Astronaut
An astronaut or cosmonaut is a person trained by a human spaceflight program to command, pilot, or serve as a crew member of a spacecraft. Although reserved for professional space travelers, the terms are sometimes applied to anyone who travels into space, including scientists, politicians and tourists; until 2002, astronauts were sponsored and trained by governments, either by the military or by civilian space agencies. With the suborbital flight of the funded SpaceShipOne in 2004, a new category of astronaut was created: the commercial astronaut; the criteria for what constitutes human spaceflight vary. The Fédération Aéronautique Internationale Sporting Code for astronautics recognizes only flights that exceed an altitude of 100 kilometers. In the United States, professional and commercial astronauts who travel above an altitude of 50 miles are awarded astronaut wings; as of 17 November 2016, a total of 552 people from 36 countries have reached 100 km or more in altitude, of which 549 reached low Earth orbit or beyond.
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. Three of the 24–Jim Lovell, John Young and Eugene Cernan–did so twice; the three current astronauts who have flown without reaching low Earth orbit are spaceplane pilots Joe Walker, Mike Melvill, Brian Binnie, who participated in suborbital missions. As of 17 November 2016, under the U. S. definition, 558 people qualify as having reached space, above 50 miles altitude. Of eight X-15 pilots who exceeded 50 miles in altitude, only one exceeded 100 kilometers. Space travelers have spent over 41,790 man-days in space, including over 100 astronaut-days of spacewalks; as of 2016, the man with the longest cumulative time in space is Gennady Padalka, who has spent 879 days in space. Peggy A. Whitson holds the record for the most time in space by 377 days. 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, Dr. Hugh Dryden, discussed whether spacecraft crew members should be called astronauts or cosmonauts.
Dryden preferred "cosmonaut", on the grounds that flights would occur in the cosmos, while the "astro" prefix suggested flight to the stars. Most NASA Space Task Group members preferred "astronaut", which survived by common usage as the preferred American term; when the Soviet Union launched the first man into space, Yuri Gagarin in 1961, they chose a term which anglicizes to "cosmonaut". In English-speaking nations, a professional space traveler is called an astronaut; the term derives from the Greek words ástron, meaning "star", nautes, meaning "sailor". 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. In Les Navigateurs de l'Infini by J.-H. Rosny aîné, the word astronautique 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.
The first known formal use of the term astronautics in the scientific community was the establishment of the annual International Astronautical Congress in 1950, the subsequent founding of the International Astronautical Federation the following year. NASA applies the term astronaut to any crew member aboard NASA spacecraft bound for Earth orbit or beyond. NASA uses the term as a title for those selected to join its Astronaut Corps; the European Space Agency uses the term astronaut for members of its Astronaut Corps. By convention, an astronaut employed by the Russian Federal Space Agency is called a cosmonaut in English texts; the word is an anglicisation of the Russian word kosmonavt, one who works in space outside the Earth's atmosphere, a space traveler, which derives from the Greek words kosmos, meaning "universe", nautes, meaning "sailor". Other countries of the former Eastern Bloc use variations of the Russian word kosmonavt, such as the Polish kosmonauta. Coinage of the term kosmonavt has been credited to Soviet aeronautics pioneer Mikhail Tikhonravov.
The first cosmonaut was Soviet Air Force pilot Yuri Gagarin the first person in space. Valentina Tereshkova, a Russian factory worker, was the first woman in space, as well as the first civilian among the Soviet cosmonaut or NASA astronaut corps to make a spaceflight. On March 14, 1995, Norman Thagard became the first American to ride to space on board a Russian launch vehicle, thus became the first "American cosmonaut". "Yǔ háng yuán" is used for astronauts and cosmonauts in general, while "Hángtiān yuán" is used for Chinese astronauts. Here, "Hángtiān" is defined as the navigation of outer space within the local star system, i.e. solar system. The phrase "tài kōng rén" is used in Hong Kong and Taiwan; the term taikonaut is used by some English-language news media organizations for professional space travelers from China. The word has featured in the Longman and Oxford English dictionaries, the latter of which desc
Expedition 2
Expedition 2 was the second long-duration spaceflight aboard the International Space Station following Expedition 1. Its three-person crew stayed aboard the station from March to August 2001. In addition to station maintenance, the crew assisted in several station assembly missions, welcomed the first space tourist Dennis Tito, conducted some scientific experiments; the crew consisted of one Russian, Commander Yury Usachev, two American flight engineers Susan Helms and James Voss. The three had been to the station in the previous year, during the 10-day mission STS-101 in May 2000; the Expedition 2 crew was brought to the station aboard Space Shuttle Discovery during mission STS-102. The Expedition's increment began when Discovery docked on 10 March 2001, bringing Expedition 1 to an end. In addition to the Space Shuttle flights which brought the crew to and from the station, there were two visiting Space Shuttle missions and one Soyuz mission which docked with the ISS during Expedition Two. In August Discovery returned to rotate the long-duration crews again, bringing the crew of the next expedition.
The Expedition 2 increment ended when Discovery undocked from the station on 20 August 2001. All three crew members had visited the International Space Station together in May 2000 aboard STS-101. In addition to this spaceflight, the Expedition 2 Commander Yuri Usachev had two other spaceflights, both of which were long-duration missions aboard Mir. In addition to STS-101, flight engineer Susan Helms had three other spaceflights, all of which were Space Shuttle missions. James Voss had three other spaceflights, all of which were Space Shuttle missions. Expedition 2, the second long-term crew for the International Space Station arrived in March 2001, they returned to Earth on mission STS-105, 22 August 2001 after having spent 163 days aboard the station and 167 days in space. Only Voss performed a spacewalk on STS-101, along with Jeffrey Williams. During this expedition, research facilities launched to the Space Station included a Human Research Facility, two EXPRESS Racks, one of which contains the Active Rack Isolation System and the Payload Equipment Restraint System.
They prepared the Destiny laboratory to enable upcoming experiments to be conducted. A major focus was on gaining a better understanding of how to protect crew members from radiation while working and living in space. Radiation exposure in high doses over long periods of time can damage human cells and cause cancer or injury to the central nervous system; the three-member Expedition 2 crew launched on 8 March 2001 on Space Shuttle Discovery during mission STS-102. They docked with the International Space Station on 10 March, but the Expedition 2 increment didn't begin until the previous crew undocked from the station on 18 March; the first visitors to the station during Expedition 2 was the crew of STS-100, when they docked Space Shuttle Endeavour with the ISS on 21 April 2001. They spent eight days docked to the station; the primary objective of this mission was to deliver and install the Canadarm2 on the ISS, a robotic arm similar to the Canadarm, used on some Space Shuttle flights. A mission in 2002, STS-111, would deliver a movable base platform which would allow the Canadarm2 to have a larger range.
On the day after the Space Shuttle undocked, the Russian spacecraft Soyuz TM-32 docked to the station, carrying two cosmonauts with previous spaceflight experience, as well as Dennis Tito, the first space tourist. This 8 day mission is sometimes referred to as ISS EP-1, ISS-2S, Soyuz 2 Taxi Flight, or by its launching spacecraft Soyuz TM-32; the Commander of this visiting mission was Kazakh cosmonaut Talgat Musabayev, on two long-duration missions aboard the space station Mir in the 1990s. The other crew member of ISS EP-1 was Yuri Baturin, who had one other spaceflight, Mir EP-4, a visiting mission to Mir launched with the spacecraft Soyuz TM-28. Baturin's first mission occurred during the long-duration mission Mir EO-25, so he and Musabayev had been in space together prior to ISS EP-1. In July, Space Shuttle Atlantis docked with the station for an eight-day visit as a part of STS-104; the main objective of this mission was to install the Quest Joint Airlock onto the station. The STS-104 crew performed 3 spacewalks.
First spacewalk. The spacewalkers helped as Susan Helms, using the station's robotic arm, lifted the new station airlock from Atlantis' payload bay and moved it to the station's Unity module. During much of the 5 hour, 59 minute spacewalk, Jim Reilly worked from a foot platform attached to the end of the shuttle's robotic arm, operated by Janet Kavandi. After the spacewalk, crew members inside the Station attached connections to the airlock to prevent thermal damage. Second spacewalkThe second spacewalk which happened on 18 July, lasted 6 hours, 29 minutes; the internal hatches between the shuttle and station were closed at the end of Flight Day 6 so Atlantis' cabin pressure could be lowered in preparation for the second spacewalk. The major objective was to connect an oxygen and a nitrogen tank. Susan Helms operated the station arm to lift the tanks from the shuttle's payload bay and maneuver them to the new airlock. At the airlock, Mike Gernhardt and Jim Reilly latched the tanks in place and connected cables and hoses.
The spacewalkers were able to get ahead of schedule and install another oxygen tank, leaving only one tank
Expedition 8
Expedition 8 was the eighth expedition to the International Space Station. Perigee: 384 km Apogee: 396 km Inclination: 51.6° Period: 92 min Docked: 20 October 2003 - 07:15:58 UTC Undocked: 29 April 2004 - 20:52:09 UTC Time Docked: 192 days, 13 h, 36 min, 11 s Expedition 8 Commander and NASA Station Science Officer Michael Foale, Flight Engineer Alexander Kaleri and ESA Astronaut Pedro Duque docked the Soyuz TMA-3 with the International Space Station at 07:15:58 UTC on 20 October 2003. At the time of docking, both spacecraft orbited the Earth above Russia. Once the Expedition 7 crew undocked and Kaleri settled down to work, beginning a more than six-month stint focused on Station operations and maintenance; the new station crew, along with Duque, launched from the Baikonur Cosmodrome in Kazakhstan at 05:38:03 UTC, on 18 October 2003. Foale and Kaleri departed the station for earth aboard the Soyuz TMA-3 spacecraft on 29 April 2004 along with ESA Astronaut André Kuipers, who had arrived with the Expedition 9 crew aboard Soyuz TMA-4 nine days earlier.
The Expedition 8 crew conducted the first two-person spacewalk at the International Space Station. Unlike previous spacewalks conducted by ISS crews, there was not a crewmember inside the Station as the spacewalkers worked outside; the spacewalk was based out of the Pirs docking compartment. This was the 52nd spacewalk devoted to Space Station assembly and maintenance, bringing the cumulative total to 322 hours and 32 minutes, it was the 27th based out of the Station, bringing the total to 17 minutes. This article incorporates public domain material from websites or documents of the National Aeronautics and Space Administration. Expedition 8 Photography
Apsis
The term apsis refers to an extreme point in the orbit of an object. It denotes either the respective distance of the bodies; the word comes via Latin from Greek, there denoting a whole orbit, is cognate with apse. Except for the theoretical possibility of one common circular orbit for two bodies of equal mass at diametral positions, there are two apsides for any elliptic orbit, named with the prefixes peri- and ap-/apo-, added in reference to the body being orbited. All periodic orbits are, according to Newton's Laws of motion, ellipses: either the two individual ellipses of both bodies, with the center of mass of this two-body system at the one common focus of the ellipses, or the orbital ellipses, with one body taken as fixed at one focus, the other body orbiting this focus. All these ellipses share a straight line, the line of apsides, that contains their major axes, the foci, the vertices, thus the periapsis and the apoapsis; the major axis of the orbital ellipse is the distance of the apsides, when taken as points on the orbit, or their sum, when taken as distances.
The major axes of the individual ellipses around the barycenter the contributions to the major axis of the orbital ellipses are inverse proportional to the masses of the bodies, i.e. a bigger mass implies a smaller axis/contribution. Only when one mass is sufficiently larger than the other, the individual ellipse of the smaller body around the barycenter comprises the individual ellipse of the larger body as shown in the second figure. For remarkable asymmetry, the barycenter of the two bodies may lie well within the bigger body, e.g. the Earth–Moon barycenter is about 75% of the way from Earth's center to its surface. If the smaller mass is negligible compared to the larger the orbital parameters are independent of the smaller mass. For general orbits, the terms periapsis and apoapsis are used. Pericenter and apocenter are equivalent alternatives, referring explicitly to the respective points on the orbits, whereas periapsis and apoapsis may refer to the smallest and largest distances of the orbiter and its host.
For a body orbiting the Sun, the point of least distance is the perihelion, the point of greatest distance is the aphelion. The terms become apastron when discussing orbits around other stars. For any satellite of Earth, including the Moon, the point of least distance is the perigee and greatest distance the apogee, from Ancient Greek Γῆ, "land" or "earth". For objects in lunar orbit, the point of least distance is sometimes called the pericynthion and the greatest distance the apocynthion. Perilune and apolune are used. In orbital mechanics, the apsides technically refer to the distance measured between the barycenters of the central body and orbiting body. However, in the case of a spacecraft, the terms are used to refer to the orbital altitude of the spacecraft above the surface of the central body; these formulae characterize the pericenter and apocenter of an orbit: Pericenter Maximum speed, v per = μ a, at minimum distance, r per = a. Apocenter Minimum speed, v ap = μ a, at maximum distance, r ap = a.
While, in accordance with Kepler's laws of planetary motion and the conservation of energy, these two quantities are constant for a given orbit: Specific relative angular momentum h = μ a Specific orbital energy ε = − μ 2 a where: a is the semi-major axis: a = r per + r ap 2 μ is the standard gravitational parameter e is the eccentricity, defined as e = r ap − r per r ap + r per = 1 − 2 r ap r per + 1 Note t
NASA
The National Aeronautics and Space Administration is an independent agency of the United States Federal Government responsible for the civilian space program, as well as aeronautics and aerospace research. NASA was established in 1958; the new agency was to have a distinctly civilian orientation, encouraging peaceful applications in space science. Since its establishment, most US space exploration efforts have been led by NASA, including the Apollo Moon landing missions, the Skylab space station, the Space Shuttle. NASA is supporting the International Space Station and is overseeing the development of the Orion Multi-Purpose Crew Vehicle, the Space Launch System and Commercial Crew vehicles; the agency is responsible for the Launch Services Program which provides oversight of launch operations and countdown management for unmanned NASA launches. NASA science is focused on better understanding Earth through the Earth Observing System. From 1946, the National Advisory Committee for Aeronautics had been experimenting with rocket planes such as the supersonic Bell X-1.
In the early 1950s, there was challenge to launch an artificial satellite for the International Geophysical Year. An effort for this was the American Project Vanguard. After the Soviet launch of the world's first artificial satellite 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, urged immediate and swift action. On January 12, 1958, NACA organized a "Special Committee on Space Technology", headed by Guyford Stever. On January 14, 1958, NACA Director Hugh Dryden published "A National Research Program for Space Technology" stating: 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 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. While this new federal agency would conduct all non-military space activity, the Advanced Research Projects Agency was created in February 1958 to develop space technology for military application. On July 29, 1958, Eisenhower signed the National Aeronautics and Space Act, establishing NASA; when it began operations on October 1, 1958, NASA absorbed the 43-year-old NACA intact. A NASA seal was approved by President Eisenhower in 1959. 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, now working for the Army Ballistic Missile Agency, which in turn incorporated the technology of American scientist Robert Goddard's earlier works. Earlier research efforts within the US Air Force and many of ARPA's early space programs were transferred to NASA.
In December 1958, NASA gained control of the Jet Propulsion Laboratory, a contractor facility operated by the California Institute of Technology. The agency's leader, NASA's administrator, is nominated by the President of the United States subject to approval of the US Senate, reports to him or her and serves as senior space science advisor. Though space exploration is ostensibly non-partisan, the appointee is associated with the President's political party, a new administrator is chosen when the Presidency changes parties; the only exceptions to this have been: Democrat Thomas O. Paine, acting administrator under Democrat Lyndon B. Johnson, stayed on while Republican Richard Nixon tried but failed to get one of his own choices to accept the job. Paine was confirmed by the Senate in March 1969 and served through September 1970. Republican James C. Fletcher, appointed by Nixon and confirmed in April 1971, stayed through May 1977 into the term of Democrat Jimmy Carter. Daniel Goldin was appointed by Republican George H. W. Bush and stayed through the entire administration of Democrat Bill Clinton.
Robert M. Lightfoot, Jr. associate administrator under Democrat Barack Obama, was kept on as acting administrator by Republican Donald Trump until Trump's own choice Jim Bridenstine, was confirmed in April 2018. Though the agency is independent, the survival or discontinuation of projects can depend directly on the will of the President; the first administrator was Dr. T. Keith Glennan appointed by Republican President Dwight D. Eisenhower. During his term he brought together the disparate projects in American space development research; the second administrator, James E. Webb, appointed by President John F. Kennedy, was a Democrat who first publicly served under President Harry S. Truman. In order to implement the Apollo program to achieve Kennedy's Moon la
Yuri Malenchenko
Yuri Ivanovich Malenchenko is a retired Russian cosmonaut. Malenchenko became the first person to marry in space, on 10 August 2003, when he married Ekaterina Dmitrieva, in Texas, while he was 240 miles over New Zealand, on the International Space Station; as of June 2016, Malenchenko ranks second for career time in space due to his time on both Mir and the International Space Station. He is a former Commander of the International Space Station. Malenchenko was born in Khrushchev, Kirovohrad Oblast, Ukrainian SSR, he and his wife Ekaterina Dmitrieva have one child. Malenchenko graduated from the Kharkiv Military Aviation School in 1983, attended the Zhukovsky Air Force Engineering Academy, graduating in 1993. Malenchenko was awarded: Hero of the Russian Federation, the National Hero of Kazakhstan medal, Military award of excellence, Commendation medal, Achievement medal, Jubilee Medal "70 Years of the Armed Forces of the USSR" Meritorious Service Medals 1st, 2nd and 3rd class. After graduation from the Military Aviation School, he served as a pilot, senior pilot and multi-ship flight lead from 1983 till 1987 in the Odessa Region.
In 1987 he was selected as a cosmonaut, arrived at the Gagarin Cosmonaut Training Center. From December 1987 to June 1989 Malenchenko underwent a course of general space training. After completion of the course, he was qualified as a test-cosmonaut. Between September 1989 to December 1993 he was taking advanced training courses in preparation for spaceflight. In January–July, 1993 Malenchenko trained as commander of the Mir-14 reserve crew, he completed training as a backup commander of the Mir-15 crew from July 1993 to January 1994. From February to June 1994 Malenchenko trained for the Mir-16 mission. On July 1, 1994, Malenchenko and Talgat Musabayev lifted off to space on board the Soyuz TM-19 spacecraft with Malenchenko in command of the Soyuz. Following a two-day solo flight the Soyuz docked with Mir on July 3, 1994. Main goal of the mission was the exchange of the resident crew. Malenchenko and cosmonaut Valeri Polyakov became the 16th resident Mir crew, with Malenchenko in command; the crew conducted medical experiments in materials science.
There were many problems during the mission, which ended with the first successful manual docking of a Progress supply ship at Mir by Malenchenko. On November 4, 1994, Malenchenko and Ulf Merbold returned to Earth aboard their Soyuz capsule after landing 88 km northeast of Arkalyk. Aboard Soyuz TM-19 and Mir complex Malenchenko spent 22 hours, 53 minutes in space. Malenchenko served as a mission specialist for STS-106. Space Shuttle Atlantis lifted off from the Kennedy Space Center on September 8, 2000. On flight day two, Atlantis completed a successful rendezvous and docking with the ISS; the objectives of the mission were to bring supplies to the International Space Station and to prepare the Zvezda Service Module for the arrival of the first resident crew. During the 12-day mission, the shuttle crew spent a week inside the ISS unloading supplies from both a double SPACEHAB cargo module in the rear of Atlantis's cargo bay and from Progress M1-3, docked to the aft docking port of Zvezda. After circling the globe for 186 orbits, Atlantis landed on September 19, 2000, at Runway 15, KSC.
The mission lasted 19 hours and 12 minutes. Malenchenko with astronaut Edward Lu lifted on board the Soyuz TMA-2 spacecraft from the Baikonur Cosmodrome on April 26, 2003, to the ISS; the spacecraft docked with the ISS on April 28, 2003. Malenchenko served as the Soyuz commander, after docking with the ISS they exchanged with the resident crew on board ISS and became the seventh station crew, Expedition 7, he was the commander of the Expedition 7, during his stay on the station, Malenchenko became the first person to get married in space. Soyuz TMA-2 returned to Earth on October 28, with both the Expedition 7 crew as well as Pedro Duque on board; the spacecraft landed at 02:40 UTC near Arkalyk. Aboard Soyuz TMA-2 and the ISS, Malenchenko spent 22 hours and 46 minutes in space. Malenchenko with NASA astronaut Peggy Whitson and Malaysian spaceflight participant Sheikh Muszaphar Shukor blasted off to space on October 10, 2007, on Soyuz TMA-11 from the Baikonour Cosmodrome, he served as the Soyuz commander.
The Soyuz spacecraft docked with the ISS after 2 days of autonomous flight on October 12, 2007. Malenchenko joined the ISS Expedition 16 crew as Flight Engineer 1; the Soyuz capsule landed in Kazakhstan on April 19, 2008, bringing back Malenchenko and South Korean spaceflight participant Yi So-Yeon. Similar to Soyuz TMA-1 and Soyuz TMA-10, Soyuz TMA-11 performed a ballistic reentry, a reentry steeper than a normal reentry, due to a malfunction and landed 475 km from intended landing point, north of Arkalyk. Although the crew were recovered with no injuries, the spacecraft's hatch and antenna suffered burn damage during the unusual reentry, he accumulated 191 days, 19 hours and 8 minutes time in space during Soyuz TMA-11 and ISS Expedition 16 missions. Malenchenko conducted his second career spacewalks during the Mir-16 mission, he and Musabayev performed two spacewalks on September 9, 1994 and September 14, 1994, in which the station's external insulation was repaired. The first and second spacewalks lasted 5 hours and 6 minutes, 6 hours and 1 minute respectively.
Malenchenko performed his third career spacewalk during the STS-106 mission to the ISS. On flight day three, Malenchenko and NASA astronaut Ed Lu conducted a 6-hour and 14 minute space walk; the spacewalk started at 04:55 GMT on September 11 when the two spacewalkers exited the shuttle's airlock. The spacewalk's objective focused on routing and connecting
Expedition 5
Expedition 5 was the fifth long-duration stay on the International Space Station. The crew, consisting of three people, remained in space for 184 days, 178 of which were spent aboard the ISS. Expedition 5 was a continuation of an uninterrupted human presence in space, as of January 2019, begun by Expedition 1 in 2000-2001; the crew of Expedition 5 launched to space aboard the Space Shuttle Endeavour aboard the STS-111 mission on 5 June 2002. Their tenure aboard the station, did not occur until they docked with the ISS two days on 7 June. Perigee: 384 km Apogee: 396 km Inclination: 51.6° Period: 92 min The Expedition Five crew took charge of ISS operations on 7 June 2002. An official ceremony between Expedition crews took place 10 June, with the ceremonial ringing of the station's brass bell, symbolizing the transfer of command; the Expedition Five crew carried out 25 new investigations on board the ISS, as well as continued with various science investigations begun before their stay. The crew wrapped up a 184-day stay in space when they returned home on STS-113 7 December 2002.
Space Shuttle Endeavour delivered the Expedition 5 crew during mission STS-111 which launched 5 June 2002. The fifth crew to live aboard the International Space Station was led by Russian Valery Korzun and joined by fellow Cosmonaut Sergei Treshchev and U. S. Astronaut Peggy A. Whitson, both flight engineers. While on board, Dr. Whitson was named NASA's first ISS Science Officer by NASA Administrator O'Keefe; the Expedition Five crewmembers conducted two spacewalks during their stay at the International Space Station. Both were used Russian Orlan space suits; this article incorporates public domain material from websites or documents of the National Aeronautics and Space Administration. Expedition 5 Photography ISS Expedition Five Crew
This article incorporates public domain material from websites or documents of the National Aeronautics and Space Administration.
