Extravehicular activity (EVA) is any activity done by an astronaut or cosmonaut outside a spacecraft beyond the Earth’s appreciable atmosphere. The term most commonly applies to a spacewalk made outside a craft orbiting Earth (such as the International Space Station), but also has applied to lunar surface exploration (commonly known as moonwalks) performed by six pairs of American astronauts in the Apollo program from 1969 to 1972. On each of the last three of these missions, astronauts also performed deep-space EVAs on the return to Earth, to retrieve film canisters from the outside of the spacecraft. Astronauts also used EVA in 1973 to repair launch damage to Skylab, the United States’ first space station.
A “Stand-up” EVA (SEVA) is where the astronaut does not fully leave a spacecraft, but is completely reliant on the spacesuit for environmental support.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 and electrical power can be supplied through an umbilical cable; no propulsion is needed to return to the spacecraft), or untethered. 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.
Russia, the United States and China have demonstrated the capability to conduct an EVA.
STS-116 was a Space Shuttle mission to the International Space Station (ISS) flown by Space Shuttle Discovery. Discovery lifted off on 9 December 2006 at 20:47:35 EST. A previous launch attempt on 7 December had been canceled due to cloud cover. It was the first night launch of a space shuttle since STS-113 in November 2002.
The mission is also referred to as ISS-12A.1 by the ISS program. The main goals of the mission were delivery and attachment of the International Space Station’s P5 truss segment, a major rewiring of the station’s power system, and exchange of ISS Expedition 14 personnel. The shuttle landed at 17:32 EST on 22 December 2006 at Kennedy Space Center 98 minutes off schedule due to unfavorable weather conditions. This mission was particularly notable to Sweden, being the first spaceflight of a Scandinavian astronaut, Christer Fuglesang.
STS-116 was the final scheduled space shuttle launch from Pad 39B as NASA reconfigured it for Ares I launches. The only remaining use of Pad 39B by the shuttle was as a reserve for the STS-400 Launch On Need mission to rescue the crew of STS-125, the final Hubble Space Telescope servicing mission, if their shuttle became damaged.
After STS-116, Discovery entered a period of maintenance. Its next mission would be STS-120 starting on 23 October 2007.