There are large deposits of ice in the Moon’s permanently shadowed craters. The challenge is harvesting it for a future lunar base. Solar-powered rovers can’t operate in the permanent darkness of the craters. Engineers have developed a design for an ice-mining rover powered by americium-241, which has a half-life of 432 years. This could give the rover enough electricity to operate for decades, heating the ice and trapping water vapor and other volatiles as they escape.