Advanced Stirling Radioisotope Generator (ASRG). Courtesy Lockheed Martin.
Radioisotope Power Systems (RPS) are being considered for a wide range of future NASA space science and exploration missions. As the Vision for Space Exploration is implemented, it is quite possible that RPS will be used for the human lunar outpost as a general utility power source. RPS could also be coupled with electric propulsion (Radioisotope Electric Propulsion or REP) to reduce the launch mass, decrease the trip time, or increase the payload mass for some outer planet science missions.
Radioisotope Power Systems are a popular choice for certain NASA missions because of their advantages over the alternative space power options such as solar arrays, batteries, etc... RPS offers high reliability, long life, and predictable power production regardless of operating environment. RPS operating life can easily exceed 10 years, due in part to the use of well-known materials, rigorous component testing, and a plutonium (Pu-238) heat source with an 87.7 year half-life. A major motivation for using RPS on NASA missions is their ability to produce continuous, reliable electrical power in remote and often severe environments, with no reliance on sunlight. Some past NASA missions to the outer planets could not have been performed without RPS, and some spacecraft continue to operate far beyond their original expectation due in large part to the long life RPS.
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 the technology for the next generation of RPS. 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).
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