Radioisotope fueled thermophotovoltaic power systems for space applications

Thermo-photovoltaic (TPV) based power systems are of particular interest to any system requiring solid state long life power, such as deep space missions. General Atomics has done extensive testing and development in small-scale TPV power systems in the milli-Watt to 10s of Watts scale. The most significant contributions have been in the electrical testing of a watt-scale TPV system and in studying neutron degradation in a mW-scale, fueled TPV power source. When comparing competing technologies for use with a radioisotope heat source, a critical criteria is that the power generating technology is not subject to excessive degradation due to exposure to the heat source radiation or space based radiation. This paper describes the analysis, modeling and testing of 0.6 eV Indium Gallium Arsenide (InGaAs) fueled TPV devices with special consideration paid to neutron degradation. The purpose of the paper is to present the research showing the relative device degradation as observed in actual radioisotope fueled power systems, as well as the design space and considerations of an electrically heated TPV power system. As part of General Atomics Internal Research and Development (IRAD) program the microscale mW power level MIPS was scaled up to designs at the single Watt and multi Watt level. Neutron degradation of 0.6% per year of the InGaAs TPV devices has been predicted and measured for Plutonium 238 radioisotope heat sources. Leading from the small scale TPV power system work, larger scale systems were designed and an electrically heated 1-2 Watt scale of TPV power system has been tested to assess system efficiency and power output relative to thermal input. In addition, designs for high power systems to many 10s of Watts have been developed based on standard NASA GPHS heat sources.