Multi-Mission Radioisotope Thermoelectric Generator

The multi-mission radioisotope thermoelectric generator (MMRTG) is a sophisticated type of radioisotope thermoelectric generator (RTG) that has been specifically designed and developed for NASA space missions. This innovative energy system is under the jurisdiction of the United States Department of Energy's Office of Space and Defense Power Systems within the Office of Nuclear Energy.

Function and Use

An MMRTG functions as a nuclear battery, converting heat generated by the natural radioactive decay of plutonium-238 into electricity. This process is facilitated through solid-state thermoelectric couples that take advantage of the Seebeck effect, one of the Onsager reciprocal relations. The resulting temperature gradient generates an electron flow, thus producing electrical power.

The MMRTG has proven to be a reliable and safe power source, capable of providing continuous electricity and heat to spacecraft and their scientific instruments. This makes it particularly suitable for long-duration missions where solar power is insufficient, such as deep space explorations or missions to planets with little sunlight.

Historical Context and Applications

Over the past four decades, the United States has launched 26 missions utilizing 45 RTGs. Some notable missions include the Mars Science Laboratory (MSL), the Curiosity rover, and the Perseverance rover. The MMRTG powering these rovers was designed and built by Aerojet Rocketdyne in collaboration with Teledyne.

Mars Science Laboratory (Curiosity Rover)

The Curiosity rover, launched as part of the Mars Science Laboratory mission, utilizes an MMRTG to conduct its exploration on the Martian surface. The MMRTG provides a steady supply of electrical power and heat, enabling Curiosity to operate its scientific instruments even in the harsh conditions of Mars.

Perseverance Rover

Similarly, the Perseverance rover, which landed on Mars in 2021, is equipped with an MMRTG. This power source supports the rover's mission to search for signs of past microbial life and collect samples for potential return to Earth.

Future Missions

The MMRTG is also slated for use in future missions, such as the Dragonfly mission to Titan, Saturn's largest moon. Dragonfly will use the heat from its RTG to power its multi-rotor vehicle, designed to transport scientific instruments across Titan's varied landscapes.

Technological Contributions

The development of MMRTGs has spurred advancements in thermoelectric materials, such as skutterudites, which are known for their high efficiency in converting heat to electricity. These materials are also utilized in the general-purpose heat source designs that power various RTGs and Stirling radioisotope generators.