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Solar Dynamic Ground Test Demonstration

In 1995 a government/industry team designed, built, and tested a 2 kWe Solar Dynamic energy conversion system at NASAís Lewis Research Center. This project completed the first ever full-scale test of a non-photovoltaic power system designed for use in space.

The Solar Dynamic space power system consists of a solar concentrator, a solar receiver, a turbine-driven alternator (turboalternator), and a waste heat rejection system. The solar concentrator measures 4.75 m wide by 4.55 m tall and uses seven hexagonal mirrored panels to focus energy into the solar receiver. The receiver transfers heat to the systemís working fluid while it also stores heat during shaded periods of LEO. The Closed Brayton Cycle turboalternator uses a helium-xenon mixture as the working fluid. The turbine and brushless alternator are attached to a single shaft. The turboalternator is gas cooled. The waste heat rejection system employs two identical radiator panels, each measuring 1.77 m by 3.66 m with a radiating surface area of 12.96 square meters. The heat rejection system contains n-heptane coolant fluid, and it is coupled to the turboalternator by two gas-to-liquid heat exchangers.

The entire Solar Dynamic system was tested in Tank 6 at NASAís Lewis Research Center. Tank 6 accurately simulates the harsh environment of LEO with nine 30 kW Xenon lamps representing the sun, a constant wall temperature of 78 K, and a vacuum. The facility also uses a water cooled shutter to simulate the changing light conditions of LEO. Finally, Tank 6 has an electric load simulator which can handle as much as 4 kWe.

Testing consisted of repeated simulated orbits, in which the system experiences 66 minutes of sun and 27 minutes of shade each. The system operated at between 48,000 and 52,000 RPM, generating between 300 We and 2 kWe. Overall efficiency was in excess of 15%, and the engine cycle operated at an efficiency of over 26%. The next stage of testing will occur in LEO aboard the space shuttle. Plans are in the works for a Solar Dynamic system aboard both Mir and the International Space Station Alpha.

A Solar Dynamic power conversion system could be very useful to The Artemis Project. Because the system is designed for use in LEO, the solar receiver and heat rejection system may not be suited for operation on Luna without modification. This system does not solve the challenging problem of energy storage during the Lunar night either, but it may provide a reliable, efficient way to generate power during the day. Artemis will probably require a staging base in LEO, so this system may be very well suited for use there.

More information about the Solar Dynamic Ground Test Demonstration can be found in the two NASA Technical Memorandums that accompany this document, "Initial Results From the Solar Dynamic (SD) Ground Test Demonstration (GTD) Project at NASA Lewis" and "Update of the 2 kW Solar Dynamic Ground Test Demonstration Program" (NASA TM 107004 and NASA TM 106730). These two documents also contain a long list of used references.

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