NASA’s Mars Rover Will Be Powered by US-Made Plutonium

On Thursday, NASA is expected to launch its new Mars rover, Perseverance, on a mission to search for signs of ancient life on the Red Planet . It’s the agency’s largest and most autonomous Martian explorer yet. It’s also the first to be powered entirely with American plutonium.At the heart of Perseverance is a small “nuclear battery” the size of a beer keg called a radioisotope thermoelectric generator, or RTG. Unlike the nuclear reactors that create electricity on Earth , RTGs don’t have to initiate or sustain a fission reaction to generate power. They don’t even have any moving parts. Instead, they passively harvest the natural heat produced by the decay of plutonium-238 and convert it into electricity. They can reliably provide energy and heat to a spacecraft for decades—the two plutonium-powered Voyager probes launched in the late 1970s are still transmitting from interstellar space —and have been NASA’s go-to power source for more than two dozen deep-space missions.
“Plutonium-238 is a unique isotope of plutonium that principally decays by alpha radiation, and because of that, it generates a lot of heat,” says Robert Wham, the plutonium supply program manager at Oak Ridge National Laboratory, which is now responsible for making the stuff for NASA. “For a small spacecraft like Perseverance, you don’t want fission power. You just want thermal decay.”Perseverance is only the second Mars rover to use nuclear power as its main source of electrical energy. The agency’s first three rovers—Sojourner, Spirit, and Opportunity—all used solar power, but this meant they ran the risk of losing power completely when enough dust accumulated on the panels . Starting with Curiosity, which arrived on the Red Planet in 2012, NASA engineers switched to nuclear power as the rover’s main source of energy. It was a bold choice considering that, at the time, the US stockpile of nuclear fuel for space missions was dwindling and there wasn’t a single facility in the US capable of making more.

Plutonium-238 is handled in a hot cell at the Radioisotope Engineering Development Center at ORNL. Photograph: Jason Richards/ORNL
Plutonium-238 isn’t used in nuclear weapons (that’s its sister isotope, plutonium-239). But as the Cold War wound down in the late 1980s, the US stopped manufacturing all flavors of plutonium to comply with disarmament protocols. “Most of the plutonium-238 was from the Savannah River Site, which at the time was a defense facility rather than a national lab,” says Wham, referring to the Georgia site that formerly produced most of the materials for US nuclear weapons. Today, the Savannah River Site is one of the most contaminated places on the planet due to the nuclear waste buried on the premises from these activities.