A few previous threads have mentioned that the Project Rho (Atomic Rockets) site pretty much dismisses the idea of stealth in space, given that waste heat is inevitable and easily detectable. Now of course an enormously hot reaction jet is going to make stealth useless, but if your SF scenario has some sort of gravity drive, or the ship is coasting, then I don’t understand is why the following isn’t possible: have an actively refrigerated shield on one side of a craft, and the heat radiators on the other side. IOW, eliminate a heat signature in one direction, which might be useful in many situations.
Wouldn’t heat radiate in a lot of different directions regardless of the refrigeration shield in the front?
If you want to have a pair of humans, in space, under stealth, I agree that it would be difficult. But if you have something like a remote space laser, it seems like it would be simple enough to put it into a super low energy standby mode. The hard part would be getting it to boot up, fire, and dump all of its heat fast enough to not be tracked down.
For anything relatively low-power, you can try and dump all of the heat on just the sun-facing side, so its difficult to detect that it’s not just reflected heat.
Or if you encapsulate your device in a deep, heat reflecting dish with a layer of insulation around it, then people would need to be looking into the face of the dish to detect you.
David Brin described “refrigeration lasers” in his novel “Sundiver.” You pump all your waste heat out into space that way, and hope that no one stumbles into the narrow beam.
(And if they do…they’ll regret it more than you will!)
ISTM that the heat radiators would have to be would have to pretty precisely direct it in the opposite direction of the cooling side/direction of travel. But that would mean not ever changing direction.
eta: ooh. Could you store heat in some ejectable pod?
In the Mass Effect games this very issue is exactly what makes the player’s craft slash alien sex party bus unique : it’s a stealth ship, in space. Which is theoretically not possible.
To be fair, the way the game’s world does it does involve magic (sorry, “element zero” and its concomitent, titular effect on mass when exposed to an electric current) to some extent but the gist of it is : you trap the reactor and its emissions inside a shell of heat-absorbing material. You put layers upon layers of insulating Space Lead between that material and the exterior of the ship. Once in a while, you dump off and replace the by-now-superheated radiator material and reveal your position, but hopefully by then you’ve already did what you came here all sneaky-like to do or can zoom away before it becomes an issue.
No, I’m not sure that is how physics work either, but then again I don’t *know *that it isn’t, which is good 'nuff for me 
If memory serves, the Mass Effect type of stealth system is an internal heat sink, whereas most spacecraft have deelies on their hulls that radiate waste heat constantly.
This stealth system is described as having a limited duration because the heat sink can only store so much heat before it starts to broil the entire crew.
So more like an early submarine in a way, stealthy to a point but only for a particular duration before you have to switch it off (or ‘surface’) or risk danger.
Radiation can only be detected if you intercept it - so if it’s being radiated away from you, you won’t see it (unless it reflects off something else)
The problem is in order to make a ship stealthy in space, you need to make it look like just another piece of space. That is to say, a dark, empty void with maybe a bit of background radiation.
The Laws of Thermodynamics basically make this impossible. All that heat from your engines, life support and other systems has to go somewhere and the vacuum of space is a great insulator. It’s very hard to just “dump your heat” as there is no medium to dump it into.
For the ship to not radiate any heat, it would have to be encased in some sort of perfectly insulating material, which I don’t think exist.
And a laser doesn’t project heat, it projects photons (light). And pretty inefficiently at that as lasers themselves tend to create a lot of heat.
Light and thermal radiation are all forms of electromagnetic radiation. Photons aren’t just for light, you know.
I understand that, but who says the heat has to radiate omni-directionally?
Yes, perhaps I should have been more specific. It sounded like the plan is to somehow grab all the thermal radiation produced by the ship, convert them into photons or X-rays or dump it into the ships exhaust or whatever and project it in a direction away from someone trying to detect the ship. I don’t think that’s possible, at least not with lasers as currently designed today or in the foreseeable future.
And to expand on another idea - even if you could insulate the ship so that it appears on the outside to be at absolute zero (or at whatever temperature the background radiation of the universe is), that means all the heat produced by the ship is either trapped inside the insulating shell, or the heat has been efficiently transferred away and interior of the ship is also at absolute zero. Either options not being so great for the crew.
Yeah I’m pretty sure that violates the second law of thermodynamics. Concentrating all that heat energy into a laser is just going to produce more heat.
Does Buck Godot use warp drive?
While speaking in real and almost plausible fictional ways to do this, do I have it wrong or isn’t the case that if we manage to make a warp drive work that that does take care of the problem?
IIUC since space is warped it’s not only the ship but any heath around it that follows it in the warped space field. If there was heat coming out of the warp field the ones looking for it would find it, but until it was too late. Unless there are more fantastic detectors they are not likely to detect signals at a speed faster than light.
How long would heat be detectable in space? If, for instance, you were to dump the heat once an hour, omnidirectionally, how long after dumping the heat would it still be detectable before it’s too diffuse to detect?
You’ve just defined my kitchen refrigerator as impossible.
Well, no, but lasers are intrinsically inefficient devices. The only ways you can achieve population inversions are to either
1.) create the system so that it has a population inversion, as in chemical lasers. In this case you’re using up chemical energy that’s been stored in chemical bonds, though, so it’s no use in getting rid of waste heat.
2.) pumping from a lower level (usually a ground state) to a higher level which then decays to a slightly lower level. One of the first such laser systems suggested was the 4-level color center system, although this was not the first laser built, and it was years until they finally did get one going. Color center lasers have achieved 80% light-to-light efficiency, which isn’t all that great, really. More recently, various atomic gas-staste lasers have achieved in excess of 95% efficiency, getting close to 99%. This is much better, but a.) there’s stiull a couple of percent energy lost to heat; and b.) in these lasers – as with the color center lasers – this efficiency is light-to-light, which means that you have to “drive” them with either another laser, or a bank of light-emitting diodes, or something like that — which has a much worse efficiency than the laser itself.
Bottom line, generated laser light, by any means, dumps a lot of waste heat into the environment. That’s why powerful; lasers have water cooling lines of radiator fins and fans blowing. In space, you’d need radiator fins. But that’s just what you’re tryiung to avoid.
As for “channeling your waste heat into a laser” – good luck persuading your random, all over the frequency spectrum energy to selectively pump a laser band. Even if you had a perfectly efficient laser, with almost perfect whatever-to-light efficiency, the idea is doomed from the start.
And your kitchen refrigerator isn’t impossible, but it’d have a huge heat signature in space, too.
Why isn’t anyone addressing the OP: could you radiate waste heat directionally?
If you could direct its flow, then presumably you could store it in any ejectable object. Maybe have some balls of metal on board for the purpose.