NASA relies on pu-238 to power long-lasting spacecraft batteries that transform heat into electricity. With foreign and domestic supplies dwindling, NASA officials are worried the shortage will prevent the agency from sending spacecraft to the outer planets and other destinations where sunlight is scarce. Thorium reactors produce PU-238 as a “free” byproduct. In 2009 Congress denied a request to produce more Pu-238 by traditional means, instead relying on Russia to sell us the plutonium. (Remember the Russian reset?) Russia made their last delivery in 2010. PU-238 production has since been restarted by converting Ne-237 to Pu-238 at a cost of 8 million dollars per kilogram. The Ceres-Dawn spacecraft used over 22 Kg of Pu-238 as electricity generator.