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The various configurations being considered for Space Station Freedom have resulted in a moving target for tomorrow's demand for EVA and the requirements that will be imposed on the Extravehicular Mobility Unit (EMU). The Shuttle EMU is baselined to perform the assembly and operational activities of station and is currently undergoing the necessary incremental re-certification. This paper presents the evolution of an EMU from two perspectives. First, evolution is discussed within the context of continuously improving the life support system and the space suit assembly from the Mercury Program to NASA's current flight EMU. This includes a status of the on-going enhancements and a discussion on the merits of additional improvements. The second perspective describes evolution for future programs involving significant differences in mission requirements and environments.

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.

In 1993 the United States and Russia signed an historic agreement committing both countries to a broad range of cooperative activities in space. This agreement included the “development of a common space suit.” This paper describes the major elements of a Common Space suit System (CSS) approach, presents the current status of flight planning towards implementing the agreement, and discusses some future challenges. Planning the CSS program revealed different theoretical “levels of commonality,” ranging from minimum interoperability to a concept of a single, common design embodying common manufacturing and full interchangeability. Reviewing these reveals some of the practical limitations to commonality that relate to both evolution (of existing U.S. and Russian space suits) and revolution (a brand new space suit).