The movement and work carried out by an astronaut outside a spacecraft. The term usually refers to activity undertaken from a space shuttle or space station in orbit, but Moon walks—the only true space walks—are also EVAs. An EVA is necessary for operations carried out in space, such as repairs to spacecraft, that cannot be accomplished using a remote-control arm. The Soviet cosmonaut Alexei Leonov completed the first EVA (10 minutes) on 18 March 1965. The US astronaut Edward White undertook the first EVA for NASA (36 minutes) on 3 June 1965.

During an EVA the astronaut wears an extravehicular mobility unit (EMU), a combined spacesuit and life-support system. The extravehicular life-support system (ELSS) was an early chest pack worn by astronauts aboard Gemini spacecraft. It was attached to a 7.5-m umbilical cord and supplied communications, spacesuit pressure, and emergency oxygen in the event of failure of the umbilical supply. The Apollo spacesuits had a portable life-support system, while space shuttle suits have a primary life-support system.

The extravehicular visor assembly (EVVA) is a transparent shell that fits over a space helmet to reduce light and heat, and to protect against solar radiation and micrometeoroid impacts. A coating of gold on the sun visor reflects the light and heat, while adjustable eyeshades provide additional protection from glare. The assembly also contains a television camera and lighting attachment. Skylab astronauts wore a similar Skylab extravehicular visor assembly (SEVA).

http://www.spaceflightnow.com/station/stage5a/fdf/evastats.html Breakdown of space-walk duration by space programme (Gemini, Apollo, and so on) and general extravehicular activity statistics. A downloadable Adobe document has more information about the space walks made during specific missions.