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A semi free-piston Stirling engine alternator, called NALSEM500, has been experimentally studied since April 1994, as part of a space solar power technology program in NAL (National Aerospace Laboratory). The Stirling alternator is one of candidates for future space power applications, and will be integrated with the solar cavity receiver subsystem, having both Na heat pipes and thermal energy storage. Through a series of preliminary bench tests, it was found that the efficiency of the linear alternator was significantly low as compared to our initial design. To improve the alternator performance, some design modifications of the magnet assembly and stator core have been made. As a result, the thermodynamic efficiency of 33% and system efficiency of 20% was obtained.

A fundamental study was performed to develop a high efficiency solar heat receiver for a solar energy experiment mission on the Japan experiment module - exposed facility of the international space station. It is composed of a solar heat absorber, thermal energy storage and heat pipes. This system is aimed to transport solar thermal energy to a bottoming system with an efficiency of 80 %. Thermal analysis of each component was performed to assess its design approach. One ground testing model of the solar receiver was designed and fabricated in 1998, and then would be experimentally evaluated in 1999 at a test vacuum chamber of National Aerospace Laboratory.

A conceptual model of a life support system which circulates material using a physicochemical treatment has been designed. This self-contained partially circulated life support system, called SEPAL, comprises a water electrolysis system using a PEM (Polymer Electrolysis Membrane) and solar collector for a Sabatier reactor. The lack of buoyancy in microgravity causes liquid-gas separation and interferes with conventional water electrolysis. This problem can be solved by supplying water in the vapor phase through molecule size pores in the NAFION electrolysis membrane. This new system connects to a Sabatier reactor, which provides the water vapor for the electrolysis system. This paper describes test results of the main system elements and preliminary test results of the oxygen and hydrogen production system. With a small satellite making use of surplus lifting capacity, the experiment is proposed to demonstrate this circulated life support system.