NASA may soon have to cut its deep-space missions short.
A Government Accountability Office report released last week shows that NASA is running low on the nuclear fuel essential for long-distance space travel.
The report came right before the first meeting of the reinstated National Space Council, in which Vice President Mike Pence reaffirmed the U.S.'s commitment to space exploration. But NASA's supply of plutonium-238 may only last another eight years, translating to an uncertain future for U.S. deep-space missions powered by radioactive isotopes.
The U.S. hasn't made plutonium-238 since 1988, leaving NASA with only 77 pounds of the radioactive isotope, Business Insider reports. And because the compound decays, only about half of the current stash could actually still power a spacecraft. This stockpile wouldn't have even fueled Cassini's 20-year mission, which used more than 50 pounds of plutonium-238 before it ended in September.
But NASA isn't ditching deep space just yet. The Department of Energy plans to start producing plutonium-238 again in 2019. By 2020, NASA expects to launch its next plutonium-powered mission: another Mars rover.
Just like everything in space exploration, it seems that plutonium production is an exercise in patience.