Human spaceflight

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Apollo 11 crewmember Buzz Aldrin walks on the Moon, 1969
International Space Station crewmember Tracy Caldwell Dyson views the Earth, 2010

Human spaceflight (also referred to as manned spaceflight) is space travel with a crew aboard the spacecraft. When a spacecraft is crewed, it can be operated directly, as opposed to being remotely operated or autonomous.

The first human spaceflight was launched by the Soviet Union on 12 April 1961 as a part of the Vostok program, with cosmonaut Yuri Gagarin aboard. Humans have been continually present in space for 15 years and 23 days on the International Space Station.

Since the retirement of the US Space Shuttle in 2011, only Russia and China have maintained domestic human spaceflight capability with the Soyuz program and Shenzhou program. Currently, all crewed flights to the International Space Station use Soyuz vehicles, which remain attached to the station to allow quick return if needed. The United States is developing commercial crew transportation to facilitate domestic access to ISS and low Earth orbit, as well as the Orion vehicle for beyond-low Earth orbit applications.

While spaceflight has typically been a government-directed activity, commercial spaceflight has gradually been taking on a greater role. The first private human spaceflight took place on 21 June 2004, when SpaceShipOne conducted a suborbital flight, and a number of non-governmental companies have been working to develop a space tourism industry. NASA has also played a role to stimulate private spaceflight through programs such as Commercial Orbital Transportation Services (COTS) and Commercial Crew Development (CCDev). With its 2011 budget proposals released in 2010,[1] the Obama administration moved towards a model where commercial companies would supply NASA with transportation services of both crew and cargo to low Earth orbit. The vehicles used for these services could then serve both NASA and potential commercial customers. Commercial resupply of ISS began two years after the retirement of the Shuttle, and commercial crew launches could begin by 2017.[2]


First human spaceflights[edit]

Suborbital human spaceflight
Name Years Flights
Mercury 1961 2
X-15 1963 2
Soyuz 18a 1975 1
SpaceShipOne 2004 3
Orbital human spaceflight
Name Years Flights
Vostok 1961—63 6
Mercury 1962—63 4
Voskhod 1964 2
Gemini 1965—66 10
Soyuz 1967—present 124
Apollo 1968—69 2
Skylab 1973 3
Apollo-Soyuz 1975 2
Space Shuttle 1981—2011 135
Shenzhou 2003—present 5
Lunar human spaceflight
Name Years Flights
Apollo 1968—72 9

The first human spaceflight took place on 12 April 1961, when cosmonaut Yuri Gagarin made one orbit around the Earth aboard the Vostok 1 spacecraft, launched by the Soviet space program. Valentina Tereshkova became the first woman in space aboard Vostok 6 on 16 June 1963. Both spacecraft were launched by Vostok 3KA launch vehicles. Alexei Leonov made the first spacewalk when he left Voskhod 2 on 8 March 1965. Svetlana Savitskaya became the first woman to do so on 25 July 1984.

The United States became the second nation to put a human in space with the suborbital flight of astronaut Alan Shepard aboard Freedom 7 as part of Project Mercury. The spacecraft was launched on 5 May 1961 on a Redstone rocket. The first U.S. orbital flight was that of John Glenn aboard Friendship 7, launched 20 February 1962 on an Atlas rocket. From 1981 to 2011, the U.S. conducted all its human spaceflight missions with reusable space shuttles. Sally Ride became the first American woman in space in 1983. Eileen Collins was the first female shuttle pilot, and with shuttle mission STS-93 in 1999 she became the first woman to command a U.S. spacecraft.

China became the third nation to achieve independent human spaceflight capability when Yang Liwei launched into space on a Chinese-made vehicle, the Shenzhou 5, on 15 October 2003. The first Chinese woman, Liu Yang, was launched in June 2012 aboard Shenzhou 9. Previous European (Hermes) and Japanese (HOPE-X) domestic human spaceflight programs were abandoned after years of development, as was the first Chinese attempt, the Shuguang spacecraft.

The farthest destination for a human spaceflight mission has been the Moon. The only manned missions to the Moon have been those conducted by NASA as part of the Apollo program. The first such mission, Apollo 8, orbited the Moon but did not land. The first Moon landing mission was Apollo 11, during which—on 21 July 1969—Neil Armstrong and Buzz Aldrin became the first people to set foot on the Moon. Six missions landed in total, numbered Apollo 11–17, excluding Apollo 13. Altogether 12 men walked on the Moon, the only humans to have been on an extraterrestrial body in history. The Soviet Union discontinued its program for lunar orbiting and landing of human spaceflight missions in 1974 when Valentin Glushko became General Designer of NPO Energiya.[3]

The longest single human spaceflight is that of Valeri Polyakov, who left Earth on 8 January 1994, and did not return until 22 March 1995 (a total of 437 days 17 h 58 min 16 s). Sergei Krikalyov has spent the most time of anyone in space, 803 days, 9 hours, and 39 minutes altogether. The longest period of continuous human presence in space is 15 years and 23 days on the International Space Station, exceeding the previous record of almost 10 years (or 3,634 days) held by Mir, spanning the launch of Soyuz TM-8 on 5 September 1989 to the landing of Soyuz TM-29 on 28 August 1999.

For many years beginning in 1961, only two countries, the USSR (later Russia) and the United States, had their own astronauts. Citizens of other nations flew in space, beginning with the flight of Vladimir Remek, a Czech, on a Soviet spacecraft on 2 March 1978, in the Interkosmos programme. As of 2010, citizens from 38 nations (including space tourists) have flown in space aboard Soviet, American, Russian, and Chinese spacecraft.

Post-shuttle gap in United States human spaceflight capability[edit]

Under the Bush administration, the Constellation Program included plans for retiring the Shuttle program and replacing it with the capability for spaceflight beyond low Earth orbit. In the 2011 United States federal budget, the Obama administration cancelled Constellation for being over budget and behind schedule while not innovating and investing in critical new technologies.[4] For beyond low earth orbit human spaceflight NASA is developing the Orion spacecraft to be launched by the Space Launch System. Under the Commercial Crew Development plan, NASA will rely on transportation services provided by the private sector to reach low earth orbit, such as Space X's Falcon 9/Dragon V2, Sierra Nevada Corporation's Dream Chaser, or Boeing's CST-100. The period between the retirement of the shuttle in 2011 and the initial operational capability of new systems in 2017, similar to the gap between the end of Apollo in 1975 and the first space shuttle flight in 1981, is referred to by a presidential Blue Ribbon Committee as the U.S. human spaceflight gap.[5] Commercial sub-orbital spacecraft aimed at the space tourism market such as Scaled Composites SpaceshipTwo to be operated by Virgin Galactic, and XCOR's Lynx spaceplane are under development and could reach space before 2017.[6]

Space programs[edit]

Countries that have had human spaceflight programs (dark blue)
An Apollo spacecraft with docking equipment, as photographed by the Soyuz crew during the Apollo-Soyuz mission. Human spaceflight has been a forum for both competition and cooperation.

Human spaceflight programs have been conducted by the former Soviet Union/Russian Federation, the United States, the People's Republic of China and by private spaceflight company Scaled Composites.

The Indian Space Research Organization (ISRO) begun work on pre project activities of human space flight mission programme.[7] The objective of Human Spaceflight Programme is to undertake a human spaceflight mission to carry a crew of two to Low Earth Orbit (LEO) and return them safely to a predefined destination on earth. The programme is proposed to be implemented in defined phases. Currently, the pre project activities are progressing with a focus on the development of critical technologies for subsystems such as Crew Module (CM), Environmental control and Life Support System (ECLSS), Crew Escape System, etc. A study for undertaking human space flight to carry human beings to low earth orbit and ensure their safe return has been made by the department. The department has initiated pre-project activities to study technical and managerial issues related to undertaking crewed missions with an aim to build and demonstrate the country’s capability. The program envisages the development of a fully autonomous orbital vehicle carrying 2 or 3 crew members to about 300 km low earth orbit and their safe return.

Several other countries and space agencies have announced and begun human spaceflight programs by their own technology, Japan (JAXA), Iran (ISA) and Malaysia (MNSA).

Current programs[edit]

The following space vehicles and spaceports are currently used for launching human spaceflights:

The following space stations are currently maintained in Earth orbit for human spaceflight:

  • International Space Station (US and Russia) assembled in orbit: altitude 409 kilometers (221 nautical miles), 51.65° inclination; crews transported by Soyuz spacecraft
  • Tiangong-1 (Chinese): altitude 363 kilometers (196 nautical miles), 42.77° inclination; crews transported by Shenzhou spacecraft

Historical programs[edit]

Space vehicles are spacecraft used for transportation between the Earth's surface and outer space, or between locations in outer space. The following space vehicles have been used in the past for human spaceflight, with the spaceports they were launched from:

Space stations are designed for human habitation in orbit for extended periods. The first stations were designed for sorties (temporary individual missions), while later ones have been designed for continuous, permanent or semi-permanent habitation. The following space stations have been maintained in Earth orbit in the past:

  • Salyut (Soviet), a series of sortie stations, ostensibly for civilian purposes; four successful
  • Almaz (Soviet), a series of three military sortie stations; these were disguised as Salyuts
  • Skylab, a (US) sortie station: altitude 270 nautical miles (500 kilometers), 50° inclination; launched 14 May 1973; manned for 167 days in three missions; uncontrolled reentry 11 July 1979
  • Mir (Soviet/Russian), the first semi-permanent space station: altitude 354 kilometers (191 nautical miles), 51.6° inclination; constructed in orbit 20 February 1986 to 23 April 1996; occupied 4,592 days; reentered 23 March 2001
Mir, a former space station where many human spaceflight records were achieved orbiting the Earth
International Space Station under construction

Numerous private companies attempted human spaceflight programs in an effort to win the $10 million Ansari X Prize. The first private human spaceflight took place on 21 June 2004, when SpaceShipOne conducted a suborbital flight. SpaceShipOne captured the prize on 4 October 2004, when it accomplished two consecutive flights within one week. SpaceShipTwo, launching from the carrier aircraft White Knight Two, is planned to conduct regular suborbital space tourism.

Most of the time, the only humans in space are those aboard the ISS, whose crew of six spends up to six months at a time in low Earth orbit.

NASA and ESA use the term "human spaceflight" to refer to their programs of launching people into space. These endeavors have also been referred to as "manned space missions."

Aleksandr Skvortsov (cosmonaut) Soichi Noguchi Timothy Creamer Oleg Kotov Maksim Surayev Jeffrey Williams Nicole Stott Robert Thirsk Roman Romanenko Frank De Winne Timothy Kopra Michael R. Barratt Gennady Padalka Koichi Wakata Sandra Magnus Yuri Lonchakov Michael Fincke Gregory Chamitoff Oleg Kononenko Sergey Volkov Garrett Reisman Léopold Eyharts Daniel Tani Yuri Malenchenko Peggy Whitson Clayton Anderson Oleg Kotov Fyodor Yurchikhin Sunita Williams Mikhail Tyurin Michael Lopez-Alegria Thomas Reiter Jeffrey Williams Pavel Vinogradov Valery Tokarev William McArthur John Philips Sergei Krikalev Salizhan Sharipov Leroy Chiao Michael Fincke Gennady Padalka Alexander Kaleri Michael Foale Edward Lu Yuri Malenchenko Donald Pettit Nikolai Budarin Kenneth Bowersox Sergei Treshchev Peggy Whitson Valery Korzun Carl Walz Daniel Bursch Yury Onufrienko Vladimir Dezhurov Mikhail Tyurin Frank Culbertson James Voss Susan Helms Yuri Usachev Yuri Gidzenko Sergei Krikalev William Shepherd Aleksandr Kaleri Sergei Zalyotin Jean-Pierre Haigneré Viktor Afanasyev Sergei Avdeyev Gennady Padalka Nikolai Budarin Talgat Musabayev Andrew Thomas David Wolf Pavel Vinogradov Anatoly Solovyev Michael Foale Aleksandr Lazutkin Vasili Tsibliyev Jerry Linenger John Blaha Aleksandr Kaleri Valery Korzun Shannon Lucid Yury Usachev Yuri Onufrienko Thomas Reiter Sergei Avdeyev Yuri Gidzenko Nikolai Budarin Anatoly Solovyev Norman Thagard Gennady Strekalov Vladimir Dezhurov Yelena Kondakova Aleksandr Viktorenko Talgat Musabayev Yuri Malenchenko Valeri Polyakov Yury Usachev Viktor Afanasyev Aleksandr Serebrov Vasili Tsibliyev Aleksandr Poleshchuk Gennadi Manakov Sergei Avdeyev Anatoly Solovyev Aleksandr Kaleri Aleksandr Viktorenko Aleksandr Volkov Sergei Krikalev Anatoly Artsebarsky Musa Manarov Viktor Afanasyev Gennady Strekalov Gennadi Manakov Aleksandr Balandin Anatoly Solovyev Aleksandr Serebrov Aleksandr Viktorenko Sergei Krikalev Aleksandr Volkov Valeri Polyakov Musa Manarov Vladimir Titov Aleksandr Aleksandrov Yuri Romanenko Aleksandr Laveykin Vladimir Solovyov Leonid Kizim Vladimir Solovyov Leonid Kizim Alexander Volkov Vladimir Vasyutin Vladimir Dzhanibekov Viktor Savinykh Oleg Atkov Vladimir Solovyov Leonid Kizim Aleksandr Pavlovich Aleksandrov Vladimir Lyakhov Valentin Lebedev Anatoli Berezovoy Viktor Savinykh Vladimir Kovalyonok Valery Ryumin Leonid Popov Valery Ryumin Vladimir Lyankhov Aleksandr Ivanchenkov Vladimir Kovalyonok Gerogi Grencho Yuri Romanenko Yuri Glazkov Viktor Gorbatko Vitali Zholobov Boris Volynov Vitali Sevastyanov Pyotr Klimuk Aleksei Gubarev Georgi Grechko Pavel Popovich Yuri Artyukhin Edward Gibson William Pogue Gerald Carr Owen Garriot Jack Lousma Alan Bean Joeseph Kerwin Paul Weitz Pete Conrad Vladislav Volkov Viktor Patsayev Georgi Dobrovolski ISS Tiangong-1 Skylab Mir Salyut 7 Salyut 6 Salyut 5 Salyut 4 Salyut 3 Salyut 1 SpaceShipOne SpaceShipOne flight 17P SpaceShipOne flight 16P SpaceShipOne flight 15P Shenzhou program Shenzhou 10 Shenzhou 9 Shenzhou 7 Shenzhou 6 Shenzhou 5 Space Shuttle Atlantis STS-135 STS-132 STS-129 STS-125 STS-122 STS-117 STS-115 STS-112 STS-110 STS-104 STS-98 STS-106 STS-101 STS-86 STS-84 STS-81 STS-79 STS-76 STS-74 STS-71 STS-66 STS-46 STS-45 STS-44 STS-43 STS-37 STS-38 STS-36 STS-34 STS-30 STS-27 STS-61-B STS-51-J X-15 X-15 Flight 91 X-15 Flight 90 Space Shuttle Discovery STS-133 STS-131 STS-128 STS-119 STS-124 STS-120 STS-116 STS-121 STS-114 STS-105 STS-102 STS-92 STS-103 STS-96 STS-95 STS-91 STS-85 STS-82 STS-70 STS-63 STS-64 STS-60 STS-51 STS-56 STS-53 STS-42 STS-48 STS-39 STS-41 STS-31 STS-33 STS-29 STS-26 STS-51-I STS-51-G STS-51-D STS-51-C STS-51-A STS-41-D Apollo Program Apollo-Soyuz Test Project Apollo 17 Apollo 16 Apollo 15 Apollo 14 Apollo 13 Apollo 12 Apollo 11 Apollo 10 Apollo 9 Apollo 8 Apollo 7 Space Shuttle Endeavour STS-134 STS-130 STS-127 STS-126 STS-123 STS-118 STS-113 STS-111 STS-108 STS-100 STS-97 STS-99 STS-88 STS-89 STS-77 STS-72 STS-69 STS-67 STS-68 STS-59 STS-61 STS-57 STS-54 STS-47 STS-49 Space Shuttle Challenger STS-51-L STS-61-A STS-51-F STS-51-B STS-41-G STS-41-C STS-41-B STS-8 STS-7 STS-6 Project Gemini Gemini XII Gemini XI Gemini X Gemini IX-A Gemini VIII Gemini VI-A Gemini VII Gemini V Gemini IV Gemini III Gemini 2 Gemini 1 Space Shuttle Columbia STS-107 STS-109 STS-93 STS-90 STS-87 STS-94 STS-83 STS-80 STS-78 STS-75 STS-73 STS-65 STS-62 STS-58 STS-55 STS-52 STS-50 STS-40 STS-35 STS-32 STS-28 STS-61-C STS-9 STS-5 STS-4 STS-3 STS-2 STS-1 Skylab Skylab 4 Skylab 3 Skylab 2 Project Mercury Mercury-Atlas 9 Mercury-Atlas 8 Mercury-Atlas 7 Mercury-Atlas 6 Mercury-Redstone 4 Mercury-Redstone 3 Soyuz programme Soyuz TMA-12M Soyuz TMA-11M Soyuz TMA-10M Soyuz TMA-09M Soyuz TMA-08M Soyuz TMA-07M Soyuz TMA-06M Soyuz TMA-05M Soyuz TMA-04M Soyuz TMA-03M Soyuz TMA-22 Soyuz TMA-02M Soyuz TMA-21 Soyuz TMA-20 Soyuz TMA-01M Soyuz TMA-19 Soyuz TMA-18 Soyuz TMA-17 Soyuz TMA-16 Soyuz TMA-15 Soyuz TMA-14 Soyuz TMA-13 Soyuz TMA-12 Soyuz TMA-11 Soyuz TMA-10 Soyuz TMA-9 Soyuz TMA-8 Soyuz TMA-7 Soyuz TMA-6 Soyuz TMA-5 Soyuz TMA-4 Soyuz TMA-3 Soyuz TMA-2 Soyuz TMA-1 Soyuz TM-34 Soyuz TM-33 Soyuz TM-32 Soyuz TM-31 Soyuz TM-30 Soyuz TM-29 Soyuz TM-28 Soyuz TM-27 Soyuz TM-26 Soyuz TM-25 Soyuz TM-24 Soyuz TM-23 Soyuz TM-22 Soyuz TM-21 Soyuz TM-20 Soyuz TM-19 Soyuz TM-18 Soyuz TM-17 Soyuz TM-16 Soyuz TM-15 Soyuz TM-14 Soyuz TM-13 Soyuz TM-12 Soyuz TM-11 Soyuz TM-10 Soyuz TM-9 Soyuz TM-8 Soyuz TM-7 Soyuz TM-6 Soyuz TM-5 Soyuz TM-4 Soyuz TM-3 Soyuz TM-2 Soyuz T-15 Soyuz T-14 Soyuz T-13 Soyuz T-12 Soyuz T-11 Soyuz T-10 Soyuz T-10-1 Soyuz T-9 Soyuz T-8 Soyuz T-7 Soyuz T-6 Soyuz T-5 Soyuz 40 Soyuz 39 Soyuz T-4 Soyuz T-3 Soyuz 38 Soyuz 37 Soyuz T-2 Soyuz 36 Soyuz 35 Soyuz 34 Soyuz 33 Soyuz 32 Soyuz 31 Soyuz 30 Soyuz 29 Soyuz 28 Soyuz 27 Soyuz 26 Soyuz 25 Soyuz 24 Soyuz 23 Soyuz 22 Soyuz 21 Soyuz 19 Soyuz 18 Soyuz 18a Soyuz 17 Soyuz 16 Soyuz 15 Soyuz 14 Soyuz 13 Soyuz 12 Soyuz 11 Soyuz 10 Soyuz 9 Soyuz 8 Soyuz 7 Soyuz 6 Soyuz 5 Soyuz 4 Soyuz 3 Soyuz 1 Voskhod programme Vostok programme

National spacefaring attempts[edit]

This section lists all nations which have explored human spaceflight programs. This should not to be confused with nations with citizens who have traveled into space including space tourists, flown or intended to fly by foreign country's or non-domestic private space systems – these are not counted as national spacefaring attempts in this list.
Nation/Organization Space agency Term(s) for space traveler First launched astronaut Date Spacecraft Launcher Type
 Union of Soviet Socialist Republics
Soviet space program
(OKB-1 Design Bureau)
космонавт (same word in:) (Russian)(Ukrainian)
Yuri Gagarin 12 April 1961 Vostok spacecraft Vostok Orbital
 United States of America National Aeronautics and Space Administration (NASA) astronaut
spaceflight participant
Alan Shepard (suborbital) 5 May 1961 Mercury spacecraft Redstone Suborbital
 United States of America National Aeronautics and Space Administration (NASA) astronaut
spaceflight participant
John Glenn (orbital) 20 February 1962 Mercury spacecraft Atlas LV-3B Orbital
 People's Republic of China Space program of the People's Republic of China 宇航员 (Chinese)
航天员 (Chinese)
... 1973 (abandoned) Shuguang 1 Long March 2A -
 People's Republic of China Space program of the People's Republic of China 宇航员 (Chinese)
航天员 (Chinese)
... 1981 (abandoned) Piloted FSW Long March 2 -
Not the esa logo.png European Space Agency CNES / European Space Agency (ESA) spationaute (French)
... 1992 (abandoned) Hermes Ariane V -
Russian Federal Space Agency (Roscosmos)
космонавт (Russian)
Alexander Viktorenko, Alexander Kaleri 17 March 1992 Soyuz-TM Soyuz-U2 Soyuz TM-14 to MIR
Iraq Ba'athist Iraq
... رجل فضاء (Arabic)
rajul faḍāʼ
رائد فضاء (Arabic)
rāʼid faḍāʼ
ملاح فضائي (Arabic)
mallāḥ faḍāʼiy
... 2001 (abandoned) ... Tammouz 2 or 3 -
Japan State of Japan National Space Development Agency of Japan (NASDA) 宇宙飛行士 (Japanese)
uchūhikōshi or
... 2003 (abandoned) HOPE-X H-II -
 People's Republic of China China National Space Administration (CNSA) 太空人 (Chinese)
tàikōng rén
宇航员 (Chinese)
航天员 (Chinese)
Yang Liwei 15 October 2003 Shenzhou spacecraft Long March 2F Orbital
India India Indian Space Research Organisation (ISRO) Vyomanaut
... after 2017 [10] Orbital Vehicle (OV) GSLV Mk III -
Iran Islamic Republic of Iran Iranian Space Agency (ISA) کیهان نورد (Persian)
kayhan navard [11]
... 2017 (planned)[12][13] ISA manned spacecraft ... -
Not the esa logo.png European Space Agency European Space Agency (ESA) astronaut ... 2020 (approved conceptually but full development not begun)[14][15][16][17] ARV phase-2 Ariane V -
Japan State of Japan Japan Aerospace Exploration Agency (JAXA) 宇宙飛行士 (Japanese)
uchūhikōshi or
... 2025 (planned)[citation needed] HTV-based spacecraft H-IIB -

Safety concerns[edit]

There are two main sources of hazard in space flight: those due to the environment of space which make it hostile to the human body, and the potential for mechanical malfunctions of the equipment required to accomplish space flight.

Environmental hazards[edit]

Planners of human spaceflight missions face a number of safety concerns.

Life support[edit]

Main article: Life support system

The immediate needs for breathable air and drinkable water are addressed by the life support system of the spacecraft.

Medical issues[edit]

Medical consequences such as possible blindness and bone loss have been associated with human space flight.[18][19]

On 31 December 2012, a NASA-supported study reported that spaceflight may harm the brain of astronauts and accelerate the onset of Alzheimer's disease.[20][21][22]

In October 2015, the NASA Office of Inspector General issued a health hazards report related to space exploration, including a human mission to Mars.[23][24]

See also: Weightlessness
The effects of microgravity on fluid distribution around the body (greatly exaggerated).

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 of bone density, decreased muscle strength and endurance, postural instability, and reductions in aerobic capacity. Over time these deconditioning effects can impair astronauts’ performance or increase their risk of injury.[25]

In a weightless environment, astronauts put almost no weight on the back muscles or leg muscles used for standing up. Those muscles then start to weaken and eventually get smaller. If there was an emergency at landing, the loss of muscles, and consequently the loss of strength could be a serious problem. Astronauts can lose up to 20% of their muscle mass on spaceflights lasting five to eleven days.[26] When they return to Earth, they will be considerably weakened and will be out of action for a while.[citation needed] Those who return from long-duration flights are not even allowed to drive a car for the next 21 days.[27]

Astronauts experiencing weightlessness will often lose their orientation, get motion sickness, and lose their sense of direction as their bodies try to get used to a weightless environment. When they get back to Earth, or any other mass with gravity, they have to readjust to the gravity and may have problems standing up, focusing their gaze, walking and turning. Importantly, those body motor disturbances after changing from different gravities only get worse the longer the exposure to little gravity.[citation needed] These changes will affect operational activities including approach and landing, docking, remote manipulation, and emergencies that may happen while landing. This can be a major roadblock to mission success.[citation needed]

In addition, after long space flight missions, male astronauts may experience severe eyesight problems.[28][29][30][31][32] Such eyesight problems may be a major concern for future deep space flight missions, including a manned mission to the planet Mars.[28][29][30][31][33]

Comparison of Radiation Doses - includes the amount detected on the trip from Earth to Mars by the RAD on the MSL (2011 - 2013).[34]

Without proper shielding, the crews of missions beyond low Earth orbit (LEO) might be at risk from high-energy protons emitted by solar flares. Lawrence Townsend of the University of Tennessee and others have studied the most powerful solar flare ever recorded. That flare was seen by the British astronomer Richard Carrington in September 1859. Radiation doses astronauts would receive from a Carrington-type flare could cause acute radiation sickness and possibly even death.[35]

Another type of radiation, galactic cosmic rays, presents further challenges to human spaceflight beyond low Earth orbit.[36]

There is also some scientific concern that extended spaceflight might slow down the body’s ability to protect itself against diseases.[37] Some of the problems are a weakened immune system and the activation of dormant viruses in the body. Radiation can cause both short and long term consequences to the bone marrow stem cells which create the blood and immune systems. 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.[citation needed]


During long missions, astronauts are isolated and confined into small spaces. Depression, cabin fever and other psychological problems may impact the crew's safety and mission success.[citation needed]

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 their limited existing resources and medical advice from the ground.

Mechanical hazards[edit]

Space flight requires much higher velocities than ground or air transportation, which in turn requires the use of high energy 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 carry the potential for fire or explosive destruction, space capsules generally employ some sort of launch escape system, consisting either of a tower-mounted solid fuel rocket to quickly carry the capsule away from the launch vehicle (employed on Mercury, Apollo, and Soyuz), or else ejection seats (employed on Vostok and Gemini) to carry astronauts out of the capsule and away for individual parachute landing.

Such a system is not always practical for multiple crew member vehicles (particularly spaceplanes), depending on location of egress hatch(es). When the single-hatch Vostok capsule was modified to become the 2 or 3-person Voskhod, 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. The Space 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.

In the only usage of a launch escape system on a manned flight, the Soyuz 7K-ST No. 16L launch on September 26, 1983 was aborted by a launch vehicle fire 90 seconds before liftoff. Both cosmonauts aboard landed safely.

The only crew fatality during launch occurred on January 28, 1986, when the Space Shuttle Challenger broke apart 73 seconds after liftoff, due to failure of a solid rocket booster seal which caused separation of the booster and failure of the external fuel tank, resulting in explosion of the fuel. All seven crew members were killed.

Reentry and landing[edit]

The single pilot of Soyuz 1, Vladimir Komarov was killed when his capsule's parachutes failed during an emergency landing on April 24, 1967, causing the capsule to crash.

The crew of seven aboard the Space Shuttle Columbia were killed on reentry after completing a successful mission in space on February 1, 2003. A wing leading edge reinforced carbon-carbon heat shield had been damaged by a piece of frozen external tank foam insulation which broke off and struck the wing during launch. Hot reentry gasses entered and destroyed the wing structure, leading to breakup of the orbiter vehicle.

Artificial atmosphere[edit]

There are two basic choices for an artificial atmosphere: either an Earth-like mixture of oxygen in 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 for extravehicular activity.

Use of a gas mixture carries risk of decompression sickness (commonly known as "the bends") when transitioning to or from the pure oxygen space suit environment. There have also been instances of injury and fatalities caused by suffocation in the presence of too much nitrogen and not enough oxygen.

  • In 1960, McDonnell Aircraft test pilot G.B. North passed out and was seriously injured when testing a Mercury cabin / spacesuit atmosphere system in a vacuum chamber, due to nitrogen-rich air leaking from the cabin into his space suit feed.[38] This incident led NASA to decide on a pure oxygen atmosphere for the Mercury, Gemini, and Apollo spacecraft.
  • In 1981, three pad workers were killed by a nitrogen-rich atmosphere in the aft engine compartment of the Space Shuttle Columbia at the Kennedy Space Center Launch Complex 39.[39]
  • In 1995, two pad workers were similarly killed by a nitrogen leak in a confined area of the Ariane 5 launch pad at Guiana Space Centre.[40]

A pure oxygen atmosphere carries 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 of Apollo 1 during a ground test at Cape Kennedy Air Force Station Launch Complex 34 on January 27, 1967, and spread rapidly. The high pressure (increased even higher by the fire) prevented removal of the plug door hatch cover in time to rescue the crew. All three, Gus Grissom, Edward H. White, and Roger Chaffee, were killed.[41] This led NASA to use a nitrogen/oxygen atmosphere before launch, and low pressure pure oxygen only in space.


The March 1966 Gemini 8 mission was aborted in orbit when an attitude control system thruster stuck in the on position, sending the craft into a dangerous spin which threatened the lives of Neil Armstrong and David 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 a static 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 and Fred Haise, were threatened by failure of a cryogenic liquid 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 loss of its remaining oxygen in a span of 130 minutes. This in turn caused loss of electrical power provided by fuel cells to the command spacecraft. The crew managed to return to Earth safely by using the lunar 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. This necessitated 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.

Fatality risk[edit]

As of 2015, 18 crew members have died during actual spaceflight missions (see table). Over 100 others have died in accidents during activity directly related to spaceflight or testing.

Year Deaths Mission Known or likely cause Accident description
1967 1 Soyuz 1 Trauma from crash landing Landing parachutes malfunctioned, resulting in a crash landing.
1971 3 Soyuz 11 Asphyxia Valve opened upon Orbital Module separation before re-entry, causing descent module to depressurize. The crew are considered to be the only humans to have died in space - all other disasters on this list occurred well below the Kármán line that marks the edge of space.
1986 7 STS-51L Space Shuttle Challenger Asphyxia from cabin breach or trauma from water impact[42] An O-ring inter-segment seal in the right Solid Rocket Booster failed, allowing hot gases to penetrate the casing of the booster. Escaping hot exhaust gas burned through a strut connecting the booster to the External Tank, which led to failure of the tank. The result was rapid combustion of the fuel in the external tank which gave the appearance of an explosion. The orbiter itself did not explode, but rather broke up due to abnormal aerodynamic forces.
2003 7 STS-107 Space Shuttle Columbia Asphyxia from cabin breach, trauma from dynamic load environment as orbiter broke up[43] During launch, a piece of insulation foam broke off of the External Tank and struck the left wing, damaging a reinforced carbon-carbon panel on the wing's leading edge. Although the foam strike was detected after the launch, it was not seen as a concern, and the extent of the damage went undetected. As the shuttle re-entered the atmosphere, hot atmospheric gases penetrated through the hole, leading to structural failure of the wing. Eventually, the shuttle lost control and subsequently disintegrated.

See also[edit]



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  • David Darling: The complete book of spaceflight. From Apollo 1 to Zero gravity. Wiley, Hoboken NJ 2003, ISBN 0-471-05649-9.
  • Wiley J. Larson (Hrsg.): Human spaceflight – mission analysis and design. McGraw-Hill, New York NY 2003, ISBN 0-07-236811-X.
  • Donald Rapp: Human missions to Mars – enabling technologies for exploring the red planet. Springer u. a., Berlin u. a. 2008, ISBN 978-3-540-72938-9.
  • Haeuplik-Meusburger: Architecture for Astronauts – An Activity based Approach. Springer Praxis Books, 2011, ISBN 978-3-7091-0666-2

External links[edit]