Advanced power for planetary missions

Abstract

Radioisotope power systems are an enabling and essential technology for missions to the outer planets. Previous planetary missions such as Voyagers I and II, Galileo, Ulysses, and Cassini have relied on Radioisotope Thermoelectric Generators (RTGs). These RTGs, while demonstrating outstanding reliability and extremely long life, have relatively low power conversion efficiency. Advanced power systems now being developed offer the prospect of significant improvement in efficiency with corresponding reduction in the plutonium fuel required. The Advanced Radioisotope Power System (ARPS) being developed by Lockheed Martin under contract from DOE, utilizes cells that rely on Alkali Metal Thermal to Electric Conversion (AMTEC) as a means of energy conversion. AMTEC cells currently under development are fabricated from refractory alloys, capable of matching the elevated temperature of the General Purpose Heat Source previously used in RTGs. Preliminary design of the power system is based on the requirement to provide two generators for each mission, with each generator capable of providing a minimum of 105 watts of electrical power, six years after launch. The selected generator configuration includes a stack of four GPHS modules, with 16 AMTEC cells arranged on four sides surrounding the stack. This paper will describe the preliminary design of the generator, and will provide estimates of the mass, performance, and thermal characteristics.