Office of Space and Defense Power Systems

The Department of Energy (DOE) and its predecessors have provided radioisotope power systems that have safely enabled deep space exploration and national security missions for five decades. Radioisotope power systems (RPSs) convert the heat from the decay of the radioactive isotope plutonium-238 (Pu-238) into electricity. RPSs are capable of producing heat and electricity under the harsh conditions encountered in deep space for decades. They have proven safe, reliable, and maintenance-free in missions to study the moon and all of the planets in the solar system except Mercury. The RPS-powered New Horizons spacecraft transited the Pluto system on July 14, 2015, and will continue on to explore other objects in the Kuiper belt. DOE maintains the infrastructure to develop, manufacture, test, analyze, and deliver RPSs for space exploration and national security missions. DOE provides two general types of systems – power systems that provide electricity, such as radioisotope thermoelectric generators (RTGs), and small heat sources called radioisotope heater units (RHUs) that keep spacecraft components warm in harsh environments. DOE also maintains responsibility for nuclear safety throughout all aspects of the missions and performs a detailed analysis in support of those missions.