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What about lasers for emitting waste heat? Obviously there are practical issues with having powerful-enough lasers essentially powered by a heat engine, but are

• NortySpock 6y ago
  I think you're going to run into problems turning waste heat into usable energy, because it implies there's a cold sink already that you can use to convert the temperature differential into electrical energy to drive your laser. High end laser efficacy ranges from 30% to 50%?[1] But regardless, you're asking to get low-entropy energy out of high-entropy energy, and that's one of those "you can't win or break-even at thermodynamics in a closed system" kind of thing. Since spaceships come conveniently jacketed in a vacuum-insulating outer layer (i.e. space :) you're still stuck with some variant of radiative heat transfer, and "a big piece of metal being used as a infrared heat radiator because we pushed heat into it using a refrigerator loop) is still the cheapest option. The last option techie that I've ever heard for rejecting heat already onboard on a spaceship (and this is pure technobabble from proposals about Star Wars ships massive power generation needs) would be some magical way to convert heat into neutrinos, which, since neutrinos can pass though most matter, could be inside the ship and still function as a heat rejection mechanism. [2] [1] https://www.laserfocusworld.com/lasers-sources/article/16547048/photonic-frontiers-highefficiency-optical-pumping-going-green-cranks-up-the-laser-power https://www.laserfocusworld.com/lasers-sources/article/16547... [2] https://www.theforce.net/swtc/power.html https://www.theforce.net/swtc/power.html