For the first time since the 1960s, NASA will be operating fission reactors that may be used in space.

As NASA makes plans to one day send humans to Mars, one of the key technical gaps the agency is working to fill is how to provide enough power on the Red Planet’s surface for fuel production, habitats, and other equipment. One option: small nuclear fission reactors, which work by splitting uranium atoms to generate heat, which is then converted into electric power.