NASA’s Perseverance Mars rover, which launched July 30 to explore potential life on Mars, is being powered by a somewhat surprising source to those outside of the space industry: radioactive plutonium. NASA turned to Plutonium-238, which is not the kind of plutonium used for weapons, as a reliable alternative to solar power.
“NASA likes to explore, and we have to explore in some very distant locations, dusty locations, dark locations and harsh environments,” said June Zakrajsek, a nuclear fuel expert at NASA’s Glenn Research Center in Ohio. “When we’re in those kinds of environments, solar energy sometimes does not provide the power that we need. The light just does not get to those locations like we would need it.”
While solar power missions have occurred, such as the InSight lander and Opportunity rover, dust storms blocking the sun proved to be a hinderance. Perseverance instead has a multimission radioisotope thermoelectric generator (MMRTG) that is expected to power the spacecraft for approximately 14 years. The MMRTG was similarly used on the Curiosity rover, which launched in 2011 and continues to roam Mars. Unlike the Curiosity, this latest rover has U.S.-made plutonium.
In 2012, NASA focused on using nuclear power for energy. Unfortunately, U.S. stockpiles were limited and there were no facilities capable of making it. So, NASA took it upon itself to make its own at the Department of Energy’s Oak Ridge National Laboratory in Tennessee. A 2015 breakthrough resulted in the first plutonium-238 production in decades. Further research and development helped streamline the production process.
“Plutonium-238 is a unique isotope of plutonium that principally decays by alpha radiation, and because of that, it generates a lot of heat,” said Robert Wham, ORNL plutonium supply program manager for NASA. “For a small spacecraft like Perseverance, you don’t want fission power. You just want thermal decay.”
Experience with Curiosity’s MMRTG played a role in developing the new system for Perseverance, which took seven years. The MMRTG turns heat from radioactive decay into electricity, which produces 110 watts of power and charges two main rechargeable lithium-ion batteries. The generated heat also assists in ensuring the rover’s tools and system maintain proper operating temperatures.
The journey to creating the plutonium started with a different element: neptunium. After a two-month process of irradiating with neutrons in a nuclear reactor, it changes into the desired element. Since safety is a must when it comes to anything nuclear, ceramic is added in. This addition minimizes the chances of this material being broken into small pieces that could be released into the air or ingested. Additionally, each pellet is encased in iridium to contain the radioactive fuel in the unlikely event that it makes its way back to Earth, and each module is surrounded by the same materials used in a missile nose cone.
As Perseverance begins its journey to Mars, with a landing date of February 18, 2021, NASA is also focused on its next nuclear-powered mission. The Dragonfly drone is scheduled to take off in 2026 to explore Titan, Saturn’s largest moon.
Interested in other ways nuclear power is being explored? Check out Tiny Nuclear Reactor Could Be the Future of Nuclear Energy and Bill Gates to Build Small Nuclear Power Plants to Supplement Solar and Wind Power.