Extra-vehicular activity
Extra-vehicular activity (
EVA) is work done by an
astronaut away from the Earth and outside of his or her
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 the
command module pilot did an EVA to retrieve film canisters on the return trip.
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, in contrast, is not considered to have made an EVA until at least his head is outside the spacecraft. The term stand-up EVA (SEVA) is used for being partly outside.
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. For untethered EVAs during space flight, capability of returning to the spacecraft is essential; see
Manned Maneuvering Unit (MMU).
* The first EVA was carried out by Soviet cosmonaut
Aleksei Leonov on
March 18 1965 from the
Voskhod 2 spacecraft.
* The first woman to perform an EVA was Cosmonaut
Svetlana Savitskaya on
July 25 1984 while aboard the
Salyut 7 space station.
* The first EVA by an American astronaut was made on
1965 June 3 by
Edward White during the
Gemini 4 mission. 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 astronaut 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 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 EVA to perform an
in-flight repair of the Space Shuttle 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 on the Space Shuttle
Discovery's heat shield, after engineers determined they might cause damage to the shuttle upon re-entry. Robinson successfully removed the loose material while the
Discovery was docked to the
International Space Station.
|
During an EVA the astronaut is far from help |
An EVA is dangerous for a number of different reasons. The primary one is
collision with
space debris. Orbital velocity at 300 km above the Earth (typical for a
Space Shuttle mission) is 7.7 km/s. This is 10 times the speed of a
bullet, so the
kinetic energy of a small particle with a mass 1/100th that of a bullet (e.g. a fleck of paint or a grain of sand) is equal to that of a bullet. Every space mission creates more orbiting debris, so this problem will continue to worsen (see also
Kessler Syndrome).
Another reason for danger is that external environments in space are harder to simulate before the mission. 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 spacewalker becoming separated from their craft or suffering a spacesuit puncture which would depressurize the suit, causing
anoxia and rapid death if the spacewalker 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 is undisclosed, but it was either
Jerry L. Ross or
Jay Apt). However, the puncturing object, which stabbed the astronaut's hand as well, held in place, resulting in no detectable depressurization. In fact, the puncture was not noticed until after the spacewalkers were safely back inside
Atlantis. [
1]
Aleksei Leonov's EVA did not pass smoothly, although this was not reported at the time. Reportedly his spacesuit was overinflated due to vacuum conditions and so had to be vented, in order to return through the
airlock.
As of 2006, no catastrophic incident has ever occurred during an extra-vehicular activity, and no astronaut or cosmonaut has ever died during one. Still, some scientists are developing tele-operated robots for outside construction work, to potentially eliminate the need for human EVAs.
NASA exhaustively researched and tested all equipment to be used during EVA. Included in this research was a wrist timepiece that would withstand the extremes of the outer space environment. After purchasing samples of the top branded chronographs (i.e. Rolex, Omega, Longines, etc) and putting them through lab testing (including extreme cold/hot temperatures, humidity, G-forces, etc.), only the Omega Speedmaster model passed the NASA tests. It became the only approved watch for EVA during the Gemini project, was the first watch worn on the moon and continues to be the only watch that may be worn during EVA.
*
Space Suit*
Manned Maneuvering Unit*
List of spacewalks*
NASA JSC Oral History Project Walking to Olympus: An EVA Chronology PDF document.*
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)]]
