space walk

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.

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 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 2009^[update], Russia, the United States, and China are the only countries with a demonstrated capability to conduct an EVA.

EVA hazards

Tear in glove during STS-118

Astronaut Bruce McCandless on an untethered EVA.

Spacewalks are dangerous for a number of different reasons, and are avoided for routine tasks. Consequently, EVAs are often planned late in the project development when problems are discovered, or sometimes even during an operational mission.

The primary danger is collision with space debris.^[2][3] Velocity while orbiting 300 km above the Earth (typical for a space shuttle mission) is 7.7 km/s. This is approximately ten times the speed of a bullet. Nearly every space mission creates more orbiting debris, so this problem will continue to worsen.^[3] Other possible problems include an astronaut becoming separated from his or her craft or suffering a spacesuit puncture which would depressurize the suit, causing anoxia and rapid death if the astronaut is not brought into a pressurized spacecraft immediately. Another reason for danger is that external environments in space are harder to simulate before the mission, although approximate simulations can be achieved at facilities like the Hydro-labs in Star City's Gagarin Training Center and NASA's Neutral Buoyancy Laboratory.

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 original 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]

No catastrophic incident has ever occurred during an extra-vehicular activity, and no astronaut has ever died during one.^[6] Nevertheless, given the considerable hazards inherent in EVAs, some scientists are working to develop tele-operated robots for outside construction work, in order to reduce or potentially eliminate the need for human EVAs.

Camp out

For EVAs from the International 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]

EVA milestones

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.

Stephen Robinson riding the robotic arm during STS-114, doing a first in-flight repair of the Space Shuttle.(Landmass in the backdrop is the Bari region of Somalia).

Capability milestones

• The first EVA was carried out by Alexey Leonov on March 18, 1965 from the Voskhod 2 spacecraft.
• The first EVA that was other than a spacewalk was made by American 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 EVA in deep space (not on the moon or in the Earth's orbit) was made by Al Worden, on the return trip of Apollo 15. This was done two more times: by Ken Mattingly on Apollo 16 and by Ron Evans on Apollo 17.
• The first untethered spacewalk was 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. See photo in the previous section.
• 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 hand-capture and repair a non-functional Intelsat VI-F3 satellite. See photo at right.
• The first EVA to perform an in-flight repair of the space orbiter 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. See photo at right.
• The longest EVA was 8 hours and 56 minutes, performed by Susan J. Helms and James S. Voss on March 11, 2001.^[11]

Personal cumulative duration records

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

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.

• The first EVA by an American was made on June 3, 1965 by Edward White during the Gemini 4 mission.
• 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.
• The first woman to perform an EVA was Russian 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 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.
• 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 March 13, 2001, Andy Thomas became the first Australian-born person to perform an EVA, though he is a naturalized US citizen.
• On April 22, 2001, Chris Hadfield became the first Canadian to perform an EVA, while installing the Canadarm2 onto the International Space Station.

See also

Human spaceflight portal

References

External links

• 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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