PARTS OF A MULTI-MISSION RADIOISOTOPE THERMOELECTRIC GENERATOR (MMRTG)
Figure 4.5 from Emily Lakdawalla’s 2018 book The Design and Engineering of Curiosity

Aerojet Rocketdyne, in collaboration with Teledyne, recently delivered the electrical power generator for NASA’s Mars 2020 rover to the U.S. Department of Energy’s (DOE) Idaho National Laboratory (INL), where it will be fueled, tested and readied for flight. In addition to providing the primary power source for the rover, Aerojet Rocketdyne is also playing a critical role in spacecraft propulsion for the journey to Mars.

The Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) will supply electrical power to the rover as it traverses the red planet, collecting samples for a potential return to Earth by a future mission. A similar device supplied by Aerojet Rocketdyne continues to power the Mars Curiosity rover, which has been exploring the Martian surface since 2012.

The MMRTG converts heat generated by the natural decay of plutonium-238 into electricity. Radioisotope power sources, which also provide heat to a spacecraft’s components, are typically used on long-duration deep space missions, where the great distance from the sun dramatically reduces the effectiveness of solar arrays.

“We’re best known for propulsion, but our role in supporting space programs certainly does not end there,” said Eileen Drake, Aerojet Rocketdyne CEO and president. “We’ve built lithium-ion batteries for the International Space Station, provide nuclear generators for deep space missions like the Mars rovers, and are building the electrical power system for Sierra Nevada’s Dream Chaser.”

Aerojet Rocketdyne was awarded a DOE contract in 2003 to develop and produce MMRTGs. In addition to the MMRTG for the Curiosity rover, the DOE authorized assembly of two additional flight units: one for Mars 2020 and one for a future mission. One unit will be fueled for Mars 2020, and the other unit will remain unfueled and in reserve for a future mission.