Despite the fact that early STS planning did not include any provisions for manned Extravehicular Activity (EVA), the orbiter airlock and Extravehicular Mobility Units (EMU's) or “spacesuits” were eventually incorporated in the Space Transportation System. Events have amply demonstrated the value of manned EVA. It is concluded that EVA will continue to be required for STS missions and for the Space Station.
The reasons that space vehicles may need servicing are presented, e.g., reliability/-MTBF, preventive maintenance, wear-out and degradation, damage, updating, and replacement. The functions that man can perform EVA are then reviewed, e.g., inspect/assess, reconfigure, repair, replace components, debris capture, checkout and verify. Some of the functions that man can perform easily in EVA but are difficult for machines/teleoperators are reviewed. These include: Engage/disengage, manipulate small objects, remove/replace, align, apply discrete forces and torques, fasten, override, MLI manipulation, and giving something a kick!
Finally, the extension of EVA operations from Shuttle to Space Station servicing is discussed.