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hwillis parent
Per wiki: radiators reject 100-350 watts per m^2 and weigh ~12 kg per m^2. Not unlikely you would need 10x as much radiator as server. You need about as much area for radiators as you do for solar panels, but radiators are much heavier.

That also makes nuclear totally infeasible- since turbines are inefficient you'd need 2.5x as many radiators to reject waste heat. Solar would be much lighter.

https://en.wikipedia.org/wiki/Spacecraft_thermal_control#Rad...

perihelions
Nuclear power is very feasible in space. Perhaps you're overlooking that radiated power scales with the quartic of absolute temperature (T⁴); it's not difficult at all to radiate heat from a hot object, as it is for a room-temperature one.

(How hot? I won't quote a number, but space nuclear reactors are generally engineered around molten metals).

hwillis OP
Yeah, fair to say its feasible. ROSA on the ISS produces 240 W/m^2 and weighs 4 kg/m^2.

The S6W reactor in the seawolf submarines run at ~300 C and produce 177 MW waste heat for 43 MWe. If the radiators are 12 kg/m^2 and reject 16x as much heat (call it 3600 W/m^2) then you can produce 875 watts of electricity per m^2 and 290 watts at the same weight as the solar panels. Water coolant at 300 C also needs to be pressurized to 2000+ PSI, which would require a much heavier radiator, and the weight of the reactor, shielding, turbines and coolant makes it very hard to believe it could ever be better than solar panels, but it isn't infeasible.

Plus, liquid metal reactors can run at ~600 C and reject 5x as much heat per unit area. They have their own problems: it would be extremely difficult to re-liquify a lead-bismuth mix if the reactor is ever shut off. I'm also not particularly convinced that radiators running at higher temperatures wouldn't be far heavier, but for a sufficiently large station it would be an obvious choice.

perihelions
It goes up to 1,344 °C with Li, I think—it's a very different engineering space from the stuff on Earth.

The Soviet ones used K (or maybe NaK eutectic); there's a ring of potassium metal dust around the Earth people track by radar (highly reflective)—a remnant from one of them exploding.

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