Recognizing the challenge and complexity of building the International Space Station, NASA has worked for more than a decade to develop and flight test the necessary space walk equipment; refine space walk training procedures; and build space walk, or extravehicular activity (EVA), experience among astronauts, engineers and flight controllers. Since 1991, astronauts have conducted more than a dozen "practice" space walks during space shuttle flights. In addition, two service missions for the Hubble Space Telescope have helped prepare the astronauts for the intricate work needed to build the station. Many of the astronauts who gained experience during these practice space walks will bring that knowledge to bear during future space walks as the station's orbital assembly begins.
Flight-testing EVA equipment designed for use aboard the International Space Station began on the first space walk NASA conducted after the Space Shuttle's return to flight following the Challenger accident. On Shuttle mission STS-37, in April 1991, astronauts Jerry Ross and Jay Apt performed a space walk to test a Crew and Equipment Translation Aid (CETA) cart designed for use in assisting astronauts to move about the football field-long truss of the completed station. Two such carts are now planned for launch to the station during its assembly, and Ross trained to be the lead space walker on the first station assembly mission, Shuttle mission STS-88. Since 1991, other space walks have evaluated new tethers, tools, foot restraints, handling large masses, a jet pack "life jacket," spacesuit enhancements and even the planned station lettering and toolboxes.
To prepare for International Space Station assembly, NASA announced the first International Space Station EVA assembly crew, Ross and Jim Newman on STS-88, in August 1996. In June 1997, five more crews of station assembly space walkers were named to complete the first six Shuttle assembly missions, some of them more than two years ahead of their scheduled mission, much earlier than is traditional. The early naming of crew members has allowed the astronauts additional time to train for their complex and crucial missions.