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Solar and wind power are not sufficient for spacecraft, and many other applications. Fusion power still has very interesting applications.

• moloch-hai 4y ago
  Most likely, spacecraft will rely on power delivered via laser. If anybody succeeds in working out D-3He fusion, that could work in a spacecraft. (D-T, no.) We could probably scare up enough 3He to use for that, if there weren't too many.
  • PaulHoule 4y ago
    If anybody in the universe is doing interstellar travel I think they would have developed D-D fusion which is somewhat more difficult than D-³He or D-T fusion but probably possible with the a scaled up version of the same machine. Outside the frost line there is a lot of water and a higher percentage of D relative to H so it seems possible to "live off the land" between the stars without being dependent on starshine. A D-D reactor would produce ³He and T, a lot of those products would burn up in the reactor because the reaction rates are high but it would probably be possible to separate some of those out and use it as a breeder reactor that makes fuel for D-³He and D-T reactors elsewhere. I could picture the big D-D reactor running on a large comet or dwarf planet like Pluto producing D-³He for smaller reactors on spacecraft. (D-T not only produces a lot of neutrons but the T has a half life of 12 or so years and won't last for long journies.) My guess is that interstellar travelers would develop a lifestyle that works around the frost line, where generic bodies above a certain size have liquid water inside. If they were grabby they might consume Ceres or Pluto but might not really care about dry, idiosyncratic worlds like the Earth and Mars.
    • moloch-hai 4y ago
      Anybody doing interstellar travel should hang their collective head-analog in shame if they haven't mastered aneutronic p-11B fusion yet. (They will need to have figured out how to reflect xrays.) Having got used to spending interminable ages out in the infinite chill void, they probably have come to prefer being there, so have no desire to roast deep in a stellar gravity well. Their equipment might not even work if warmed too much.
• rini17 4y ago
  Solar is completely sufficient for 99% of applications.
  • iso1631 4y ago
    How do you power a moon base with solar? 14 days of battery? Fine. How do you power a Europa base with Solar? A Neptune probe?
    • rini17 4y ago
      Since we're talking in present tense that's the remaining 1%. Moon base can be fine with power beamed from a satellite or plain mirrors in orbit, no atmosphere in the way. Might end up being still cheaper than hauling nuclear reactor there plus all the infra to reliably dump waste heat from it.
      • iso1631 4y ago
        "Solar and wind power are not sufficient for spacecraft" I guess you're right that solar is useful for 99% of spacecraft -- in that they use it currently. Not a very useful observation "and many other applications" Power in polar regions. How well does Solar work in Antarctica? Or Alaska for that matter?
        • moloch-hai 4y ago
          It works super-great, collected in the tropics and shipped in chemical form. Before you object to depending on imported liquid fuel, consider that most of the world does already. The main difference is that literally anybody can make it, not just "oil exporting countries" and "fuel refiners". And, will. And export excess production when local tankage is full.
          • iso1631 4y ago
            Last I looked, round-tripping solar via liquid fuel and back to electricity was under 2% before transport costs