The US Department of Energy (DOE) recently completed its largest shipment of heat source Plutonium 238 since the reinvigoration of domestic production over ten years ago. The June delivery, consisting of 0.5 kilograms (a little over a pound) of new heat source plutonium oxide, was transported from Oak Ridge National Laboratory (ORNL) to Los Alamos National Laboratory, where it will be transformed into the heat source pellets needed to fuel NASA’s radioisotope power systems for deep space missions. This latest shipment puts DOE and NASA on track to achieve their average continuous production target of 1.5 kilograms per year by 2026, a level sufficient to support all current planned missions, including the Europa mission to Jupiter’s icy moon.
Plutonium-238, produced by irradiating neptunium-237 in a nuclear reactor, is the critical fuel that has powered 26 NASA space missions. Unlike solar panels, which only generate electricity during the day, plutonium-238 is self-warming. It provides a steady flow of power that keeps instruments, structures, and other onboard systems operational and free from damage, even in harsh conditions far from the sun.
For example, Plutonium-238 operates the spectrometers, magnetometers, and radiometers that help the Voyager probes fulfill their remarkable missions. It’s also used by the Mars rover Curiosity and NASA’s New Horizons spacecraft to keep their onboard instruments, structures, and systems warm. It’s a crucial technology for planetary science missions, especially those that go into the outer solar system without sunlight or where harsh environments make solar power impractical.
Despite this critical role, many planetary scientists have realized that NASA needs more of the special plutonium necessary for future exploration of the far reaches of the solar system. The agency’s stockpile is dwindling, and the cost of revitalizing it will continue to drain its planetary science budget, making some missions that might otherwise be feasible impossible.
As a result, the Appropriations Committee of the House of Representatives has approved $10 million next year to restart DOE’s capability to produce plutonium-238 at its national laboratories in Idaho and Tennessee. The DOE’s Office of Nuclear Energy has begun funding the effort, but more money is needed to revive the program and ensure it can be sustained.
Plutonium-238 is a rare and precious resource. It takes weeks to prepare it for use in space, and each kilogram requires millions of dollars to create. Suppose NASA’s supply of the isotope runs out. In that case, it will close doors to scientific discovery that might never reopen — robotic probes that burrow beneath ocean-bearing ice, ships that sail Saturn’s liquid ethane seas, and more. The time to fund the plutonium-238 restart is now. This is a once-in-a-generation opportunity to unlock the mystery of our solar system.
