Plutonium-238 is the fuel that is driving the Mars rover Curiosity across the Martian landscape. It flew the New Horizons spacecraft to Pluto and beyond, and is still powering the Voyager probe into the depths of space 38 years after it was launched. It's a fuel that is in high demand and very short supply.
Last year, it came to light that there was only enough plutonium-238 to make three more batteries for NASA missions, a potentially devastating shortfall, and one that NASA has been working to remedy. Now, it seems like there is hope. This week, the Department of Energy (DOE) announced that in collaboration with NASA, they have succeeded in producing plutonium-238, the first time the substance has been made on American soil in 27 years.
It's been a long time coming. In 2013, funding for the project was secured, and the slow wheels of production started rolling. Now, two years later, the process has yielded 50 grams (1.8 ounces) of precious plutonium-238, the first to be made in the country since the Savannah River Plant closed down in 1988. It's not a very large amount--the Mars 2020 rover, for example, needs about 8.8 pounds of the stuff to operate--but it's a start.
Plutonium-238 is different from plutonium used in nuclear weapons and power stations, though it is still highly radioactive. As plutonium-238 decays into Uranium-234, it gives off huge amounts of heat, enough to be harnessed into electric energy in NASA's nuclear batteries, called radioisotope thermoelectric generators or RTGs. The heat has an additional benefit of keeping scientific instruments warm enough to function in the frigid void of space.
Plutonium-238 started out as a byproduct of the nuclear bomb-making process, but eventually as nuclear weapons ceased to be manufactured, the supply dried up, first in the United States, then in Russia. There is now only about 77 pounds left in the United States, and only about half of that is still of high enough quality to be used on space missions. The DOE and NASA hope that next year they will be able to produce 12 ounces of plutonium-238, eventually scaling up to producing 3.3 pounds per year.
Watch the DOE's short video about their achievement (complete with Back To The Future clips) below.