Powered by plutonium

At this very moment, two rovers—Curiosity and Perseverance—are exploring the surface of Mars. Their mission is to gather data to help scientists understand the potential for life on the Red Planet. The rovers capture images, take samples, record sounds, and chronicle the weather.

Curiosity has been exploring Mars for 12 years, and Perseverance has been on the move for nearly 3 years with potentially a decade more to go, but neither use solar power nor have a refueling source. How do they keep it up?

The rovers are powered by plutonium-238, an isotope of the radioactive element plutonium. Plutonium-238 generates heat as it decays. This heat, which is converted to electricity by a generator, can power a device in deep space—for a very long time.

“Something like the Mars rover requires a lot of energy,” says Dave Kolman, the program director for Power Systems Programs and Integration at Los Alamos National Laboratory, where plutonium heat sources are manufactured. “The cold temperatures and long distance to the sun require a reliable power source that has to be radioisotope power.”

In addition to powering the Mars rovers, plutonium heat sources manufactured at the Laboratory’s Plutonium Facility have powered the Galileo mission to Jupiter (1989­–2003), the Cassini mission to Saturn (1997–2017), and others. In 2027, plutonium-238 will power the Dragonfly mission to Saturn’s largest moon, Titan.

“We’ve pressed and made almost every heat source for NASA in the past 50 years right here at Los Alamos,” says product engineer Nicholas Wozniak.

“When it comes to heat sources, we’re the only place that can do this.”
- Nicholas Wozniak

The Laboratory produces approximately 10 to 15 heat sources annually. On paper, the process is simple: plutonium-238 is either pulled from existing inventory or arrives fresh from Oak Ridge National Laboratory; turned into an oxide (powder); pressed into small pellets; encapsulated; and sent to Idaho National Laboratory, where the encapsulated pellets are stored until they’re placed on spacecraft and blasted into the cosmos.

In reality, manufacturing heat sources is a long and complicated process due to the complexity of plutonium. Handling the radioactive element requires highly trained workers and special equipment, such as a hot press, which is a hybrid furnace and hydraulic press that heats plutonium-238 to extremely high temperatures while compressing it into the right shape and density.

The Laboratory is also continually improving its heat sources. The plutonium pellets that will power the Dragonfly mission, for example, will be smaller and lighter than those on the Curiosity rover. They’ll also be used to keep parts of the rotorcraft lander from freezing. “The waste heat from the power system is a key aspect of our thermal design,” explains Zibi Turtle, the principal investigator of the Dragonfly mission and a scientist at the Johns Hopkins Applied Physics Laboratory. “The surface of Titan is very cold, but we can keep the interior of the lander warm and cozy using the heat from plutonium-238 pellets manufactured at Los Alamos.” ★