Sone Yoshitsugu

The fuel cell for space applications has special system requirements, such as operational conditions and designs due to its isolated low gravitational and closed environment, which is much different from that for terrestrial use. Polymer electrolyte fuel cell (PEFC) system for space applications has been studying in our group and several subsystems and operating methods were developed. We manufactured the 18-cell stack and assembled fuel cell system for space utilizations. It showed stable performance for 1,100 hours under various operational conditions. These results could realize the simple and practical PEFC system for space application. A small and light-weight PEFC system with these subsystems has also been developed and several properties were assessed.

This paper describes the initial on-orbit results of the small scientific satellite "INDEX" (REIMEI) for aurora observation and demonstration of advanced satellite technologies. REIMEI is a small satellite with 72kg mass, and is provided with three-axis attitude control capabilities for aurora observation. REIMEI was launched into a nearly sun synchronous polar orbit on Aug. 23^<rd>, 2005 (UT) from Baikonur, Kazakstan by Dnepr rocket. REIMEI satellite functions work satisfactorily in the orbit. The first imaging observations of aurora were successfully performed above the southern polar region in Sep. 16^<th>, 2005.

In order to develop lithium-ion cells for space applications, applicability evaluation on 10-100 Ah-class lithium-ion cells is being performed by simulating satellite 's operation at Japan Aerospace Exploration Agency (JAXA). So far, 20.000 cycles for low-Earth-orbit (LEO) and 1,200 cycles for geostationary-Earth-orbit (GEO) satellite simulation testing have been completed. These results respectively correspond to about 3- and 13-year LEO and GEO satellite operations, indicating good applicability of lithium-ion cells as satellite power. The simulation testing of H-IIA transfer vehicle (HTV) operation disclosed that lithium-ion cells were applicable for this short-term mission even with a high charge rate.

In order to develop lithium ion polymer cells for space applications, the life cycle test of the commercial lithium ion polymer cells made from four different companies is being performed by simulating the low-earth-orbit satellite operation. So far, 5000 cycles have been completed, and good cycling performance was obtained for the cells manufactured from companies D and A. The higher charge rate of 1 C was found to be inappropriate for the long-term operation of lithium ion polymer cells. Furthermore, the effect of decompression surroundings on cycling performances of lithium ion polymer cells made from Company D was evaluated. As a short-term result, it was found that the cells might be charged and discharged normally even under decompression surroundings.

Targeting the applications to the transfer vehicle for short-term missions and the larger space craft in future, PEFC systems are under development at NASDA. For the space applications under closed environment, we are developing the system where the fuel is perfectly consumed and the excess oxygen is recycled. First, we designed the system with 100W-class fuel cell. Through our tests, we revealed that humidifier is not necessary in the case of using pure hydrogen and oxygen. Furthermore, we prepared 1 kW-class fuel cell stuck and demonstrated its performance without humidification.