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A fresh look at the use of astronaut time to conduct and support Extravehicular Activity (EVA) can help guide the evolution of next generation EVA systems. Studies have shown that less than 20% of the flight crew time for EVA (prior/during/post) is currently spent directly on productive tasks. In the future, longer missions, larger and more complex orbiting platforms and on-orbit maintenance of EVA equipment will drive this percentage even lower. Study of where the remaining 80% of the flight crew time presently goes indicates where improvements could be aggressively pursued for next generation systems. With the high cost per manhour on orbit, and estimated needs for 200 or more crew hours of EVA annually for space station, these improvements are clearly worthwhile. Current use of crew time before, during and after EVA were analyzed, and major uses of time identified.

With the advent of manned spacecraft opportunities requiring routine and complex extravehicular activities (EVA) a new concept for heat rejection is mandatory in order to realize maximum crewmember productivity. An optimum extravehicular mobility unit (EMU) thermal control system must be capable of successful operation without requiring expendables and without introducing contaminants into the environment, and be readily regenerable. This paper presents a regenerable non-venting thermal control subsystem requirements specification generated for a Shuttle-related EMU, identifies candidate concepts capable of fulfilling the requirements for each thermal control subsystem application, evaluates each candidate concept with respect to the subsystem requirements, and selects the best approach for each requirement.