: Thanks to its copious emission of alpha particles and its 88-year half-life, plutonium-338 is a potent and useful source of energy for powering spacecraft whose missions take them to places where using solar power would be infeasible. The isotope's advantages are offset by its short supply. Producing 238
Pu isotope entails irradiating actinides extracted from spent nuclear fuel. To make efficient use of 238
Pu, NASA had been developing a novel power source: Heat from the isotope would drive a Stirling engine, which, in turn, would drive an electrical generator. Citing budgetary pressure, NASA announced last week that it would cease funding two such generators being built by the US Department of Energy. What's more, the need to conserve supplies of 238
Pu has become less pressing, now that DOE has resumed its previously stalled production of the isotope.