Multi-Mission Radioisotope Thermoelectric Generator

The multi-mission radioisotope thermoelectric generator (MMRTG) is a type of radioisotope thermoelectric generator developed for NASA space missions such as the Mars Science Laboratory (MSL), under the jurisdiction of the United States Department of Energy's Office of Space and Defense Power Systems within the Office of Nuclear Energy. The MMRTG was developed by an industry team of Aerojet Rocketdyne and Teledyne Energy Systems.

Space exploration missions require safe, reliable, long-lived power systems to provide electricity and heat to spacecraft and their science instruments. A uniquely capable source of power is the radioisotope thermoelectric generator (RTG) – essentially a nuclear battery that reliably converts heat into electricity. Radioisotope power has been used on eight Earth orbiting missions, eight missions travelling to each of the outer planets as well as each of Apollo missions following 11 to Earth's moon. Some of the outer Solar System missions are the Pioneer, Voyager, Ulysses, Galileo, Cassini and New Horizons missions. The RTGs on Voyager 1 and Voyager 2 have been operating since 1977. Similarly, Radioisotope Heat Units (RHUs) were used to provide heat to critical components on Apollo 11 as well as the first two generations of Mars rovers. In total, over the last four decades, 26 missions and 45 RTGs have been launched by the United States.

RTGs convert the heat from the natural decay of a radioisotope into electricity. The MMRTG's heat source is plutonium-238 dioxide. Solid-state thermoelectric couples convert the heat to electricity. Unlike solar arrays, the RTGs are not dependent upon the Sun, so they can be used for deep space missions.

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