Editing Extravehicular activity (section)

==Development history==
[[NASA]] planners invented the term ''extravehicular activity'' (abbreviated with the acronym EVA) in the early 1960s for the [[Apollo program]] to land humans on the Moon, because the astronauts would leave the spacecraft to collect [[moon rock|lunar material samples]] and deploy scientific experiments. To support this, and other Apollo objectives, the [[Project Gemini|Gemini program]] was spun off to develop the capability for astronauts to work outside a two-person Earth orbiting spacecraft. However, the [[Soviet Union]] was fiercely competitive in holding the early lead it had gained in crewed spaceflight, so the [[Communist Party of the Soviet Union|Soviet Communist Party]], led by [[Nikita Khrushchev]], ordered the conversion of its single-pilot [[Vostok (spacecraft)|Vostok]] capsule into a two- or three-person craft named [[Voskhod spacecraft|Voskhod]], in order to compete with [[Gemini program|Gemini]] and [[Apollo (spacecraft)|Apollo]].<ref name="Siddiqi 384-6">{{cite book
 |title= Sputnik and the Soviet Space Challenge
 |last= Siddiqi
 |first= Asif A.
 |year= 2003a
 |publisher= [[University Press of Florida]]
 |location= Gainesville
 |isbn= 0-8130-2627-X
}}</ref> The Soviets were able to launch two Voskhod capsules before U.S. was able to launch its first crewed Gemini.

The Voskhod's [[avionics]] required cooling by cabin air to prevent any kind of overheating, therefore an [[airlock]] was required for the spacewalking [[cosmonaut]] to exit and re-enter the cabin while it remained pressurized. Unusually, and by contrast, the Gemini avionics did not require air cooling, allowing the spacewalking astronaut to exit and re-enter the depressurized cabin through an open hatch. Because of this, the [[United States|American]] and [[Soviet Union|Soviet]] space programs developed different definitions for the duration of an EVA. The Soviet (now [[Russia]]n) definition begins when the outer airlock hatch is open and the cosmonaut is in [[vacuum]]. An American EVA began when the astronaut had at least their head outside the spacecraft.<ref>''Walking to Olympus'', p. ix.</ref> The U.S. has changed its EVA definition since.<ref>{{Cite book |last=Dasch |first=E. Julius |url=http://oxfordreference.com/view/10.1093/acref/9780191842764.001.0001/acref-9780191842764 |title=A Dictionary of Space Exploration |date=2018 |publisher=Oxford University Press |editor-last=O’Meara |editor-first=Stephen James |volume=1 |language=en |doi=10.1093/acref/9780191842764.001.0001|isbn=978-0-19-184276-4 }}</ref><ref>{{Cite book |url=https://msis.jsc.nasa.gov/ |title=Man-Systems Integration Standards |publisher=NASA |year=1995 |edition=Revised B |volume=one |location= |language=en |chapter=Extravehicular Activity}}</ref>

===<span class="anchor" id="First spacewalk">First instance</span>===
[[File:FirstSpaceWalk.png|thumb|right|[[Alexei Leonov]] performs the first spacewalk during [[Voskhod 2]].]]

The first EVA was performed on March 18, 1965, by Soviet cosmonaut [[Alexei Leonov]], who spent 12 minutes and 9 seconds outside the [[Voskhod 2]] spacecraft. Carrying a white metal backpack containing 45 minutes' worth of breathing and pressurization oxygen, Leonov had no means to control his motion other than pulling on his {{convert|15.35|m|abbr=on}} tether. After the flight, he claimed this was easy, but his [[space suit]] ballooned from its internal pressure against the vacuum of space, stiffening so much that he could not activate the shutter on his chest-mounted camera.<ref name="portree"/>

At the end of his space walk, the suit stiffening caused a more serious problem: Leonov had to re-enter the capsule through the inflatable cloth airlock, {{convert|1.2|m|abbr=on}} in diameter and {{convert|2.5|m|abbr=on}} long. He improperly entered the airlock head-first and got stuck sideways. He could not get back in without reducing the pressure in his suit, risking "[[decompression sickness|the bends]]". This added another 12 minutes to his time in vacuum, and he was overheated by {{convert|1.8|C-change|F-change}} from the exertion. It would be almost four years before the Soviets tried another EVA. They misrepresented to the press how difficult Leonov found it to work in [[weightlessness]] and concealed the problems encountered until after the end of the [[Cold War]].<ref name="portree">{{cite web |url=http://www.jsc.nasa.gov/history/walking/EVAChron.pdf |title=Walking to Olympus: An EVA Chronology |access-date=2015-07-30 |last1=Portree |first1=David S. F. |first2=Robert C. |last2=Treviño |date=October 1997 |work=Monographs in Aerospace History Series #7 |publisher=NASA History Office |pages=1–2}}</ref><ref name=First-Spacewalk>{{cite web |url=https://www.bbc.co.uk/news/special/2014/newsspec_9035/index.html |title=The First Spacewalk How the first human to take steps in outer space nearly didn't return to Earth |last1=Rincon |first1=Paul |last2=Lachmann |first2=Michael |date=October 13, 2014 |work=BBC News |archive-url=https://web.archive.org/web/20160216020616/http://www.bbc.co.uk/news/special/2014/newsspec_9035/index.html |archive-date=February 16, 2016 |access-date=2014-10-19}}</ref>

===Project Gemini===
[[File:EdWhiteFirstAmericanSpacewalker.1965.ws.jpg|thumb|[[Ed White (astronaut)|Ed White]] performs the first American spacewalk during [[Gemini IV]].]]

The first American spacewalk was performed on June 3, 1965, by [[Ed White (astronaut)|Ed White]] from the second crewed [[Project Gemini|Gemini]] flight, [[Gemini IV]], for 21 minutes. White was tethered to the spacecraft, and his oxygen was supplied through a {{convert|25|ft|adj=on}} [[umbilical cable|umbilical]], which also carried communications and biomedical instrumentation. He was the first to control his motion in space with a [[Hand-Held Maneuvering Unit]], which worked well but only carried enough propellant for 20 seconds. White found his tether useful for limiting his distance from the spacecraft but difficult to use for moving around, contrary to Leonov's claim.<ref name="portree"/> However, a defect in the capsule's hatch latching mechanism caused difficulties opening and closing the hatch, which delayed the start of the EVA and put White and his crewmate at risk of not getting back to Earth alive.<ref name="mcdivittoh">Oral History Transcript / [http://www.jsc.nasa.gov/history/oral_histories/McDivittJA/mcdivittja.pdf James A. McDivitt] / Interviewed by Doug Ward / Elk Lake, Michigan – June 29, 1999.</ref>

No EVAs were planned on the next three Gemini flights. The next EVA was planned to be made by [[David Scott]] on [[Gemini VIII]], but that mission had to be aborted due to a critical spacecraft malfunction before the EVA could be conducted. Astronauts on the next three Gemini flights ([[Eugene Cernan]], [[Michael Collins (astronaut)|Michael Collins]], and [[Richard F. Gordon Jr.|Richard Gordon]]), performed several EVAs, but none was able to successfully work for long periods outside the spacecraft without tiring and overheating. Cernan attempted but failed to test an Air Force [[Astronaut Maneuvering Unit]] which included a self-contained oxygen system.

On November 13, 1966, [[Edwin "Buzz" Aldrin]] became the first to successfully work in space without tiring during [[Gemini XII]], the last Gemini mission. Aldrin worked outside the spacecraft for 2 hours and 6 minutes, in addition to two stand-up EVAs in the spacecraft hatch for an additional 3 hours and 24 minutes. Aldrin's interest in [[scuba diving]] inspired the use of [[Neutral buoyancy simulation as a training aid|underwater EVA training]] to simulate weightlessness, which has been used ever since to allow astronauts to practice techniques of avoiding wasted muscle energy.

===<span class="anchor" id="First EVA crew transfer">First crew transfer</span>===
On January 16, 1969, Soviet cosmonauts [[Aleksei Yeliseyev]] and [[Yevgeny Khrunov]] transferred from [[Soyuz 5]] to [[Soyuz 4]], which were docked together. This was the second Soviet EVA, and it would be almost another nine years before the Soviets performed their third.<ref name="portree"/>

===<span class="anchor" id="Apollo lunar EVA">Apollo missions</span>===
[[File:Aldrin Apollo 11 original.jpg|thumb|right|[[Buzz Aldrin]] walks on the Moon during the pioneering [[Apollo 11]] mission in 1969.]]

American astronauts [[Neil Armstrong]] and [[Buzz Aldrin]] performed the first EVA on the lunar surface on July 21, 1969 ([[UTC]]), after landing their [[Apollo 11]] [[Apollo Lunar Module|Lunar Module]] spacecraft. This first Moon walk, using self-contained [[portable life support system]]s, lasted 2 hours and 36 minutes. A total of fifteen Moon walks were performed among six Apollo crews, including [[Pete Conrad|Charles "Pete" Conrad]], [[Alan Bean]], [[Alan Shepard]], [[Edgar Mitchell]], [[David Scott]], [[James Irwin]], [[John Young (astronaut)|John Young]], [[Charles Duke]], [[Eugene Cernan]], and [[Harrison Schmitt|Harrison "Jack" Schmitt]]. Cernan was the last Apollo astronaut to step off the surface of the Moon.<ref name="portree"/>

[[File:Astronaut Charles Duke with a hammer on the lunar surface - pone.0006614.s003.ogv|thumb|[[Charles Duke]] with a hammer on the lunar surface]]

[[Apollo 15]] [[Apollo command and service module|command module]] pilot [[Al Worden]] made an EVA on August 5, 1971, on the return trip from the Moon, to retrieve a film and data recording canister from the service module. He was assisted by Lunar Module Pilot James Irwin standing up in the Command Module hatch. This procedure was repeated by [[Ken Mattingly]] and Charles Duke on [[Apollo 16]], and by [[Ronald Evans (astronaut)|Ronald Evans]] and Harrison Schmitt on [[Apollo 17]].<ref name="portree"/>

===<span class="anchor" id="Post-Apollo EVAs">Post-Apollo</span>===
The first EVA repairs of a spacecraft were made by [[Pete Conrad|Charles "Pete" Conrad]], [[Joseph P. Kerwin|Joseph Kerwin]], and [[Paul J. Weitz]] on May 26, June 7, and June 19, 1973, on the [[Skylab 2]] mission. They rescued the functionality of the launch-damaged [[Skylab]] [[space station]] by freeing a stuck [[solar panels on spacecraft|solar panel]], deploying a solar heating shield, and freeing a stuck circuit breaker relay. The Skylab 2 crew made three EVAs, and a total of ten EVAs were made by the three Skylab crews.<ref name="portree"/> They found that activities in weightlessness required about 2{{frac|1|2}} times longer than on Earth because many astronauts suffered [[spacesickness]] early in their flights.<ref name="reusestudy">''[https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19790075817_1979075817.pdf Skylab Reuse Study]'', p. 3-53. Martin Marietta and Bendix for NASA, September 1978.</ref>

After Skylab, no more EVAs were made by the United States until the advent of the [[Space Shuttle]] program in the early 1980s. In this period, the Soviets resumed EVAs, making four from the [[Salyut 6]] and [[Salyut 7]] space stations between December 20, 1977, and July 30, 1982.<ref name="portree"/>

When the United States resumed EVAs on April 7, 1983, astronauts started using an [[Extravehicular Mobility Unit]] (EMU) for self-contained life support independent of the spacecraft. STS-6 was the first Space Shuttle mission during which a spacewalk was conducted. Also, for the first time, American astronauts used an airlock to enter and exit the spacecraft like the Soviets. Accordingly, the American definition of EVA start time was redefined to when the astronaut switches the EMU to battery power.<ref>{{cite news|title=Second all-female spacewalk devoted to space station battery replacements|author=William Harwood|date=January 15, 2020|url=https://www.cbsnews.com/news/second-all-female-spacewalk-nasa-astronauts-space-station-live-stream-today-2020-01-15/
|publisher=CBS News|access-date=May 25, 2023}}</ref>

Numerous EVAs were conducted during the assembly of the [[International Space Station|ISS]], often using the [[Quest Joint Airlock]], designed to support both U.S. EMUs, and Russian Orlan space suits.

===<span class="anchor" id="Chinese EVA">By China</span>===
[[File:Shenzhou-15 spacewalk.jpg|Astronaut Fei Junlong performing a spacewalk on the Tiangong Space Station|thumb]]
[[China]] became the third [[country]] to independently carry out an EVA on September 27, 2008, during the [[Shenzhou 7]] mission. Chinese taikonaut [[Zhai Zhigang]] completed a 22-minute spacewalk wearing the Chinese-developed [[Feitian space suit]], with taikonaut [[Liu Boming (astronaut)|Liu Boming]] wearing the Russian-derived [[Orlan space suit]] assisting him in the process. Zhai completely exited the craft, while Liu stood by at the airlock, straddling the portal.

Since 2021, China has carried out several more EVAs lasting several hours for the construction of the [[Tiangong space station]]. In December 2024 China's [[Cai Xuzhe]] and [[Song Lingdong]] set the current record for the longest EVA at 9 hours and six minutes.<ref name=":0" /><ref name=":1">{{Cite web |author1=Mike Wall |date=2024-12-18 |title=Chinese astronauts perform record-breaking 9-hour spacewalk outside Tiangong space station (video) |url=https://www.space.com/space-exploration/human-spaceflight/chinese-astronauts-conduct-record-breaking-9-hour-spacewalk-outside-tiangong-space-station-photos |access-date=2025-01-14 |website=Space.com |language=en-US}}</ref> 

=== By SpaceX ===
American company [[SpaceX]] conducted the first private sector-financed EVA on September 12, 2024. Entrepreneur [[Jared Isaacman]] and SpaceX engineer [[Sarah Gillis]] briefly ventured outside a [[SpaceX Dragon|Dragon]] capsule, for a stand-up EVA (SEVA) during the [[Polaris Dawn]] mission to conduct [[Space suit|spacesuit]] mobility testing. <ref>{{Cite news |last=Patel-Carstairs |first=Sunita |date=12 September 2024 |title=SpaceX Polaris Dawn: Billionaire Jared Isaacman becomes first person to take part in private spacewalk |url=https://news.sky.com/story/spacex-polaris-dawn-billionaire-jared-isaacman-becomes-first-person-to-take-part-in-private-spacewalk-13213265 |url-status=live |archive-url=https://web.archive.org/web/20240912121617/https://news.sky.com/story/spacex-polaris-dawn-billionaire-jared-isaacman-becomes-first-person-to-take-part-in-private-spacewalk-13213265 |archive-date=12 September 2024 |access-date=12 September 2024 |work=[[Sky News]]}}</ref> The other two crew members were exposed to the vacuum of space in the capsule, but did not leave it.<ref>{{cite news|url=https://www.space.com/spacex-polaris-dawn-first-private-spacewalk|title=SpaceX Polaris Dawn astronauts perform historic 1st private spacewalk in orbit (video)|publisher=space.com|date=12 September 2024|access-date=12 September 2024}}</ref> SpaceX plans to launch at least two more missions involving an EVA,<ref>{{cite web|url=https://thetimes.com/world/us-world/article/polaris-dawn-spacex-what-comes-next-commercial-space-85258s8rv |newspaper=[[The Times]] |date=September 12, 2024 |first=Jacqui |last=Goddard |title=SpaceX's success redefines the commercial space frontier, but what's next? |access-date=September 12, 2024}}</ref> including one that involves SpaceX's still-in-development [[SpaceX Starship|Starship]] launch vehicle.<ref>{{cite web|url=https://www.washingtonpost.com/technology/2024/09/12/spacex-polaris-dawn-spacewalk-astronauts/ |first=Christian |last=Davenport |newspaper=[[The Washington Post]] |date=September 12, 2024 |title=SpaceX Polaris astronauts complete first spacewalk by private citizens |access-date=September 12, 2024}}</ref>