# Heat Sinks



## James Coote (Feb 18, 2012)

I've been reading one of the major problems envisioned with spaceships is getting rid of all the excess heat generated by a nuclear reactor or other engine, as there isn't much of an atmosphere in space to transfer it to

So I thought, why not have a system where ships all have heat-sinks, essentially giant cool-packs, that warm up over the course of a journey. When they arrive at a station, they dump the heat sink for the station to deal with and pick up a nice new frosty one. The stations have massive radiators and other systems (such as pipes to/from a planet surface) to get rid of the excess heat

Does this sound plausible or have I missed some holes in the theory?


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## Vertigo (Feb 18, 2012)

I think you might be pushing it a little. You would need literally massive amounts of material, even if it started out close to absolute zero. Your drive would now have to push all that extra mass as well as the ship itself. More likely would be to use something cheap and relatively available such as Hydrogen as your coolant and just sling it (or use it as fuel) as it heats up. However I still suspect the amount needed to provide anything like enough cooling for a longish trip would be prohibitive. 

I think radiation fins would be more likely. Remember it is only dissipating heat by convection that won't work in space. Dissipating it by radiation will work fine, though it is not as efficient a mechanism.

Ultimately I think that by the time we are capable of such travel we will have much more efficient engines where this will not be as big a problem.


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## clovis-man (Feb 18, 2012)

So tomorrow's spaceship will look like this.







Don't laugh. It *IS* a Krell after all.


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## Vertigo (Feb 18, 2012)

Don't laugh but actually yes it's quite likely! Except probably bigger fins relative to the main body! Actually quite a few sf authors have addressed this with, typically, radiation fins that are deployed after departure as they would probably be very vulnerable and take too much space when docking.


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## James Coote (Feb 19, 2012)

I guess if I wanted to make it work, I'd have to invent some super-awesome coolant that's also too expensive to just throw away except in an emergency. And even then, longer journey ships would primarily rely on radiators


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## Stephen Palmer (Feb 19, 2012)

Isn't there a bit in the first three Alastair Reynolds novels where they cool things by doing maths?


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## David B (Feb 19, 2012)

Some of that heat may be useful.

Thermoelectric generators have a hot side and a cold side. The greater the temperature differential between either side, the more power/electricity is generated inbetween them.


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## Ursa major (Feb 19, 2012)

Stephen Palmer said:


> Isn't there a bit in the first three Alastair Reynolds novels where they cool things by doing maths?


How odd. I never had Reynolds down as a formulaic writer.


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## Pyan (Feb 19, 2012)

clovis-man said:


> Don't laugh. It *IS* a Krell after all.



You mean...it's really from Altair IV? Where's its tail?


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## Metryq (Feb 19, 2012)

As Vertigo suggested, by the time we're seriously considering interstellar flight, engines may be more efficient. One way to get rid of waste heat is to dump it overboard with some of the reaction mass. The engines that took astronauts to the Moon used "regenerative cooling," which is a fancy way of saying that some of the fuel ran through pipes around the nozzle to keep the nozzle from burning up. The action also pre-heated the fuel for a more efficient burn. The SR-71 spy plane—which flew so fast it heated up from atmospheric friction—also dumped heat from the airframe overboard with exhaust fuel.

Interplanetary flights will most likely coast most of the way. So if the on-board reactor is used to power the rest of the ship—and not merely drive the engine—there won't be any waste mass to flush the heat. Depending on the ship's power requirements, this could become a very serious problem. One likely solution to the "Pioneer anomaly" is waste heat from the on-board RTGs and electronics. (The solution is still being confirmed.) If such a relatively tiny power system is causing that much of a problem, what will happen with really big ships? Will this be a problem even if radiators don't melt?


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## chrispenycate (Feb 19, 2012)

If you can get a really efficient heat pump going, you can concentrate your waste heat until radiant cooling gets quite efficient; and not just drive heat either (you can freewheel a fair amount of a stellar trip). Even life support generates more thermal energy than is convenient to eliminate in a vacuum (yes, adiabatic expansion of steering jets does nicely). 

Anyone remember "Sundiver", by David Brin? There, being in an environment  in which it is difficult to radiate off excess heat (the sun's photosphere, warmish) they use a laser at a shorter wavelength simultaneously as a cooling system and drive. Now that requires efficiency.


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## clovis-man (Feb 19, 2012)

pyan said:


> You mean...it's really from Altair IV? Where's its tail?


 
The company did name itself after the *Forbidden Planet* race. But nobody knows what they looked like, except perhaps Dr. Morbius.


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## Colum Paget (Aug 6, 2012)

Stephen Palmer said:


> Isn't there a bit in the first three Alastair Reynolds novels where they cool things by doing maths?



Yes, there is. It's based on a genuine phenomenon in quantum computing called "Algorithmic cooling"


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## Colum Paget (Aug 6, 2012)

James Coote said:


> I've been reading one of the major problems envisioned with spaceships is getting rid of all the excess heat generated by a nuclear reactor or other engine, as there isn't much of an atmosphere in space to transfer it to
> 
> So I thought, why not have a system where ships all have heat-sinks, essentially giant cool-packs, that warm up over the course of a journey. When they arrive at a station, they dump the heat sink for the station to deal with and pick up a nice new frosty one. The stations have massive radiators and other systems (such as pipes to/from a planet surface) to get rid of the excess heat
> 
> Does this sound plausible or have I missed some holes in the theory?



Surely the best way of dealing with the heat is to find some super-efficient means of transferring it to the reaction mass that you're shooting out the back of the ship?


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