Didn't know this, NASA's Plutonium-238 situation "Cry Foul Finding And Funding Fuel" (via Satnews Publishers)

Well there you go, I didn't realize that (a) the US didn't make its own plutonium for the thermoelectric generators for spacecraft and (b) they USED to buy it from Russia but there is no deal in place now and (c) Congress won't pony up for US production. This shortage is starting to affect approved and planed missions. Yet another thing I like about doing ground-based science.