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I'm doing research for a space opera with some hard sci-fi elements. One faction does use radiators (dusty plasma particles held in magnetic fields- which would create the effect of glowing wings on warships) for their starships, while I'm thinking another faction would use something else so I'm open for ideas.

This other faction centers on genome manipulation instead, so I figure their starships would be using something akin to biological heatsinks? Or perhaps they engineer microorganisms that could absorb heat and cool off using some sort of reverse exothermic reaction? Any ideas welcome.

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    $\begingroup$ reverse exothermic reaction - an endothermic reaction $\endgroup$ – Slarty Sep 24 '17 at 19:42
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    $\begingroup$ (1) Why would "dust particles held in magnetic fields" be good radiators? How does the heat get from particle to particle? (2) If the "genome manipulation faction" has the mechanical knowledge & ability to build spaceships, they have the knowledge and ability to build "regular" radiators. $\endgroup$ – RonJohn Sep 24 '17 at 22:26
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    $\begingroup$ @RonJohn The OP did not ask for an 'efficient mechanism', just an 'alternate mechanism'. Use dust particles as a heat sink. Transfer internal heat into them, eject them into the magnetic field in space, where they radiate their heat, and when they 'cool down', bring them back into the ship. No loss of mass (think generation ship, where you can not afford any loss of mass). Dust particles have a far greater surface area, thus more radiation, greater efficiency. Ask a bricklayer to build a house, he will build it of brick. Ask a carpenter, she will build it from wood.. $\endgroup$ – Justin Thyme Sep 24 '17 at 23:23
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    $\begingroup$ "while I'm thinking another faction would use something else ". Why? When you start to try to conjure up story/world elements just because, and not for any reason that adds anything to the plot or the world, then you are heading down the wrong path. Think Chekhov's Gun and ask yourself: "Will these exotic heat sinks become relevant at any point?". If the answer is "no", then do not add them. You muddle up the whole thing if you add unnecessary fluff without any purpose or thought. $\endgroup$ – MichaelK Sep 25 '17 at 7:44
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    $\begingroup$ If you say "for flavour by creating a sense of the factions being very different"... well ok then: make them be different then, and not just do the exact same thing with only a minor variation. Make them not need to shed heat. Suppose for instance they have highly efficient processes that create very little waste heat. Make waste being abhorrent to them. Suppose for instance they need the heat because the little they lose to space is making their craft become too cold if it goes on unchecked. $\endgroup$ – MichaelK Sep 25 '17 at 7:52

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  1. Thermal radiation. Read this Dec 2014 article from IEEE Spectrum Magazine about some Stanford scientists who developed a solution to passively radiate thermal energy directly to outer space... even from the surface of the planet.

  2. Re-use. Remember that space is cold. Some of your generated heat will be used to heat the ships. Remember that the old Apollo missions actually had heaters on board because the equipment didn't generate enough heat to keep the astronauts warm.

EDIT: While space's background temperature is on average -455 °F, which most people consider to be cold, the reality is that, due to the low particle count, where you are is easily heated by solar radiation. However, it doesn't change the fact that empirical evidence (the Apollo moon missions are a great start) prove that without heaters, people freeze in space. The reason simple radiators don't work is because you need somewhere to transfer the heat too, and that's where the low particle count comes into play and why alternatives are valuable.

  1. Finally, consider a thermolelectric generator, which is a passive device that converts thermal gradients into electricity.
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    $\begingroup$ +1 - Just finished reading the thermalelectric generator link. Interesting possibilities if we can find a common/cheap element or alloy that can do the trick! $\endgroup$ – Henry Taylor Sep 24 '17 at 20:04
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    $\begingroup$ The key phrase there is "thermal gradient" you still need radiators to cool the ship to maintain the gradient. $\endgroup$ – John Sep 24 '17 at 20:59
  • $\begingroup$ Take the innards of any Koolatron thermoelectric cooler. If it is not plugged in, and the inside is cooler than the outside, then you can get a current flow through the plug. If you short across the plug, you will actually reverse the process and decrease the temperature difference (warm up the insides, if it were set up as a cooler). In your spaceship, one side of the junction would be inside the ship, the other side would be outside. Store the current in a battery. $\endgroup$ – Justin Thyme Sep 24 '17 at 21:01
  • $\begingroup$ ctd No, you can't put two junctions into a box and have a perpetual motion machine - one side set up to convert electrical flow to a temperature difference, and the other one to use the temperature difference to generate the current. $\endgroup$ – Justin Thyme Sep 24 '17 at 21:01
  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – HDE 226868 Sep 25 '17 at 21:51
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Biological or chemical heatsinks work fine for short bursts but will not be enough to cool the ship for days or months, you will eventually need radiators. the term you are looking for is an endothermic reaction, an extreme endothermic reaction. This already in use today it is called chemical cooling.

It is horribly inefficient but it is at least possible, and inefficient may not matter, the reactants will be continuously used up so they will still need back up radiators for when they run out of "coolant" aka reactants.

Best case they use radiators most of the time but use a chemical reaction for short periods, but this could be a way to protect fragile radiators during combat, simply retract them and rely on endothermic reactions for a short time, then when combat is over re extend the radiators, they could even reverse the reaction and radiate the heat out using radiators to reset the system.this is heat sequestration more than anything and it has a really short working time (high mass to the amount of heat you can sequester) so you need radiators if you plan on being in space for any significant amount of time. But during combat they would not be using radiators which is the closest I think you can get to not having them at all.

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  • $\begingroup$ Now add this to a process such as photosynthesis and you have the ability to use chemistry as a catalyst, in the sense that the reactants are not used up. Plants do it all the time. They do not need radiators to 'get rid' of the stored energy, until they actually convert it back to work. Nor is the reaction 'extremely endothermic'. $\endgroup$ – Justin Thyme Sep 24 '17 at 23:41
  • $\begingroup$ No the reactant is used up because running it in reverse generates heat, more heat than it consumes running forward, you can't run it in reverse at the same time you are using it to sequester heat. If it is not endothermic it is not cooling the ship, also photosynthesis actually generates heat. $\endgroup$ – John Sep 24 '17 at 23:48
  • $\begingroup$ That is not the concept of a catalyst. See Catalytic Combustion for Supplying Energy for Endothermic Reaction for the concept. 'Attention has been focused on the recuperative and direct coupling employed to process fuels in order to obtain hydrogen, especially for a distributed use as feed for small scale fuel cells systems.' $\endgroup$ – Justin Thyme Sep 25 '17 at 0:07
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    $\begingroup$ @JustinThyme who said anything about a catalyst? all a catalyst does is change the activation energy not the total energy exchanged, it's largely irrelevant in a closed system . the system in the paper is not a closed system it is about small scale heat reclamation as part of a much larger open system with a large gradient, so it has nothing to do with the proposed scenario. $\endgroup$ – John Sep 25 '17 at 3:50
  • $\begingroup$ @JustinThyme: John's right here. Storing the energy via an endothermic reaction will inevitably yield as much energy, plus whatever energy you used to reverse the endothermic reaction. That's fine if the ships can get to somewhere actually cold (like an atmosphere), extend radiators, or take their time radiating the heat away (Short bursts of combat followed by longer periods of hibernation?), but not if they have nowhere to put the heat. $\endgroup$ – Joe Bloggs Sep 25 '17 at 7:02
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Radiators on a space ship in a vacuum would have to operate by heat radiation as the other common means of dissipating heat – by conduction and convection - would not work in space. Not a radiator (but an alternative means of cooling nonetheless), would be allowing an on board liquid to evaporate into the vacuum of space.

Radiators could be made much more effective by using a compression and evaporation cycle similar to that used in refrigerators. It would also be possible to connect such systems in series using different gas/liquid combinations in such a way that the final radiator became a concentrated heat source and was better able to radiate heat into space.

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  • $\begingroup$ how do you get the liquid back? $\endgroup$ – njzk2 Sep 25 '17 at 5:45
  • $\begingroup$ You don't, although it could serve a duel purpose for instance attitude control or propulsion $\endgroup$ – Slarty Sep 25 '17 at 7:55
  • $\begingroup$ @njzk2 The liquid is lost. The tradeoff is that this is a much faster way of getting rid of heat. - Though for a somewhat hard sci-fi setting this does not seem likely to be worth the extra mass. $\endgroup$ – Taemyr Sep 25 '17 at 10:35
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In order to cool off your ship, you have to somehow get rid of the excess heat. As the Three Laws of Thermodynamics go: you can't win, you can't break even, and you always lose. No matter what you do, you will generate heat that you must get rid of.

Radiators are pretty much the best method for doing this. A classic radiator is just a piece of metal exposed to the vacuum of space. This includes the hull of your ship. Heat will leave the radiator in the form of infrared radiation. However, this process is slow and requires you to have rather large pieces of metal jutting out from your ship. The benefit is that it is very simple and does not require you to use any other resources.

Another simple method of getting rid of your heat would be to concentrate the heat into some material with a high heat capacity, then eject it from your ship. This way would get rid of the heat more quickly, but the downside is that you would constantly be losing material. You'd have to replenish your heat sinks every so often.

As some of the other comments and answers have pointed out, you can also recycle your heat. Many spacecraft, like Voyager, Curiosity, and Cassini (RIP), used radioisotope thermoelectric generators (RTGs) for power. These converted the heat from the decay of radioactive Uranium into electricity. Some of the heat is also used to keep the spacecraft warm. Now, depending on the size of your ship, this may or may not be enough to keep it cool.

Your ship will radiate heat to space across its entire surface, regardless of whether or not you have radiators. Since surface area increases as size squared while volume increases as size cubed (commonly known as the cube-square law), the larger a ship gets, its surface area will increase at a lower rate. That means that if you have a small ship that only holds a few people, the heat loss from the body of the ship itself might be enough to prevent excess heat buildup. But for a large ship with lots of people and equipment, the heat will build up faster than it can be used to generate electricity and heat the ship. Even if you use some heat for electricity generation, that process is relatively inefficient, and you will always end up with more heat at the end than you had at the beginning.

So no matter what you do, for a large enough ship, you will have to get rid of heat. And there are only two ways to do that in space - by radiating it away or by ejecting hot materials.

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    $\begingroup$ Life sciences make a total mockery of thermodynamics. The CN tower defies anything the laws would predict. Life BUILDS. Life increases energy concentration. Life reduces disorder and randomness. In fact, the life sciences forced physics to introduce the concept of reversible processes. Wherever you have life, you have a local reversal of entropy. The OP specifically states that biological processes are to be considered. A plant that takes heat and stores it as a sugar. Eject the sugar into space. $\endgroup$ – Justin Thyme Sep 24 '17 at 20:47
  • $\begingroup$ I've also heard several versions of the saying. I just like the one I stated the best. $\endgroup$ – Phiteros Sep 24 '17 at 21:03
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    $\begingroup$ @JustinThyme There are two major flaws in that argument: 1) A living organism is not a closed system; it interacts with its environment and the rest of the universe. Through biological processes, its entropy may change, but the energy of the entire system - the organism and the universe - will always increase. 2) Entropy is not equivalent to disorder, and it is not a macroscopic phenomenon. I'd advise reading up on microstates, for instance. $\endgroup$ – HDE 226868 Sep 25 '17 at 4:46
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I think it would make the most sense for the biological cooling to be based off of how animals on Earth stay cool. However, animals on Earth actually tend to use natural radiators.

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The ears of an elephant work like radiators, when the elephant is hot blood is directed to the ears, where the large surface area allows for maximum heat dispersion.

Heat sinks would also tend to be ineffective on a spaceship, as without a way to remove the heat the heat would simply build until critical. Heat sinks only make sense if the heat can then be removed from that point, either because the heat sink is a thermal-electric generator like @JBH mentioned, or because the heat sink is then jettisoned.

If one kind of ship were to not use radiators it might make more sense for it to be the non-biological ships that do not radiate heat.

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This is an extension of @JBH's third point...

Why waste your heat by radiating it out to space? Direct energy conversion from heat to electrical energy (or to chemical energy in the case of your genetic manipulators) is much more efficient. Now in a more compact form, the former heat can be stored until needed.

Just because we earth-bound humans don't currently know how to do it doesn't mean it is impossible.

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    $\begingroup$ It is impossible. The laws of thermodynamics won't allow perfect conversion of heat to other forms of energy. No matter what you do, you'll be left with some heat. $\endgroup$ – Phiteros Sep 24 '17 at 20:05
  • $\begingroup$ A biological process that converts heat to some form of stored energy like sugar, the same way plants convert light to stored energy through photosynthesis. If you make it based on biological life sciences instead of based on physical science, there are lots of options. Life processes do not follow entropy. They are the opposite of entropy, something that physics tends to ignore. The existence of the CN tower defies entropy. Life sciences, in fact, forced physicists to consider reversible processes. $\endgroup$ – Justin Thyme Sep 24 '17 at 20:42
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    $\begingroup$ Biology does not reverse entropy; it's bound by the exact same rules. Watch this video for an explanation. $\endgroup$ – Phiteros Sep 24 '17 at 20:45
  • $\begingroup$ @Phiteros Do your best to convince me that a bee hive has not reduced randomness and concentrated energy. Every single life process reduces randomness and increases energy. Given enough life, the universe would be completely organized and energy would be completely concentrated. $\endgroup$ – Justin Thyme Sep 24 '17 at 20:52
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    $\begingroup$ @JustinThyme It looks like you do not fully understand how entropy works. Watch that video. In a closed system, entropy can never be decreased. Yes, life can reduce entropy locally, but it does so by increasing entropy on a larger scale. In the context of this question, you have to consider the ship as a closed system. A plant could take in heat to create a sugar, but it can only do so by increasing the entropy (heat) of the whole system, aka the ship. $\endgroup$ – Phiteros Sep 24 '17 at 20:53
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Anything that converts heat to some other form of energy. I suggest light using LEDs.

The device – which has a conventional efficiency of greater than 200% – behaves as a kind of optical heat pump that converts lattice vibrations into infrared photons, cooling its surroundings in the process. The possibility of such a device was first predicted in 1957, but a practical version had proved impossible to create until now.

The spaceships would be very, very bright, but very cool. Mind you, the conservation of energy still applies - you would have to regularly take on fuel to replace the lost energy.

The general rule of thumb currently in biology seems to be that if it can be done using natural elements, then some biological process is using it. Perhaps the home planet of the ship designers have creatures that have evolved such a process for cooling themselves in a very hot environment, so radiation cooling is not an option. Like fireflies on earth use chemical luminescence. Synthesizing this biological process should be possible by a civilization advanced enough.

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    $\begingroup$ +1 - Spectacular Answer. That humble little hyperlink with the "light" label leads to a spectacular article about this new technological breakthrough. Wonder if you can point the led at a solar panel and get electricity from the heat. Also wonder how the efficiency of such a system would stack up against our current steam based heat-to-electricity conversion methods. Wow! Thanks for posting! $\endgroup$ – Henry Taylor Sep 24 '17 at 20:01
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    $\begingroup$ The conversion of heat to other forms of energy will work up to a point, but you will always end up with more heat than you started with. It's simple thermodynamics. Conversion will really only delay the problem, so it becomes a question of "how often do you make port". $\endgroup$ – Phiteros Sep 24 '17 at 20:04
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    $\begingroup$ this is still a radiator just a horribly inefficient one, heat radiated out via radiators is light just non-visible light. You are not going to cool your ship this way without building bigger led radiators, (which begs the question why not just use more efficient normal infrared radiators) $\endgroup$ – John Sep 24 '17 at 21:02
  • $\begingroup$ @Phiteros Not if you emit the other form of energy outside of the ship. The question was to come up with an alternative to a thermal radiator. Using light is an alternative to a thermal radiator. Different mechanisms. You don't need huge heat sinks. You don't need to transfer the heat from deep the inside of the ship through heat conduits, vents or air flow, spreading the heat around as you do so. Just beam it out from deep inside through a light tube. $\endgroup$ – Justin Thyme Sep 24 '17 at 21:09
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    $\begingroup$ @JustinThyme Radiation = light. You're just changing the wavelength. And doing so would create heat. No matter what process you use, be it mechanical, biological, or electrical, you will generate some heat. The question is simply "Does your process eject heat into space faster than the ejection process produces it?". $\endgroup$ – Phiteros Sep 24 '17 at 21:12
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There are a few alternatives to traditional radiators and heat sinks, but if you are going to try to be "hard sci-fi" you don't have many real options. The "Dust radiator wings" you are describing is actually a real thing called a liquid droplet radiator.

But you can induce cooling via expansion, which is much how a modern A/C works. You have slowly expanding gas "lungs" in your ship that constantly absorb heat. This is really just a fancy heat sink but it's a biological-type option.

A REALLY fancy heat sink would be a trapped black hole that could absorb IR radiation. The black hole is held in a magnetic bottle and you just dump all your heat into it, never to be seen again. Obviously the energy required to hold the black hole would probably exceed it's ability to absorb heat (some of which would get blasted back as Hawking radiation) and it'd be really hard moving all that mass around (even a tiny black hole would probably mass far more than the rest of the ship, and such a small black hole wouldn't have the gravitational pull to haul in much IR radiation) but perhaps some handwaving could make this an extremely efficient, long lasting heat sink.

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  • $\begingroup$ The problem with that is that a small enough black hole emits radiation (and eventually explodes). $\endgroup$ – Keith Morrison Jan 24 '18 at 8:30
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Consider for a moment a spaceship and how it does what it does. They get around by expelling mass in a direction opposite to how they want to accelerate. Most spaceships will lose mass over time, that's just how engines work in space. So why not take advantage of that? If you're in a fairly futuristic sci-fi setting, you're probably doing a whole lot of accelerating to get to places. Use your engine's fuel as a heat sink and pump that hot gas out of your exhaust, cooling down your ship. This way, you get a near constant way to ditch excess heat.
You can do the same thing with maneuvering thrusters. These are often either gas or smaller versions of your main thrusters. If they're miniaturised versions of your main thrust, your problem's solved. If they're gas based, use water. Store it in talks, dump your excess heat in there (Water's real good for storing heat) and vent steam opposite the direction where you want to go instead of whatever you used before.

If you've got a warship, you have another option: your ammunition. Presuming you're no longer reliant on old chemical weapons but have gone into the realm of rail or coil weapons, you can probably dump a fair bit of excess heat into those chunks of tungsten you're about to fling at your enemy. Same deal with torpedoes or missiles: when you're fueling them up, use your hot fuel/water and get it off your ship. They need fuel anyway and you're going to be losing the mass, so why not make use of it?

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    $\begingroup$ A spaceship that uses the solar wind is propelled without loosing mass. There are lots of non-inertial-mass propulsion systems. $\endgroup$ – Justin Thyme Sep 27 '17 at 15:36
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If you generate more heat than you can use (and you probably will, space is a really good insulator for all that it's also extremely cold) you will need to do some kind of radiation/dump procedure somewhere along the line, it's the intermediate steps that make the difference. Here's some options others have mentioned and some that they haven't:

  1. Thermocouples basically your heat problem makes a stop as electricity on the way to being secondary waste heat that you have to deal with. The only way these really work is if you have concentrated sources, either from concentrating waste heat somehow or from intercepting heat near source (reactor walls, engine baffles, etc...).

  2. Evaporative cooling, using either the evaporation of fluid, or better yet the decompression of gas, you can soak up a lot of heat relatively quickly, especially with the gas option. Then you use compression to re-liquefy the resulting vapour and concentrate the heat of vapourisation where it can be used for a thermocouple interface. This system can also be used to either A. delay heat radiation for the purposes of stealth, simply leaving the vapour in gas phase will delay the necessity to radiate heat externally or B. to deal with large amounts of heat being dumped into the ship's internal environment, such as might occur in battle.

A biological system is probably going to have an easier time with the evaporation/vapourisation option. Eventually though you have to get rid of the heat so once things reach a head and you have to dump heat externally you have three basic options:

  1. Radiant surfaces, large sheets, probably composed of a Beryllium/Tungsten alloy for maximum heat capacity, that can be heated by an internal working fluid and used repeatedly and for sustained periods.

  2. Sacrificial material, large shrouds, probably of a very similar material to the radiators above, of graded thickness that evaporate into space when heated by electrical resistance, or some kind of direct Infrared pumped onto or through the material.

  3. Concentrated thermal emission, basically Infrared lasers pumping pure heat out into space, these can be used for communications or possibly for point defense if that's a thing in your universe.

For my money any of the external options are equally appropriate for biological or mechanised systems, it's just the details that would vary.

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Has anyone considered just storing the heat and dissipating it later? In some space operas, ships have cubic kilometers on mass that could be heated by a few degrees for massive heat dumping. You don't have to dump the heat externally. You don't have to assume that a ship's temperature is in a constant steady state, it could be dynamic.

A biological based ship can easily do this with veins of fluid, from hot places to cold.

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  • $\begingroup$ Yes, it's been considered. Yes, it also has issues. $\endgroup$ – Keith Morrison Jan 24 '18 at 9:06
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All spaceships doing anything interesting for any non-trivial duration need radiators. The only exceptions are orbital launch rockets, who don't spend enough time out there to matter, and satellites and probes, who only sit there, take pretty pictures and occasionally thrusting for a bit with a small, low-power thruster.

Then there is everyone's favourite rule-breaking spaceship, the Hydrogen Steamer. It is designed, after all, to both have long endurance and give negligible amounts of radiation, so of course it doesn't have any radiator, relying entirely on its massive cryogenic hydrogen heatsink/propellant reserve instead.

As a spacecraft, particularly a combat spacecraft, its performances are rather disastrous - the same way a submarine can have rather disastrous performances compared to a surface craft. So this may give a Battle of the Atlantic feeling to your setting: one faction with conventional warships patrolling the skies, the other investing in stealthy strike ships doing their best to avoid conventional engagements. Such faction may or may not have conventional, radiator-equipped warships in addition, or may rely entirely on interplanetary ICBM-like Hydrogen Steamer missiles with high-performance terminal stages for conventional combat.

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Koolatron coolers use the peltier effect to move heat from inside the cooler to the outside using an electric current. Place peltier junctions all along the sides of the spaceship, just like these coolers. This answer has been alluded to elsewhere, but no specific mention of the peltier junction and the regular commercial use of it in coolers, used extensively today. The greater the temperature gradient from inside to outside, the greater the effect. It is like a heat pump on steroids.

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I think the answer you are looking for is solid state thermoelectric heating/cooling. https://thermoelectricsolutions.com/why-solid-state-thermoelectric-technology/ They are simply plates made of certain materials that absorb heat and transform it into electricity. These could absorb the heat from most of your extremely hot spots like weapons, sensors, reactors, etc. And then convert them to electricity without emitting alot of heat outwards, in the process cooling the device and provididng you with usable energy. They take up little to no space and have no moving parts and are self contained so they can be used without external ship componenets.

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