5-7. Free-piston Stirling Technology for Space Power JACK G. SLABY Summary An overview is presented of the NASA Lewis Research Center free-piston Stirling engine activities directed toward space power. This work is being carried out under NASA's new Civil Space Technology Initiative (CSTI). The overall goal of CSTI's High Capacity Power element is to develop the technology base needed to meet the long duration, high capacity power requirements for future NASA space missions. The Stirling cycle offers an attractive power conversion concept for space power needs. SPDE Summary Discussed in this paper is the completion of the Space Power Demonstrator Engine (SPDE) testing—culminating in the generation of 25 kW of engine power from a dynamically balanced opposed-piston Stirling engine at a temperature ratio of 2.0. Engine efficiency was approximately 22%. The SPDE recently has been divided into two separate single-cylinder engines, called Space Power Research Engines (SPRE), that now serve as test beds for the evaluation of key technology disciplines. These disciplines include hydrodynamic gas bearings, high-efficiency linear alternators, space qualified heat pipe heat exchangers, oscillating flow code validation, and engine loss understanding. The success of the SPDE at 650 K has resulted in a more ambitious Stirling endeavour—the design, fabrication, test and evaluation of a designed-for-space 25 kW per cylinder Stirling Space Engine (SSE). The SSE will operate at a hot metal temperature of 1050 K using superalloy materials. This design is a low temperature confirmation of the 1300 K design. It is the 1300 K free-piston Stirling power conversion system that is the ultimate goal; to be used in conjunction with the SP-100 reactor. The approach to this goal is in three temperature steps. However, this paper concentrates on the first two phases of this program—the 650 K SPDE and the 1050 K SSE. Introduction NASA Lewis started work on free-piston Stirling engines around 1977. Today, approximately 20 professionals are engaged in free-piston Stirling technology at NASA Lewis. These free-piston projects include (a) NASA's new Civil Space Technology Initiative (CSTI), which will comprise the major emphasis of this paper, (b) a NASA Lewis project, identified as the Advanced Stirling Conversion Systems (ASCS), to develop Stirling engine technology for terrestrial solar energy conversion that is Jack G. Slaby, Lewis Research Center, Cleveland, OH 44135, USA. Paper number IAF-ICOSP89-5-7.
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