General atomics radioisotope fueled thermophotovoltaic power systems for space applications

Radioisotope thermo-photovoltaic (RTPV) based power systems are of particular interest to any system requiring solid state long life power, such as deep space missions. In the interest of furthering the development of RTPV technology to enable cost-efficient science missions, General Atomics has done extensive testing and development of thermo-photovoltaic (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 fueled prototype testing of a mW-scale power system that has been run 500+ days continuously at Oak Ridge National Laboratory. As part of the Micro-Isotope Power Source Program (MIPS) funded by the DARPA Microtechnologies Office (MTO), General Atomics developed a mW-scale power source designed for 10+ year life. 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 have been 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. System performance of over 10% electric to thermal conversion efficiency has been demonstrated and relies on high density and purity Plutonium 238 fuel. In addition, designs for higher power systems up to many 10s of Watts have been developed based on standard NASA GPHS heat sources which use similar encapsulation geometry as the NASA-designed aeroshell, carbon fiber sleeve and graphite impact shell (to facilitate launch approval for space missions).