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. The use of a SP-100-type reactor assures compliance with safety requirements and expedites the flight safety approval process while, at the same time, providing flight performance verification for a heat source technology with the growth potential to meet future national needs for higher power levels. A 15-kWe, Atlas IIAS-launched system using the compact, conductively coupled multi-couple converters being developed under the SP-100 program to support a first flight system launch in 1999 is also described.