From Wikipedia, the free encyclopedia.
Extra-vehicular activity (EVA) is work done by an astronaut away from the earth outside of the spacecraft: in space flight or while on the Moon (see List of lunar astronauts) or possibly in the future on another planet or moon. In the early days of space flight it was called 'space walk'. EVAs may be tethered (the astronaut is connected to the spacecraft, oxygen can be supplied through a tube, no propulsion is needed to return to the spacecraft) and unthetered. For unthetered EVAs during space flight, capability of returning to the spacecraft is essential, see Manned maneuvering unit.
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 she was aboard the Salyut 7 space station. The first untethered EVA was by United States astronaut Bruce McCandless on February 7, 1984, during the Space Shuttle Challenger mission 41-B; he was subsequently joined by astronaut Robert L. Stewart during the mission.
An EVA is dangerous for a number of different reasons. The primary one is collision with 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 (e.g. a fleck of paint or a grain of sand) is equal to that of a bullet with a mass that is 100 times as large. Every space mission creates more orbiting debris, so this problem will continue to become worse.
Scientists are developing tele-operated robots for outside construction work, to eliminate the need for EVAs.
See also:
- Spacesuit
- Manned Maneuvering Unit
External link
Also name of mechas in Neon Genesis Evangelion.
