An Experimental Stirling Engine for Use in Space Solar Dynamic Power Systems: Preliminary Tests KUNIHISA EGUCHI, SACHIO OGIWARA & TSUTOMO FUJIWARA Summary The Stirling cycle engine has proved to be the most promising candidate of various thermodynamic cycle engines used to convert solar to electrical energy. As part of the National Aerospace Laboratory’s solar dynamic power technology program, our project has been to design and build a model of a free piston Stirling engine generator. We plan to provide a fundamental understanding of the engine operations and thermodynamic characteristics. Preliminary results are given in this paper, along with comments on future design modifications. Introduction Towards the mid 1990s large amounts of power will need to be made available for space development projects such as the future space station and the Free Flying Unit. The primary energy sources available in space are solar energy or nuclear power from small portable units such as were used on the Voyager missions. Design options for converting the raw energy into electricity run along the lines of photovoltaic, thermionic, thermoelectric and dynamic energy converters. Performance requirements for such power conversion systems are high efficiency, high reliability and a long life expectancy. An additional constraint—clearly related to minimization of size and weight—is the cost of transport to orbit and the cost of any in-space operations. It is well known that as of now the solar cell/battery system has proved highly reliable for electrical power generation of less than 10 kWe. A current NASA SP-100 project has concentrated on the dynamic power technology needed to meet an electrical demand of several 100-1000 kWe, assuming nuclear power is to be used a decade after the IOC version of the space station [1,2]. Researchers in the ESA and West Germany have already proposed the free piston Stirling engine as the best choice for any future space dynamic power systems [3,4]. During 1986-87 the feasibility of using solar heat engine systems was assessed at NASDA’s Tsukuba Space Center in Japan [5]. Japan’s National Aerospace Laboratory (NAL) has conducted a design study [6] on the dynamic conversion of solar to electric power with an eye towards any space-based applications. The study evaluated two different 30 kWe Brayton and Stirling cycle K. Eguchi, Leader, S. Ogiwara & T. Fujiwara, Research Engineers, the Sixth Research Group involved in space energy system, Space Technology Research Group, National Aerospace Laboratory, 7-44-1 Jindaiji- Higashi, Chofu, Tokyo 182, Japan.
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