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The development of a fuel cell energy storage system (FCESS) for the Extravehicular Mobility Unit (EMU) carried out by Ergenics Power Systems, Inc. (EPSI) under NASA contract is now in its fourth year, The applicability of this promising technology for the EMU has been well established and its advantages for this and other aerospace applications are clearly apparent. The combination of excellent cycle life and shelf life, high gravimetric and volumetric energy density, and rapid rechargeability make this technology a cost effective and technically attractive choice. The program, initiated with a conceptual design, has progressed successfully through the breadboard stage. Presently, the technology is being refined through the design, fabrication and testing of a vacuum rated system. The current status of these tasks is summarized In the following text.

The paper gives an update on an advanced development effort carried out under NASA Johnson Space Center (NASA/JSC) NAS 9-17775 by Ergenics Power Systems, Inc. (EPSI). The work was initiated in April 1987 to design and build a Fuel Cell Energy Storage System (FCESS) bench-test unit for the Space Station Freedom Extravehicular Mobility Unit (EMU). Fueled by oxygen and hydride stored hydrogen, the FCESS is being considered as an alternative to the EMU zinc-silver oxide battery. Superior cycle life and quick recharge are its main attributes. Design and performance of a non-venting 28V, 34 Ahr system with 7 amp rating are discussed. The FCESS is comprised of a 32-cell proton exchange membrane (PEM) stack, a metal hydride storage vessel and a control subsystem. The stack design incorporates passive product-water removal and thermal integration with the hydride vessel. The hydride vessel stores enough fuel for 5 hours.