Extra-vehicular activity (EVA) is any activity done by an astronaut or cosmonaut outside of a spacecraft beyond the Earth's appreciable atmosphere. The term most commonly applies to a spacewalk made outside a craft orbiting Earth (such as the International Space Station), but also has applied to lunar surface exploration (commonly known as moonwalks) performed by six pairs of American astronauts in the Apollo program from 1969 to 1972. On each of the last three of these missions, astronauts also performed deep-space EVAs on the return to Earth, to retrieve film canisters from the outside of the spacecraft. Astronauts also used EVA in 1973 to repair launch damage to Skylab, the United States' first space station.
A "Stand-up" EVA (SEVA) is where the astronaut does not fully leave a spacecraft, but is completely reliant on the spacesuit for environmental support. Its name derives from the astronaut "standing up" in the open hatch, usually to film or assist a spacewalking astronaut.
EVAs may be either tethered (the astronaut is connected to the spacecraft; oxygen and electrical power can be supplied through an umbilical cable; no propulsion is needed to return to the spacecraft), or untethered. Untethered spacewalks were only performed on three missions in 1984 using the Manned Maneuvering Unit (MMU), and on a flight test in 1994 of the Simplified Aid for EVA Rescue (SAFER). A SAFER is a safety device worn on tethered U.S. EVAs, since the capability of returning to the spacecraft is essential.
NASA planners invented the term extra-vehicular activity in the early 1960s for the Apollo program to land men on the Moon, because the astronauts would leave the spacecraft to collect lunar material samples and deploy scientific experiments. To support this, and other Apollo objectives, the Gemini program was spun off to develop the capability for astronauts to work outside a two-man Earth orbiting spacecraft. However, the Soviet Union was fiercely competitive in holding the early lead it had gained in manned spaceflight, so the Soviet Communist Party, led by Nikita Khrushchev, ordered the hasty conversion of its single-pilot Vostok capsule into a two- or three-person craft named Voskhod, in order to compete with Gemini and Apollo. The Soviets were able to launch two Voskhod capsules before the first manned Gemini was launched.
The Soviets' avionics technology was not as advanced as that of the United States, so the Voskhod cabin could not have been left depressurized by an open hatch; otherwise the air-cooled electronics would have overheated. Therefore a spacewalking cosmonaut would have to enter and exit the spacecraft through an airlock. By contrast, the Gemini capsule's avionics were designed so the cabin could be exposed to the vacuum of space when one of two large hatches was opened, so no airlock was required, and both the spacewalking astronaut and his companion command pilot were in vacuum during the EVA. Due to the different designs of the spacecraft, the American and Soviet space programs define the duration of an EVA differently. The Soviet (now Russian) definition is the time when the outer airlock hatch is open and the cosmonaut is in a vacuum. An American EVA begins when the spacewalking astronaut has at least his head outside of the spacecraft.
As they had with the first satellite and first man in space, the Soviets again stunned the world on March 18, 1965 with the first spacewalk (and the first EVA) performed by Alexey Leonov from the Voskhod 2 spacecraft, for 12 minutes outside the spacecraft. Leonov had no means to control his motion other than pulling on his 50.7-foot (15.5 m) 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.
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, 3.96 feet (1.21 m) in diameter and 8.25 feet (2.51 m) long. After his spacewalk, 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 "the bends". This added another 12 minutes to his time in vacuum, and he was overheated by 1.8 °C (3.2 °F) 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.
The first American spacewalk was performed on June 3, 1965, by Edward H. White, II from the second manned Gemini flight, Gemini 4, for 21 minutes, on a 25-foot (7.6 m) tether. White 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. 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.
No EVAs were planned on the next three Gemini flights. The next EVA was planned to be made by David Scott on Gemini 8, 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, and Richard Gordon), performed several EVAs, but none was able to successfully work for long periods outside the spacecraft without tiring and overheating.
Finally, on November 13, 1966, Edwin "Buzz" Aldrin became the first to successfully work in space without tiring, on the Gemini 12 last flight. 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 underwater EVA training to simulate weightlessness, which has been used ever since to allow astronauts to practice techniques of avoiding wasted muscle energy.
On January 16, 1969, the Soviet Union achieved the first EVA crew transfer from one spacecraft to another when 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.
The first EVA on the lunar surface was performed by Americans Neil Armstrong and Buzz Aldrin on July 21, 1969 (UTC), after the Apollo 11 Moon landing. This first Moon walk lasted 2 hours, 36 minutes. A total of fifteen Moon walks were performed by members of six Apollo crews, including Charles "Pete" Conrad, Alan Bean, Alan Shepard, Edgar Mitchell, David Scott, James Irwin, John Young, Charles Duke, Eugene "Gene" Cernan, and Dr. Harrison "Jack" Schmitt. Cernan was the last Apollo astronaut to step off the surface of the Moon.
File:Astronaut Charles Duke with a hammer on the lunar surface - pone.0006614.s003.ogv The first EVA in deep space was made on August 5, 1971, by American Al Worden, to retrieve a film and data recording canister from the Apollo 15 Service Module on the return trip from the Moon. Worden was assisted by James Irwin, doing a standup EVA in the Command Module hatch. This was repeated by Ken Mattingly and Charles Duke on Apollo 16 and by Ronald Evans and Harrison Schmitt on Apollo 17.
The first EVA repairs of a spacecraft were made by Charles "Pete" Conrad, 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 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. They found that activities in weightlessness required about 2 1/2 times the duration as on Earth because many astronauts suffered spacesickness early in their flights.
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.
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. 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.
- The first metalwork in open space consisting in works of welding, brazing and metal spraying were conducted by cosmonauts Svetlana Savitskaya and Vladimir Dzhanibekov of the Soviet Union on July 25, 1984. To perform these activities a specially designed URI multipurpose tool was used during a 3 hr, 30 min EVA outside the Salyut 7 space station.
- The first untethered spacewalk was made by American Bruce McCandless II on February 7, 1984, during Challenger mission STS-41-B, utilizing the Manned Maneuvering Unit. He was subsequently joined by Robert L. Stewart during the 5 hour 55 minute spacewalk. Such a self-contained spacewalk was first attempted by Eugene Cernan in 1966 on Gemini 9A, but Cernan could not reach the maneuvering unit without tiring.
- The first three-person EVA was performed on May 13, 1992, as the third EVA of STS-49, the maiden flight of Endeavour. Pierre Thuot, Richard Hieb, and Thomas Akers conducted the EVA to hand-capture and repair a non-functional Intelsat VI-F3 satellite. As of 2013[update] it was the only three-person EVA.
- The first EVA to perform an in-flight repair of the Space Shuttle was by American Steve Robinson on August 3, 2005, during "Return to Flight" mission STS-114. Robinson was sent to remove two protruding gap fillers from Discovery's heat shield, after engineers determined there was a small chance they could affect the shuttle upon re-entry. Robinson successfully removed the loose material while Discovery was docked to the International Space Station.
- The longest EVA as of 2007, was 8 hours and 56 minutes, performed by Susan J. Helms and James S. Voss on March 11, 2001.
Personal cumulative duration records
- Russian Anatoly Solovyev holds both the record for most EVAs and for the greatest cumulative duration spent in EVA (16 EVAs; 82 hr and 22 min).
- Michael Lopez-Alegria holds the American record (10 EVAs; 67 hr and 40 min).
- Christer Fuglesang holds the European (non-Russian) record (5 EVAs; 31 hr and 55 min).
National, ethnic and gender firsts
- The first woman to perform an EVA was Soviet Svetlana Savitskaya on July 25, 1984 while aboard the Salyut 7 space station. Her EVA lasted 3 hours and 35 minutes.
- The first American woman to perform an EVA was Kathryn D. Sullivan on October 11, 1984 during Space Shuttle Challenger mission STS-41-G.
- The first EVA by a non-Soviet, non-American was made on December 9, 1988 by Jean-Loup Chrétien of France during a three-week stay on the Mir space station.
- The first EVA by a Briton was on February 9, 1995 by Michael Foale (who carries dual British-American citizenship).
- The first EVA by a black African-American was on February 9, 1995 by Bernard A. Harris, Jr..
- The first EVA by a Japanese astronaut was made on November 25, 1997 by Doi Takao during STS-87.
- The first EVA by an Australian-born person was on March 13, 2001 by Andy Thomas (although he is a naturalized US citizen).
- The first EVA by a Canadian was made on April 22, 2001 by Chris Hadfield. During his spacewalk, Hadfield installed the Canadarm2 onto the International Space Station.
- The first EVA by a Scandinavian astronaut was made on December 12, 2006 by Christer Fuglesang.
- The first EVA by a Chinese astronaut was made on September 27, 2008 by Zhai Zhigang during Shenzhou 7 mission. The spacewalk, using a Feitian space suit, made China the third country to independently carry out an EVA.
- The first EVA by an Italian astronaut was made on July 9, 2013 by Luca Parmitano along with NASA Astronaut Chris Cassidy during Expedition 36 on the International Space Station.
The first spacewalk, that of the Soviet cosmonaut Alexey Leonov was commemorated in several Eastern Bloc stamps (see the stamps section in the Alexey Leonov article). Since the Soviet Union did not distribute diagrams or images of the Voskhod spacecraft at the time, the spaceship depiction in the stamps was purely fictional.
The US Post Office issued the Accomplishments in Space stamp in 1967. Along with astronaut Ed White, the issue depicts the Gemini IV spacecraft in orbit.
For EVAs from the International Space Station, NASA now routinely employs a camp out procedure to reduce the risk of decompression sickness. This was first tested by the Expedition 12 crew. During a camp out, astronauts sleep overnight prior to an EVA in the airlock, and lower the air pressure to 10.2 psi (70 kPa), compared to the normal station pressure of 14.7 psi (101 kPa). Spending a night at the lower air pressure helps flush nitrogen from the body, thereby preventing "the bends".
|Commons has media related to Extra-vehicular activity.|
- PDF document.
- Astronaut space walk picture
- NASDA Online Space Notes
- Apollo Extravehicular mobility unit. Volume 1: System description - 1971 (PDF document)
- Apollo Extravehicular mobility unit. Volume 2: Operational procedures - 1971 (PDF document)
- Skylab Extravehicular Activity Development Report - 1974 (PDF document)
- Analysis of the Space Shuttle Extravehicular Mobility Unit - 1986 (PDF document)
- NASA Space Shuttle EVA tools and equipment reference book - 1993 (PDF document)
- Preparing for an American EVA on the ISS - 2006