What options are available for generating electricity in a space colony if it is at the planet's darkest point all year around without help from nearby outposts?

  • 3
    $\begingroup$ @Osm strictly speaking, none of the planets have a side that's dark all year round. That would require the planet to be tidally locked 1:1 with the Sun, like the Moon is tidally locked to the Earth. For many years it was thought that this was the case for Mercury, but it turned out to be tidally locked in an unusual 3:2 resonance. $\endgroup$
    – Roger Wood
    Sep 24, 2022 at 2:49
  • $\begingroup$ On any planet? On Earth, there are a variety of solutions. $\endgroup$ Sep 24, 2022 at 3:41
  • 1
    $\begingroup$ On any planet? Mercury and Venus are too hot for a space colony. The gas giants like Jupiter and Saturn got no solid surface for a colony. The dwarf planet Pluto is too far away and too cold. So only Mars is left. $\endgroup$
    – Uwe
    Sep 25, 2022 at 3:32

2 Answers 2


You can read my answer here for more information.

But in short, Radioisotope Thermoelectric Generators or RTGs for short are a good way of producing energy and are independent of light. Fission reactors are also another way, and are more efficient cost-efficient than RTGs (also independent of light).

Your question's "best" is a bit vague though.

It is said by WorldNuclear.org - Nuclear Reactors for space that:

RTGs are used when spacecraft require less than 100 kW. Above that, fission systems are much more cost effective than RTGs.

Overall, nuclear fission plants are expensive to build, but cheap to run and very efficient, while RTGs are less expensive, and quite inefficient due to the chief disadvantage of using them is their low conversion efficiency of heat to electrical energy. RTGs can run for about 14 years while fission reactors can last for 60 years.

  • 3
    $\begingroup$ RTGs also have the rather serious problem that their power output cannot be controlled or turned off in any way, which means that large high-powered ones are seriously problematic from a handling standpoint. $\endgroup$
    – ikrase
    Sep 24, 2022 at 3:34
  • 5
    $\begingroup$ RTGs aren't a viable solution for a colony, they aren't powerful enough unless you scale them up massively. $\endgroup$
    – GdD
    Sep 24, 2022 at 20:33
  • 2
    $\begingroup$ They're a bad solution to colony power in multiple ways due to the issue ikrase mentioned. The decay heat starts out at a maximum and drops off with an exponential curve no matter what the actual power requirements are, and if using thermoelectric conversion, the thermoelectric junctions lose performance over time and electrical power output drops even faster. And of course you need a reactor to make the RTG fuel in the first place: they're not an alternative to reactors, they're something that you can do for certain specialized applications if you have reactors. $\endgroup$ Sep 25, 2022 at 21:38

What options are available for generating electricity in a space colony if it is at the planet's darkest point all year around without help from nearby outposts?

  1. Starlight and cosmic rays: If we find ourselves in this situation, there are several meagre sources of energy that would likely be insufficient to light one LED per thousand square kilometers; like starlight and cosmic rays.

Potentially informative:


  1. Geothermal energy is always possible. The question doesn't specify atmosphere or no atmosphere which will affect the equilibrium temperature distribution of the planet, but because of non-zero thermal conductivity of rock from the sunlit side and possible heat flow from the interior and core from radiopacity and leftover heat from planetary formation, the surface and sub-surface temperatures are going to be somewhat warmer than the CMB temperature of 2.7 Kelvin. So we can build some kind of heat pump-like system or Stirling engine that will convert heat flow from the planetary surface or subsurface out through radiators into space. This will be really, really challenging to make efficient and useful and it will be completely different depending on if there is an atmosphere (and on what kind of greenhouse gasses its made of) or not.

  2. Wind and hydro power may be possible, again the question doesn't say anything about the planet so this applies or not on a case-by-case basis.

  3. Nuke 'em if you got 'em; A reactor or just natural radioactive decay will generate heat which you probably need (again, depends on planet) and there are efficient engines that can convert this to mechanical energy which can generate electricity much more efficiently than passive RTG technology based on thermopiles.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.