BOX 1.1

What Is a Radioisotope Power System?

Radioisotope power systems (RPSs) are compact, rugged spacecraft power systems that provide reliable, long-lived power in harsh environments where other power systems such as solar arrays are not practical. RPSs are not nuclear reactors. They do not use nuclear fission or fusion to produce energy. Instead, they produce heat through the natural radioactive decay of plutonium-238 (238Pu). All U.S. RPSs launched to date have used solid-state thermoelectric converters to convert this heat into electricity. Such RPSs have supported 26 NASA and Department of Defense missions since 1961. Advanced Stirling Radioisotope Generators, which are still under development, use a more efficient dynamic energy conversion system to generate electricity.

U.S. RPSs have an outstanding safety and reliability record. RPSs have never caused a spacecraft failure, and almost 50 years of effort have been invested in the engineering, safety, analysis, and testing of RPSs. Safety features are incorporated into the design of RPSs, extensive testing has demonstrated that they can withstand severe conditions associated with a wide spectrum of credible accidents, and mission experience has demonstrated that they can operate continuously for decades.

FINDING. Production of 238Pu. The United States has not produced 238Pu since the Department of Energy shut down its nuclear weapons production reactors in the late 1980s.


Chapter 2 provides background information on space exploration, the case for using RPSs and 238Pu, NASA and DOE roles and responsibilities, and nuclear safety. Chapter 3 examines 238Pu supply and demand and the importance of immediate action to reestablish domestic production of 238Pu. Chapter 4 reviews the performance of various RPSs, related research and development, and the importance of completing the development of ASRGs with all deliberate speed.



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