Extravehicular activity

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Cosmonaut Sergey Volkov works outside the International Space Station on August 3, 2011. Volkov during Russian EVA28.jpg
Cosmonaut Sergey Volkov works outside the International Space Station on August 3, 2011.
Stephen Robinson riding the Canadarm2 during STS-114, doing a first in-flight repair of the Space Shuttle. The landmass in the backdrop is the Bari region of Somalia. Sts114 033.jpg
Stephen Robinson riding the Canadarm2 during STS-114, doing a first in-flight repair of the Space Shuttle. The landmass in the backdrop is the Bari region of Somalia.

Extravehicular activity (EVA) is any activity done by an astronaut or cosmonaut outside 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). On March 18, 1965, Alexei Leonov became the first human to perform a spacewalk, exiting the capsule during the Voskhod 2 mission for 12 minutes and 9 seconds. The term also 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 July 21, 1969, Neil Armstrong became the first human to perform a moonwalk, outside his lunar lander on Apollo 11 for 2 hours and 31 minutes. On the last three Moon missions astronauts also performed deep-space EVAs on the return to Earth, to retrieve film canisters from the outside of the spacecraft. Astronauts Pete Conrad, Joseph Kerwin, and Paul Weitz also used EVA in 1973 to repair launch damage to Skylab, the United States' first space station.

Contents

A "Stand-up" EVA (SEVA) is when an astronaut does not fully leave a spacecraft, but is completely reliant on the spacesuit for environmental support. [1] Its name derives from the astronaut "standing up" in the open hatch, usually to record 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 safety device worn on tethered U.S. EVAs.

The Soviet Union/Russia, the United States, the European Space Agency and China have conducted EVAs.

Development history

NASA planners invented the term extravehicular activity (abbreviated with the acronym EVA) 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 crewed spaceflight, so the Soviet Communist Party, led by Nikita Khrushchev, ordered the conversion of its single-pilot Vostok capsule into a two- or three-person craft named Voskhod, in order to compete with Gemini and Apollo. [2] 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 overheating, therefore an airlock was required for the spacewalking cosmonaut to exit and re-enter the cabin while it remained pressurized. 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 American and Soviet space programs developed different definitions for the duration of an EVA. The Soviet (now Russian) 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 his head outside the spacecraft. [3] The USA has changed its EVA definition since.[ citation needed ]

First spacewalk

Alexei Leonov performs the first spacewalk during Voskhod 2 FirstSpaceWalk.png
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 15.35 m (50.4 ft) 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. [4]

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, 1.2 m (3 ft 11 in) in diameter and 2.5 m (8 ft 2 in) 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 "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. [4] [5]

Project Gemini

Ed White performs the first American spacewalk during Gemini IV EdWhiteFirstAmericanSpacewalker.1965.ws.jpg
Ed White performs the first American spacewalk during Gemini IV

The first American spacewalk was performed on June 3, 1965, by Ed White from the second crewed Gemini flight, Gemini IV, for 21 minutes. White was tethered to the spacecraft, and his oxygen was supplied through a 25-foot (7.6 m) 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. [4] 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. [6]

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, and 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 underwater EVA training to simulate weightlessness, which has been used ever since to allow astronauts to practice techniques of avoiding wasted muscle energy.

First EVA crew transfer

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. [4]

Apollo lunar EVA

Buzz Aldrin walks on the Moon during the pioneering Apollo 11 mission in 1969 Aldrin Apollo 11 original.jpg
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 Lunar Module spacecraft. This first Moon walk, using self-contained portable life support systems, lasted 2 hours and 36 minutes. A total of fifteen Moon walks were performed among six Apollo crews, including Charles "Pete" Conrad, Alan Bean, Alan Shepard, Edgar Mitchell, David Scott, James Irwin, John Young, Charles Duke, Eugene Cernan, and Harrison "Jack" Schmitt. Cernan was the last Apollo astronaut to step off the surface of the Moon. [4]

Charles Duke with a hammer on the lunar surface

Apollo 15 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 and Harrison Schmitt on Apollo 17. [4]

Post-Apollo EVAs

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. [4] They found that activities in weightlessness required about 212 times longer than on Earth because many astronauts suffered spacesickness early in their flights. [7]

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. [4]

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.[ citation needed ]

Chinese EVA

China became the third country to independently carry out an EVA on September 27, 2008 during the Shenzhou 7 mission. Chinese astronaut Zhai Zhigang completed a spacewalk wearing the Chinese-developed Feitian space suit, with astronaut Liu Boming wearing the Russian-derived Orlan space suit to help him. Zhai completely exited the craft, while Liu stood by at the airlock, straddling the portal.

Milestones

Capability milestones

Untethered U.S. astronaut Bruce McCandless uses a manned maneuvering unit. Photo taken by Robert "Hoot" Gibson Bruce McCandless II during EVA in 1984.jpg
Untethered U.S. astronaut Bruce McCandless uses a manned maneuvering unit. Photo taken by Robert "Hoot" Gibson
Capture of Intelsat VI in 1992 on STS-49. This hand-capture of a satellite is the only EVA to date to be performed by three astronauts. Three Crew Members Capture Intelsat VI - GPN-2000-001035.jpg
Capture of Intelsat VI in 1992 on STS-49. This hand-capture of a satellite is the only EVA to date to be performed by three astronauts.

Personal cumulative duration records

National, ethnic and gender firsts

International Space Station assembly EVA made during the STS-116 mission. Robert Curbeam (with red stripes) together with Christer Fuglesang over Cook Strait, New Zealand. STS-116 spacewalk 1.jpg
International Space Station assembly EVA made during the STS-116 mission. Robert Curbeam (with red stripes) together with Christer Fuglesang over Cook Strait, New Zealand.
Anatoly Solovyev holds the record for time spent during spacewalks: 82+ hours over 16 separate outings, seen here performing an EVA outside Mir space station in 1997 SolovyevEVA.jpg
Anatoly Solovyev holds the record for time spent during spacewalks: 82+ hours over 16 separate outings, seen here performing an EVA outside Mir space station in 1997

Commemoration

The first spacewalk, made by Soviet cosmonaut Alexei Leonov, was commemorated in 1965 with several Eastern Bloc stamps (see Alexei Leonov#Stamps). Since the Soviet Union did not publish details of the Voskhod spacecraft at the time, the spaceship depiction in the stamps was purely fictional.

The U.S. Post Office issued a postage stamp in 1967 commemorating Ed White's first American spacewalk. The engraved image has an accurate depiction of the Gemini IV spacecraft and White's space suit. [19]

Alexei Leonov, Voskhod 2, First Spacewalk
U.S.S.R. commemorative issue of 1965 Soviet Union-1965-Stamp-0.10. Voskhod-2. First Spacewalk.jpg
Alexei Leonov, Voskhod 2, First Spacewalk
U.S.S.R. commemorative issue of 1965
Accomplishments in Space
U.S. Commemorative Issue of 1967 US Space Walk 1967 Issue-5c.jpg
Accomplishments in Space
U.S. Commemorative Issue of 1967

Designations

NASA "spacewalkers" during the Space Shuttle program were designated as EV-1, EV-2, EV-3 and EV-4 (assigned to mission specialists for each mission, if applicable). [20] [21]

Camp-out procedure

For EVAs from the International Space Station, NASA employed a camp-out procedure to reduce the risk of decompression sickness. [22] This was first tested by the Expedition 12 crew. During a camp out, astronauts sleep overnight in the airlock prior to an EVA, lowering the air pressure to 10.2 psi (70 kPa), compared to the normal station pressure of 14.7 psi (101 kPa). [22] Spending a night at the lower air pressure helps flush nitrogen from the body, thereby preventing "the bends". [23] [24] More recently astronauts have been using the In-Suit Light Exercise protocol rather than camp-out to prevent decompression sickness. [25] [26]

See also

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A space suit is a garment worn to keep a human alive in the harsh environment of outer space, vacuum and temperature extremes. Space suits are often worn inside spacecraft as a safety precaution in case of loss of cabin pressure, and are necessary for extravehicular activity (EVA), work done outside spacecraft. Space suits have been worn for such work in Earth orbit, on the surface of the Moon, and en route back to Earth from the Moon. Modern space suits augment the basic pressure garment with a complex system of equipment and environmental systems designed to keep the wearer comfortable, and to minimize the effort required to bend the limbs, resisting a soft pressure garment's natural tendency to stiffen against the vacuum. A self-contained oxygen supply and environmental control system is frequently employed to allow complete freedom of movement, independent of the spacecraft.

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Voskhod 2 Soviet manned spacecraft

Voskhod 2 was a Soviet crewed space mission in March 1965. The Vostok-based Voskhod 3KD spacecraft with two crew members on board, Pavel Belyayev and Alexei Leonov, was equipped with an inflatable airlock. It established another milestone in space exploration when Alexei Leonov became the first person to leave the spacecraft in a specialized spacesuit to conduct a 12-minute spacewalk.

Alexei Leonov Soviet cosmonaut, first person to perform spacewalk

Alexei Arkhipovich Leonov was a Soviet and Russian cosmonaut, Air Force major general, writer, and artist. On 18 March 1965, he became the first person to conduct a spacewalk, exiting the capsule during the Voskhod 2 mission for 12 minutes and 9 seconds.

Manned Maneuvering Unit

The Manned Maneuvering Unit (MMU) is an astronaut propulsion unit that was used by NASA on three Space Shuttle missions in 1984. The MMU allowed the astronauts to perform untethered extravehicular spacewalks at a distance from the shuttle. The MMU was used in practice to retrieve a pair of faulty communications satellites, Westar VI and Palapa B2. Following the third mission the unit was retired from use. A smaller successor, the Simplified Aid For EVA Rescue (SAFER), was first flown in 1994, and is intended for emergency use only.

Apollo–Soyuz First joint U.S.–Soviet space flight

Apollo–Soyuz was the first international space mission, carried out jointly by the United States and the Soviet Union in July 1975. Millions of people around the world watched on television as a United States Apollo module docked with a Soviet Union Soyuz capsule. The project, and its memorable handshake in space, was a symbol of détente between the two superpowers. It is generally considered to mark the end of the Space Race, which had begun in 1957 with the launch of Sputnik 1.

STS-104 human spaceflight

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Extravehicular Mobility Unit Series of semi-rigid two-piece space suit models from the United States

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History of spaceflight aspect of the history of astronautics, and of the exploration or conquest of outer space and of the solar system outside Earth

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Astronaut propulsion unit

An astronaut propulsion unit is used to move an astronaut relative to the spaceship during a spacewalk. The first astronaut propulsion unit was the Hand-Held Maneuvering Unit (HHMU) used on Gemini 4.

References

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