The Real Reason Why Radiators Aren't Popular in Science Fiction

[jjabrams55]

Anybody here that knows stuff about science knows spaceships need some way to dump waste heat, since there is no air to conduct thermal energy to.

People will tell you that you never see them in science fiction movies (even harder scifi ones with few exceptions) is because they are ugly.

While that may be true to some extent, I don't really think that's the full story.

The truth is, if you're going to include radiators on a ship, then they have to be big enough for whatever it's doing. Not everybody knows how to calculate that, nor is everybody willing to.

The only other option to avoid ugly, easy to shoot off radiators is to convert 100% of your waste heat into electricity, but I'm almost certain that breaks the conservation of energy theory science holds dear, which I don't think has been proven wrong yet. At the very least, with efficient enough waste heat conversion to electricity (may be actually possible someday with metamaterials), smaller radiator fins could be possible on big ships.

That said, how big of radiator fins would say... the Enterprise need? Or a Klingon BOP? Assuming they lose the technobabble that gets rid of their waste heat?​

 

[Bick]

Couldn't the hull of spaceships act as a radiator itself, if engineered the right way?

 

[Pyan]

In H. Paul Honsinger's Man of War series, heat is stored in large heatsinks on board the ships - they have to bleed the excess off into space after a certain amount of time running the engines. There's a scene in one of the books where they have to take a chance of being picked up by infra-red scanners whilst hiding (because they've gone too long without doing this), which leads to plot complications...

 

[jjabrams55]

Couldn't the hull of spaceships act as a radiator itself, if engineered the right way?

I suppose, but then you would have a glowing hull. It's actually not a bad idea.

You had better not be doing it during battle though. A hot hull would be like butter to enemy fire.

Even if you had a hull that did the waste heat thing, you would need some sort of heat sink to use when in battle. You don't want a hot hull during battle likely. So you would probably use large tanks of coolant.

Your doomed when they run out though, because you will be forced to have your hull glowing all the time. No battle for you mate.

You could, you would just be very vulnerable.

But still, novel idea, I never though of such an idea.

Metamaterials in theory could do this, if advanced enough. You could just radiate ALL HEAT outward from the hull,making the center of the ship zero degrees celsius.

Your command center would be farther away from the center from that reason.

 

[chrispenycate]

Heat pump technology. The hotter you can make your radiator (and the blacker) the more efficient it gets, and the smaller it can be. Concentrate the heat to a couple of thousand degrees K, and you can even put a reflector on it and aim the heat away from the enemy, and thus indetectable.

Oh, and converting heat energy into electricity only contradicts the second law of thermodynamics, which is a statistical a law, not a conservation law. Makes it a bit easier to write round. But unfortunately, since all the electrical energy ends up as heat sooner or later (although perhaps much later) so we're only putting off the problem. And we're generating heat all the time, not just inefficiencies of machines, but lifeforms.

We have two viable heat pump technologies; there might be a hundred more.

 

[jjabrams55]

Heat pump technology. The hotter you can make your radiator (and the blacker) the more efficient it gets, and the smaller it can be. Concentrate the heat to a couple of thousand degrees K, and you can even put a reflector on it and aim the heat away from the enemy, and thus indetectable.

Oh, and converting heat energy into electricity only contradicts the second law of thermodynamics, which is a statistical a law, not a conservation law. Makes it a bit easier to write round. But unfortunately, since all the electrical energy ends up as heat sooner or later (although perhaps much later) so we're only putting off the problem. And we're generating heat all the time, not just inefficiencies of machines, but lifeforms.

We have two viable heat pump technologies; there might be a hundred more.

Hmmm... so what you're saying is, we need to develop heat resistant materials that don't currently exist?

Materials that could stay on the surface of the sun for hours at a time before melting?

If you could do that, you could just use your short, small radiators for a while, and then reduce the power usage of the ship until they cooled down.

Sounds reasonable.

 

[chrispenycate]

I don't know if they exist yet or not. The filament of a tungsten halide lightbulb would easily be refractory enough to do the job. Unfortunately a gas expansion/contraction heat pump can't concentrate enough heat to get to the requisite temperature, while semiconductor cooling – even diamond semiconductors won't remain semi that hot.

But where there's two unrelated technologies producing the same result, likelyhood is that there will be a third, or more, one of which might operate hot.

If you could get the beam concentrated enough it might even function as a drive.

 

[jjabrams55]

I don't know if they exist yet or not. The filament of a tungsten halide lightbulb would easily be refractory enough to do the job. Unfortunately a gas expansion/contraction heat pump can't concentrate enough heat to get to the requisite temperature, while semiconductor cooling – even diamond semiconductors won't remain semi that hot.

But where there's two unrelated technologies producing the same result, likelyhood is that there will be a third, or more, one of which might operate hot.

If you could get the beam concentrated enough it might even function as a drive.

Well to be honest, I was actually thinking of using traditional radiators, just allow them to take more heat so they can radiate a lot more heat away from the spaceship.

Occasionally they would need to cool and the spaceship would run on low power mode, kind on like your computer does.

 

[chrispenycate]

You could have a secondary, mass wasting cooling system, based either on the adiabatic expansion of gas or the latent heat of vaporisation. So you either carry cylinders of highly compressed gas (probably hydrogen or helium) or you evaporate some liquid – I'd go for water, widely available, nice high thermal capacity, but for a tendency to freeze in the nozzles (wouldn't that be ironic? Interior of the ship at 315°K, can't cool down 'cause the pipes are frozen). Perhaps ethanol? Sorry sir, your 25 year scotch was used to cool the ship down in the last engagement?

I'm not generally designing warships; more transport vessels, and tacking on a couple of weapons as an afterthought. But I don't think developing a temporary atmosphere will spoil their stealth too much, and will render their trajectory quite unpredictable to anyone not au fait with the emissions. Don't forget the principal protection against laser weapons (well, any radiant energy beam weapons {what do you do when you're manoeuvering close to a star? You can't rotate the ship to spread the cooking?} is mirror plating, and an energy radiator can't, by definition, be mirror plated at the frequency it's designed to radiate. So, not only for detection reasons, it's better to maintain it aimed away from your enemy.

So, the temporary (and thin) atmosphere means that in space people can hear you scream, and an explosion has a support for a shock wave. Laser beams are defocused and refracted, and incoming missiles hit resistance and quite possibly believe they've arrived, exploding well away for their target (unless they're smart missiles, but then they might debate philosophy instead of committing suicide).

Which means your local defences are modified too; but you can measure your local environment, while your foes won't get the information for several minutes.

Depending on your generators you might well not be able to run in 'hibernate' mode, and be able to bring them up to full power instantaneously. Big generators (and on ships like this we're talking about generation levels equivalent to the entire energy generated on Earth now) frequently have delays in changing modes. Care to be running on battery mode in a battle?

 

[adomol]

In Alastair Reynolds Revelation Space universe, he tackles the problem of waste heat with something called a cryo-arithmetic engine. Here is the way he describes it:

Cryo-arithmetic engines are a specific class of quantum computer. When certain algorithms are executed on processors of this architecture, it leads to a local violation of the Second law of thermodynamics: the computer gets colder instead of hotter. Consequently, cryo-arithmetic engines have massive industrial ramifications; such engines abound in asteroid factories, where their calculations can drain away the heat of starship construction.
Cryo-arithmetic engines are also used by modern 'stealthed' lighthuggers; they cool the exterior of the ship to the temperature of ambient space.

 

[Vince W]

I think the simplest solution is not to create heat at all. A future reactor could be some sort of quantum engine where the reaction energy (fusion/fission/mentos & coke) is converted directly to the form of energy needed to power the ship and all its functions.

 

[Wendigo]

A future reactor could be some sort of quantum engine where the reaction energy (fusion/fission/mentos & coke) is converted directly to the form of energy needed to power the ship and all its functions.

The catch with this- assuming you want to maintain scientific plausibility- is that it's impossible to have 100% conversion without at least some waste heat. Even if you did, you'd still face energy loss, and therefore heat, when you actually used it- e.g. the electricity moving through your wires will lose energy as heat, and the electronics they power will always produce at least some. Even the lights would produce at least some waste heat on the side. Even transforming electricity from one voltage to another- so the same form of energy- isn't perfect.

 

[JonH]

I'm not sure you need radiators if you use plasma drives. Collect the interstellar medium through the front, compress it and pump it out of the back as uber-hot plasma. If you can get your waste heat into the gas before turning it into plasma, you'll be ejecting it into space through conduction rather than radiation.

I'm not sure how the corona of the sun works, but I know it's many orders of magnitude hotter than the photosphere, so perhaps plasma is the way to go.

 

[Mirannan]

JonH - I'm not sure anyone claims to know how the solar corona works, specifically how it is so much hotter than the photosphere - but the consensus appears to be that it's heated by some method other than convection or conduction - maybe some sort of process involving magnetic fields.

Actually, the temperature of the corona is something of a red herring. Temperature is a concept that is of much more limited importance when the medium is very diluted, as is the case for the corona. To illustrate this, the temperature of the solar wind around Earth's orbit is in the hundreds of thousands of degrees but that fact makes very little difference to anything - because the stuff is so thin that its heat content is negligible. The same applies to the upper reaches of Earth's atmosphere, too, to a lesser degree.

And finally, ejecting heat into a vacuum by conduction is flat-out impossible.

 

[JonH]

I was suggesting conducting the heat into matter, i.e. the collected gasses, and then ejecting that matter as part of a reaction drive mechanism. I can't see why that would be impossible.

 

[nightdreamer]

There are three ways to get rid of waste heat. (1) Radiation, which takes up a lot of surface area. This picture shows 9 of the 10 radiation panels on the ISS, and they take up about as much space as the station itself. Furthermore, radiation panels have to be spaced out so that radiated heat isn't simply reabsorbed by the next panel. (2) Ablative/evaporative cooling, which someone mentioned above. (3) Heat absorption by cold materials, which is why US space suits (and probably others) carry big chunks of ice. Unfortunately, 2 and 3 are only suitable for close, short-term use because they can't be regenerated in space.

In general, except where waste heat is highly localized, you can't get rid of it by converting it to energy because you need a temperature differential. Once a spaceship is universally warm, you're screwed without one of the three options in paragraph one. It's thermodynamics, which no technology in for foreseeable future (and I can see pretty far) will be able to circumvent.

Radiators aren't popular probably because the whole thermodynamics problem is so difficult that treating it correctly would ruin just about any story you might want to write. The Enterprise would have melted in its own heat before it got to its first destination. I'm normally a stickler for scientific accuracy, but this is one problem that I do ignore, since there is no good solution for it. Proper handling of thermodynamics would have left us without The Lensman Series, Star Trek, Star Wars, Flash Gordon, you name it.

 

[Dave]

Can't we dump the excess heat through into an alternative dimension and pollute someone else's universe? Given our history of dealing with waste this seems like a solution we would have no ethical problems with.

 

[Ray McCarthy]

I'd not worry about waste heat on the Star Trek Enterprise. A dozen other things are less feasible.

Make the ship REALLY big, (which allows less mass to be used on Ion Drive as you can have a linear accelerator.). The Linear Accelerator Superstructure / frame work (2km to 20km long) is the radiator. Simple.

Heat pumps can move internal heat to that structure. They are of limited value to help radiate heat by making a radiator hotter as they become more inefficient the higher the "uphill" temperature. You have to cascade them and need very large final radiator.

My planet <-> Starship 'Flitters' have to limit their re-entry atmospheric braking and use plasma rockets, but if a larger deceleration is needed then the reaction mass (water) is heated by the heat pumps cooling skin. Eventually it vents super heated steam via "rocket" ports to assist braking.

Heat is a problem. People rely on water evaporating. Camels just let their temperature rise in a way that would kill any other mammal! (They also store water in the blood, not hump!)

 

[portman]

The solution would be simple if it were a British ship - if you had a biggish Starship with say 100 people on board, you'd need all that waste heat energy for the water boilers to fullfill the constant demand for Tea...

 

[Bick]

The solution would be simple if it were a British ship - if you had a biggish Starship with say 100 people on board, you'd need all that waste heat energy for the water boilers to fullfill the constant demand for Tea...

Toby Frost has doubtless addressed this exact issue in his Cpt Smith novels...