[augusto-moura]

I don't know the exact reasons why Vikram didn't get a fission reactor. But I can assume from similar missions:

1. Solar is pretty good as far as Mars and it gets worse as it travel further from the Sun. This is why most probes that travel past Mars need a nuclear reactor (Voyager, Pioneer, Cassini, etc). Going closer to the sun they get even better

2. Sending radioactive materials on rockets presents a risk and it is avoided if possible, lunar probes are usually cheaper and can still benefit from solar, so no need for nuclear. Imagine throwing plutonium in the atmosphere in the case of an accident

3. Nuclear reactors in probes are small and rely on decay radiation, they _usually_ have pretty small powet output, solar has a lot

4. And last but not least, price, solar is much cheaper than nuclear

[mmooss]

> fission reactor

Am I wrong that the plutonium in the Voyagers is not in a fission reactor but in an RTG (Radioisotope Thermoelectric Generator), which converts the heat from the plutonium into electricity. ?

I suppose the heat is result of fission, but I don't think an RTG is what is meant by a fission reactor. ??

[Vecr]

Voyager uses a RTG. The USSR used some full-on nuclear reactors in space, but as far as I know no one else publicly did.

Edit: Yep, not sure how I forgot about that.

[joeyo]

The US put a fission reactor in space too. They did it first, in fact: https://en.wikipedia.org/wiki/SNAP-10A

Edit: it’s apparently still there and will be for a long time (!) albeit non-functional:

  > Decay date: April 3, 5966 (planned)

[wrycoder]

Fission reactor without a moderator!