NASA’s Perseverance Mars rover gets its nuclear power source

The rover’s Multi-Mission Radioisotope Thermoelectric Generator, or MMRTG, was transferred from a preparation building to the Atlas 5 rocket’s Vertical Integration Facility, and was hoisted by crane onto a work platform near the top of the 197-foot-tall (60-meter) launcher.

Technicians inserted the power generator through an access door on the Atlas 5’s payload shroud, then placed the device on the aft end of the Perseverance rover through an opening on the spacecraft’s backshell, which encloses the rover and its landing system during the journey from Earth to Mars. The 99-pound (45-kilogram) unit was installed onto the rover Monday, according to Mary MacLaughlin, a NASA spokesperson.

After connecting mounting bolts and mating electrical lines, ground crews powered up the rover using the newly-installed MMRTG.
The power source was the final major component to be added to the Perseverance rover before its scheduled launch next week. The rover is the centerpiece of NASA’s $2.4 billion Mars 2020 mission.

The Multi-Mission Radioisotope Thermoelectric Generator, or MMRTG before fueling

“At this point, the spacecraft has been powered on and will remain so around the clock,” said Dave Gruel, manager of Assembly, Test and Launch Operations, or ATLO, for the Mars 2020 mission. “The launch operations team will continue to monitor the health of the spacecraft to ensure it’s ‘go’ for launch — nothing glamorous, but an important part of the job.” Developed by the U.S. Department of Energy, the MMRTG works by converting heat from the natural radioactive decay of plutonium-238 — a special non-weapons grade isotope of plutonium — into electricity. The generator contains 10.6 pounds (4.8 kilograms) of plutonium dioxide fuel. The device produces about 110 watts of power at the start of Perseverance’s mission, roughly equivalent to the power draw of a light bulb. The MMRTG’s power efficiency declines by a few percent per year.

The MMRTG will charge two lithium-ion batteries on the Perseverance rover. The batteries will power the robot during times of peak power usage, when NASA says power demand can reach 900 watts during science operations on Mars. Nearly 95 percent of the energy produced by the MMRTG will be in the form of excess heat. That will help keep the Perseverance rover’s internal electronics warm in the cold temperatures at the Martian surface. The MMRTG is the latest in a line of nuclear power sources and heaters used on more than 30 U.S. space missions since 1961. The one-ton Perseverance rover is a near-clone of NASA’s Curiosity rover, which launched in 2011 and landed on Mars in August 2012. Perseverance carries an upgraded suite of scientific instruments, including improved cameras and a payload to demonstrate producing oxygen from carbon dioxide in Martian atmosphere, a key capability for future human expeditions.

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