Extra-vehicular activity

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Mike Fossum works on the Kibo Module (JPM) during the second spacewalk of STS-124.

Extra-vehicular activity (EVA) is work done by an astronaut away from the Earth, and outside of a spacecraft. The term most commonly applies to an EVA made outside a craft orbiting Earth (a spacewalk), but also applies to an EVA made on the surface of the Moon (a moonwalk). In the later lunar landing missions (Apollo 15, 16, and 17) the command module pilot (CMP) did an EVA to retrieve film canisters on the return trip; he was assisted by the lunar module pilot (LMP) who remained at the open CM hatch. These trans-Earth EVAs were the only spacewalks ever conducted in deep space to date.

Due to the different designs of the early spacecraft, the American and Soviet space programs also define an EVA differently. Russians define an EVA as occurring when a cosmonaut is in a vacuum. An American astronaut EVA begins when the astronaut switches the Extravehicular Mobility Unit (EMU) to battery power. A "Stand-up" EVA (SEVA) is where the astronaut does not fully exit 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 film or assist a spacewalking astronaut.

EVAs may be either tethered (the astronaut is connected to the spacecraft, oxygen can be supplied through a tube, no propulsion is needed to return to the spacecraft) or untethered. When the tether performs life support functions such as providing oxygen, it is called an umbilical. 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.

As of 2008, Russia, the United States, and China are the only countries with the capability to conduct an EVA.

[edit] EVA hazards

Tear in glove during STS-118

Astronaut Bruce McCandless on an untethered EVA. During an untethered EVA, the astronaut is far from help.

Spacewalks are dangerous for a number of different reasons. The primary one is collision with space debris.^[2][3] Velocity while orbiting 300km above the Earth (typical for a space shuttle mission) is 7.7 km/s. This is approximately ten times the speed of a bullet. This means that a particle approximately 100 times smaller than a bullet, would have the same effect at that velocity. Nearly every space mission creates more orbiting debris, so this problem will continue to worsen.^[3]

Another reason for danger is that external environments in space are harder to simulate before the mission, though approximate simulations can be achieved at facilities like the Hydro-labs in Star City's Gagarin Training Center and NASA's Neutral Buoyancy Laboratory. Space walks are avoided for routine tasks because of their danger. As a result the EVAs are often planned late in the project development when problems are discovered, or sometimes even during an operational mission. The exceptional danger involved in EVAs inevitably leads to emotional pressures on astronauts.

Other possible problems include a space walker becoming separated from his or her craft or suffering a spacesuit puncture which would depressurize the suit, causing anoxia and rapid death if the space walker is not brought into a pressurized spacecraft quickly.

One astronaut has suffered a spacesuit puncture. During STS-37, a small rod punctured the glove of one of the astronauts (the name was not disclosed, but it was either Jerry L. Ross or Jay Apt). The puncturing object held in place, resulting in no detectable depressurization, and was not noticed until after the space walkers were safely back inside Atlantis.^[4]

Alexey Leonov's EVA did not pass smoothly either. During the EVA, Leonov's suit became overinflated to the point he could no longer re-enter or seal the door of the airlock on Voskhod 2. Because he was breathing pure oxygen, he was able to reduce his suit pressure to under 4 psi (28 kPa) and, with effort, climb back inside.^[5]

As of 2008, no catastrophic incident has ever occurred during an extra-vehicular activity, and no astronaut or cosmonaut has ever died during one.^[6] Given the considerable hazards inherent in EVAs, and the resultant risk to astronauts, some scientists are working to develop tele-operated robots for outside construction work, to potentially eliminate or reduce the need for human EVAs.

[edit] Camp out

For EVAs from the space station, NASA now routinely employs a camp out procedure to reduce the risk of decompression sickness.^[7] 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).^[7] Spending a night at the lower air pressure helps flush nitrogen from the body, thereby preventing "the bends".^[8][9]

[edit] EVA milestones

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.

Stephen Robinson riding the robotic arm during STS-114.

• The first EVA was carried out by Alexey Leonov on March 18, 1965 from the Voskhod 2 spacecraft.

• The first EVA by an American astronaut was made on June 3, 1965 by Edward White during the Gemini 4 mission.

• The first EVA that was a moonwalk rather than a spacewalk was made by American astronaut Neil Armstrong on July 20, 1969 when the Apollo 11 Lunar Module Eagle landed on the Moon. He was joined by crewmate Buzz Aldrin, and their EVA lasted 2 hours and 32 minutes.

• The first untethered spacewalk was by American astronaut Bruce McCandless II on February 7, 1984, during Challenger mission STS-41-B. He was subsequently joined by astronaut Robert L. Stewart during the 5 hour 55 minute spacewalk.

• The first woman to perform an EVA was Cosmonaut 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 make an EVA was Kathryn D. Sullivan, who stepped into space on October 11, 1984 during Space Shuttle Challenger mission STS-41-G.

• The first (and only) three-person EVA was performed on May 13, 1992, as the third EVA of STS-49, the maiden flight of Endeavour.^[10] Pierre Thuot, Richard Hieb, and Thomas Akers conducted the EVA to capture and repair a non-functional Intelsat VI-F3 satellite, and equipped the satellite with a new motor, that after release, moved it into its planned geosynchronous orbit.

• The first EVA by a non-Soviet, non-American astronaut was made on December 9, 1988 by Jean-Loup Chrétien of France during a three-week stay on the Mir space station.

• On February 9, 1995, Bernard A. Harris, Jr. and Michael Foale became the first African American and the first Briton, respectively, to perform an EVA.

• On April 22, 2001, Chris Hadfield became the first Canadian to perform an EVA, while installing the Canadarm2 on to the International Space Station.

• The first EVA to perform an in-flight repair of the space orbiter was by American astronaut 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 was 8 hours and 56 minutes, performed by Susan J. Helms and James S. Voss on March 11, 2001.^[11]

• Anatoly Solovyev holds the record for most spacewalks (16), and total duration (82 hours, 22 minutes).^[11]

• Captain Michael Lopez-Alegria holds the all time American record for number of EVAs (10), and for total EVA duration (67 hours and 40 minutes).^[11]

• The first EVA by a Chinese astronaut was made on September 27, 2008 by Zhai Zhigang during Shenzhou 7 mission. Zhai Zhigang's spacewalk, using a Feitian space suit, made China the third country to independently carry out an EVA.

[edit] See also

[edit] References

[edit] External links

Wikimedia Commons has media related to: Extra-vehicular activity

• NASA JSC Oral History Project Walking to Olympus: An EVA Chronology PDF document.
• NASDA Online Space Notes^{[dead link]}
• 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)

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