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Human spaceflight (also referred to ascrewed spaceflight, or more historicallymanned spaceflight) isspaceflight with a crew or passengers aboard aspacecraft, often with the spacecraft being operated directly by the onboard human crew. Spacecraft can also beremotely operated from ground stations on Earth, orautonomously, without any direct human involvement. People trained for spaceflight are calledastronauts (American or other),cosmonauts (Russian), ortaikonauts (Chinese); and non-professionals are referred to asspaceflight participants orspacefarers.[1]
The first human in space wasSoviet cosmonautYuri Gagarin, who launched as part of the Soviet Union'sVostok program on12 April 1961 at the beginning of theSpace Race. On 5 May 1961,Alan Shepard became the first American in space, as part ofProject Mercury. Humans traveled tothe Moon nine times between 1968 and 1972 as part of the United States'Apollo program, and have had a continuous presence in space for 25 years and 21 days on theInternational Space Station (ISS).[2] On 15 October 2003, the first Chinese taikonaut,Yang Liwei, went to space as part ofShenzhou 5, the first Chinese human spaceflight. As of March 2025, humans have not traveled beyondlow Earth orbit since theApollo 17lunar mission in December 1972.
Currently, theUnited States, Russia, and China are the only countries withpublic or commercial human spaceflight-capable programs.Non-governmental spaceflight companies have been working to develop human space programs of their own, e.g. forspace tourism or commercialin-space research. The first private human spaceflight launch was asuborbital flight onSpaceShipOne on June 21, 2004. The first commercialorbital crew launch was bySpaceX in May 2020, transportingNASA astronauts to theISS under United States government contract.[3]
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Human spaceflight capability was first developed during theCold War between the United States and the Soviet Union (USSR). These nations developedintercontinental ballistic missiles for the delivery ofnuclear weapons, producing rockets large enough to be adapted to carry the firstartificial satellites intolow Earth orbit.
After the first satellites were launched in 1957 and 1958 by the Soviet Union, the US began work onProject Mercury, with the aim of launching men into orbit. The USSR was secretly pursuing theVostok program to accomplish the same thing, and launched the first human into space, the cosmonautYuri Gagarin. On 12 April 1961, Gagarin was launched aboardVostok 1 on aVostok 3KA rocket and completed a single orbit. On 5 May 1961, the US launched its firstastronaut,Alan Shepard, on a suborbital flight aboardFreedom 7 on aMercury-Redstone rocket. Unlike Gagarin, Shepard manuallycontrolled his spacecraft's attitude.[4] On 20 February 1962,John Glenn became the first American in orbit, aboardFriendship 7 on aMercury-Atlas rocket. The USSR launched five more cosmonauts in Vostokcapsules, including the first woman in space,Valentina Tereshkova, aboardVostok 6 on 16 June 1963. Through 1963, the US launched a total of two astronauts in suborbital flights and four into orbit. The US also made twoNorth American X-15 flights (90 and91, piloted byJoseph A. Walker), that exceeded theKármán line, the 100 kilometres (62 mi) altitude used by theFédération Aéronautique Internationale (FAI) to denote the edge of space.
In 1961, US PresidentJohn F. Kennedy raised the stakes of the Space Race by setting the goal of landing a man on theMoon and returning him safely to Earth by the end of the 1960s.[5] That same year, the US began theApollo program of launching three-man capsules atop theSaturn family of launch vehicles. In 1962, the US beganProject Gemini, which flew 10 missions with two-man crews launched byTitan II rockets in 1965 and 1966. Gemini's objective was to support Apollo by developing American orbital spaceflight experience and techniques to be used during the Moon mission.[6]
Meanwhile, the USSR remained silent about their intentions to send humans to the Moon and proceeded to stretch the limits of their single-pilot Vostok capsule by adapting it to a two or three-personVoskhod capsule to compete with Gemini. They were able to launch two orbital flights in 1964 and 1965 and achieved the firstspacewalk, performed byAlexei Leonov onVoskhod 2, on 8 March 1965. However, the Voskhod did not have Gemini's capability to maneuver in orbit, and the program was terminated. The US Gemini flights did not achieve the first spacewalk, but overcame the early Soviet lead by performing several spacewalks, solving the problem of astronaut fatigue caused by compensating for the lack of gravity, demonstrating the ability of humans to endure two weeks in space, and performing the firstspace rendezvous anddocking of spacecraft.
The US succeeded in developing theSaturn V rocket necessary to send the Apollo spacecraft to the Moon, and sentFrank Borman,James Lovell, andWilliam Anders into 10 orbits around the Moon inApollo 8 in December 1968. In 1969,Apollo 11 accomplished Kennedy's goal by landingNeil Armstrong andBuzz Aldrin on the Moon on 21 July and returning them safely on 24 July, along with Command Module pilotMichael Collins. Through 1972, a total of six Apollo missions landed 12 men to walk on the Moon, half of which droveelectric powered vehicles on the surface. The crew ofApollo 13—Jim Lovell,Jack Swigert, andFred Haise—survived an in-flight spacecraft failure, they flew by the Moon without landing, and returned safely to Earth.
During this time, the USSR secretly pursuedcrewed lunar orbiting and landing programs. They successfully developed the three-personSoyuz spacecraft for use in the lunar programs, but failed to develop theN1 rocket necessary for a human landing, and discontinued their lunar programs in 1974.[7] Upon losing the Moon race they concentrated on the development ofspace stations, using the Soyuz as a ferry to take cosmonauts to and from the stations. They started with a series ofSalyut sortie stations from 1971 to 1986.
In 1969, Nixon appointed his vice president,Spiro Agnew, to head a Space Task Group to recommend follow-on human spaceflight programs after Apollo. The group proposed an ambitiousSpace Transportation System based on areusable Space Shuttle, which consisted of a winged, internally fueled orbiter stage burning liquid hydrogen, launched with a similar, but largerkerosene-fueled booster stage, each equipped with airbreathing jet engines for powered return to a runway at theKennedy Space Center launch site. Other components of the system included a permanent, modular space station; reusablespace tug; andnuclear interplanetary ferry, leading to ahuman expedition to Mars as early as 1986 or as late as 2000, depending on the level of funding allocated. However, Nixon knew the American political climate would not support congressional funding for such an ambition, and killed proposals for all but the Shuttle, possibly to be followed by the space station.Plans for the Shuttle were scaled back to reduce development risk, cost, and time, replacing the piloted fly-back booster with two reusablesolid rocket boosters, and the smaller orbiter would use an expendableexternal propellant tank to feed its hydrogen-fueledmain engines. The orbiter would have to make unpowered landings.
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In 1973, the US launched theSkylab sortie space station and inhabited it for 171 days with three crews ferried aboard an Apollo spacecraft. During that time, PresidentRichard Nixon and Soviet general secretaryLeonid Brezhnev were negotiating an easing of Cold War tensions known asdétente. During the détente, they negotiated theApollo–Soyuz program, in which an Apollo spacecraft carrying a special docking adapter module would rendezvous and dock withSoyuz 19 in 1975. The American and Soviet crews shook hands in space, but the purpose of the flight was purely symbolic.
The two nations continued to compete rather than cooperate in space, as the US turned to developing the Space Shuttle and planning the space station, which was dubbedFreedom. The USSR launched threeAlmaz military sortie stations from 1973 to 1977, disguised as Salyuts. They followed Salyut with the development ofMir, the first modular, semi-permanent space station, the construction of which took place from 1986 to 1996.Mir orbited at an altitude of 354 kilometers (191 nautical miles), at anorbital inclination of 51.6°. It was occupied for 4,592 days and made a controlled reentry in 2001.
The Space Shuttle started flying in 1981, but the US Congress failed to approve sufficient funds to makeSpace Station Freedom a reality. A fleet of four shuttles was built:Columbia,Challenger,Discovery, andAtlantis. A fifth shuttle,Endeavour, was built to replaceChallenger, which was destroyed inan accident during launch that killed 7 astronauts on 28 January 1986. From 1983 to 1998, twenty-two Shuttle flights carried components for aEuropean Space Agency sortie space station calledSpacelab in the Shuttle payload bay.[8]
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The USSR copied the US's reusableSpace Shuttle orbiter, which they calledBuran-class orbiter or simplyBuran, which was designed to be launched into orbit by the expendableEnergia rocket, and was capable of robotic orbital flight and landing. Unlike the Space Shuttle,Buran had no main rocket engines, but like the Space Shuttle orbiter, it used smaller rocket engines to perform its final orbital insertion. A single uncrewed orbital test flight took place in November 1988. A second test flight was planned by 1993, but the program was canceled due to lack of funding and thedissolution of the Soviet Union in 1991. Two more orbiters were never completed, and the one that performed the uncrewed flight was destroyed in a hangar roof collapse in May 2002.
The dissolution of the Soviet Union in 1991 brought an end to the Cold War and opened the door to true cooperation between the US and Russia. The Soviet Soyuz and Mir programs were taken over by the Russian Federal Space Agency, which became known as theRoscosmos State Corporation. TheShuttle-Mir Program included American Space Shuttles visiting theMir space station, Russian cosmonauts flying on the Shuttle, and an American astronaut flying aboard a Soyuz spacecraft for long-duration expeditions aboardMir.
In 1993, PresidentBill Clinton secured Russia's cooperation in converting the planned Space StationFreedom into theInternational Space Station (ISS). Construction of the station began in 1998. The station orbits at an altitude of 409 kilometers (221 nmi) and an orbital inclination of 51.65°. Several of the Space Shuttle's 135 orbital flights were to help assemble, supply, and crew the ISS. Russia has built half of the International Space Station and has continued its cooperation with the US.
China was the third nation in the world, after the USSR and US, to send humans into space. During theSpace Race between the two superpowers, which culminated withApollo 11 landing humans on the Moon,Mao Zedong andZhou Enlai decided on 14 July 1967 that China should not be left behind, and initiated their own crewed space program: the top-secret Project 714, which aimed to put two people into space by 1973 with theShuguang spacecraft. NineteenPLAAF pilots were selected for this goal in March 1971. The Shuguang-1 spacecraft, to be launched with theCZ-2A rocket, was designed to carry a crew of two. The program was officially canceled on 13 May 1972 for economic reasons.
In 1992, underChina Manned Space Program (CMS), also known as "Project 921", authorization and funding was given for the first phase of a third, successful attempt at crewed spaceflight. To achieve independent human spaceflight capability, China developed theShenzhou spacecraft andLong March 2F rocket dedicated to human spaceflight in the next few years, along with critical infrastructures like a new launch site and flight control center being built. The first uncrewed spacecraft,Shenzhou 1, was launched on 20 November 1999 and recovered the next day, marking the first step of the realization of China's human spaceflight capability. Three more uncrewed missions were conducted in the next few years in order to verify the key technologies. On 15 October 2003Shenzhou 5, China's first crewed spaceflight mission, putYang Liwei in orbit for 21 hours and returned safely back toInner Mongolia, making China the third nation to launch a human into orbit independently.[9]
The goal of the second phase of CMS was to make technology breakthroughs inextravehicular activities (EVA, or spacewalk),space rendezvous, anddocking to support short-term human activities in space.[10] On 25 September 2008 during the flight ofShenzhou 7,Zhai Zhigang andLiu Boming completed China's first EVA.[11] In 2011, China launched theTiangong 1 target spacecraft andShenzhou 8 uncrewed spacecraft. The two spacecraft completed China's first automatic rendezvous and docking on 3 November 2011.[12] About 9 months later,Tiangong 1 completed the first manual rendezvous and docking withShenzhou 9, which carried China's first female astronautLiu Yang.[13]
In September 2016,Tiangong 2 was launched into orbit. It was a space laboratory with more advanced functions and equipment thanTiangong 1. A month later,Shenzhou 11 was launched and docked withTiangong 2. Two astronauts enteredTiangong 2 and were stationed for about 30 days, verifying the viability of astronauts' medium-term stay in space.[14] In April 2017, China's first cargo spacecraft,Tianzhou 1 docked withTiangong 2 and completed multiple in-orbit propellant refueling tests, which marked the successful completion of the second phase of CMS.[14]
The third phase of CMS began in 2020. The goal of this phase is to build China's own space station,Tiangong.[15] The first module ofTiangong, theTianhe core module, was launched into orbit by China's most powerful rocketLong March 5B on 29 April 2021.[16] It was later visited by multiple cargo and crewed spacecraft and demonstrated China's capability of sustaining Chinese astronauts' long-term stay in space.
According to CMS announcement, all missions of Tiangong Space Station are scheduled to be carried out by the end of 2022.[17] Once the construction is completed,Tiangong will enter the application and development phase, which is poised to last for no less than 10 years.[17]
TheEuropean Space Agency began development of theHermes shuttlespaceplane in 1987, to be launched on theAriane 5 expendable launch vehicle. It was intended to dock with the EuropeanColumbus space station. The projects were canceled in 1992 when it became clear that neither cost nor performance goals could be achieved. No Hermes shuttles were ever built. The Columbus space station was reconfigured as theEuropean module of the same name on the International Space Station.[18]
Japan (NASDA) began the development of theHOPE-X experimental shuttle spaceplane in the 1980s, to be launched on itsH-IIA expendable launch vehicle. A string of failures in 1998 led to funding reductions, and the project's cancellation in 2003 in favor of participation in the International Space Station program through theKibō Japanese Experiment Module andH-II Transfer Vehicle cargo spacecraft. As an alternative to HOPE-X, NASDA in 2001 proposed theFuji crew capsule for independent or ISS flights, but the project did not proceed to the contracting stage.[citation needed]
From 1993 to 1997, theJapanese Rocket Society [ja],Kawasaki Heavy Industries, andMitsubishi Heavy Industries worked on the proposedKankoh-maruvertical-takeoff-and-landingsingle-stage-to-orbit reusable launch system. In 2005, this system was proposed for space tourism.[19]
According to a press release from theIraqi News Agency dated 5 December 1989, there was only one test of theAl-Abid space launcher, whichIraq intended to use to develop its own crewed space facilities by the end of the century. These plans were put to an end by theGulf War of 1991 and the economic hardships that followed.[20]
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Under the George W. Bush administration, theConstellation program included plans for retiring the Space Shuttle program and replacing it with the capability for spaceflight beyond low Earth orbit. In the2011 United States federal budget, the Obama administration canceled Constellation for being over budget and behind schedule, while not innovating and investing in critical new technologies.[21] As part of theArtemis program, NASA is developing theOrion spacecraft to be launched by theSpace Launch System. Under theCommercial Crew Development plan, NASA relies on transportation services provided by the private sector to reach low Earth orbit, such asSpaceX Dragon 2, theBoeing Starliner orSierra Nevada Corporation'sDream Chaser. The period between the retirement of the Space Shuttle in 2011 and the first launch into space ofSpaceShipTwoFlight VP-03 on 13 December 2018 is similar to the gap between the end ofApollo in 1975 and thefirst Space Shuttle flight in 1981, and is referred to by a presidential Blue Ribbon Committee as the U.S. human spaceflight gap.
 | This section needs to beupdated. Please help update this article to reflect recent events or newly available information.(September 2024) |
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Since the early 2000s, a variety ofprivate spaceflight ventures have been undertaken. As of November 2024,[update]SpaceX[22] andBoeing[23] have launched humans to orbit,[note 1] whileBlue Origin has launched 8 crewed flights, six of which crossed theKármán line.[24][note 2]Virgin Galactic has launched crew to a height above 80 km (50 mi) on a suborbital trajectory.[26] Several other companies, includingSierra Nevada andCopenhagen Suborbitals, have developed crewed spacecraft.[27][28] SpaceX, Boeing, Blue Origin, and Virgin Galactic plan to fly commercial passengers in the emergingspace tourism market.[29]
SpaceX has developedCrew Dragon flying onFalcon 9. It first launched astronauts to orbit and to the ISS in May 2020 as part of theDemo-2 mission. Developed as part of NASA'sCommercial Crew Development program, the capsule is also available for flights with other customers. A first tourist mission,Inspiration4, launched in September 2021.[30]
Boeing developed theStarliner capsule as part of NASA's Commercial Crew Development program, which is launched on aUnited Launch AllianceAtlas V launch vehicle.[31] Starliner made an uncrewed flight in December 2019. A second uncrewed flight attempt was launched in May 2022.[32] A crewed flight to fully certify Starliner was launched in June 2024.[33] Similar to SpaceX, development funding has been provided by a mix ofgovernment andprivate funds.[34][35]
Virgin Galactic is developingSpaceshipTwo, a commercialsuborbital spacecraft aimed at thespace tourism market. It reached space in December 2018.[26]
Blue Origin is in a multi-yeartest program of theirNew Shepard vehicle and has carried outthirty one launches as of May 2025, including twenty uncrewed test flights and eleven crewed flights. The first crewed flight, carrying founderJeff Bezos, his brotherMark Bezos, aviatorWally Funk, and 18-year oldOliver Daemen launched on July 20, 2021.[36]
Over the decades, a number of spacecraft have been proposed for spaceliner passenger travel. Somewhat analogous to travel byairliner after the middle of the 20th century, these vehicles are proposed totransport large numbers of passengers to destinations in space, or on Earth viasuborbital spaceflights. To date, none of these concepts have been built, although a few vehicles that carry fewer than 10 persons are currently in thetest flight phase of their development process.[citation needed]
One large spaceliner concept currently in early development is theSpaceX Starship, which, in addition to replacing theFalcon 9 andFalcon Heavylaunch vehicles in the legacy Earth-orbitmarket after 2020, has been proposed by SpaceX for long-distance commercial travel on Earth, flying 100+ people suborbitally between two points in under one hour, also known as "Earth-to-Earth".[37][38][39]
Smallspaceplane or smallcapsule suborbital spacecraft have been under development for the past decade or so; as of 2017[update], at least one of each type is under development. BothVirgin Galactic andBlue Origin have craft in activedevelopment: theSpaceShipTwo spaceplane and theNew Shepard capsule, respectively. Both would carry approximately a half-dozen passengers up to space for a brief time of zero gravity before returning to the launch location.XCOR Aerospace had been developing theLynx single-passenger spaceplane since the 2000s,[40][41] but development was halted in 2017.[42]
Participation and representation of humanity in space has been an issue ever since the first phase of space exploration.[43] Some rights of non-spacefaring countries have been secured through internationalspace law, declaring space the "province of all mankind", though the sharing of space by all humanity is sometimes criticized asimperialist and lacking.[43] In addition to the lack of international inclusion, the inclusion of women andpeople of color has also been lacking. To make spaceflight more inclusive, organizations such as theJustspace Alliance[43] andIAU-featuredInclusive Astronomy[44] have been formed in recent years.
The first woman to ever enter space wasValentina Tereshkova. She flew in 1963, but it was not until the 1980s that another woman entered space. At the time, all astronauts were required to be military test pilots; women were not able to enter this career, which is one reason for the delay in allowing women to join space crews.[45] After the rules were changed,Svetlana Savitskaya became the second woman to enter space; she was also from theSoviet Union.Sally Ride became the next woman to enter space and the first woman to enter space through the United States program.Since then, eleven other countries have allowed women astronauts. The first all-female spacewalk occurred in 2018, byChristina Koch andJessica Meir. These two women had both participated in separate spacewalks with NASA. The first mission to the Moon with a woman aboard is planned for 2024.
Despite these developments, women are still underrepresented among astronauts and especially cosmonauts. More than 600 people have flown in space but only 75 have been women.[46] Issues that block potential applicants from the programs, and limit the space missions they are able to go on, are, for example:
This is a list of major milestones achieved by country. Recorded is the first citizen and first spacecraft from each respective country to accomplish each milestone, regardless of mission type or intended outcome.
Sally Ride became the first American woman in space, in 1983.Eileen Collins was the first female Shuttle pilot, and with Shuttle missionSTS-93 in 1999 she became the first woman to command a U.S. spacecraft.
For many years, the USSR (later Russia) and the United States were the only countries whose astronauts flew in space. That ended with the 1978 flight of Vladimir Remek. As of 2010[update], citizens from 38 nations (includingspace tourists) have flown in space aboard Soviet, American, Russian, and Chinese spacecraft.
Human spaceflight programs have been conducted by the Soviet Union–Russian Federation, the United States,Mainland China, and by Americanprivate spaceflight companies.
The following space vehicles andspaceports are currently used for launching human spaceflights:
The followingspace stations are currently maintained in Earth orbit for human occupation:
Most of the time, the only humans in space are those aboard the ISS, which generally has a crew of 7, and those aboard Tiangong, which generally has a crew of 3.
NASA andESA use the term "human spaceflight" to refer to their programs of launching people into space. These endeavors have also formerly been referred to as "manned space missions", though this is no longer official parlance according to NASA style guides, which call forgender-neutral language.[53]
Under theIndian Human Spaceflight Program, India was planning to send humans into space on its orbital vehicleGaganyaan before August 2022, but it has been delayed to 2024, due to the COVID-19 pandemic. TheIndian Space Research Organisation (ISRO) began work on this project in 2006.[54][55] The initial objective is to carry a crew of two or three tolow Earth orbit (LEO) for a 3-to-7-day flight in aspacecraft on aLVM 3 rocket and return them safely for a water landing at a predefined landing zone. On 15 August 2018,Indian Prime MinisterNarendra Modi, declared India will independently send humans into space before the 75thanniversary of independence in 2022.[56] In 2019, ISRO revealed plans for aspace station by 2030, followed by a crewed lunar mission. The program envisages the development of a fully-autonomous orbital vehicle capable of carrying 2 or 3 crew members to an about 300 km (190 mi) low Earth orbit and bringing them safely back home.[57]
Since 2008, theJapan Aerospace Exploration Agency had developed theH-II Transfer Vehicle cargo-spacecraft-based crewed spacecraft andKibō Japanese Experiment Module–based small space laboratory.
NASA is developing a plan to land humans on Mars by the 2030s. The first step has begun withArtemis I in 2022, sending an uncrewedOrion spacecraft to adistant retrograde orbit around the Moon and returning it to Earth after a 25-day mission.
SpaceX is developingStarship, a fully reusable two-stage system, with near-Earth and cislunar applications and an ultimate goal of landing on Mars. The upper stage of the Starship system, also called Starship, has had 9 atmospheric test flights as of September 2021. The firsttest flight of the fully integrated two-stage system occurred in April 2023. Amodified version of Starship is being developed for theArtemis program.
Several other countries and space agencies have announced and begun human spaceflight programs using natively developed equipment and technology, including Japan (JAXA),Iran (ISA), andNorth Korea (NADA). The plans for theIranian crewed spacecraft are for a small spacecraft and space laboratory.North Korea'sspace program has plans for crewed spacecraft and small shuttle systems.
There are two main sources of hazard in space flight: those due to the hostile space environment, and those due to possible equipment malfunctions. Addressing these issues is of great importance for NASA and other space agencies before conducting the first extended crewed missions to destinations such as Mars.[65]
Planners of human spaceflight missions face a number of safety concerns.
The basic needs for breathable air and drinkable water are addressed by thelife support system of the spacecraft.
Astronauts may not be able to quickly return to Earth or receive medical supplies, equipment, or personnel if a medical emergency occurs. The astronauts may have to rely for long periods on limited resources and medical advice from the ground.
The possibility ofblindness and ofbone loss have been associated with humanspace flight.[66][67]
On 31 December 2012, aNASA-supported study reported that spaceflight may harm the brains ofastronauts and accelerate the onset ofAlzheimer's disease.[68][69][70]
In October 2015, theNASA Office of Inspector General issued ahealth hazards report related tospace exploration, which included the potential hazards of ahuman mission to Mars.[71][72]
On 2 November 2017, scientists reported, based onMRI studies, that significant changes in the position and structure of the brain have been found in astronauts who have takentrips in space. Astronauts on longer space trips were affected by greater brain changes.[73][74]
Researchers in 2018 reported, after detecting the presence on theInternational Space Station (ISS) of fiveEnterobacter bugandensis bacterial strains, nonepathogenic to humans, thatmicroorganisms on ISS should be carefully monitored to assure a healthy environment forastronauts.[75][76]
In March 2019, NASA reported that latentviruses in humans may be activated during space missions, possibly adding more risk to astronauts in future deep-space missions.[77]
On 25 September 2021,CNN reported that an alarm had sounded during theInspiration4 Earth-orbital journey on theSpaceX Dragon 2. The alarm signal was found to be associated with an apparent toilet malfunction.[78]
Medical data from astronauts in low Earth orbits for long periods, dating back to the 1970s, show several adverse effects of a microgravity environment: loss ofbone density, decreased muscle strength and endurance, postural instability, and reductions in aerobic capacity. Over time thesedeconditioning effects can impair astronauts' performance or increase their risk of injury.[79]
In a weightless environment, astronauts put almost no weight on the backmuscles or leg muscles used for standing up, which causes the muscles to weaken and get smaller. Astronauts can lose up to twenty per cent of their muscle mass on spaceflights lasting five to eleven days. The consequent loss of strength could be a serious problem in case of a landing emergency.[80] Upon returning to Earth fromlong-duration flights, astronauts are considerably weakened and are not allowed to drive a car for twenty-one days.[81]
Astronauts experiencing weightlessness will often lose their orientation, getmotion sickness, and lose their sense of direction as their bodies try to get used to a weightless environment. When they get back to Earth, they have to readjust and may have problems standing up, focusing their gaze, walking, and turning. Importantly, those motor disturbances only get worse the longer the exposure to weightlessness.[82] These changes can affect the ability to perform tasks required for approach and landing, docking, remote manipulation, and emergencies that may occur while landing.[83]
In addition, after longspace flight missions, male astronauts may experience severeeyesight problems, which may be a major concern for future deep space flight missions, including acrewed mission to the planetMars.[84][85][86][87][88][89] Long space flights can also alter a space traveler's eye movements.[90]
Without proper shielding, the crews of missions beyond low Earth orbit might be at risk from high-energy protons emitted bysolar particle events (SPEs) associated withsolar flares. If estimated correctly, the amount of radiation that astronauts would be exposed to from a solar storm similar to that of the most powerful in recorded history, theCarrington Event, would result inacute radiation sickness at least, and could even be fatal "in a poorly shielded spacecraft".[92][better source needed] Another storm that could have inflicted a potentially lethal dose of radiation on astronauts outside Earth's protectivemagnetosphere occurred during theSpace Age, shortly afterApollo 16 landed and beforeApollo 17 launched.[93] This solar storm,which occurred in August 1972, could potentially have caused any astronauts who were exposed to it to suffer from acute radiation sickness, and may even have been lethal for those engaged inextravehicular activity or on the lunar surface.[94]
Another type of radiation, galacticcosmic rays, presents further challenges to human spaceflight beyond low Earth orbit.[95]
There is also some scientific concern that extended spaceflight might slow down the body's ability to protect itself against diseases,[96] resulting in a weakenedimmune system and the activation of dormantviruses in the body.Radiation can cause both short- and long-term consequences to the bone marrow stem cells from which blood and immune-system cells are created. Because the interior of a spacecraft is so small, a weakened immune system and more active viruses in the body can lead to a fast spread of infection.[97]
During long missions, astronauts are isolated and confined in small spaces.Depression, anxiety,cabin fever, and other psychological problems may occur more than for an average person and could impact the crew's safety and mission success.[98] NASA spends millions of dollars on psychological treatments for astronauts and former astronauts.[99] To date, there is no way to prevent or reduce mental problems caused by extended periods of stay in space.
Due to these mental disorders, the efficiency of astronauts' work is impaired; and sometimes they are brought back to Earth, incurring the expense of their mission being aborted.[100] A Russian expedition to space in 1976 was returned to Earth after the cosmonauts reported a strong odor that resulted in a fear of fluid leakage; but after a thorough investigation, it became clear that there was no leakage or technical malfunction. It was concluded by NASA that the cosmonauts most likely hadhallucinated the smell.
It is possible that the mental health of astronauts can be affected by the changes in the sensory systems while in prolonged space travel.
During astronauts' spaceflight, they are in an extreme environment. This, and the fact that little change is taking place in the environment, will result in the weakening of sensory input to the astronauts' seven senses.
Space flight requires much higher velocities than ground or air transportation, and consequently requires the use of highenergy density propellants for launch, and the dissipation of large amounts of energy, usually as heat, for safe reentry through the Earth's atmosphere.
Since rockets have the potential for fire or explosive destruction,space capsules generally employ some sort oflaunch escape system, consisting either of a tower-mounted solid-fuel rocket to quickly carry the capsule away from thelaunch vehicle (employed onMercury,Apollo, andSoyuz, the escape tower being discarded at some point after launch, at a point where an abort can be performed using the spacecraft's engines), or elseejection seats (employed onVostok andGemini) to carry astronauts out of the capsule and away for individual parachute landings.
Such a launch escape system is not always practical for multiple-crew-member vehicles (particularlyspaceplanes), depending on the location of egress hatch(es). When the single-hatch Vostok capsule was modified to become the 2 or 3-personVoskhod, the single-cosmonaut ejection seat could not be used, and no escape tower system was added. The two Voskhod flights in 1964 and 1965 avoided launch mishaps. TheSpace Shuttle carried ejection seats and escape hatches for its pilot and copilot in early flights; but these could not be used for passengers who sat below the flight deck on later flights, and so were discontinued.
There have been only two in-flight launch aborts of a crewed flight. The first occurred onSoyuz 18a on 5 April 1975. The abort occurred after the launch escape system had been jettisoned when the launch vehicle's spent second stage failed to separate before the third stage ignited and the vehicle strayed off course. The crew finally managed to separate the spacecraft, firing its engines to pull it away from the errant rocket, and both cosmonauts landed safely. The second occurred on 11 October 2018 with the launch ofSoyuz MS-10. Again, both crew members survived.
In the first use of a launch escape system on the launchpad, before the start of a crewed flight, happened during the plannedSoyuz T-10a launch on 26 September 1983, which was aborted by a launch vehicle fire 90 seconds before liftoff. Both cosmonauts aboard landed safely.
The only crew fatality during launch occurred on 28 January 1986, when theSpace ShuttleChallenger broke apart 73 seconds after liftoff, due to the failure of asolid rocket booster seal, which caused the failure of theexternal fuel tank, resulting in an explosion of the fuel and separation of the boosters. All seven crew members were killed.
Tasks outside a spacecraft require use of aspace suit. Despite the risk of mechanical failures while working in open space, there have been no spacewalk fatalities. Spacewalking astronauts routinely remain attached to the spacecraft with tethers and sometimes supplementary anchors. Un-tethered spacewalks were performed on three missions in 1984 using theManned Maneuvering Unit, and on a flight test in 1994 of theSimplified Aid For EVA Rescue (SAFER) device.
The single pilot ofSoyuz 1,Vladimir Komarov, was killed when his capsule's parachutes failed during an emergency landing on 24 April 1967, causing the capsule to crash.
On 1 February 2003, the crew of seven aboard theSpace Shuttle Columbia werekilled on reentry after completing asuccessful mission in space. A wing-leading-edgereinforced carbon-carbon heat shield had been damaged by a piece of frozenexternal tank foam insulation that had broken off and struck the wing during launch. Hot reentry gasses entered and destroyed the wing structure, leading to the breakup of theorbiter vehicle.
There are two basic choices for an artificial atmosphere: either an Earth-like mixture of oxygen and an inert gas such as nitrogen or helium, or pure oxygen, which can be used at lower than standard atmospheric pressure. A nitrogen–oxygen mixture is used in the International Space Station and Soyuz spacecraft, while low-pressure pure oxygen is commonly used in space suits forextravehicular activity.
The use of a gas mixture carries the risk ofdecompression sickness (commonly known as "the bends") when transitioning to or from the pure oxygen space suit environment. There have been instances of injury and fatalities caused by suffocation in the presence of too much nitrogen and not enough oxygen.
A pure oxygen atmosphere carries the risk of fire. The original design of the Apollo spacecraft used pure oxygen at greater than atmospheric pressure prior to launch. An electrical fire started in the cabin ofApollo 1 during a ground test atCape Kennedy Air Force Station Launch Complex 34 on 27 January 1967, and spread rapidly. The high pressure, increased by the fire, prevented removal of theplug door hatch cover in time to rescue the crew. All three astronauts—Gus Grissom,Ed White, andRoger Chaffee—were killed.[104] This led NASA to use a nitrogen–oxygen atmosphere before launch, and low-pressure pure oxygen only in space.
The March 1966Gemini 8 mission was aborted in orbit when anattitude control system thruster stuck in the on position, sending the craft into a dangerous spin that threatened the lives ofNeil Armstrong andDavid Scott. Armstrong had to shut the control system off and use the reentry control system to stop the spin. The craft made an emergency reentry and the astronauts landed safely. The most probable cause was determined to be an electrical short due to astatic electricity discharge, which caused the thruster to remain powered even when switched off. The control system was modified to put each thruster on its own isolated circuit.
The third lunar landing expedition,Apollo 13, in April 1970, was aborted and the lives of the crew—James Lovell,Jack Swigert, andFred Haise—were threatened after the failure of acryogenicliquid oxygen tank en route to the Moon. The tank burst when electrical power was applied to internal stirring fans in the tank, causing the immediate loss of all of its contents, and also damaging the second tank, causing the gradual loss of its remaining oxygen over a period of 130 minutes. This in turn caused a loss of electrical power provided byfuel cells to thecommand spacecraft. The crew managed to return to Earth safely by using thelunar landing craft as a "life boat". The tank failure was determined to be caused by two mistakes: the tank's drain fitting had been damaged when it was dropped during factory testing, necessitating the use of its internal heaters to boil out the oxygen after a pre-launch test; which in turn damaged the fan wiring's electrical insulation because the thermostats on the heaters did not meet the required voltage rating due to a vendor miscommunication.
The crew ofSoyuz 11 were killed on 30 June 1971 by a combination of mechanical malfunctions; the crew wereasphyxiated due to cabin decompression following the separation of their descent capsule from the service module. A cabin ventilation valve had been jolted open at an altitude of 168 kilometres (104 mi) by the stronger-than-expected shock of explosive separation bolts, which were designed to fire sequentially, but in fact had fired simultaneously. The loss of pressure became fatal within about 30 seconds.[105]
As of December 2015[update], 23 crew members have died in accidents aboard spacecraft. Over 100 others have died in accidents during activities directly related to spaceflight or testing.
| Date | Mission | Accident cause | Deaths | Cause of death |
|---|---|---|---|---|
| 27 January 1967 | Apollo 1 | Electrical fire in the cabin, spread quickly by 16.7 psi (1.15 bar) pure oxygen atmosphere and flammable nylon materials in cabin and space suits, during pre-launch test; inability to removeplug door hatch cover due to internal pressure; rupture of cabin wall allowed outside air to enter, causing heavy smoke and soot | 3 | Cardiac arrest fromcarbon monoxide poisoning |
| 24 April 1967 | Soyuz 1 | Malfunction of primary landing parachute, and entanglement of reserve parachute; loss of 50% electrical power and spacecraft control problems necessitating emergency abort | 1 | Trauma from crash landing |
| 15 November 1967 | X-15 Flight 3-65-97 | The accident board found that the cockpit instrumentation had been functioning properly, and concluded that pilotMichael J. Adams had lost control of the X-15 as a result of a combination of distraction, misinterpretation of his instrumentation display, and possiblevertigo. The electrical disturbance early in the flight degraded the overall effectiveness of the aircraft's control system and further added to pilot workload. | 1 | Vehicle breakup |
| 30 June 1971 | Soyuz 11 | Loss of cabin pressurization due to valve opening upon Orbital Module separation before re-entry | 3 | Asphyxia |
| 28 January 1986 | STS-51LSpace ShuttleChallenger | Failure ofO-ring inter-segment seal in oneSolid Rocket Booster in extreme cold launch temperature, allowing hot gases to penetrate casing and burn through a strut connecting booster to theExternal Tank; tank failure; rapid combustion of fuel; orbiter breakup from abnormal aerodynamic forces | 7 | Asphyxia from cabin breach, or trauma from water impact[106] |
| 1 February 2003 | STS-107Space ShuttleColumbia | Damagedreinforced carbon-carbon heat shield panel on wing's leading edge, caused by a piece ofExternal Tank foam insulation broken off during launch; penetration of hot atmospheric gases during re-entry, leading to structural failure of the wing, loss of control and disintegration of the orbiter | 7 | Asphyxia from cabin breach, trauma from dynamic load environment as orbiter broke up[107] |
| 31 October 2014 | SpaceShipTwoVSSEnterprise powered drop-test | Copilot error: premature deployment of "feathering" descent air-braking system caused the disintegration of the vehicle in flight; pilot survived, copilot died | 1 | Trauma from crash |
"We basically awarded based on the proposals that we were given", Kathy Lueders, NASA commercial crew program manager, said in a teleconference with reporters after the announcement. "Both contracts have the same requirements. The companies proposed the value within which they were able to do the work, and the government accepted that".
[the] spaceship portion of the BFR, which would transport people on point-to-point suborbital flights or on missions to the moon or Mars, will be tested on Earth first in a series of short hops. ... a full-scale Ship doing short hops of a few hundred kilometers altitude and lateral distance ... fairly easy on the vehicle, as no heat shield is needed, we can have a large amount of reserve propellant and don't need the high area ratio, deep space Raptor engines.
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