Power generation considerations in a solar bimodal receiver

The Integrated Solar Upper Stage (ISUS), or solar bimodal stage provides both propulsive thrust for efficient orbital transfer(s) and electrical power generation for the spacecraft. The combined propulsive and power systems allow the solar bimodal system to effectively compete for a variety of missions. Once on station, thermionic converters are used to supply continuous electrical power to the satellite, even during periods when the spacecraft is in the Earth´s shadow. The key to continuous power supply is thermal energy storage. The ISUS propulsion system also benefits through the use of thermal storage. By utilizing a graphite receiver, large amounts of sensible heat can be stored for later power generation. Waste heat is radiated to space through the use of heat pipes. Clearly, the graphite mass must be minimized without sacrificing electrical power capability. Voltage and current characteristics are carefully designed to operate within acceptable ranges. The detailed design of the receiver/absorber/converter (RAG) power system must meet these requirements with as little impact to the remainder of the bimodal system as possible. This paper addresses the key design considerations of a solar bimodal receiver as a power plant. Factors including the thermal storage and heat transfer from the graphite receiver to the thermionic converters, the support structures, electrical insulation and converter string design is discussed