The closed-cycle hydrogen-oxygen PEM regenerative fuel cell (RFC) at the NASA Glenn Research Center (NASA Glenn) has successfully demonstrated closed cycle operation at rated power for multiple charge-discharge cycles. During charge cycle the RFC has absorbed input electrical power simulating a solar day cycle ranging from zero to 15 kWe peak, and delivered steady 5 kWe output power for periods exceeding 8 hr. Orderly transitions from charge to discharge mode, and return to charging after full discharge, have been accomplished without incident. Continuing test operations focus on: (1) Increasing the number of contiguous uninterrupted charge discharge cycles (2) Increasing the performance envelope boundaries (3) Operating the RFC as an energy storage device on a regular basis (4) Gaining operational experience leading to development of fully automated operation (5) Developing instrumentation and in situ fluid sampling strategies to monitor health and anticipate breakdowns This publication is available from the NASA Center for AeroSpace Information, 301-621-0390.
Free-piston Stirling engine (FPSE) and linear alternator (LA) technology is combined with radioisotope heat sources to produce a compact dynamic isotope power system (DIPS) suitable for.multihundred-watt space applications which appears competitive with advanced radioisotope thermoelectric generators (RTGs).Unlike earlier DIPS concepts based on closed cycle Brayton conversion, the small Stirling DIPS is scaleable to multihundred-watt power levels or lower. The FPSE/LA convertor, which is not subject to the tip clearance to swept area scaling limitation of turbomachinery, remains a high efficiency convertor in sizes ranging from tens of kilowatts down to only a few watts. At multihundred-watt unit size, the FPSE can be directly integrated with the government-furnished General Purpose Heat Source (GPHS) via radiative coupling; the resulting dynamic isotope power system has a size and weight that compares favorably with the advanced modular (Mod) RTG, but requires less than a third the amount of isotope fuel. Thus the FPSE extends the high efficiency advantage of dynamic systems into a power range never previously considered competitive for DIPS. This results in lower fuel cost and reduced radiological hazard per delivered electrical watt.Having sucessfully flown on several earlier space missions, free-piston Stirling technology
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