[tarre]

In fact the fission[1] part in such small scale is hard. Curiosity and other probes using thermonuclear batteries harness alpha decay[2], which is relatively easy as it happens whether or not you want it to happen, but creates also much less power. In that case the hard part is to obtain material with appropriate half-life and other properties. Perhaps best material for this is Pu-238, which is far more expensive to create than weapons grade plutonium.

1. https://en.m.wikipedia.org/wiki/Nuclear_fission

2. https://en.m.wikipedia.org/wiki/Alpha_decay

[theptip]

I don't think "thermonuclear" is the right term for the batteries in probes. Wikipedia says "thermoelectric"[1], as the electricity is generated directly by thermocouples.

"Thermonuclear" usually refers to the sorts of fusion reactions found in stars and modern nuclear warheads.

[1]: https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_ge...

[tarre]

Thanks for correction. Unfortunately I'm not able to edit it anymore.

[SigmundA]

Sorry I wasn't using the strict term of fission[1].

This reactor says it uses U-235 which would be full fission similar to the US SNAP-10A[2] or Russian BES-5 RTG[3]

So yes the fission part is more complicated than a P-238 alpha decay RTG. Perhaps I mischaracterized the R&D complexity on the reactor portion, although it has been done before.

1. https://physics.stackexchange.com/questions/35303/alpha-deca...

2. https://en.wikipedia.org/wiki/SNAP-10A

3. https://en.wikipedia.org/wiki/BES-5

[tarre]

I didn't know about those reactors. Interesting.

When writing the answer, I didn't even consider, that those reactors need to be fast reactors. In retrospect it is obvious, but makes controlling the power even harder.