D.J. Newman and M. Barratt, Chapter 22: "Life Support and Performance Issues for Extravehicular Activity (EVA)," Fundamentals of Space Life Sciences, S. Churchill, ed., Krieger Publishing Co., Melbourne, Florida, 1997.
Dava Newman, Ph.D. and Michael Barratt, M.D.
Defining the goals for future human space endeavors is a challenge now facing all spacefaring nations. Given the high costs and associated risks of sending humans into Earth orbit or beyond - to lunar or Martian environments, the nature and extent of human participation in space exploration and habitation are key considerations. Adequate protection for humans in orbital space or planetary surface environments must be provided. The Space Shuttle, Mir Space Station, Salyut-Soyuz, and Apollo programs have proven that humans can perform successful extravehicular activity (EVA) in microgravity and on the Lunar surface.
Since the beginning of human exploration above and below the surface of the Earth, the main challenge has been to provide the basic necessities for human life support that are normally provided by nature. A person subjected to the near vacuum of space would survive only a few minutes unprotected by a spacesuit. Body fluids would vaporize without a means to supply pressure, and expanded gas would quickly form in the lungs and other tissues, preventing circulation and respiratory movements. EVA is a key and enabling operational resource for long-duration missions which will establish human presence beyond the Earth into the solar system. In this chapter, EVA is used to describe space activities in which a crew member leaves the spacecraft or base and is provided life support by the spacesuit. To meet the challenge of EVA, many factors including atmosphere composition and pressure, thermal control, radiation protection, human performance, and other areas must be addressed.
Compared to Earth-based capabilities, performance during in-space EVA is enhanced for some functions and degraded for others. EVA offers many advantages for accomplishing space missions. The astronaut is present at the worksite and has the following capabilities: flexibility, dexterous manipulation, human visual interpretation, human cognitive ability, and real time approaches to problems. The factors which may degrade performance include pressure suit encumbrance, prebreathe requirements, insufficient working volume, limited duration, sensory deprivation, and poor task or tool design . EVA, as well as robotics and automation, expand the scope of space operations. A thorough understanding of EVA capabilities will help bring about the integration of humans and machines for future missions. In addition to microgravity EVAs, the partial gravity environments of the Moon and Mars require advanced EVA hardware and performance capabilities.
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