If Congress denies domestic production and the Russian deadlock continues, there appears to be only one answer to the plutonium deficit: ESA.
"To see see ourselves as a serious planetary science partner on the world stage with the United States, we're building up our nuclear capability for European-built RTGs," David Southwood, ESA's director of science and robotic exploration, said in an interview with Spaceflight Now. "We are building for a pretty major capability being available in Europe in the 2020s."
Southwood also hinted that Pu-238 isn't necessarily the only fuel that can be used with RTGs. Americium-241 has the advantage of a longer half-life, meaning these pellets will fuel RTGs for longer, but at a reduced energy output. Another big drawback with swapping americium for plutonium is that americium is more hazardous.
"Plutonium-238 is an alpha emitter, and you can shield alpha particles with a piece of paper," Adams said. "It's neutrons that damage people, and americium is more a neutron emitter than plutonium-238."