NASA is running out of plutonium. The space agency uses Pu-238 to fuel many of its deep space missions, including New Horizons, Voyager, the Curiosity rover, and the Mars 2020 rover. These long-lasting batteries were the byproducts of nuclear weapons manufacturing, and now that the world is making less of those, NASA’s stockpile of plutonium fuel is dwindling.
In December, the U.S. made its first fresh plutonium in almost 30 years. It was a relatively small amount–1.8 ounces, compared to the 8.8 pounds that a rover like Curiosity requires–but it’s a start. In 2016, the Department of Energy (DOE) aims to produce 12 ounces of the stuff.
At today’s meeting of NASA’s Outer Planets Assessment Group, Rebecca Onuschak from the DOE explained how the government plans to get better at making plutonium for deep space missions.
For starters, they’re going to upgrade a lot of the equipment that’s being used to produce Pu-238 at the Los Alamos, Idaho, and Oak Ridge national laboratories. This includes new furnaces, thermal vacuum chambers, and hot presses.
Although the DOE used a new process to manufacture its plutonium, some of the hot presses they’re using were built in the 1950s, Onuschak said, joking that they’re “vintage.”
Upgrading the equipment will make creating plutonium safer and more reliable.
The agency is also looking at new ways to improve and scale up the process. “We’re trying to make it as nimble as it can be,” said Onuschak.
Right now the DOE is looking into a new process that could potentially double their plutonium output, while creating a higher-quality product. It’s also cheaper. The secret appears to be in using “a pure neptunium dioxide pellet clad in zircaloy.”
Over the next year or so, DOE will figure out how to make these pellets, then bombard them with radiation to see if they work as expected.
The plutonium problem
The US government stopped making Pu-238 in 1988. Russia sold some to NASA in the 1990s and 2000s, but it stopped selling around 2009 – most likely because its Cold War-era stockpile ran out.
So as the space agency planned new plutonium-powered missions and used up its supply, researchers increasingly sounded alarms on Capitol Hill.
The complexity of producing more Pu-238, hard-to-peg cost estimates, and disagreements within Congress stalled funding for a resupply project for about two decades.
As a result, NASA today has about 77 pounds (35 kg) left (though the Department of Defence has a separate stockpile).
However, because Pu-238 decays, only about half of NASA’s stockpile is still fresh and hot enough for NASA’s needs.
This is not enough for another mission like Cassini, which used more than 50 pounds (23 kg). Yet space scientists hope to send similar spacecraft to explore hidden oceans on moons of Jupiter and Saturn; revisit Uranus, Neptune, and Pluto; and travel to other cold, mysterious, far-flung destinations for the first time.
“All of these missions would require nuclear power,” Alan Stern, the former head of science at NASA and principal investigator of the New Horizons mission, told Business Insider.
That’s why space scientists celebrated in July 2011 when Congress approved US$10 million in new funding to restart Pu-238 production for the first time since the Cold War.
The DOE manages the plutonium resupply project, since federal regulations prevent NASA from handling the nuclear material. The project’s goal is to revitalise the ageing plutonium in NASA’s stockpile and bulk it up with fresh plutonium.
By December 2015, the DOE had created 50 grams of mission-ready plutonium for NASA. That amount has since doubled to about 100 grams (just more than two golf balls’ worth of mass), and another 100 grams are expected to come out of reactors in coming months.