Scientists Find a New Way To Create the Plutonium That Powers Deep Space Missions

A long-simmering crisis for deep space missions ends before it could become a problem.

© NASA   A long-simmering crisis for deep space missions ends before it could become a problem.

By David Grossman, Popular Mechanics

It appears that the U.S.'s plutonium-238 shortage is coming an end. The radioisotope is crucial for fueling long-term deep space missions, but as of 2017, a shortage was on the horizon. But innovations from the Oak Ridge National Lab (ORNL) have automated its creation allowing for more than double the plutonium-238 pellets made per week.

What make radioactive isotopes like plutonium-238 so important is that they have an unstable atomic nucleus that emits energy when made stable. Radioisotopes are used in everything from medical sterilization to art restoration. But of the 2,900 radioisotopes known to man, "plutonium-238 (238Pu) is the only practical isotope for fueling" the radioisotope power systems (RPSs) for deep-space flights, according to a National Research Council report. 

Among the reasons for this is 238Pu's remarkable half-life of 87.7 years, which allows it to be used for well over a century while still producing almost the exact same heat. It's a big part of why the Voyager probes are still able to fly.

But like many aspects of the first Space Race, 238Pu was seen mainly as a tool of the Cold War. As the Soviet Union began to pose less of a threat, domestic production was halted in 1988 and NASA has been using reserves ever since. By 2015, there appeared to be only enough to power NASA missions through the 2020s. 

Now, ORNL has automated a crucial part of the 238Pu creation process-the creation of neptunium oxide-aluminum pellets. Neptunium is a radioactive metal element, and when these pellets are further irradiated, they create what's known has neptunium-238, which rapidly decays into usable 238Pu.

"Automating part of the 238Pu production process is helping push annual production from 50 grams to 400 grams, moving closer to NASA's goal of 1.5 kilograms per year by 2025," says ORNL's Bob Wham in a press statement. "The automation replaces a function our team did by hand and is expected to increase the output of pressed pellets from 80 to 275 per week."

© Genevieve Martin and Jenny Woodbery/Oak Ridge National Laboratory, U.S. Dept. of Energy   These are the machines used to automated part of plutonium-238 process.

With that increased production, future projects similar to Cassini and the Mars 2020 Rover can be built knowing that they'll have fuel sources that will last long past their launch date.