For crucial space missions, NASA will very rarely create a power source from plutonium-238, which it has only a limited supply of. This, for the uninitiated, is a very rare radioactive metal — so rare that NASA banned the use of radioisotope thermoelectric generators for scientists who want to submit proposals for space missions.

Until now, that is. The space agency has finally lifted the ban on the use of plutonium-powered radioactive batteries in its Discovery program, which seeks space missions that cost will cost no more than $500 million. Researchers had been previously banned from pitching ideas to NASA if their proposals required the use of RTGs as power sources. Not anymore.

Radioisotope Thermoelectric Generators

NASA has used RTGs to power some of its spacecraft dating back to the 1960s. However, it decided eventually to ban its use since the United States has a very limited supply. But now, after consulting with the Department of Energy, it seems the country has enough to accommodate NASA's future space programs. The news was confirmed by James Green, NASA's planetary science division director.

"After analysis and consultation with the Department of Energy, NASA's Planetary Science Division is pleased to announce that the ban on the use of Radio-isotope Power Systems (RPS) by proposers responding to the upcoming Discovery 2018 Announcement of Opportunity (AO) has been removed," Green wrote in the memo.

The news should please scientists since power is one of the most crucial aspects of any space mission. More importantly, nuclear power could open up more doors for how much more NASA's missions can do in space.

Most spacecraft incorporate solar panels, which acquires light from the sun and converts it into usable energy. Solar power is fundamental in space missions that place spacecraft within proximity of the sun, but not so in deep space missions because the sunlight gets less potent as a spacecraft travels farther and farther away from it. This is where RTGs come in, of course, which NASA uses for deep-space missions, such as the New Horizons and Voyager spacecraft.

Plutonium-238

For the past 30 years, the county has had a low supply of plutonium-238. But things have changed in recent years. In 2015, the Oak Ridge National Laboratory restarted production of plutonium-238 aided by funding from NASA.

NASA will open submissions for proposals in 2019, with the finalist being chosen two years later in 2021.