> esa doesn't have a suitable supply of plutonium 238 In fact, the link you give explicitly mentions safety and political risks in addition to availability. >

> esa doesn't have a suitable supply of plutonium 238 In fact, the link you give explicitly mentions safety and political risks in addition to availability. > not only are there sourcing issues with Pu-238 (reserves are running low and production is not high enough), there are safety concerns and political issues related with its use in RTGs. Furthermore, it's not an accident they don't have any Pu-238. The lack of it is deeply connected to the general fear of doing anything radioactive, and hence no effort to develop production capability. It's clear ESA is being forced to consider nuclear power sources simply because it's almost impossible to fulfill certain missions without them. But the fact that they are willing to consider it when absolutely necessary does not mean they haven't seriously scaled down mission potential in the past by using solar power.