The alkali metal thermal-to-electric converter for Solar System exploration

AMTEC, the Alkali Metal Thermal to Electric Converter, is a direct thermal to electric energy conversion device; it has been demonstrated to perform at high power densities, with open circuit voltages in single electrochemical cells up to 1.6 V and current densities up to 2.0 A/cm/sup 2/. It is a sodium concentration cell which uses a /spl beta/"-alumina solid electrolyte (BASE) tube as a separator between a high pressure region containing liquid sodium at 900-1300 K and a low pressure region containing a condenser at 400-700 K. As a power system, AMTEC is expected to deliver /spl sim/20 W/kg with a 15-20% thermal to electric conversion efficiency. AMTEC has been baselined as the power conversion system for the Ice and Fire missions in NASA\´s X2000 Program and is being developed as part of the NASA/DoE Advanced Radioisotope Power Systems Program. This paper discusses the basic operating principles of AMTEC as well as the evolution of design and materials selection for power converters for spacecraft in the X2000 program. Life and degradation studies of AMTEC cells and converters are underway at JPL and are considered in this paper.