A Ground Test Demonstration (GTD) of a 2 kW SD space power system was completed at the NASA Glenn Research Center. The test included an off-axis solar concentrator, heat receiver with thermal energy storage (TES), recuperated-Brayton cycle heat engine, and waste heat radiator in a thermal vacuum environment. The TES, a LiF-CaF2 phase change material contained in canisters surrounding the gas flow tubes, was used to heat the working fluid during the eclipse to allow continuous power production through the orbit, eliminating the need for rechargeable batteries. The testing was conducted with a solar simulator to provide a complete solar-to-electrical system demonstration. Cycle efficiencies (ratio of alternator power to heat input) of the Brayton unit were measured at 29% and orbital efficiencies (ratio of electrical energy output to solar energy collected over an orbit) were measured at 17%. From 1994 to 1998, the system had accumulated nearly 800 hours of operation including 33 ambient start-ups and 372 orbit cycles.
A flight version of the 2 kW system, which utilized a similar receiver and Brayton engine to the ground test system and a Russian designed concentrator and radiator, was planned for 1998 but was cancelled due to Shuttle manifest changes. A significant portion of the flight receiver, engine, and controls were completed prior to the project’s cancellation and some of the flight development hardware was integrated with the GTD testbed for performance characterization. Allied Signal Aerospace Systems Equipment of Tempe, Arizona served as prime contractor for both the GTD and Flight Demonstration projects.