NPR says that NASA has not made any new Plutonium-238 since the 1980s, instead opting to borrow from Mother Russia. And because they use up to 5kg of the material each year, it would take eight years worth of production to begin satisfying demand again. But the requested $US30 million from Congress is only a start — the full Plutonium-238 production program could cost up to $US150 million.
Because it gets so cold in deep space (reaching absolute zero), spacecraft travelling out that far need a fuel generating a lot of heat, so they can convert that energy to electricity. Plutonium-238 naturally generates a serious amount of heat as it goes through radioactive decay, so it’s often the fuel of choice for these NASA adventures, such as voyages to Saturn and beyond.
According to a Johns Hopkins planetary scientist, NASA has enough Plutonium left to fuel the next Mars Rover mission, and maybe enough to test out some new power generators. After that, they need more scratch for more fuel. [NPR via MIT Tech Review]