interior to the outer surface, to convert some of that heat flow from the isotope capsule to low voltage DC; the conversion system is well developed for space use [6], Multiple series-parallel strings of several hundred thermoelectric couples are designed to accommodate failure of any element in the string with only partial degradation. Table III summarizes the performance and mass breakdown of a Mars rover power system based on the GPHS-RTG. Power conditioning and controls, structure, and the 350 W/h energy storage elements are included in this estimate. Mod-RTG The Mod-RTG [7] is the evolutionary successor to the GPHS-RTG. Based on improvements in the thermoelectric couples the BOL converter efficiency is expected to increase to 7.6 which, combined with packaging refinements over the GPHS-RTG will further improve specific power. Table IV summarizes the performance and mass breakdown for a Mod-RTG based power system configured for the MRSR mission. Closed Brayton Cycle The closed Brayton cycle (CBC) dynamic system has been advocated by Rockwell [8] as power source for this vehicle. Known advantages cited for dynamic systems are their higher thermal efficiencies. The conversion efficiences historically demonstrated by dynamic systems have ranged from 20-30%. For an isotope system, this translates to less waste heat rejected and to considerably reduced fuel inventory per electrical watt delivered; resulting in a significant heat source mass reduction. The technology base for this system is the Brayton Isotope Power System (BIPS) developed by the Garrett Corporation for NASA in the late 1970s [9]. The BIPS was a recuperated system consisting of a small single shaft turboalternator (the mini-BRU), one or more heat source assemblies with source heat exchangers, waste heat exchangers and a pumped loop radiator. It was designed to provide 500-2100 electrical watts using
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