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The Inmarsat 2 spacecraft constellation consists of four operating spacecraft, with the first launched in October 1990. The spacecraft thermal design was modelled and validated through an extensive test program, which included solar thermal vacuum tests. Additionally, an on-orbit thermal balance test was performed on the protoflight spacecraft, and the results were compared to thermal model predictions. On-station thermal performance has been excellent, with the exception of the infrared earth sensors, which required design modifications for later flights. Lower than expected solar absorptance degradation has been minimal on the thermal radiators. Evidence of hot soakback from liquid apogee engine firings were observed during transfer orbit. Results of the Inmarsat 2 program demonstrate that detailed modelling and a comprehensive test program will produce a reliable thermal control system.

Early flight mission objectives can be met with a Space Reactor Power System (SRPS) using thermoelectric conversion in conjunction with fast spectrum, lithium-cooled reactors. This paper describes two system design options using thermoelectric technology to accommodate an early launch. In the first of these options, radiatively coupled Radioisotope Thermoelectric Generator (RTG) unicouples are adapted for use with a SP-100-type reactor heat source (Deane 1992). Unicouples have been widely used as the conversion technology in RTGs and have demonstrated the long-life characteristics necessary for a highly reliable SRPS (Hemler 1992). The thermoelectric leg height is optimized in conjunction with the heat rejection temperature to provide a mass optimum 6-kWe system configured for launch on a Delta II launch vehicle. The flight-demonstrated status of this conversion technology provides a high confidence that such a system can be designed, assembled, tested, and launched by 1996.