[wcoenen]

There were indeed real nuclear reactors with thermoelectrics being launched in the cold war.

However, thermoelectrics have an efficiency well below 10% (maybe a bit better with this improvement but not much). For that reason, future reactors in space will likely use Stirling engines instead.

[mechhacker]

Correct. Space stirling designs* (and tested engines) have been much more performant than the RTG designs

*I spent part of my career working on these devices and saw many of them running in labs