Many of my favorite ideas for space exploration, such as large outer solar system probes, or the Mars Direct human Mars exploration proposal, require nuclear reactors to supply the high-power requirements of the spacecraft. However I have never very much liked the idea of a large amount of refined uranium being put on top of a possible bomb (the rocket fuel). I am specifically concerned the possibility of the rocket exploding, sending radioactive uranium around the globe in a mini-Chernobyl.

Assuming we will not be getting fusion reactors anytime soon, what alternatives are there to nuclear fission power where solar power is not enough for a mission. Also, since there needs to be a high-power source on the surface of a planet (Mars) for Mars Direct, what high-power sources could be used on a planet such as Mars?

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    $\begingroup$ Uranium-235 when the reactor has not worked at all is rather harmless. So, your fears of a launch accident are, quoting Mark Twain, slightly exaggerated. $\endgroup$ Jul 31 '13 at 20:10
  • $\begingroup$ Spacecraft have limited solar array size because of launch mass, but once you have the equipment on Mars to manufacture solar panels, potential power is unlimited. $\endgroup$
    – gerrit
    Jul 31 '13 at 20:40
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    $\begingroup$ @hunter2 - I wish us all good luck finding hydrothermal sources on Mars (seriously). $\endgroup$ Aug 1 '13 at 6:36
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    $\begingroup$ As gently noted by @DeerHunter, your premise of refined Uranium being dangerously radioactive is false. There may be reasons to consider alternatives, but the launch of radioactive material is not one of them. Good reasons are cost and schedule. It costs a lot to develop, build, and test a new nuclear system, and it takes a long time. $\endgroup$
    – Mark Adler
    Sep 3 '13 at 17:37
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    $\begingroup$ @TheHighFrontier In one cubic kilometer of sea water, there is 3.3 tons of uranium. Are you really worried that a satellite using about... say, 0.1 tons of uranium might plonk down in the Atlantic with its 300+ million cubic kilometers of water? $\endgroup$
    – MichaelK
    Feb 8 '18 at 8:57

This answer is really a wrap-up of comments from Deer Hunter, Gerrit and Hunter2:

Your options include:

  • Solar Power: effective when close to the sun. Beyond Mars' orbit this becomes less useful for power generation
  • RTG - Radioisotope Thermoelectric Generator: this is used for long missions, and it really isn't very dangerous. These are not fission reactors - they simply generate relatively small amounts of heat through radioactive decay.
  • Hydrothermal - would work on a body with sufficient liquid with a decent temperature differential (Europa?)
  • Geothermal - would work on a geologically active body (Io?)
  • Magnetic- Jupiter and Saturn have strong magnetic fields which may be usable. Between Io and Jupiter there is a plasma torus, which may also be a source of energy

Additionally, we have a few related questions:

  • $\begingroup$ Where's "chemical" - for high power (as in force) chemical rockets are still the main way to go. RTG's are typically not high power. $\endgroup$
    – paul23
    May 11 '15 at 21:45
  • $\begingroup$ Chemical is just not long term - you have to carry too much. High Power /= sustainable. $\endgroup$
    – Rory Alsop
    May 11 '15 at 21:59
  • $\begingroup$ The question did however not include sustainability. And for missions to mars chemical rockets are a viable choice. $\endgroup$
    – paul23
    May 11 '15 at 22:01

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