Additional Radioisotope Power Systems: Survive, Operate, and Thrive on the Lunar Surface

The use of radioisotope power systems (RPS) has been critical in enabling many of NASA’s deep-space missions, and the need for these systems continues to grow as the space agency expands its exploration frontiers. Previous RPS missions conducted unheralded science including the Voyager, Galileo, Ulysses, Cassini, New Horizons (Pluto), and multiple Mars rovers. The most used RPS isotope, plutonium-238 (Pu-238), has enabled NASA to conduct science anywhere in the solar system and has proven to be reliable and safe, but growing demand for RPS for commercial and defense applications has led to an interest in alternative isotopes for space applications. According to NASA’s recent decadal survey, the demand for missions enabled by RPS is increasing, and increasing the utilization of these systems will enable a wider range of scientific investigations. Additionally, commercial lunar landers will eventually require lunar infrastructure to survive the extremely cold (<100K) environment during the ~14-day lunar night, which will only increase demand for radioisotope heater units (RHU) on the lunar surface over the next decade. The eventual vision for landers to operate and thrive through the lunar night will increase demand for lunar RPS producing 10s to 100s of watts of electricity. Interest in utilizing RPS for national security missions has grown, highlighted by the most recent call from the Joint Energy Technology Supplying On-Orbit Nuclear Power (JETSON) program to investigate the design of a novel RPS. Additionally, future space reactors for defense programs such as Demonstration Rocket for Agile Cislunar Operations (DRACO) or JETSON require a novel regulatory approach. RPSs can thus serve as a steppingstone to address technological and operational challenges, while growing regulatory confidence for operations with nuclear materials in space. Additional isotopes that have been considered for space applications include fission products and americium-241 (Am-241). Fission products, such as strontium-90, have been used successfully for reliable power for Earth applications, while Am-241 has been proposed for deep space missions. Using alternative isotopes for RPS has several benefits, including increased RPS availability to the space industry and potentially reduced costs when compared to existing RPS. The use of fission products, for example, can be a cost-effective solution for commercial or defense missions to the Moon. The DOE is successfully satisfying the demand from NASA for its marquee missions. Additional isotopes from commercial companies and ESA have the potential to expand the scope of science that NASA is able to conduct for Discovery or Flagship missions. These isotopes can be used as radioisotope heater units to keep electronics warm, or for radioisotope thermoelectric generators or radioisotope Stirling generators to provide dependable power for years to decades. Fission products and Am-241 could support growing commercial and defense capabilities requiring use of RPS.