Realistic specific power expectations for advanced radioisotope power systems

Radioisotope power systems are being considered for a wide range of future NASA space science and exploration missions. Generally, radioisotope power systems offer the advantages of high reliability, long life, and predictable power production regardless of operating environment. Previous radioisotope power systems, in the form of radioisotope thermoelectric generators, have been used successfully on many NASA missions including Apollo, Viking, Voyager, and Galileo. NASA is currently evaluating design options for the next generation of radioisotope power systems. Of particular interest is the use of advanced, higher efficiency power conversion to replace the previous thermoelectric devices. Higher efficiency reduces the quantity of radioisotope fuel and potentially improves the radioisotope power systems specific power (watts per kilogram). Power conversion options include segmented thermoelectric, Stirling, Brayton, and thermophotovoltaic. This paper offers an analysis of the advanced 100 W-class radioisotope power system options and provides credible projections for specific power. Based on the analysis presented, radioisotope power system specific power values greater than 10 W/kg appear unlikely.