Radioisotope Heater Units – Fact Sheet
A penny shows the size of a radioisotope heater unit.
NASA/U.S. Department of Energy (DOE)
April 13, 2016
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Like a steady campfire that warms intrepid hikers in a remote forest, radioisotope heater units (RHUs) help bring dependable heat to wherever it’s needed for missions bound for the coldest corners of the solar system.
A RHU generates about one watt of heat energy from the natural radioactive decay of a small pellet of plutonium dioxide (which consists mostly of plutonium-238). This heat can be transferred directly to spacecraft structures, systems, and instruments, without the need for moving parts or intervening electronic components.