NASA’s Plutonium Tours U.S. Before Heading To Mars

The plutonium-238 that powers NASA’s rovers on Mars crisscrosses the United States first on a tour of national laboratories.
Department of Energy officials outlined the path and process of manufacturing the Pu-238 for the Perseverance Rover that launched in July and is already about two-thirds of the way to the Red Planet.
“Perseverance's nuclear heart completed its own journey of seven years and nearly 5,000 miles before finally meeting up with the rover at Kennedy Space Center in Florida,” said Matt Dozier, the host of DOE’s Direct Current podcast.
NASA uses a solid-state nuclear battery, called a Multi-Mission Radioisotope Thermoelectric Generator, instead of, say, solar arrays, so the rover can keep operating during dust storms and the Martian night. With a halflife of 90 years, Pu-238 can keep a craft powered for decades.
“What’s the secret to their longevity?” Dozier asks. “It’s not turmeric, or acai berries, or wheat germ—the Mars rovers, and dozens of other NASA missions, run on a diet of pure plutonium-238.”
The $75 million MMRTG produces about 110 watts of electricity from the heat of decaying PU-238.
Dozier interviewed DOE officials tasked with processing and securing the dangerous isotope during each step of its manufacture:
1 Idaho National Laboratory: The fuel begins its journey as neptunium-237, a by-product of nuclear reactors that’s stored at Idaho National Laboratories. “The Oak Ridge National Lab essentially calls up the Idaho National Lab and phones in a shipment, let's say, for neptunium,” said Robert Wham, program manager for the Pu-238 Supply Program at Oak Ridge. “We get neptunium on a just-in-time basis; it’s shipped to us, and then we do the chemical processing here.”
2 Oak Ridge National Laboratory: Oak Ridge mixes the Np-237 with aluminum and bombards it with radiation in a reactor for 50 to 60 days. Some of the Np-237 turns into Pu-238, which Oak Ridge technicians separate, collecting plutonium as a powder. Oak Ridge also builds an iridium cladding that should keep the plutonium contained.
“One of the things that we worry about is that if there's an accident either during launch or shortly after launch, that when these generators come back to Earth, and they'll crash into Earth at very high velocities, very high speeds,” said Easo George, an alloys expert who serves as the governor’s chair at the Department of Energy’s Oak Ridge National Laboratory and the University of Tennessee. “And we want to make sure that if—such a very low-probability event—but if something like that were to happen, that the iridium would contain the plutonium fuel and prevent it contaminating areas around where it strikes.”
3 Los Alamos National Laboratory: The Pu-238 then heads 1,400 miles west to Los Alamos National Laboratory, where technicians press it into ceramic pellets, heat it in a kiln, encapsulate it in the iridium cladding, and test it to NASA’s standards. At that point:
“It's silver in color, it's kind of round, about an inch tall, and it's fairly heavy because it is a dense material,” said Jackie Lopez-Barlow, LANL’s radioisotope power systems program manager. “So if you were to hold it in the palm of your hand, it would take up about half the size of your palm of your hand. You wouldn't want to hold it in your hand, because it's extremely hot, about 400º Celsius.”
4 Idaho National Laboratory: The fuel then hits the road again, returning to Idaho where the fuel clads will be inserted into nuclear-power systems built by Teledyne Energy Systems Incorporated and Aerojet Rocketdyne. INL performs more testing on the whole unit and then has to get the power system to Florida in time for NASA’s launch window, when Earth and Mars are closest in their orbits, an event that occurs once every 26 months.
5 Kennedy Space Center: The 2,500-mile trip from Idaho to Florida happens via semi-trailer, supervised by the Department of Energy’s National Nuclear Security Administration.
“So those guys come up to our laboratory with their tractor,” said Kelly Lively, INL’s department manager for radioisotope power systems, “and we would already have our power system inserted into a steel cask inside our transportation trailer which is a 52 foot long semi-trailer.
“You know it's a nuclear payload being transported across several state lines, so it's kind of a sobering moment.”
6 Cape Canaveral Air Force Station: After the power unit is married to the rover at Kennedy, it takes a relatively short trip to the cape to enter the nose cone of—in Perseverence’s case—an Atlas V rocket.
The Pu-238 is not weapons-grade, but that doesn’t mean the Martians couldn’t turn it to nefarious ends. It is still a proliferation risk, according to the World Nuclear Association:
“In practical terms, there are two different kinds of plutonium to be considered: reactor-grade and weapons-grade…. The two kinds differ in their isotopic composition but must both be regarded as a potential proliferation risk, and managed accordingly.”