Space power applications historically include fuel cells due to the high energy storage density of hydrogen and oxygen compared to batteries. Fuel cells are continuously under development to incorporate latest technology and focus on specific details of fuel cells systems relevant to harsh space transportation environments. The National Aeronautics and Space Administration is developing proton exchange membrane fuel cells systems for space power applications because of the potential for longer life, reduction in cost, and increase in safety compared to current alkaline fuel cell technology. Space fuel cell applications utilize oxygen instead of air, which introduces better performance but greater hazards. Circulation of reactants is beneficial for these systems to aid in removal of product water from the fuel cell stack and to humidify reactant fluid streams. Current space fuel cell prototype systems use a simple but effective pump for reactant recirculation known as a gas ejector. A gas ejector uses a high-pressure primary gas supply to produce suction to a secondary fluid at a lower pressure. A gas and water separator is then necessary to remove the fuel cell product water from the unutilized recirculated oxygen. The National Aeronautics and Space Administration is analyzing and testing several different means to separate the oxygen gas and water in both microgravity and increased gravity conditions. This paper addresses specific components and design concerns for proton exchange membrane fuel cell systems for space power applications.

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