Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000.

Stirling-cycle engines have been identified as a promising technology for the conversion of concentrated solar energy into usable electrical power. A 25kW electric system takes advantage of existing Stirling-cycle engines and existing parabolic concentrator designs. In previous work, the concentrated sunlight impinged directly on the heater head tubes of the Stirling Thermal Motors (STM) 4-120 engine.

Ambient air is drawn into a common barrier-type The engine is a low pressure, highly filter. The air then flows into the centrifugal recuperated engine. The turbo-machinery is compressor inducer section. The air is built up from commercial turbo_hargers, discharged radially through a vaned diffuser and which ensures low cost and high reliability. A exits from the compressor housing duct. This combustor will be included in the system to pressurized air continues to diffuse as it enters allow for full power production during cloud the cool inlet plenum of the recuperator. Here transients. Current estimates are that the the air is heated by the waste heat exhausting engine/alternator thermal-to-electric efficiency from the turbine. This preheated air exits the will be 30+%. The solar receiver to be supplied recuperator through a transition duct that by DLR will be an advanced version of their 'connects to the solar receiver. VOBREC volumetric receiver. This receiver has a parabolic quartz window and ceramic Within the receiver, air flows at very low foam absorber. The estimated efficiency of the

Masses of the STAR-C power system and an optimized OTR power system versus power level are investigated. The impacts of key system parameters on system performance are also addressed. The STAR-C is mass competitive below about 15 kWe, but at higher power levels the scalability is relatively poor. An optimized OTR is the least massive space nuclear power system below 25 kWe, and scales well to 50 kWe. The system parameters that have a significant impact on the scalability of the STAR-C are core thermal flux, thermionic converter efficiency, and core length to diameter ratio. The emissivity of the core surface is shown to be a relatively unimportant parameter. For an optimized OTR power system, the most significant system parameter is the maximum allowable fuel temperature. It is also shown that if advanced radiation-hardened electronics are used in the satellite payload, a very large mass savings is realized.

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