The isotope used in space missions is plutonium-238. That Scientific American article is about weapons pits made of plutonium-239. The US has a large surplus o

The isotope used in space missions is plutonium-238. That Scientific American article is about weapons pits made of plutonium-239. The US has a large surplus of stockpiled Pu-239 for weapons: https://www.energy.gov/nnsa/articles/nnsa-issues-final-surplus-plutonium-disposition-program-environmental-impact https://www.energy.gov/nnsa/articles/nnsa-issues-final-surpl... Sadly, it is of no use for space missions.