That’s convenient eh? You don’t need to provide any response because I used the mild (and accurate) pejorative of “factoid”.
Would it be possible to cool one side of the ship to near-ambient temperatures, and position the ship such that that side would face the enemy? The other side might be real hot, but the enemy wouldn’t see it.
I’m in no way arguing that the laser approach will be anything like more efficient, I’m saying it might be decided to sacrifice efficiencies for stealth. And not on any permanent basis, I’m certainly thinking of only an in-active-battle system.
If the entropy increase is by heating up an asteroid, say, or a decoy, does that still hold? I’m most definitely not talking about just “beaming the laser into space” at all. I’m talking about using the energy to do work heating up something outside the ship.
Wait–I don’t think that could make a difference. How would the laser “know” whether it’s heating up an asteroid, or extending infinitely into space? Once it leaves the ship, surely its effect on the ship is decided, regardless of when or if it ever impacts other matter.
We can’t know what kind of futuristic hull materials and tech will be available hundreds of years from now. I have no problem believing a starship, especially a military one, might have no heat signature and otherwise be stealthy.
The irony here is that I have offered [POST=21504096]repeated[/POST] [POST=21504868]explanations[/POST] of why any object in space that is generating power or doing work will have to radiate heat while you just keep repeating the term “factoid” [POST=21503487]over[/POST] and [POST=21504208]over[/POST] and [POST=21504882]over[/POST], which is not only a disingenuous argument but also by the context of your statements a misuse of the term when what you mean is “falsehood” or “fallacy”.
This is essentially what I discussed in [POST=“21504096”]post #49[/POST] above; in theory you could have a ‘ship’ that is a giant array of cooling coils one on side and massive radiator surface on the other, separated by a perfectly adiabatic (no heat transfer) barrier between them. In reality this wouldn’t look anything like a space ship in the imaginations of science fiction fans or be of any practical use other than hiding itself. In addition, the interstellar background temperature is just above that of the Cosmic Microwave Background at 2.7 K, which is as cold as anything naturally occurring in the universe, so cooling something else to fade into that background is essentially impossible in finite time without some even colder temperature reservoir to dump into or a way of externally powering a heat pump cycle. Even in interplanetary space where the background temperature may be higher because of solar wind, the luminance of a solid object is going to be much higher than that of the background, just as a 300 W light bulb is brighter than a 25 W light bulb even though both are emitting the same spectrum.
I think people are thinking about enthalpy (heat at constant pressure and volume) and entropy as physical qualities which can be shuffled around like billiard balls, but in fact these are system properties defined as a function of state relative to a baseline or in comparison to another system. You can just change or move them around in isolation; doing any kind of work (which heat transfer is a form of) always increases the entropy within a closed system and produces waste heat because all real world processes are irreversible per the third law of thermodynamics. A laser is by definition a device that produces a stream of photons at the lowest physically possible entropy (which is why lasers can be used to cool individual particles), and so operating one within a closed system produces an increase in entropy.
This isn’t just a matter of materials science or improvements in solid state heat transfer; this is a fundamental limitation of thermodynamics, which as far as we can tell is an inviolate set of fundamental rules in physics. To get around this you’d either have to have some essentially infinite cold temperature reservoir carried within the system or some kind of “Maxwell’s demon” which can sort between slow and fast moving particles to violate the second law of thermodynamics.
This is, again, notwithstanding than any plausible propulsion system using reaction principles (heating a fluid to get energy for momentum transfer) will generate large amounts of waste heat and leave a trail of hot exhaust. Unless you posit some method of propulsion that does not require power and produce heat, you’re going to be left with a big arrow pointing toward your ship and the need to do something with large amounts of waste heat regardless of how ‘stealth’ you can make the hull.
Stranger
I can imagine a temporary ‘cloak’ that involves a highly insulated energy source creating liquid cryo coolants which are then pumped through tubules in the skin of the ship, much like cryo cooling the bell of a rocket motor.
The overall heat of the ship would go up, but there would be a lag time where the surface cooled faster than the heat could penetrate from the insulated power source, which should temporarily make the ship less visible to thermal sensors. After the battle the heat pump reverses and pumps hot liquids through the tubules to speed up radiation of the heat, perhaps also by deploying additional radiators.
Probably an easier way to avoid targeting would be to deploy ‘chaff’ consisting of materials heated to the same temp as the ship’s heat signature then deployed out around it. If the battles are in the inner part of a solar system, they could be designed to remain hot from solar radiation.
Maybe the first sign of an impending invasion would be missiles that discharge thousands or millions of pieces of warm chaff.
Come to think of it, ships would have pre-prepared tanks of cryo coolant, which then run through tubules to cool the skin during battle, then cooled down again later when it’s safe at the expense of heating the ship.
But the minute the ship has to manoever it would give the game away.
To hide in space you need to be further away than the limits of resolution of the sensors used by your enemy. None of the other strategies work (although Stranger has described one possibility here)
Note that this would only work if your ship could only be observed from one direction. If your enemies’ sensors were distributed evenly throughout the Solar System then the waste heat could be seen from various angles.
If you want a high-tech heat-sink then you could try dragging a black hole around with you- but it would need to be a massive one, since small black holes are warmer than the CMBR, making you even more visible.
Maybe some kind of wormhole would work as a heat sink- but a wormhole would also probably be a very massive object, assuming you want it to be big enough to pump heat into.
None of this has anything to do with infantry. Infantry will almost certainly be replaced by remote-controlled robots/drones- and the big battle will be trying to jam, or hack, the controls or shoot the drones down before they can damage your own drones. People will mostly be safe in hidden locations, co-ordinating the attacks and trying to avoid interdiction.
When we have no factual information upon which to base a solid opinion we have an obligation to make that shit up. That’s why I love sci-fi
It doesn’t matter what kind of ‘hull materials’ you are using- if you aren’t radiating heat, then the temperature inside the ship is rising.
Unless you’ve got some sort of magical heatsink like a wormhole to dump the heat into.
Another possibility I’ve just remembered is an expanding outer shell- if your spaceship can expand to keep pace with the waste energy production, then the temperature of each square metre can remain the same.
I was a submarine officer when that came out. We used to watch it on patrol all the time because it was a hoot, but it had nothing to do with submarine combat. The book captured submarining pretty well, but the movie was ridiculous.
Submarine battles never get filmed realistically for the same reason space battles don’t. Your opponent is miles away, you spend most of your time trying to even locate them, and it all takes hours. Don’t get me wrong; the mock battles we did were intense, but they were pretty much unfilmable.
What, you think being able to remotely detonate a Sea King-launched torpedo or delivering an intelligence analyst to the USS Dallas via helicopter drop in mid-ocean deviated from reality and common sense?
It is worth pointing out that the notion of “cloaking devices” and stealth in science fiction stems from the Star Trek (original series) episode “The Balance of Terror” which was heavily inspired by WWII sea combat movies like The Enemy Below and Run Silent, Run Deep. As with everything Star Trek, it has little to do with any real science or technology but is instead a conceit invoked for the sake of an adventure plot familiar to viewers but in a space milieu. It is possible for a submaine to ‘hide’ in the ocean because there is a lot of accoustic noise, and a sufficiently quiet and slow-moving submarine can only be detected by passive listening systems by identifying particular modal signitures or an abnormally inactive signal (a so-called “hole in the water”).
Space, however, is thermally very ‘quiet’, and it is essentially impossible to make any powered device blend into the thermal background of interstellar or even interplanetary space using any method allowable by thermodynamics short of carrying around a massive thermal reservoir that is colder than the ambient temperature. In fact, it is very difficult to keep even a low power spacecraft from overheating just by the waste heat of its own electronics and other processes, which is why radioisotope thermoelectric generators (RTG) on space probes are mounted outboard and insulated from the main bus of the spacecraft.
The issue of dealing with easte heat from processes like nuclear fusion or antimatter annihilation, which are common power sources in science fiction/space opera, are almost completely neglected by nearly all stories because of the difficulty and the fact that most science fiction writers are not well versed in thermodynamics; the only instances I can think of where waste heat buildup is a plot issue is in Frederick Pohl’s short story, “The Mapmakers” and to a limited extent the James S. A. Corey Expanse series.
Stranger
I don’t think space battles will look anything at all like most SF depictions, including the Expanse and other ‘realistic’ battles. Space is too big, velocities are too large, etc. For instance, rather than shoot a missile at a ship and risk having it miss, just lay down a cloud of gravel. At interplanetary velocities, a pea sized piece of gravel will ruin your whole day. Plus, unless we have magic drives, ships will always be extremely delta-V constrained, and won’t be able to manoever much.
A more likely scenario would be an enemy ship on a Hohmann trajectory between planets, and someone firing a cloud of junk into the orbital path, which the enemy ship can do nothing about, since it has no fuel left other than what it needs to attain orbit around its destination. Energy weapons might also be a thing deployed against coasting soaceships if necessary.
Space battles that have ships manoevering around each other, jinking out the way of missiles and the like ar pe hollywood creations that generally appeal to our understanding of how airplanes fly.
And even moden airplanes are unlikely to engage in close quarters air to air combat any more. More likely, an airpcraft will fly until the enemy is within range of its fire-and-forget missiles, launch them, and go home.
Even an older F-14 could carry up to six Phoenix missiles, which could be fired from 100 miles away. You could become an ace without ever even seeing your enemy. I expect that would be true for space ‘combat’. You’d never even see who you were fighting.
Some problems are problems with basic laws of thermodynamics. This sounds like an engineering problem. As for the cold reservoir, why can’t that be an internal reservoir, pre-cooled while planetary or while near some other source of coolant? As long as it’s surrounded by excellent insulation, couldn’t you dump the heat internally?
Awhile ago when we discussed FTL travel, I came up with an analogy that I still like: imagine asking Archimedes to invent a technology that would allow a man shouting in Carthage to be heard perfectly by a man in Brittania.
Not only couldn’t he do it, he’d be smart enough and understand physics well enough to explain why it’d be impossible: the decibels produced by human vocal cords could in no way vibrate air sufficiently to stimulate the eardrum of a man fifty miles away, let alone hundreds of miles away.
He didn’t know about telephones.
When I read about how impossible certain things will be in the future, I think about Archimedes. We don’t know what we don’t know; we don’t know what solutions tomorrow’s folk will find to tomorrow’s problems.
We don’t know about tomorrow’s telephone.
I think of scientific proof in the nineteenth century that a steamship could not carry enough coal to cross the Atlantic ocean, but yours is better.
There are engineering problems you can solve to minimize how much heat is seen by the ‘enemy’ temporarily. I mentioned pumping liquid cryo fuels through the skin of the ship.
But you can’t cheat the laws of thermodynamics. If you bring coolant along for the ride, you have to account for the mass of it. Pumping coolant through the skin of the ship will raise its temperature, which means it will have to be dissipated elsewhere. All you could really do is buy yourself some time.
I can imagine a battle where a ship boosts for a location, then after the boost phase it uses cold gas thrusters to subtly alter its trajectory so that someone who calculated it by watching your exhaust signature couldn’t know exactly where you’ll be. This is assuming that you’ll be coasting for a long time so that the small change in velocity from the cold gas thrusters adds up to something significant at the other end.
Then before the ship gets within range of thermal sensors it pumps cryo fuel through the skin, cooling down substantially. But once you’ve done that you have to cool it down again, because you’re going to have to store it and pumping it back into pressure vessels will make it even hotter.
So basically your ship is a refrigerator, with the coolant coils on the outside and the pump on the inside, surrounded by heat sink materials that would get warmer and warmer the longer you ran the pumps. The only thing that makes this ‘stealthy’ is the lag time between the core of the ship heating up and the heat eventually migrating outwards to the skin. So the minute you start the process, you’re on the clock.
At some point, you could dump the heat by pumping the coolant out of the ship. I can imagine a scene where, as a last resort when the coolant system was about to overheat, the captain throws a switch which pumps the cold coolant through the heatsink, then the hot coolant is blown out of the ship as a last cloud of expanding hot gas that might give the ship enough time to start the engines and get out of Dodge.
I still think a better solution might be to dump a lot of warm chaff. Imagine black sheets of very thin thermally conductive material. Fire it out all around you as you are approaching the limit of thermal sensors, and all they’ll see is a screen full of noise. If you can’t cool the ship down to the level of the surrounding space, make the surrounding space look as hot at the ship. They’d know you were coming, but they wouldn’t be able to aim accurately at you.
From a fictional standpoint, it’s good to have limits on your tech anyway. A ‘cloaking device’ that starts heating up your ship until you turn it off or dump the coolant is a better dramatic device than a magic cloak that lets you travel unseen anywhere you want to go. In good science fiction you still need rules, and that’s especially true as the tech gets farther away from what we can do today. Otherwise it’s just fantasy in space ships, like Star Trek.
Also, the ‘thermal sensors’ would be nothing more than telescopes with cameras sensitive into the infra-red. So the limit of the thermal sensors would generally be the diffraction limit of the telescope. Ships might have large wide-field scopes for close-in targets (say, within 1,000 km or something), but a small ship should be safe from detection for quite a long time - especially if the enemy didn’t know where you were in the first place.
Attacking a ship that doesn’t know you were coming could be done like this: Come in on a trajectory that would take you on a collision course with the target. While you are still a LONG way away, simply release a huge bag of gravel . Once you’ve done that, start your engines and get out of there. The enemy suddenly sees a ship boosting on screen, but if you chilled your gravel down it would almost certainly not be able to detect it. You boost away while far, far out of range of any weapons the enemy can bring to bear, and hours or days later the cloud of gravel, maybe now half a kilometer across or something, blasts through anything in its path.
If you knew the other ship was going to stay in whatever orbit it’s currently in, you could fire that gravel from another planet if you wanted to. Put some cold gas thrusters and simple star tracker navigation on it, and it can subtly adjust its course along the way if necessary. If the trip took a long time, you could just let it cool naturally since there are almost no heat sources onboard. A small charge in the center could rip the bag and start the gravel expanding at the right point for maximum damage.
The enemy would have no idea what was coming until the cloud started impacting stuff.
Another thing to consider from the title of the thread is the notion of “infantry battles”. It really should refer better to land/planetary surface battle. Even in our day, you have different environments for land warfare dependent on where and who you are fighting. Industrial powers deploying corps and armies in open terrain will use armor and aircraft for the major movement, with infantry for handling the granular detail.
You could imagine a futuristic land battle with the infantry assembled in base units of one human in mechsuit leading and controlling a fireteam of robotic fighters, but you’d need a high reliability and robustness of C3 and an AI sophisticated enough to understand what to do if we lose signal from command.
True – and let’s be fair, the TOS cloak had limitations in the beginning, it was described as “possibly” achieving its effect by “bending of light” and carrying a very high energy demand, and in the episode it’s introduced it is suggested that you can “aim with sensors” at the cloaked vessel, even if not as accurately, so from the start it was recognized the object would NOT be utterly undetectable. (Plus a ship using the cloak would be itself unable to target accurately.)
That it took them a quarter century to figure out “the thing’s gotta have a tailpipe” is a testament to a culture that also forgot about seatbelts and surge suppressors.