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.

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Due to the different designs of the early spacecraft, the American and Russian space programs also define an EVA differently. Russian, and Soviet, spacecraft have always included an airlock and consequently Russians define an EVA as occurring when a cosmonaut is in a vacuum. Early United States spacecraft, however, did not include an airlock but instead depressurized the entire spacecraft. An American astronaut was consequently not considered to have made an EVA until at least his head was outside the spacecraft. The term stand-up EVA (SEVA) is used for being partly outside.

Related Topics:
American - Russia - Soviet - Airlock - Cosmonaut - Vacuum - Astronaut

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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) 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).

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