A greater number of manned extravehicular activities (EVAs) are anticipated for the United States Space Station compared to the few experienced on Space Shuttle missions. This requires the design of a new generation extravehicular mobility unit (EMU). Limitations inherent in the current EMU power supply--zinc silver-oxide batteries--include dry shelf-life, active wet-life, cycle-life, and recharge time, thus making its usage impractical for the Space Station.
An alternative solution, a fuel cell energy storage system (FCESS), is being explored by Ergenics Power Systems, Inc. (EPSI), Wyckoff, N.J., with funding from NASA/Johnson Space Center. The ion-exchange membrane (IEM) fuel cell under consideration utilizes hydrogen stored as a metal hydride. EPSI has demonstrated experimentally that the fuel cell/hydride technology pair should be a primary candidate EMU power supply for its high volumetric/energy density and cycle life, quick recharge, durability, EMU integration, and safety.
This paper describes the EMU (IEM) hydrogen-oxygen fuel cell being developed by EPSI including its construction, hydrogen storage, hydride recharge, waste heat and water removal.