around the world, and have been launched by Russian Proton and Soyuz rockets, and the US Space Shuttles.[159] The on-orbit assembly began in 1998, the completion of the US Orbital Segment occurred in 2009 and the completion of the Russian Orbital Segment occurred in 2010, though there are some debates of whether new modules should be added in the segment. The ownership and use of the space station is established in intergovernmental treaties and agreements[162] which divide the station into two areas and allow Russia to retain full ownership of the Russian Orbital Segment (with the exception of Zarya),[163][164] with the US Orbital Segment allocated between the other international partners.[162] Long-duration missions to the ISS are referred to as ISS Expeditions. Expedition crew members typically spend approximately six months on the ISS.[165] The initial expedition crew size was three, temporarily decreased to two following the Columbia disaster. Since May 2009, expedition crew size has been six crew members.[166] Crew size is expected to be increased to seven, the number the ISS was designed for, once the Commercial Crew Program becomes operational.[167] The ISS has been continuously occupied for the past 22 years and 173 days, having exceeded the previous record held by Mir; and has been visited by astronauts and cosmonauts from 15 different nations.[168][169] The station can be seen from the Earth with the naked eye and, as of 2023, is the largest artificial satellite in Earth orbit with a mass and volume greater than that of any previous space station.[170] The Russian Soyuz and American Dragon spacecraft are used to send astronauts to and from the ISS. Several uncrewed cargo spacecraft provide service to the ISS; they are the Russian Progress spacecraft which has done so since 2000, the European Automated Transfer Vehicle (ATV) since 2008, the Japanese H-II Transfer Vehicle (HTV) since 2009, the (uncrewed) Dragon since 2012, and the American Cygnus spacecraft since 2013.[171][172] The Space Shuttle, before its retirement, was also used for cargo transfer and would often switch out expedition crew members, although it did not have the capability to remain docked for the duration of their stay. Between the retirement of the Shuttle in 2011 and the commencement of crewed Dragon flights in 2020, American astronauts exclusively used the Soyuz for crew transport to and from the ISS[173] The highest number of people occupying the ISS has been thirteen; this occurred three times during the late Shuttle ISS assembly missions.[174] The ISS program is expected to continue to 2030,[175] after which the space station will be retired and destroyed in a controlled de-orbit.[176] Commercial Resupply Services (2008–present) Further information: Commercial Resupply Services Dragon Cygnus Commercial Resupply Services missions approaching International Space Station Commercial Resupply Services (CRS) are a contract solution to deliver cargo and supplies to the International Space Station (ISS) on a commmercial basis.[177] NASA signed its first CRS contracts in 2008 and awarded $1.6 billion to SpaceX for twelve cargo Dragon and $1.9 billion to Orbital Sciences[note 2] for eight Cygnus flights, covering deliveries to 2016. Both companies evolved or created their launch vehicle products to support the solution (SpaceX with The Falcon 9 and Orbital with the Antares). SpaceX flew its first operational resupply mission (SpaceX CRS-1) in 2012.[178] Orbital Sciences followed in 2014 (Cygnus CRS Orb-1).[179] In 2015, NASA extended CRS-1 to twenty flights for SpaceX and twelve flights for Orbital ATK.[note 2][180][181] A second phase of contracts (known as CRS-2) was solicited in 2014; contracts were awarded in January 2016 to Orbital ATK[note 2] Cygnus, Sierra Nevada Corporation Dream Chaser, and SpaceX Dragon 2, for cargo transport flights beginning in 2019 and expected to last through 2024. In March 2022, NASA awarded an additional six CRS-2 missions each to both SpaceX and Northrop Grumman (formerly Orbital).[182] Northrop Grumman successfully delivered Cygnus NG-17 to the ISS in February 2022.[183] In July 2022, SpaceX launched its 25th CRS flight (SpaceX CRS-25) and successfully delivered its cargo to the ISS.[184] In late 2022, Sierra Nevada continued to assemble their Dream Chaser CRS solution; current estimates put its first launch in early 2023.[185] Commercial Crew Program (2011–present) Further information: Commercial Crew Program NASA Commercial Crew Program logo (cropped).svg The Crew Dragon (left) and Starliner (right) approaching the ISS on their respective missions The Commercial Crew Program (CCP) provides commercially operated crew transportation service to and from the International Space Station (ISS) under contract to NASA, conducting crew rotations between the expeditions of the International Space Station program. American space manufacturer SpaceX began providing service in 2020, using the Crew Dragon spacecraft, and NASA plans to add Boeing when its Boeing Starliner spacecraft becomes operational some time after 2022[needs update].[186] NASA has contracted for six operational missions from Boeing and fourteen from SpaceX, ensuring sufficient support for ISS through 2030.[187] The spacecraft are owned and operated by the vendor, and crew transportation is provided to NASA as a commercial service. Each mission sends up to four astronauts to the ISS, with an option for a fifth passenger available. Operational flights occur approximately once every six months for missions that last for approximately six months. A spacecraft remains docked to the ISS during its mission, and missions usually overlap by at least a few days. Between the retirement of the Space Shuttle in 2011 and the first operational CCP mission in 2020, NASA relied on the Soyuz program to transport its astronauts to the ISS. A Crew Dragon spacecraft is launched to space atop a Falcon 9 Block 5 launch vehicle and the capsule returns to Earth via splashdown in the ocean near Florida. The program's first operational mission, SpaceX Crew-1, launched on 16 November 2020.[188] Boeing Starliner operational flights will now commence after its final test flight which was launched atop an Atlas V N22 launch vehicle. Instead of a splashdown, a Starliner capsule returns on land with airbags at one of four designated sites in the western United States.[189] Artemis (2017–present) Further information: Artemis program An arrowhead combined with a depiction of a trans-lunar injection trajectory forms an "A", with an "Artemis" wordmark printed underneath SLS with Orion rolling to Launch Complex 39B for tests, Mar 2022 Since 2017, NASA's crewed spaceflight program has been the Artemis program, which involves the help of US commercial spaceflight companies and international partners such as ESA, JAXA, and CSA.[190] The goal of this program is to land "the first woman and the next man" on the lunar south pole region by 2024. Artemis would be the first step towards the long-term goal of establishing a sustainable presence on the Moon, laying the foundation for companies to build a lunar economy, and eventually sending humans to Mars. The Orion Crew Exploration Vehicle was held over from the canceled Constellation program for Artemis. Artemis 1 was the uncrewed initial launch of Space Launch System (SLS) that would also send an Orion spacecraft on a Distant Retrograde Orbit.[191] NASA's next major space initiative is to be the construction of the Lunar Gateway, a small space station in lunar orbit.[192] This space station will be designed primarily for non-continuous human habitation. The first tentative steps of returning to crewed lunar missions will be Artemis 2, which is to include the Orion crew module, propelled by the SLS, and is to launch in 2024.[190] This mission is to be a 10-day mission planned to briefly place a crew of four into a Lunar flyby.[131] The construction of the Gateway would begin with the proposed Artemis 3, which is planned to deliver a crew of four to Lunar orbit along with the first modules of the Gateway. This mission would last for up to 30 days. NASA plans to build full scale deep space habitats such as the Lunar Gateway and the Nautilus-X as part of its Next Space Technologies for Exploration Partnerships (NextSTEP) program.[193] In 2017, NASA was directed by the congressional NASA Transition Authorization Act of 2017 to get humans to Mars-orbit (or to the Martian surface) by the 2030s.[194][195] In support of the Artemis missions, NASA has been funding private companies to land robotic probes on the lunar surface in a program known as the Commercial Lunar Payload Services. As of March 2022, NASA has awarded contracts for robotic lunar probes to companies such as Intuitive Machines, Firefly Space Systems, and Astrobotic.[196] On April 16, 2021, NASA announced they had selected the SpaceX Lunar Starship as its Human Landing System. The agency's Space Launch System rocket will launch four astronauts aboard the Orion spacecraft for their multi-day journey to lunar orbit where they will transfer to SpaceX's Starship for the final leg of their journey to the surface of the Moon.[197] In November 2021, it was announced that the goal of landing astronauts on the Moon by 2024 had slipped to no earlier than 2025 due to numerous factors. Artemis 1 launched on November 16, 2022 and returned to Earth safely on December 11, 2022. As of June 2022, NASA plans to launch Artemis 2 in May 2024 and Artemis 3 in December 2025.[198][199] Additional Artemis missions, Artemis 4 and Artemis 5, are planned to launch after 2025.[200] Commercial LEO Development (2021–present) The Commercial Low Earth Orbit Destinations program is an initiative by NASA to support work on commercial space stations that the agency hopes to have in place by the end of the current decade to replace the "International Space Station". The three selected companies are: Blue Origin (et al.) with their Orbital Reef station concept, Nanoracks (et al.) with their Starlab Space Station concept, and Northrop Grumman with a station concept based on the HALO-module for the Gateway station.[201] Robotic exploration Further information: List of NASA missions and List of uncrewed NASA missions Video of many of the uncrewed missions used to explore the outer reaches of space NASA has conducted many uncrewed and robotic spaceflight programs throughout its history. More than 1,000 uncrewed missions have been designed to explore the Earth and the Solar System.[133] Mission selection process NASA executes a mission development framework to plan, select, develop, and operate robotic missions. This framework defines cost, schedule and technical risk parameters to enable competitive selection of missions involving mission candidates that have been developed by principal investigators and their teams from across NASA, the broader U.S. Government research and development stakeholders, and industry. The mission development construct is defined by four umbrella programs. Explorer program Further information: Explorers Program The Explorer program derives its origin from the earliest days of the U.S. Space program. In current form, the program consists of three classes of systems - Small Explorers (SMEX), Medium Explorers (MIDEX), and University-Class Explorers (UNEX) missions. The NASA Explorer program office provides frequent flight opportunities for moderate cost innovative solutions from the heliophysics and astrophysics science areas. The Small Explorer missions are required to limit cost to NASA to below $150M (2022 dollars). Medium class explorer missions have typically involved NASA cost caps of $350M. The Explorer program office is based at NASA Goddard Space Flight Center.[202] Discovery program Further information: Discovery Program The NASA Discovery program develops and delivers robotic spacecraft solutions in the planetary science domain. Discovery enables scientists and engineers to assemble a team to deliver a solution against a defined set of objectives and competitively bid that solution against other candidate programs. Cost caps vary but recent mission selection processes were accomplished using a $500M cost cap to NASA. The Planetary Mission Program Office is based at the NASA Marshall Space Flight Center and manages both the Discovery and New Frontiers missions. The office is part of the Science Mission Directorate.[203] NASA Administrator Bill Nelson announced on June 2, 2021, that the DAVINCI+ and VERITAS missions were selected to launch to Venus in the late 2020s, having beat out competing proposals for missions to Jupiter's volcanic moon Io and Neptune's large moon Triton that were also selected as Discovery program finalists in early 2020. Each mission has an estimated cost of $500 million, with launches expected between 2028 and 2030. Launch contracts will be awarded later in each mission's development.[204] New Frontiers program Further information: New Frontiers program The New Frontiers program focuses on specific Solar System exploration goals identified as top priorities by the planetary science community. Primary objectives include Solar System exploration employing medium class spacecraft missions to conduct high-science-return investigations. New Frontiers builds on the development approach employed by the Discovery program but provides for higher cost caps and schedule durations than are available with Discovery. Cost caps vary by opportunity; recent missions have been awarded based on a defined cap of $1 Billion. The higher cost cap and projected longer mission durations result in a lower frequency of new opportunities for the program - typically one every several years. OSIRIS-REx and New Horizons are examples of New Frontiers missions.[205] NASA has determined that the next opportunity to propose for the fifth round of New Frontiers missions will occur no later than the fall of 2024. Missions in NASA's New Frontiers Program tackle specific Solar System exploration goals identified as top priorities by the planetary science community. Exploring the Solar System with medium-class spacecraft missions that conduct high-science-return investigations is NASA's strategy to further understand the Solar System.[206] Large strategic missions Further information: Large strategic science missions Large strategic missions (formerly called Flagship missions) are strategic missions that are typically developed and managed by large teams that may span several NASA centers. The individual missions become the program as opposed to being part of a larger effort (see Discovery, New Frontiers, etc.). The James Webb Space Telescope is a strategic mission that was developed over a period of more than 20 years. Strategic missions are developed on an ad-hoc basis as program objectives and priorities are established. Missions like Voyager, had they been developed today, would have been strategic missions. Three of the Great Observatories were strategic missions (the Chandra X-ray Observatory, Compton, and the Hubble Space Telescope). Europa Clipper is the next large strategic mission in development by NASA. Planetary science missions NASA continues to play a material in exploration of the Solar System as it has for decades. Ongoing missions have current science objectives with respect to more than five extraterrestrial bodies within the Solar System – Moon (Lunar Reconnaissance Orbiter), Mars (Perseverance rover), Jupiter (Juno), asteroid Bennu (OSIRIS-REx), and Kuiper Belt Objects (New Horizons). The Juno extended mission will make multiple flybys of the Jovian moon Io in 2023 and 2024 after flybys of Ganymede in 2021 and Europa in 2022. Voyager 1 and Voyager 2 continue to provide science data back to Earth while continuing on their outward journeys into interstellar space. On November 26, 2011, NASA's Mars Science Laboratory mission was successfully launched for Mars. The Curiosity rover successfully landed on Mars on August 6, 2012, and subsequently began its search for evidence of past or present life on Mars.[207][208][209] In September 2014, NASA's MAVEN spacecraft, which is part of the Mars Scout Program, successfully entered Mars orbit and, as of October 2022, continues its study of the atmosphere of Mars.[210][211] NASA's ongoing Mars investigations include in-depth surveys of Mars by the Perseverance rover and InSight). NASA's Europa Clipper, planned for launch in October 2024, will study the Galilean moon Europa through a series of flybys while in orbit around Jupiter. Dragonfly will send a mobile robotic rotorcraft to Saturn's biggest moon, Titan.[212] As of May 2021, Dragonfly is scheduled for launch in June 2027.[213][214] Astrophysics missions NASA astrophysics spacecraft fleet, credit NASA GSFC, 2022 The NASA Science Mission Directorate Astrophysics division manages the agency's astrophysics science portfolio. NASA has invested significant resources in the development, delivery, and operations of various forms of space telescopes. These telescopes have provided the means to study the cosmos over a large range of the electromagnetic spectrum.[215] The Great Observatories that were launched in the 1980s and 1990s have provided a wealth of observations for study by physicists across the planent. The first of them, the Hubble Space Telescope, was delivered to orbit in 1990 and continues to function, in part due to prior servicing missions performed by the Space Shuttle.[216][217] The other remaining active great observatory include the Chandra X-ray Observatory (CXO), launched by STS-93 in July 1999 and is now in a 64-hour elliptical orbit studying X-ray sources that are not readily viewable from terrestrial observatories.[218] Chandra X-ray Observatory (rendering), 2015 The Imaging X-ray Polarimetry Explorer (IXPE) is a space observatory designed to improve the understanding of X-ray production in objects such as neutron stars and pulsar wind nebulae, as well as stellar and supermassive black holes.[219] IXPE launched in December 2021 and is an international collaboration between NASA and the Italian Space Agency (ASI). It is part of the NASA Small Explorers program (SMEX) which designs low-cost spacecraft to study heliophysics and astrophysics.[220] The Neil Gehrels Swift Observatory was launched in November 2004 and is Gamma-ray burst observatory that also monitors the afterglow in X-ray, and UV/Visible light at the location of a burst.[221] The mission was developed in a joint partnership between Goddard Space Flight Center (GSFC) and an international consortium from the United States, United Kingdom, and Italy. Pennsylvania State University operates the mission as part of NASA's Medium Explorer program (MIDEX).[222] The Fermi Gamma-ray Space Telescope (FGST) is another gamma-ray focused space observatory that was launched to low Earth orbit in June 2008 and is being used to perform gamma-ray astronomy observations.[223] In addition to NASA, the mission involves the United States Department of Energy, and government agencies in France, Germany, Italy, Japan, and Sweden.[224] The James Webb Space Telescope (JWST), launched in December 2021 on an Ariane 5 rocket, operates in a halo orbit circling the Sun-Earth L2 point.[225][226][227] JWST's high sensitivity in the infrared spectrum and its imaging resolution will allow it to view more distant, faint, or older objects than its predecessors, including Hubble.[228] Earth Sciences Program missions (1965–present) Further information: NASA Earth Science Schematic of NASA Earth Science Division operating satellite missions as of February 2015 NASA Earth Science is a large, umbrella program comprising a range of terrestrial and space-based collection systems in order to better understand the Earth system and its response to natural and human-caused changes. Numerous systems have been developed and fielded over several decades to provide improved prediction for weather, climate, and other changes in the natural environment. Several of the current operating spacecraft programs include: Aqua,[229] Aura,[230] Orbiting Carbon Observatory 2 (OCO-2),[231] Gravity Recovery and Climate Experiment Follow-on (GRACE FO),[232] and Ice, Cloud, and land Elevation Satellite 2 (ICESat-2).[233] In addition to systems already in orbit, NASA is designing a new set of Earth Observing Systems to study, assess, and generate responses for climate change, natural hazards, forest fires, and real-time agricultural processes.[234] The GOES-T satellite (designated GOES-18 after launch) joined the fleet of U.S. geostationary weather monitoring satellites in March 2022.[235] NASA also maintains the Earth Science Data Systems (ESDS) program to oversee the life cycle of NASA's Earth science data — from acquisition through processing and distribution. The primary goal of ESDS is to maximize the scientific return from NASA's missions and experiments for research and applied scientists, decision makers, and society at large.[236] The Earth Science program is managed by the Earth Science Division of the NASA Science Mission Directorate. Space operations architecture NASA invests in various ground and space-based infrastructures to support its science and exploration mandate. The agency maintains access to suborbital and orbital space launch capabilities and sustains ground station solutions to support its evolving fleet of spacecraft and remote systems. Deep Space Network (1963–present) Further information: NASA Deep Space Network The NASA Deep Space Network (DSN) serves as the primary ground station solution for NASA's interplanetary spacecraft and select Earth-orbiting missions.[237] The system employs ground station complexes near Barstow California in the United States, in Spain near Madrid, and in Australia near Canberra. The placement of these ground stations approximately 120 degrees apart around the planet provides the ability for communications to spacecraft throughout the Solar System even as the Earth rotates about its axis on a daily basis. The system is controlled at a 24x7 operations center at JPL in Pasadena California which manages recurring communications linkages with up to 40 spacecraft.[238] The system is managed by the Jet Propulsion Laboratory (JPL).[237] Near Space Network (1983–present) Further information: Near Earth Network and Tracking and Data Relay Satellite System Near Earth Network Ground Stations, 2021 The Near Space Network (NSN) provides telemetry, commanding, ground-based tracking, data and communications services to a wide range of customers with satellites in low earth orbit (LEO), geosynchronous orbit (GEO), highly elliptical orbits (HEO), and lunar orbits. The NSN accumulates ground station and antenna assets from the Near-Earth Network and the Tracking and Data Relay Satellite System (TDRS) which operates in geosynchronous orbit providing continuous real-time coverage for launch vehicles and low earth orbit NASA missions.[239] The NSN consists of 19 ground stations worldwide operated by the US Government and by contractors including Kongsberg Satellite Services (KSAT), Swedish Space Corporation (SSC), and South African National Space Agency (SANSA).[240] The ground network averages between 120 and 150 spacecraft contacts a day with TDRS engaging with systems on a near-continuous basis as needed; the system is managed and operated by the Goddard Space Flight Center.[241] Sounding Rocket Program (1959–present) Further information: NASA Sounding Rocket Program NASA sounding rocket launch from the Wallops Flight Facility The NASA Sounding Rocket Program (NSRP) is located at the Wallops Flight Facility and provides launch capability, payload development and integration, and field operations support to execute suborbital missions.[242] The program has been in operation since 1959 and is managed by the Goddard Space Flight Center using a combined US Government and contractor team.[243] The NSRP team conducts approximately 20 missions per year from both Wallops and other launch locations worldwide to allow scientists to collect data "where it occurs". The program supports the strategic vision of the Science Mission Directorate collecting important scientific data for earth science, heliophysics, and astrophysics programs.[242] In June 2022, NASA conducted its first rocket launch from a commercial spaceport outside the US. It launched a Black Brant IX from the Arnhem Space Centre in Australia.[244] Launch Services Program (1990–present) Further information: NASA Launch Services Program Launch Services Program logo.svg The NASA Launch Services Program (LSP) is responsible for procurement of launch services for NASA uncrewed missions and oversight of launch integration and launch preparation activity, providing added quality and mission assurance to meet program objectives.[245] Since 1990, NASA has purchased expendable launch vehicle launch services directly from commercial providers, whenever possible, for its scientific and applications missions. Expendable launch vehicles can accommodate all types of orbit inclinations and altitudes and are ideal vehicles for launching Earth-orbit and interplanetary missions. LSP operates from Kennedy Space Center and falls under the NASA Space Operations Mission Directorate (SOMD).[246][247] Aeronautics Research Further information: NASA research and Aeronautics Research Mission Directorate The Aeronautics Research Mission Directorate (ARMD) is one of five mission directorates within NASA, the other four being the Exploration Systems Development Mission Directorate, the Space Operations Mission Directorate, the Science Mission Directorate, and the Space Technology Mission Directorate.[248] The ARMD is responsible for NASA's aeronautical research, which benefits the commercial, military, and general aviation sectors. ARMD performs its aeronautics research at four NASA facilities: Ames Research Center and Armstrong Flight Research Center in California, Glenn Research Center in Ohio, and Langley Research Center in Virginia.[249] NASA X-57 Maxwell aircraft (2016–present) Further information: NASA X-57 Maxwell The NASA X-57 Maxwell is an experimental aircraft being developed by NASA to demonstrate the technologies required to deliver a highly efficient all-electric aircraft.[250] The primary goal of the program is to develop and deliver all-electric technology solutions that can also achieve airworthiness certification with regulators. The program involves development of the system in several phases, or modifications, to incrementally grow the capability and operability of the system. The initial configuration of the aircraft has now completed ground testing as it approaches its first flights. In mid-2022, the X-57 was scheduled to fly before the end of the year.[251] The development team includes staff from the NASA Armstrong, Glenn, and Langley centers along with number of industry partners from the United States and Italy.[252] Next Generation Air Transportation System (2007–present) Further information: Next Generation Air Transportation System NASA is collaborating with the Federal Aviation Administration and industry stakeholders to modernize the United States National Airspace System (NAS). Efforts began in 2007 with a goal to deliver major modernization components by 2025.[253] The modernization effort intends to increase the safety, efficiency, capacity, access, flexibility, predictability, and resilience of the NAS while reducing the environmental impact of aviation.[254] The Aviation Systems Division of NASA Ames operates the joint NASA/FAA North Texas Research Station. The station supports all phases of NextGen research, from concept development to prototype system field evaluation. This facility has already transitioned advanced NextGen concepts and technologies to use through technology transfers to the FAA.[253] NASA contributions also include development of advanced automation concepts and tools that provide air traffic controllers, pilots, and other airspace users with more accurate real-time information about the nation's traffic flow, weather, and routing. Ames' advanced airspace modeling and simulation tools have been used extensively to model the flow of air traffic flow across the U.S., and to evaluate new concepts in airspace design, traffic flow management, and optimization.[255] Technology research For technologies funded or otherwise supported by NASA, see NASA spinoff technologies. Nuclear in-space power and propulsion (ongoing) NASA has made use of technologies such as the multi-mission radioisotope thermoelectric generator (MMRTG), which is a type of radioisotope thermoelectric generator used to power spacecraft.[256] Shortages of the required plutonium-238 have curtailed deep space missions since the turn of the millennium.[257] An example of a spacecraft that was not developed because of a shortage of this material was New Horizons 2.[257] In July 2021, NASA announced contract awards for development of nuclear thermal propulsion reactors. Three contractors will develop individual designs over 12 months for later evaluation by NASA and the U.S. Department of Energy.[258] NASA's space nuclear technologies portfolio are led and funded by its Space Technology Mission Directorate. Other initiatives Free Space Optics. NASA contracted a third party to study the probability of using Free Space Optics (FSO) to communicate with Optical (laser) Stations on the Ground (OGS) called laser-com RF networks for satellite communications.[259] Water Extraction from Lunar Soil. On July 29, 2020, NASA requested American universities to propose new technologies for extracting water from the lunar soil and developing power systems. The idea will help the space agency conduct sustainable exploration of the Moon.[260] Human Spaceflight Research (2005–present) Human Research Program logo.png SpaceX Crew-4 astronaut Samantha Cristoforetti operating the rHEALTH ONE on the ISS to address key health risks for space travel NASA's Human Research Program (HRP) is designed to study the effects of space on human health and also to provide countermeasures and technologies for human space exploration. The medical effects of space exploration are reasonably limited in low Earth orbit or in travel to the Moon. Travel to Mars, however, is significantly longer and deeper into space and significant medical issues can result. This includes bone loss, radiation exposure, vision changes, circadian rhythm disturbances, heart remodeling, and immune alterations. In order to study and diagnose these ill-effects, HRP has been tasked with identifying or developing small portable instrumentation with low mass, volume, and power to monitor the health of astronauts.[261] To achieve this aim, on May 13, 2022, NASA and SpaceX Crew-4 astronauts successfully tested its rHEALTH ONE universal biomedical analyzer for its ability to identify and analyzer biomarkers, cells, microorganisms, and proteins in a spaceflight environment.[262] Planetary Defense (2016–present) Further information: Planetary Defense Coordination Office and Near Earth Objects Planetary Defense Coordination Office seal.png NASA established the Planetary Defense Coordination Office (PDCO) in 2016 to catalog and track potentially hazardous near-Earth objects (NEO), such as asteroids and comets and develop potential responses and defenses against these threats.[263] The PDCO is chartered to provide timely and accurate information to the government and the public on close approaches by Potentially hazardous objects (PHOs) and any potential for impact. The office functions within the Science Mission Directorate Planetary Science division.[264] The PDCO augmented prior cooperative actions between the United States, the European Union, and other nations which had been scanning the sky for NEOs since 1998 in an effort called Spaceguard.[265] Near Earth object detection (1998–present) From the 1990s NASA has run many NEO detection programs from Earth bases observatories, greatly increasing the number of objects that have been detected. However, many asteroids are very dark and the ones that are near the Sun are much harder to detect from Earth-based telescopes which observe at night, and thus face away from the Sun. NEOs inside Earth orbit only reflect a part of light also rather than potentially a "full Moon" when they are behind the Earth and fully lit by the Sun. In 1998, the United States Congress gave NASA a mandate to detect 90% of near-Earth asteroids over 1 km (0.62 mi) diameter (that threaten global devastation) by 2008.[266] This initial mandate was met by 2011.[267] In 2005, the original USA Spaceguard mandate was extended by the George E. Brown, Jr. Near-Earth Object Survey Act, which calls for NASA to detect 90% of NEOs with diameters of 140 m (460 ft) or greater, by 2020 (compare to the 20-meter Chelyabinsk meteor that hit Russia in 2013).[268] As of January 2020, it is estimated that less than half of these have been found, but objects of this size hit the Earth only about once in 2,000 years.[269] In January 2020, NASA officials estimated it would take 30 years to find all objects meeting the 140 m (460 ft) size criteria, more than twice the timeframe that was built into the 2005 mandate.[270] In June 2021, NASA authorized the development of the NEO Surveyor spacecraft to reduce that projected duration to achieve the mandate down to 10 years.[271][272] Involvement in current robotic missions NASA has incorporated planetary defense objectives into several ongoing missions. In 1999, NASA visited 433 Eros with the NEAR Shoemaker spacecraft which entered its orbit in 2000, closely imaging the asteroid with various instruments at that time.[273] NEAR Shoemaker became the first spacecraft to successfully orbit and land on an asteroid, improving our understanding of these bodies and demonstrating our capacity to study them in greater detail.[274] OSIRIS-REx used its suite of instruments to transmit radio tracking signals and capture optical images of Bennu during its study of the asteroid that will help NASA scientists determine its precise position in the solar system and its exact orbital path. As Bennu has the potential for recurring approaches to the Earth-Moon system in the next 100–200 years, the precision gained from OSIRIS-REx will enable scientists to better predict the future gravitational interactions between Bennu and our planet and resultant changes in Bennu's onward flight path.[275][276] The WISE/NEOWISE mission was launched by NASA JPL in 2009 as an infrared-wavelength astronomical space telescope. In 2013, NASA repurposed it as the NEOWISE mission to find potentially hazardous near-Earth asteroids and comets; its mission has been extended into 2023.[277][278] NASA and Johns Hopkins Applied Physics Laboratory (JHAPL) jointly developed the first planetary defense purpose-built satellite, the Double Asteroid Redirection Test (DART) to test possible planetary defense concepts.[279] DART was launched in November 2021 by a SpaceX Falcon 9 from California on a trajectory designed to impact the Dimorphos asteroid. Scientists were seeking to determine whether an impact could alter the subsequent path of the asteroid; a concept that could be applied to future planetary defense.[280] On September 26, 2022, DART hit its target. In the weeks following impact, NASA declared DART a success, confirming it had shortened Dimorphos' orbital period around Didymos by about 32 minutes, surpassing the pre-defined success threshold of 73 seconds.[281][282] NEO Surveyor, formerly called the Near-Earth Object Camera (NEOCam) mission, is a space-based infrared telescope under development to survey the Solar System for potentially hazardous asteroids.[283] The spacecraft is scheduled to launch in 2026. Study of Unidentified Aerial Phenomena (2022–present) In June 2022, the head of the NASA Science Mission Directorate, Thomas Zurbuchen, confirmed that NASA would join the hunt for Unidentified Flying Objects (UFOs)/Unidentified Aerial Phenomena (UAPs).[284] At a speech before the National Academies of Science, Engineering and Medicine, Zurbuchen said the space agency would bring a scientific perspective to efforts already underway by the Pentagon and intelligence agencies to make sense of dozens of such sightings. He said it was "high-risk, high-impact" research that the space agency should not shy away from, even if it is a controversial field of study.[285] Collaboration NASA Advisory Council In response to the Apollo 1 accident, which killed three astronauts in 1967, Congress directed NASA to form an Aerospace Safety Advisory Panel (ASAP) to advise the NASA Administrator on safety issues and hazards in NASA's air and space programs. In the aftermath of the Shuttle Columbia disaster, Congress required that the ASAP submit an annual report to the NASA Administrator and to Congress.[286] By 1971, NASA had also established the Space Program Advisory Council and the Research and Technology Advisory Council to provide the administrator with advisory committee support. In 1977, the latter two were combined to form the NASA Advisory Council (NAC).[287] The NASA Authorization Act of 2014 reaffirmed the importance of ASAP. National Oceanic and Atmospheric Administration (NOAA) Further information: National Oceanic and Atmospheric Administration NOAA logo mobile.svg NASA and NOAA have cooperated for decades on the development, delivery and operation of polar and geosynchronous weather satellites.[288] The relationship typically involves NASA developing the space systems, launch solutions, and ground control technology for the satellites and NOAA operating the systems and delivering weather forecasting products to users. Multiple generations of NOAA Polar orbiting platforms have operated to provide detailed imaging of weather from low altitude.[289] Geostationary Operational Environmental Satellites (GOES) provide near-real-time coverage of the western hemisphere to ensure accurate and timely understanding of developing weather phenomenon.[290] United States Space Force Further information: United States Space Force United States Space Force logo.svg The United States Space Force (USSF) is the space service branch of the United States Armed Forces, while the National Aeronautics and Space Administration (NASA) is an independent agency of the United States government responsible for civil spaceflight. NASA and the Space Force's predecessors in the Air Force have a long-standing cooperative relationship, with the Space Force supporting NASA launches out of Kennedy Space Center, Cape Canaveral Space Force Station, and Vandenberg Space Force Base, to include range support and rescue operations from Task Force 45.[291] NASA and the Space Force also partner on matters such as defending Earth from asteroids.[292] Space Force members can be NASA astronauts, with Colonel Michael S. Hopkins, the commander of SpaceX Crew-1, commissioned into the Space Force from the International Space Station on December 18, 2020.[293][294][295] In September 2020, the Space Force and NASA signed a memorandum of understanding formally acknowledging the joint role of both agencies. This new memorandum replaced a similar document signed in 2006 between NASA and Air Force Space Command.[296][297] U.S. Geological Survey Further information: United States Geological Survey and Landsat 9 USGS logo green.svg The Landsat program is the longest-running enterprise for acquisition of satellite imagery of Earth. It is a joint NASA / USGS program.[298] On July 23, 1972, the Earth Resources Technology Satellite was launched. This was eventually renamed to Landsat 1 in 1975.[299] The most recent satellite in the series, Landsat 9, was launched on September 27, 2021.[300] The instruments on the Landsat satellites have acquired millions of images. The images, archived in the United States and at Landsat receiving stations around the world, are a unique resource for global change research and applications in agriculture, cartography, geology, forestry, regional planning, surveillance and education, and can be viewed through the U.S. Geological Survey (USGS) "EarthExplorer" website. The collaboration between NASA and USGS involves NASA designing and delivering the space system (satellite) solution, launching the satellite into orbit with the USGS operating the system once in orbit.[298] As of October 2022, nine satellites have been built with eight of them successfully operating in orbit. European Space Agency (ESA) Further information: European Space Agency European Space Agency logo.svg NASA collaborates with the European Space Agency on a wide range of scientific and exploration requirements.[301] From participation with the Space Shuttle (the Spacelab missions) to major roles on the Artemis program (the Orion Service Module), ESA and NASA have supported the science and exploration missions of each agency. There are NASA payloads on ESA spacecraft and ESA payloads on NASA spacecraft. The agencies have developed joint missions in areas including heliophysics (e.g. Solar Orbiter)[302] and astronomy (Hubble Space Telescope, James Webb Space Telescope).[303] Under the Artemis Gateway partnership, ESA will contribute habitation and refueling modules, along with enhanced lunar communications, to the Gateway.[304][305] NASA and ESA continue to advance cooperation in relation to Earth Science including climate change with agreements to cooperate on various missions including the Sentinel-6 series of spacecraft[306] Japan Aerospace Exploration Agency (JAXA) Further information: Japan Aerospace Exploration Agency Jaxa logo.svg NASA and the Japan Aerospace Exploration Agency (JAXA) cooperate on a range of space projects. JAXA is a direct participant in the Artemis program, including the Lunar Gateway effort. JAXA's planned contributions to Gateway include I-Hab's environmental control and life support system, batteries, thermal control, and imagery components, which will be integrated into the module by the European Space Agency (ESA) prior to launch. These capabilities are critical for sustained Gateway operations during crewed and uncrewed time periods.[307][308] JAXA and NASA have collaborated on numerous satellite programs, especially in areas of Earth science. NASA has contributed to JAXA satellites and vice versa. Japanese instruments are flying on NASA's Terra and Aqua satellites, and NASA sensors have flown on previous Japanese Earth-observation missions. The NASA-JAXA Global Precipitation Measurement mission was launched in 2014 and includes both NASA- and JAXA-supplied sensors on a NASA satellite launched on a JAXA rocket. The mission provides the frequent, accurate measurements of rainfall over the entire globe for use by scientists and weather forecasters.[309] Roscosmos Further information: Roscosmos Roscosmos logo ru.svg NASA and Roscosmos have cooperated on the development and operation of the International Space Station since September 1993.[310] The agencies have used launch systems from both countries to deliver station elements to orbit. Astronauts and Cosmonauts jointly maintain various elements of the station. Both countries provide access to the station via launch systems noting Russia's unique role as the sole provider of delivery of crew and cargo upon retirement of the space shuttle in 2011 and prior to commencement of NASA COTS and crew flights. In July 2022, NASA and Roscosmos signed a deal to share space station flights enabling crew from each country to ride on the systems provided by the other.[311] Current geopolitical conditions in late 2022 make it unlikely that cooperation will be extended to other programs such as Artemis or lunar exploration.[312] Indian Space Research Organisation Further information: Indian Space Research Organisation Indian Space Research Organisation Logo.svg In September 2014, NASA and Indian Space Research Organisation (ISRO) signed a partnership to collaborate on and launch a joint radar mission, the NASA-ISO Synthetic Aperature Radar (NISAR) mission. The mission is targeted to launch in 2024. NASA will provide the mission's L-band synthetic aperture radar, a high-rate communication subsystem for science data, GPS receivers, a solid-state recorder and payload data subsystem. ISRO provides the spacecraft bus, the S-band radar, the launch vehicle and associated launch services.[313][314] Artemis Accords Further information: Artemis Accords The Artemis Accords have been established to define a framework for cooperating in the peaceful exploration and exploitation of the Moon, Mars, asteroids, and comets. The Accords were drafted by NASA and the U.S. State Department and are executed as a series of bilateral agreements between the United States and the participating countries.[315][316] As of September 2022, 21 countries have signed the accords. They are Australia, Bahrain, Brazil, Canada, Colombia, France, Israel, Italy, Japan, the Republic of Korea, Luxembourg, Mexico, New Zealand, Poland, Romania, the Kingdom of Saudi Arabia, Singapore, Ukraine, the United Arab Emirates, the United Kingdom, and the United States.[317][318] China National Space Administration Further information: Wolf Amendment and China National Space Administration The Wolf Amendment was passed by the U.S. Congress into law in 2011 and prevents NASA from engaging in direct, bilateral cooperation with the Chinese government and China-affiliated organizations such as the China National Space Administration without the explicit authorization from Congress and the Federal Bureau of Investigation. The law has been renewed annually since by inclusion in annual appropriations bills.[319] Sustainability Environmental impact The exhaust gases produced by rocket propulsion systems, both in Earth's atmosphere and in space, can adversely affect the Earth's environment. Some hypergolic rocket propellants, such as hydrazine, are highly toxic prior to combustion, but decompose into less toxic compounds after burning. Rockets using hydrocarbon fuels, such as kerosene, release carbon dioxide and soot in their exhaust.[320] However, carbon dioxide emissions are insignificant compared to those from other sources; on average, the United States consumed 803 million US gal (3.0 million m3) of liquid fuels per day in 2014, while a single Falcon 9 rocket first stage burns around 25,000 US gallons (95 m3) of kerosene fuel per launch.[321][322] Even if a Falcon 9 were launched every single day, it would only represent 0.006% of liquid fuel consumption (and carbon dioxide emissions) for that day. Additionally, the exhaust from LOx- and LH2- fueled engines, like the SSME, is almost entirely water vapor.[323] NASA addressed environmental concerns with its canceled Constellation program in accordance with the National Environmental Policy Act in 2011.[324] In contrast, ion engines use harmless noble gases like xenon for propulsion.[325][326] An example of NASA's environmental efforts is the NASA Sustainability Base. Additionally, the Exploration Sciences Building was awarded the LEED Gold rating in 2010.[327] On May 8, 2003, the Environmental Protection Agency recognized NASA as the first federal agency to directly use landfill gas to produce energy at one of its facilities—the Goddard Space Flight Center, Greenbelt, Maryland.[328] In 2018, NASA along with other companies including Sensor Coating Systems, Pratt & Whitney, Monitor Coating and UTRC launched the project CAUTION (CoAtings for Ultra High Temperature detectION). This project aims to enhance the temperature range of the Thermal History Coating up to 1,500 °C (2,730 °F) and beyond. The final goal of this project is improving the safety of jet engines as well as increasing efficiency and reducing CO2 emissions.[329] Climate change NASA also researches and publishes on climate change.[330] Its statements concur with the global scientific consensus that the global climate is warming.[331] Bob Walker, who has advised US President Donald Trump on space issues, has advocated that NASA should focus on space exploration and that its climate study operations should be transferred to other agencies such as NOAA. Former NASA atmospheric scientist J. Marshall Shepherd countered that Earth science study was built into NASA's mission at its creation in the 1958 National Aeronautics and Space Act.[332] NASA won the 2020 Webby People's Voice Award for Green in the category Web.[333] STEM Initiatives Further information: STEM Educational Launch of Nanosatellites (ELaNa). Since 2011, the ELaNa program has provided opportunities for NASA to work with university teams to test emerging technologies and commercial-off-the-shelf solutions by providing launch opportunities for developed CubeSats using NASA procured launch opportunities.[334] By example, two NASA-sponsored CubeSats launched in June 2022 on a Virgin Orbit LauncherOne vehicle as the ELaNa 39 mission.[335] Cubes in Space. NASA started an annual competition in 2014 named "Cubes in Space".[336] It is jointly organized by NASA and the global education company I Doodle Learning, with the objective of teaching school students aged 11–18 to design and build scientific experiments to be launched into space on a NASA rocket or balloon. On June 21, 2017, the world's smallest satellite, KalamSAT, was launched.[337] Use of the metric system US law requires the International System of Units to be used in all US Government programs, "except where impractical".[338] In 1969, Apollo 11 landed on the Moon using a mix of United States customary units and metric units. In the 1980s, NASA started the transition towards the metric system, but was still using both systems in the 1990s.[339][340] On September 23, 1999, a mixup between NASA's use of SI units and Lockheed Martin Space's use of US units resulted in the loss of the Mars Climate Orbiter.[341] In August 2007, NASA stated that all future missions and explorations of the Moon would be done entirely using the SI system. This was done to improve cooperation with space agencies of other countries that already use the metric system.[342] As of 2007, NASA is predominantly working with SI units, but some projects still use US units, and some, including the International Space Station, use a mix of both.[343] Media presence NASA TV Further information: NASA TV Approaching 40 years of service, the NASA TV channel airs content ranging from live coverage of crewed missions to video coverage of significant milestones for operating robotic spacecraft (e.g., rover landings on Mars for example) and domestic and international launches.[344] The channel is delivered by NASA and is broadcast by satellite and over the Internet. The system initially started to capture archival footage of important space events for NASA managers and engineers and expanded as public interest grew. The Apollo 8 Christmas Eve broadcast while in orbit around the Moon was received by more than a billion people.[345] NASA's video transmission of the Apollo 11 Moon landing was awarded a primetime Emmy in commemoration of the 40th anniversary of the landing.[346] The channel is a product of the U.S. Government and is widely available across many television and Internet platforms.[347] NASAcast NASAcast is the official audio and video podcast of the NASA website. Created in late 2005, the podcast service contains the latest audio and video features from the NASA web site, including NASA TV's This Week at NASA and educational materials produced by NASA. Additional NASA podcasts, such as Science@NASA, are also featured and give subscribers an in-depth look at content by subject matter.[348] NASA EDGE NASA EDGE broadcasting live from White Sands Missile Range in 2010 NASA EDGE is a video podcast which explores different missions, technologies and projects developed by NASA. The program was released by NASA on March 18, 2007, and, as of August 2020, there have been 200 vodcasts produced. It is a public outreach vodcast sponsored by NASA's Exploration Systems Mission Directorate and based out of the Exploration and Space Operations Directorate at Langley Research Center in Hampton, Virginia. The NASA EDGE team takes an insiders look at current projects and technologies from NASA facilities around the United States, and it is depicted through personal interviews, on-scene broadcasts, computer animations, and personal interviews with top scientists and engineers at NASA.[note 3] The show explores the contributions NASA has made to society as well as the progress of current projects in materials and space exploration. NASA EDGE vodcasts can be downloaded from the NASA website and from iTunes. In its first year of production, the show was downloaded over 450,000 times. As of February 2010, the average download rate is more than 420,000 per month, with over one million downloads in December 2009 and January 2010.[350] NASA and the NASA EDGE have also developed interactive programs designed to complement the vodcast. The Lunar Electric Rover App allows users to drive a simulated Lunar Electric Rover between objectives, and it provides information about and images of the vehicle.[351] The NASA EDGE Widget provides a graphical user interface for accessing NASA EDGE vodcasts, image galleries, and the program's Twitter feed, as well as a live NASA news feed.[352] Astronomy Picture of the Day This section is an excerpt from Astronomy Picture of the Day.[edit] Astronomy Picture of the Day (APOD) is a website provided by NASA and Michigan Technological University (MTU). According to the website, "Each day a different image or photograph of our universe is featured, along with a brief explanation written by a professional astronomer."[353] The photograph does not necessarily correspond to a celestial event on the exact day that it is displayed, and images are sometimes repeated.[354] However, the pictures and descriptions often relate to current events in astronomy and space exploration. The text has several hyperlinks to more pictures and websites for more information. The images are either visible spectrum photographs, images taken at non-visible wavelengths and displayed in false color, video footage, animations, artist's conceptions, or micrographs that relate to space or cosmology. Past images are stored in the APOD Archive, with the first image appearing on June 16, 1995.[355] This initiative has received support from NASA, the National Science Foundation, and MTU. The images are sometimes authored by people or organizations outside NASA, and therefore APOD images are often copyrighted, unlike many other NASA image galleries.[356] When the APOD website was created, it received a total of 14 page views on its first day. As of 2012, the APOD website has received over a billion image views throughout its lifetime.[357] APOD is also translated into 21 languages daily." (wikipedia.org) "A puzzle is a game, problem, or toy that tests a person's ingenuity or knowledge. In a puzzle, the solver is expected to put pieces together (or take them apart) in a logical way, in order to arrive at the correct or fun solution of the puzzle. There are different genres of puzzles, such as crossword puzzles, word-search puzzles, number puzzles, relational puzzles, and logic puzzles. The academic study of puzzles is called enigmatology. Puzzles are often created to be a form of entertainment but they can also arise from serious mathematical or logical problems. In such cases, their solution may be a significant contribution to mathematical research.[1] Etymology The Oxford English Dictionary dates the word puzzle (as a verb) to the end of the 16th century. Its earliest use documented in the OED was in a book titled The Voyage of Robert Dudley...to the West Indies, 1594–95, narrated by Capt. Wyatt, by himself, and by Abram Kendall, master (published circa 1595). The word later came to be used as a noun, first as an abstract noun meaning 'the state or condition of being puzzled', and later developing the meaning of 'a perplexing problem'. The OED's earliest clear citation in the sense of 'a toy that tests the player's ingenuity' is from Sir Walter Scott's 1814 novel Waverley, referring to a toy known as a "reel in a bottle".[2] The etymology of the verb puzzle is described by OED as "unknown"; unproven hypotheses regarding its origin include an Old English verb puslian meaning 'pick out', and a derivation of the verb pose.[3] Genres Various puzzles Simple puzzle made of three pieces Puzzles can be categorized as:     Lateral thinking puzzles, also called "situation puzzles"     Mathematical puzzles include the missing square puzzle and many impossible puzzles — puzzles which have no solution, such as the Seven Bridges of Königsberg, the three cups problem, and three utilities problem         Sangaku (Japanese temple tablets with geometry puzzles)     A chess problem is a puzzle that uses chess pieces on a chess board. Examples are the knight's tour and the eight queens puzzle.     Mechanical puzzles or dexterity puzzles such as the Rubik's Cube and Soma cube can be stimulating toys for children or recreational activities for adults.         combination puzzles like Peg solitaire         construction puzzles such as stick puzzles         disentanglement puzzles,         folding puzzles         jigsaw puzzles. Puzz 3D is a three-dimensional variant of this type.         lock puzzles         A puzzle box can be used to hide something — jewelry, for instance.         sliding puzzles (also called sliding tile puzzles) such as the 15 Puzzle and Sokoban         tiling puzzles like Tangram         Tower of Hanoi     Metapuzzles are puzzles which unite elements of other puzzles.     Paper-and-pencil puzzles such as Uncle Art's Funland, connect the dots, and nonograms         Also the logic puzzles published by Nikoli: Sudoku, Slitherlink, Kakuro, Fillomino, Hashiwokakero, Heyawake, Hitori, Light Up, Masyu, Number Link, Nurikabe, Ripple Effect, Shikaku, and Kuromasu.     Spot the difference     Tour puzzles like a maze     Word puzzles, including anagrams, ciphers, crossword puzzles, Hangman (game), and word search puzzles. Tabletop and digital word puzzles include Bananagrams, Boggle, Bonza, Dabble, Letterpress (video game), Perquackey, Puzzlage, Quiddler, Ruzzle, Scrabble, Upwords, WordSpot, and Words with Friends. Wheel of Fortune (U.S. game show) is a game show centered on a word puzzle.     Puzzle video games         Tile-matching video game         Puzzle-platformer         Adventure game         Hidden object game         Minesweeper Puzzle solving     This section possibly contains original research. Please improve it by verifying the claims made and adding inline citations. Statements consisting only of original research should be removed. (November 2018) (Learn how and when to remove this template message) Solutions of puzzles often require the recognition of patterns and the adherence to a particular kind of ordering. People with a high level of inductive reasoning aptitude may be better at solving such puzzles than others. But puzzles based upon inquiry and discovery may be solved more easily by those with good deduction skills. Deductive reasoning improves with practice. Mathematical puzzles often involve BODMAS. BODMAS is an acronym and it stands for Bracket, Of, Division, Multiplication, Addition and Subtraction. In certain regions, PEMDAS (Parentheses, Exponents, Multiplication, Division, Addition and Subtraction) is the synonym of BODMAS. It explains the order of operations to solve an expression. Some mathematical puzzles require Top to Bottom convention to avoid the ambiguity in the order of operations. It is an elegantly simple idea that relies, as sudoku does, on the requirement that numbers appear only once starting from top to bottom as coming along.[4] Puzzle makers Puzzle makers are people who make puzzles. In general terms of occupation, a puzzler is someone who composes and/or solves puzzles. Some notable creators of puzzles are:     Ernő Rubik     Sam Loyd     Henry Dudeney     Boris Kordemsky     David J. Bodycombe     Will Shortz     Oskar van Deventer     Lloyd King     Martin Gardner     Raymond Smullyan History of jigsaw and other puzzles Main article: Jigsaw puzzle Jigsaw puzzles are perhaps the most popular form of puzzle. Jigsaw puzzles were invented around 1760, when John Spilsbury, a British engraver and cartographer, mounted a map on a sheet of wood, which he then sawed around the outline of each individual country on the map. He then used the resulting pieces as an aid for the teaching of geography.[5] After becoming popular among the public, this kind of teaching aid remained the primary use of jigsaw puzzles until about 1820.[6] The largest puzzle (40,320 pieces) is made by German game company Ravensburger.[7] The smallest puzzle ever made was created at LaserZentrum Hannover. It is only five square millimeters, the size of a sand grain. The puzzles that were first documented are riddles. In Europe, Greek mythology produced riddles like the riddle of the Sphinx. Many riddles were produced during the Middle Ages, as well.[8] By the early 20th century, magazines and newspapers found that they could increase their readership by publishing puzzle contests, beginning with crosswords and in modern days sudoku. Organizations and events There are organizations and events that cater to puzzle enthusiasts, such as:     Nob Yoshigahara Puzzle Design Competition     World Puzzle Championship     National Puzzlers' League     Puzzlehunts such as the Maze of Games     World Cube Association" (wikipedia.org) "A jigsaw puzzle is a tiling puzzle that requires the assembly of often irregularly shaped interlocking and mosaiced pieces, each of which typically has a portion of a picture. When assembled, the puzzle pieces produce a complete picture. In the 18th century, jigsaw puzzles were created by painting a picture on a flat, rectangular piece of wood, then cutting it into small pieces. Despite the name, a jigsaw was never used. John Spilsbury, a London cartographer and engraver, is credited with commercialising jigsaw puzzles around 1760. His design took world maps, and cut out the individual nations in order for them to be reassembled by students as a geographical teaching aid.[1] They have since come to be made primarily of interlocking cardboard pieces, incorporating a variety of images & designs. Typical images on jigsaw puzzles include scenes from nature, buildings, and repetitive designs—castles and mountains are common, as well as other traditional subjects. However, any picture can be used. Artisan puzzle-makers and companies using technologies for one-off and small print-run puzzles utilize a wide range of subject matter, including optical illusions, unusual art, and personal photographs. In addition to traditional flat, two-dimensional puzzles, three-dimensional puzzles have entered large-scale production, including spherical puzzles and architectural recreations. A range of jigsaw puzzle accessories, including boards, cases, frames, and roll-up mats, have become available to assist jigsaw puzzle enthusiasts. While most assembled puzzles are disassembled for reuse, they can also be attached to a backing with adhesive and displayed as art. History John Spilsbury's "Europe divided into its kingdoms, etc." (1766). He created the jigsaw puzzle for educational purposes, and called them "Dissected Maps".[2][3] John Spilsbury is believed to have produced the first jigsaw puzzle around 1760, using a marquetry saw.[1] Early puzzles, known as dissections, were produced by mounting maps on sheets of hardwood and cutting along national boundaries, creating a puzzle useful for teaching geography.[1] Royal governess Lady Charlotte Finch used such "dissected maps" to teach the children of King George III and Queen Charlotte[4][5] Cardboard jigsaw puzzles appeared in the late 1800s, but were slow to replace wooden ones because manufacturers felt that cardboard puzzles would be perceived as low-quality, and because profit margins on wooden jigsaws were larger.[1] British printed puzzle from 1874. The name "jigsaw" came to be associated with the puzzle around 1880 when fretsaws became the tool of choice for cutting the shapes. Since fretsaws are distinct from jigsaws, the name appears to be a misnomer.[1] Wooden jigsaw pieces, cut by hand Jigsaw puzzles soared in popularity during the Great Depression, as they provided a cheap, long-lasting, recyclable form of entertainment.[1][6] It was around this time that jigsaws evolved to become more complex and appealing to adults.[1] They were also given away in product promotions and used in advertising, with customers completing an image of the promoted product.[1][6] Sales of wooden puzzles fell after World War II as improved wages led to price increases, while improvements in manufacturing processes made paperboard jigsaws more attractive.[6] Demand for jigsaw puzzles saw a surge, comparable to that of the Great Depression, during the COVID-19 pandemic's stay-at-home orders.[7][8] Modern construction Paperboard jigsaw pieces Most modern jigsaw puzzles are made of paperboard as they are easier and cheaper to mass-produce. An enlarged photograph or printed reproduction of a painting or other two-dimensional artwork is glued to cardboard, which is then fed into a press. The press forces a set of hardened steel blades of the desired pattern, called a puzzle die, through the board until fully cut. The puzzle die is a flat board, often made from plywood, with slots cut or burned in the same shape as the knives that are used. The knives are set into the slots and covered in a compressible material, typically foam rubber, which ejects the cut puzzle pieces. The cutting process is similar to making shaped cookies with a cookie cutter. However, the forces involved are tremendously greater: A typical 1000-piece puzzle requires upwards of 700 tons of force to push the die through the board. Beginning in the 1930s, jigsaw puzzles were cut using large hydraulic presses that now cost hundreds of thousands of dollars. The precise cuts gave a snug fit, but the cost limited jigsaw puzzle production to large corporations. Recent roller-press methods achieve the same results at a lower cost.[citation needed] New technology has also enabled laser-cutting of wooden or acrylic jigsaw puzzles. The advantage is that the puzzle can be custom-cut to any size or shape, with any number or average size of pieces. Many museums have laser-cut acrylic puzzles made of some of their art so visiting children can assemble puzzles of the images on display. Acrylic pieces are very durable, waterproof, and can withstand continued use without the image degrading. Also, because the print and cut patterns are computer-based, missing pieces can easily be remade. By the early 1960s, Tower Press was the world's largest jigsaw puzzle maker; it was acquired by Waddingtons in 1969.[9] Numerous smaller-scale puzzle makers work in artisanal styles, handcrafting and handcutting their creations.[10][11][12][13] Variations Jigsaw puzzle software allowing rotation of pieces A three-dimensional puzzle composed of several two-dimensional puzzles stacked on top of one another A puzzle without a picture Jigsaw puzzles come in a variety of sizes. Among those marketed to adults, 300-, 500- and 750-piece puzzles are considered "smaller". More sophisticated, but still common, puzzles come in sizes of 1,000, 1,500, 2,000, 3,000, 4,000, 5,000, 6,000, 7,500, 8,000, 9,000, 13,200, 18,000, 24,000, 32,000 and 40,000 pieces. Jigsaw puzzles geared towards children typically have many fewer pieces and are typically much larger. For very young children, puzzles with as few as 4 to 9 large pieces (so as not to be a choking hazard) are standard. They are usually made of wood or plastic for durability and can be cleaned without damage. The most common layout for a thousand-piece puzzle is 38 pieces by 27 pieces, for an actual total of 1,026 pieces. Most 500-piece puzzles are 27 pieces by 19 pieces. A few puzzles are double-sided so they can be solved from either side—adding complexity, as the enthusiast must determine if they are looking at the right side of each piece. "Family puzzles" of 100–550 pieces use an assortment of small, medium and large pieces, with each size going in one direction or towards the middle of the puzzle. This allows a family of different skill levels and hand sizes to work on the puzzle together. Companies like Springbok, Cobble Hill, Ceaco, Buffalo Games and Suns Out make this type of specialty puzzle. Ravensburger, on the other hand, formerly made this type of puzzle from 2000 until 2008. There are also three-dimensional jigsaw puzzles. Many are made of wood or styrofoam and require the puzzle to be solved in a particular order, as some pieces will not fit if others are already in place. One type of 3-D jigsaw puzzle is a puzzle globe, often made of plastic. Like 2-D puzzles, the assembled pieces form a single layer, but the final form is three-dimensional. Most globe puzzles have designs representing spherical shapes such as the Earth, the Moon, and historical globes of the Earth. Also common are puzzle boxes, simple three-dimensional puzzles with a small drawer or box in the center for storage. Jigsaw puzzles can vary significantly in price depending on their complexity, number of pieces, and brand. In the US, children's puzzles can start around $5, while larger ones can be closer to $50. The most expensive puzzle to date was sold for $US27,000 in 2005 at a charity auction for The Golden Retriever Foundation.[14] Several word-puzzle games use pieces similar to those in jigsaw puzzles. Examples include Alfa-Lek, Jigsaw Words, Nab-It!, Puzzlage, Typ-Dom, Word Jigsaw, and Yottsugo.[15][citation needed] Puzzle pieces A "whimsy" piece in a wooden jigsaw puzzle A 3D jigsaw puzzle Many puzzles are termed "fully interlocking", which means that adjacent pieces are connected so that they stay attached when one is turned. Sometimes the connection is tight enough to pick up a solved part by holding one piece. Some fully interlocking puzzles have pieces of a similar shape, with rounded tabs (interjambs) on opposite ends and corresponding indentations—called blanks—on the other two sides to receive the tabs. Other fully interlocking puzzles may have tabs and blanks variously arranged on each piece; but they usually have four sides, and the numbers of tabs and blanks thus add up to four. Uniformly shaped fully interlocking puzzles, sometimes called "Japanese Style", are the most difficult because the differences in the pieces' shapes are most subtle.[citation needed] Most jigsaw puzzles are square, rectangular or round, with edge pieces with one straight or smoothly curved side, plus four corner pieces (if the puzzle is square or rectangular). However, some puzzles have edge, and corner pieces cut like the rest, with no straight sides, making it more challenging to identify them. Other puzzles utilize more complex edge pieces to form unique shapes when assembled, such as profiles of animals. The pieces of spherical jigsaw, like immersive panorama jigsaw, can be triangular-shaped, according to the rules of tessellation of the geoid primitive. Designer Yuu Asaka created "Jigsaw Puzzle 29". Instead of four corner pieces, it has five. The puzzle is made from pale blue acrylic without a picture.[16] It was awarded the Jury Honorable Mention of 2018 Puzzle Design Competition.[17] Because many puzzlers had solved it easily, he created "Jigsaw Puzzle 19" which composed only with corner pieces as revenge.[18] It was made with transparent green acrylic pieces without a picture.[19] Calculating the number of edge pieces Jigsaw puzzlers often want to know in advance how many border pieces they are looking for to verify they have found all of them. Puzzle sizes are typically listed on commercially distributed puzzles but usually include the total number of pieces in the puzzle and do not list the count of edge or interior pieces. Puzzlers, therefore, calculate the number of border pieces. To calculate B (border pieces) from P (the total piece count), follow this method:     List the prime factors of P.         For a 513-piece jigsaw, the prime factorization tree is 3×3×3×19=513     Take the square root of P and round off.         √513 ≈ 22.6         round to 23     Look for numbers in the prime factor list within ±20% of the square root of P.         Calculate 20% of the rounded square root of P.             1⁄5 × 23 = 4.6         Develop the range, ±20%, from the rounded square root of P.             23 ±4.6 = 18.4 to 27.6         Compare the range with the factor list. Define this as E1.             The factor list shows 19 in the range.     Determine the horizontal / vertical dimensions.         Divide P (the total number of pieces) by E1 to determine the horizontal / vertical dimensions, E1xE2.             513 / 19 = 27             This is probably a 19×27 puzzle.         Alternative method: take the remaining numbers from the prime factorization tree.             3x3x3 = 27     Add the four sides and subtract 4 to correct for the corner pieces, which would otherwise be counted in both the horizontal and vertical.         (27 × 2)+(19 × 2)-4 = 88 These 88 border pieces include 4 corners, 17 pieces between corners on the short sides, and 25 between corners on the long sides. Common puzzle dimensions:     1000 piece puzzle: 1026 pieces, 126 border pieces (38x27)[20] World records Largest commercially available jigsaw puzzles Pieces     Name of puzzle     Company     Year     Size [cm]     Area [m2] 60,000     What A Wonderful World     Dowdle Folk Art     2022     883 × 243     21.46 54,000     Travel around Art     Grafika     2020     864 × 204     17.63 52,110     (No title: collage of animals)     MartinPuzzle     2018     696 × 202     14.06 51,300     27 Wonders from Around the World     Kodak     2019     869 × 191     16.60 48,000     Around the World     Grafika     2017     768 × 204     15.67 42,000     La vuelta al Mundo     Educa Borras     2017     749 × 157     11.76 40,320     Making Mickey's Magic     Ravensburger     2018     680 × 192     13.06 40,320     Memorable Disney Moments     Ravensburger     2016     680 × 192     13.06 33,600     Wild Life     Educa Borras     2014     570 × 157     8.95 32,000     New York City Window     Ravensburger     2014     544 × 192     10.45 32,000     Double Retrospect     Ravensburger     2010     544 × 192     10.45 24,000     Life, The greatest puzzle     Educa Borras     2007     428 × 157     6.72 Largest-sized jigsaw puzzles The world's largest-sized jigsaw puzzle measured 5,428.8 m2 (58,435 sq ft) with 21,600 pieces, each measuring a Guinness World Records maximum size of 50 cm by 50 cm. It was assembled on 3 November 2002 by 777 people at the former Kai Tak Airport in Hong Kong.[21] Largest jigsaw puzzle – most pieces The Guinness record of CYM Group in 2011 with 551,232 pieces The jigsaw with the greatest number of pieces had 551,232 pieces and measured 14.85 × 23.20 m (48 ft 8.64 in × 76 ft 1.38 in). It was assembled on 25 September 2011 at Phú Thọ Indoor Stadium in Ho Chi Minh City, Vietnam, by students of the University of Economics, Ho Chi Minh City. It is listed by the Guinness World Records for the "Largest Jigsaw Puzzle – most pieces", but as the intact jigsaw had been divided into 3,132 sections, each containing 176 pieces, which were reassembled and then connected, the claim is controversial.[22][23] Society The logo of Wikipedia is a globe made out of jigsaw pieces. The incomplete sphere symbolizes the room to add new knowledge.[citation needed] In the logo of the Colombian Office of the Attorney General appears a jigsaw puzzle piece in the foreground. They named it "The Key Piece": "The piece of a puzzle is the proper symbol to visually represent the Office of the Attorney General because it includes the concepts of search, solution and answers that the entity pursues through the investigative activity."[24] Art and entertainment The central antagonist in the Saw film franchise is nicknamed Jigsaw,[25] due to his practice of cutting the shape of a puzzle piece from the remains of his victims. In the 1933 Laurel and Hardy short Me and My Pal, several characters attempt to complete a large jigsaw puzzle.[26] Lost in Translation is a poem about a child putting together a jigsaw puzzle, as well as an interpretive puzzle itself. Life: A User's Manual, Georges Perec's most famous novel, tells as pieces of a puzzle a story about a jigsaw puzzle maker. Jigsaw Puzzle (song), sometimes spelled "Jig-Saw Puzzle" is a song by the rock and roll band The Rolling Stones, featured on their 1968 album Beggars Banquet. In ‘‘Citizen Kane‘’ Susan Alexander Kane (Dorothy Comingore) is reduced to spending her days completing jigsaws after the failure of her operatic career. After Kane’s death when ‘’Xanadu’’ is emptied, hundreds of jigsaw puzzles are discovered in the cellar. Rhett And Link Do A Rainy Day Jigsaw Puzzle is a short video by self-described “internetainers” (portmanteau of “Internet” and “entertainers”) Rhett & Link which portrays the frustration of discovering a puzzle piece is missing. Mental health According to the Alzheimer Society of Canada, doing jigsaw puzzles is one of many activities that can help keep the brain active and may reduce the risk of Alzheimer's disease.[27] An "autism awareness" ribbon, featuring red, blue, and yellow jigsaw pieces Jigsaw puzzle pieces were first used as a symbol for autism in 1963 by the United Kingdom's National Autistic Society.[28] The organization chose jigsaw pieces for their logo to represent the "puzzling" nature of autism and the inability to "fit in" due to social differences, and also because jigsaw pieces were recognizable and otherwise unused.[29] Puzzle pieces have since been incorporated into the logos and promotional materials of many organizations, including the Autism Society of America and Autism Speaks. Proponents of the autism rights movement oppose the jigsaw puzzle iconography, stating that metaphors such as "puzzling" and "incomplete" are harmful to autistic people. Critics of the puzzle piece symbol instead advocate for a gold-colored or red infinity symbol representing diversity.[30] In 2017, the journal Autism concluded that the use of the jigsaw puzzle evoked negative public perception towards autistic individuals. They removed the puzzle piece from their cover in February 2018." (wikipedia.org)
  • Condition: New
  • Brand: Discovery
  • Year: 2020
  • Number of Pieces: 26 - 99 Pieces
  • Color: Multi-Color
  • Theme: Space
  • Features: Complete, Never Worked, Lenticular, STEM Activity
  • Material: Cardboard
  • Country/Region of Manufacture: China

PicClick Insights - NASA ASTRONAUT LENTICULAR 3D PUZZLE 50pc Last Man on Moon Apollo 17 Cernan space PicClick Exclusive

  •  Popularity - 12 watchers, 0.0 new watchers per day, 337 days for sale on eBay. Super high amount watching. 4 sold, 2 available.
  •  Best Price -
  •  Seller - 1,180+ items sold. 0% negative feedback. Great seller with very good positive feedback and over 50 ratings.

People Also Loved PicClick Exclusive