Superconductors, Stealth vs. ECM/ECCM in Space

[Darth Wong]

Two points:

1) You're forgetting that your decoy does not need to look like a rocket doing a full burn if your attacking vessel would not normally do that in plain view either. It needs to emit only enough energy to look like a ship which is trying to cloak itself and run silent.

2) You would not look like a rock moving directly toward the target, because you would presumably not plot such a course. You're just trying to get close enough to nail it with a laser or something.

[Beowulf]

Two points:

1) You're forgetting that your decoy does not need to look like a rocket doing a full burn if your attacking vessel would not normally do that in plain view either. It needs to emit only enough energy to look like a ship which is trying to cloak itself and run silent.

2) You would not look like a rock moving directly toward the target, because you would presumably not plot such a course. You're just trying to get close enough to nail it with a laser or something.

How are you going to avoid doing a burn in view of some sensor platform or other? After that, it's a matter of cross correlating them. You can't effectively do it behind a planet. Even if it's behind relative to the target, there's no reason why additional sensor platforms couldn't be seeded to take a look at where it's blocked (stick it in a trojan orbit). Either you kill it, thereby making it obvious you're attacking, and a good deal of time before the real attack comes, or you lose that stealth ability.

Even if you manage that, they can toss cheap guided munitions to figure out which is which. At which point you either make a burn to avoid it (at which point from the mass/isp/delta-V profile, you can determine mass), or you shoot it down, at which point they know who shot from the thermal bloom (if your decoys have point defense, they're rapidly getting to the point where they're ships in their own right). It might take months for the projectile to get close enough to make the determination, but it's plenty of warning.

As for the movement: So what if it's only going to be close? Take a look anyway. In astronomical terms, it's still damn close. And then it's a new rock where none was before. It may not collide this time around, but maybe next time, or the time after. So you take a look. It costs very little to take a look (couple shots with a rail gun, plus the cheap guidance for each, and then telescope time in a couple months). It'd be a very big deal to lose a spacestation or similar object.

[Darth Wong]

Why are we assuming that the defender has an unlimited number of sensor platforms which themselves are presumably unmolested by the attacker? I'm envisioning some kind of hard sci-fi conflict where two colonies in the same star system spend years knocking each others' satellites and missiles and drones down. You seem to be envisioning a situation where the defender has complete control of his area of space and only has to deal with the occasional single attacker.

[Sky Captain]

Few things to consider.

Drive system. For a space warship even hard sci fi one you would obviously want a drive that has both high thrust and high ISP to give it a good acceleration and delta V which will be handy if a too big missile spam for point defense to handle is incoming. If we stick with realistic technology there is only few drive systems that suits our needs - nuclear pulse propulsion, nuclear salt water rocket and perhaps gas core nuclear thermal rocket. That means the drive while accelerating will put out at least hundreds of gigawats of power. There is no way how that can be faked with relatively cheap decoy. It`d be like trying to fake a nuclear explosion.

Assuming conflict has lasted long enough for defender`s sensor platforms and outposts to be wiped out and all what remains is few well defended main colonies it might be possible to do a burn behind a large planet and deploy decoys that fake coasting warships IR signature in a hope to draw off some fire, but that`s all. But if both sides still have system wide sensor coverage with no blind spots then everyone will know everything what their opponents fleet are doing.

[Admiral Valdemar]

You omitted fusion and antimatter drives, but yes, the point is that such ships, even small ones, would need something to give them at least several gees worth of thrust to get out of the way of any incoming fire or debris and to react quickly to intercept orders. As stated before, the signatures for each type of engine, and even those of individual ships, will be easy to notice and document. To avoid this, you'd have to coast a long, long way with practically zero power systems online to avoid waste heat production. Approaching a system at any natural speed like this is risky in of itself. If the enemy does have the resources to monitor several AU out from several angles, then having a rock in front of you may not be enough. You may have to physically be in one to avoid any suspicion. Going at an oblique angle would add even more time, and you'd have to choose when to power-up and make a beeline for the target, because too far away and you'll still be seen and intercepted; too close, and you may not have the ability to react in time and take advantage of the target's surprise.

It is very dependant on the situation we're talking about. You can't have a catch-all stealth plan this way, but given special circumstances, you could make detection a far harder affair and merit the effort.

[Beowulf]

Why are we assuming that the defender has an unlimited number of sensor platforms which themselves are presumably unmolested by the attacker? I'm envisioning some kind of hard sci-fi conflict where two colonies in the same star system spend years knocking each others' satellites and missiles and drones down. You seem to be envisioning a situation where the defender has complete control of his area of space and only has to deal with the occasional single attacker.

As I (and Adm Valdemar) pointed out, it doesn't really matter, since you can force them to honor a threat and do something within your view. You get either a thermal bloom from the firing, drive burns to avoid it, or they take fire without responding, and are forced to deal the with damage. And since you could put a camera onto the munition, if it's really not dangerous, you've got an image, and know to stop firing. If it is, you've got a picture close in, and know which are decoys and which are the real thing.

[Admiral Valdemar]

A big problem would be even approaching a system in this way. Unless you intend to stay behind this shield for months or longer as you coast into a target area, the enemy will actively be scanning the skies beforehand, with the ability to notice what amount to fireworks today at distances that would take, even at a good clip, months to years to cross without obviously looking like an artificially powered or thrown object. You don't need to have many complex sensors around a system for this, it can be amply done from orbitals with apertures large enough to cover vast tracts of space and offer a resolution that would immediately detect anything that wasn't behind several metres of cold rock or metal. As we already look out for objects like this that could potentially devastate areas of Earth, the attacking ship would already flag itself as a potential threat, even if going at a trajectory that would miss the target site by many hundreds of thousands of kilometres.

Since the only way heat can be removed is via radiation, even a modest build up of heat within the attacking ship to maintain life support could over time be detected if it seeps into the surrounding rock or leaks out of any flaws within it. All this time, the attacking ship would have to be totally silent, with emissions control at the highest level. Only passive systems could be used, and any effective antenna wouldn't be allowed to protrude from the shield to maintain the illusion. This puts the attacker at even more of a disadvantage, given any situational awareness is squandered in the hope that silent running will offer a predictable, uneventful drift towards a critical destination where such natural objects would be even more scrutinised than would be today (especially given advances in telescopes, interferometers, LIDAR, radar and so on. With the target no doubt having the home advantage of more resources to deal with too, they can dictate when and where combat would take place and be able to expend more energy in dealing with threats. The target could have mass drivers and lasers tagging anything within a security zone, regardless of suspicion. Given lightspeed weapons, at least a couple of light-seconds radius could be used as a buffer around any such critical facility, say, a space colony. The attacker would be limited not only in energy of entering the combat area (they cannot increase their attack velocity, deploy weaponry or use anything but the most basic of sensors), but the resources and time that is allowed of the defender who, unless critically inept and suffering losses that amount to being a one-on-one ship battle rather than a colony vs. attack ship, gives them a significant advantage in how to deal with any potential threats.

[Ender]

I'm reminded of the Simpsons. "I'm a Mathemagcian!". No magic involved, simple calculation. Doppler shift gives you exhaust velocity, luminosity gives you mass flow. Thrust is exhaust velocity times mass flow. Divide thrust by observed acceleration and you get mass.

How does this disprove the notion that at great distances, you can fake these things by adjusting a drone's active emissions? The whole point of ECM is to produce fake emissions; why are we assuming that its emissions must be its natural rocket emissions? And yes, I know that if you assume arbitrary resolution for the sensor device you can make out the difference, but I'm still not seeing why people should be assuming that.

Beowulf covered this, you really can't.

Even if you assume you were cold, with all onboard power supplies shut down for everything, you'd still show up and you came in system. The local solar constant it going to heat you up. You may only get upto, say 150 K, (temp of an asteroid IIRC) but against a background of 3 K you show up easily.

So you look like a rock; why doesn't that count as stealth?

We're talking about a hard sci-fi environment, aren't we? In such an environment, everything takes months. We're not talking about an object streaking in at 0.9c.

You don't look like a rock, you just have at least the same heat signature as one. You still have all the non-natural features of a man made craft that show up when they point a telescope at you. However, even if you made yourself look like a rock like that, you still stand out. We are tracking the position of thousands of asteroids now, and adding more each year. Given the threat and opportunity they present, we can expect a heavily orbitally industrialized power to be even more thorough in that regard. It isn't like they fly all over the place, Newton is firmly in the driver's seat. So now a completely new rock has appeared out of nowhere on course towards you installations. You don't think that will trip any warning bells?

On the question of an arbitrarily high resolution being unsupported, the converse is true. Use a interferometer array. With the given separation between telescopes being literally intrastellar in length, NOT achieving insanely high resolutions is hard to defend.


The only way I can think of stealth in space is with space stations/colonies and the old shell game. Mine a bunch of asteroids and comets. At a later date build hidden bases in some of them. The enemy is kept guessing as to which are abandoned, which are civilian colonies, and which are military bases. And the mass of the body is enough that you can pump the waste heat from your reactor into it and it won't noticeably change the radiation from the body. Bury the for your particle beam or laser in the mined out tunnels and the airlock doors over it prevent the telescopes from seeing it. When you want to kill something, cycle them open just long enough to fire and shut them again. Distances mean that you can move your base to another asteroid before they track it back to you. Though this isn't really stealth, so much as it is "interplanetary sniper fight"

[Darth Wong]

Question: just how close do you guys think the attacking vessel has to get? It seems to me that you're still stuck in Star Trek mode, as if the attacker has to get close enough to spit on the target. If it's so close that you can view its physical appearance in detail with a telescope, it's close enough for it to nail you with a laser.

[Ender]

Question: just how close do you guys think the attacking vessel has to get?

Depends on the weapon and scitech, but for lasers I run under the assumption of about a light second. More than that and the delay gets a bit much, less than 10^4 km and you are basically tailgating in space. Obviously particle beams and rail guns are much closer, 10^3-10^4 km varying with the speed and diffusion. Missiles, depending on the tech in the scenario, will either be closer, or further out than the lasers.

It seems to me that you're still stuck in Star Trek mode, as if the attacker has to get close enough to spit on the target. If it's so close that you can view its physical appearance in detail with a telescope, it's close enough for it to nail you with a laser.

No. With a telescope for observation the time lag doesn't really come into play at all. Physics is the captain, with the pilot just along for the ride, which puts some hard limits on how fast a situation can change. With fighting the lightspeed lag is of high importance, for weapons fire, counter maneuvers, and targeting sensors. So you can watch someone from months of travel time out and their actual actions won't matter until the final days. I expect real space combat would be similar to knife fight (for a metaphor) - a lot of positioning, counter positioning and watching the other guy, with it all ending in a brief flurry of violence in a few seconds leaving one guy heavily bleeding and the other guy dead.

[Admiral Valdemar]

Question: just how close do you guys think the attacking vessel has to get? It seems to me that you're still stuck in Star Trek mode, as if the attacker has to get close enough to spit on the target. If it's so close that you can view its physical appearance in detail with a telescope, it's close enough for it to nail you with a laser.

We can view via IR and visible, passive detectors today at up to multiple AU distances. That is far and away beyond any effective laser, particle beam or guided/dumb projectile weapon. Firing at that range would be a folly itself, given the time for any missile, even a thosuands of gee accelerating one, would allow for even the most lethargic point-defence system time to react. A laser would have to be monumentally powerful with an aperture in the tens of metres diameter to allow any coherent beam to impact with any real force at several light seconds, and that presents a phenomenal cooling problem too. Your ship would have to be a large vehicle requiring an even larger shield or rock, which suffers the inverse square law with respect to dissipating waste heat, thus compounding our previous issue.

Furthermore, there is no reason an active sensor need be used by the enemy. You'd never know you were detected until it was too late, and what with the stealth configuration of the attacker making them unable to manoeuvre or observe, they would have to assume they had passed all defences, or give up the charade. If the enemy detects the incoming threat, they can happily track it until it does get within weapons effective range, whereby it will be eliminated with extreme prejudice as soon as it shows a hint of bringing its own weapons and drive systems online.

If you're attacking a stationary target, like a colony, then you could attack much simpler using ballistics, but the range against is negating any real advantage there. If your enemy is manoeuvring (and there's no reason to assume otherwise), then any target solutions predetermined are useless without allowing your ship to engage its own sensors and move also.

[Beowulf]

Question: just how close do you guys think the attacking vessel has to get? It seems to me that you're still stuck in Star Trek mode, as if the attacker has to get close enough to spit on the target. If it's so close that you can view its physical appearance in detail with a telescope, it's close enough for it to nail you with a laser.

There's three variables in play to determine this. First is beam dispersion (only applies to directed energy weapons). This is a frequency dependent attribute, so grasers will have better values than masers. However, actually generating a graser beam is difficult. Best is likely x-ray (we do know how to make x-ray lasers). Of course, there's the flipside to this of penetration. Some is good. Too much is bad, because you won't deposit enough energy in any one place to cause a kill. Particle beams must be electrically neutral to have a good beam dispersion.

The second is lag. Your shots are no longer going where the enemy was. Best you can get is mere light speed. It gets a bit worse for particle beams, and is the worst with mass drivers. However, mass drivers do have an advantage in this: the rounds can be guided, which can help beat lag. However, see variable 3.

The last is point defense. The better the point defense, the lower the range you can use a guided weapon. On the other hand, at the point where we're most likely at, detection and tracking of missiles is probably close to perfect. At which point the best you can hope for is to overload the point defense. This is essentially range independent.

In any case, you're likely to start firing in the light second range. It keeps the lag down to manageable levels. However, this still depends on how maneuverable the opposition is (the more maneuverable, the better able they are to use lag to keep from getting hit).

[Strider]

The only way I can think of stealth in space is with space stations/colonies and the old shell game. Mine a bunch of asteroids and comets. At a later date build hidden bases in some of them. The enemy is kept guessing as to which are abandoned, which are civilian colonies, and which are military bases. And the mass of the body is enough that you can pump the waste heat from your reactor into it and it won't noticeably change the radiation from the body. Bury the for your particle beam or laser in the mined out tunnels and the airlock doors over it prevent the telescopes from seeing it. When you want to kill something, cycle them open just long enough to fire and shut them again. Distances mean that you can move your base to another asteroid before they track it back to you. Though this isn't really stealth, so much as it is "interplanetary sniper fight"

What about a different version of this idea? Set up shop way far out in the system, in the Kuiper Belt (or in a very long term scenario, Oort Cloud even). Grab lots of biggish iceballs, mount rockets on them, and shoot them all at the planet, in a slow, ugly stream. Once they're already on the correct orbit, blow them up with proper energy so that the smallish pieces of them will separate but all intersect the target's eventual position within a light-second radius or so. Among this giant stream of crap, hide some weapons platforms buried in rocks that will activate when near the target and attempt to destroy it.

You don't naturally have any cover in space, but that doesn't mean you can't generate some. Of course, this strategy presumes you can get enough of a foothold out in the Kuiper Belt to create a big enough stream of debris that it can't all be mopped up before it reaches the target (This debris *should* be small enough to burn up in atmosphere since many little pieces gives them more to clean up). Remember, you can generate many tiny rocks for the target to deal with for the cost of one set of iceball rockets and some well planted explosives.

[Samuel]

The only way I can think of stealth in space is with space stations/colonies and the old shell game. Mine a bunch of asteroids and comets. At a later date build hidden bases in some of them. The enemy is kept guessing as to which are abandoned, which are civilian colonies, and which are military bases. And the mass of the body is enough that you can pump the waste heat from your reactor into it and it won't noticeably change the radiation from the body. Bury the for your particle beam or laser in the mined out tunnels and the airlock doors over it prevent the telescopes from seeing it. When you want to kill something, cycle them open just long enough to fire and shut them again. Distances mean that you can move your base to another asteroid before they track it back to you. Though this isn't really stealth, so much as it is "interplanetary sniper fight"

What about a different version of this idea? Set up shop way far out in the system, in the Kuiper Belt (or in a very long term scenario, Oort Cloud even). Grab lots of biggish iceballs, mount rockets on them, and shoot them all at the planet, in a slow, ugly stream. Once they're already on the correct orbit, blow them up with proper energy so that the smallish pieces of them will separate but all intersect the target's eventual position within a light-second radius or so. Among this giant stream of crap, hide some weapons platforms buried in rocks that will activate when near the target and attempt to destroy it.

You don't naturally have any cover in space, but that doesn't mean you can't generate some. Of course, this strategy presumes you can get enough of a foothold out in the Kuiper Belt to create a big enough stream of debris that it can't all be mopped up before it reaches the target (This debris *should* be small enough to burn up in atmosphere since many little pieces gives them more to clean up). Remember, you can generate many tiny rocks for the target to deal with for the cost of one set of iceball rockets and some well planted explosives.

If it can't be all mopped up, why not have the iceballs ram the target?

[Strider]

The only way I can think of stealth in space is with space stations/colonies and the old shell game. Mine a bunch of asteroids and comets. At a later date build hidden bases in some of them. The enemy is kept guessing as to which are abandoned, which are civilian colonies, and which are military bases. And the mass of the body is enough that you can pump the waste heat from your reactor into it and it won't noticeably change the radiation from the body. Bury the for your particle beam or laser in the mined out tunnels and the airlock doors over it prevent the telescopes from seeing it. When you want to kill something, cycle them open just long enough to fire and shut them again. Distances mean that you can move your base to another asteroid before they track it back to you. Though this isn't really stealth, so much as it is "interplanetary sniper fight"

What about a different version of this idea? Set up shop way far out in the system, in the Kuiper Belt (or in a very long term scenario, Oort Cloud even). Grab lots of biggish iceballs, mount rockets on them, and shoot them all at the planet, in a slow, ugly stream. Once they're already on the correct orbit, blow them up with proper energy so that the smallish pieces of them will separate but all intersect the target's eventual position within a light-second radius or so. Among this giant stream of crap, hide some weapons platforms buried in rocks that will activate when near the target and attempt to destroy it.

You don't naturally have any cover in space, but that doesn't mean you can't generate some. Of course, this strategy presumes you can get enough of a foothold out in the Kuiper Belt to create a big enough stream of debris that it can't all be mopped up before it reaches the target (This debris *should* be small enough to burn up in atmosphere since many little pieces gives them more to clean up). Remember, you can generate many tiny rocks for the target to deal with for the cost of one set of iceball rockets and some well planted explosives.

If it can't be all mopped up, why not have the iceballs ram the target?

The assumed target has an atmosphere, which the iceballs are too small to survive reentry in. That's how there are so many.

[Samuel]

The assumed target has an atmosphere, which the iceballs are too small to survive reentry in. That's how there are so many.

Then compact them together. Or cover them with a layer of something that won't burn away as fast.

[Starglider]

You omitted fusion and antimatter drives, but yes, the point is that such ships, even small ones, would need something to give them at least several gees worth of thrust to get out of the way of any incoming fire or debris and to react quickly to intercept orders. As stated before, the signatures for each type of engine, and even those of individual ships, will be easy to notice and document.

This is not correct. At the very least, mass drivers (throwing cold slugs) have negligable signature. Photon drives have virtually zero signature; unless you're directly in the thrust axis all you can see is backscatter from any space dust present. Ion drives can have zero signature if the ions are thoroughly neutralised before ejection; as I understand it existing ion drives have such insignificant signature that they're practically undetectable. Of course all of these drives are less practical (at least for combat maneuvering) than drives based on exhausting hot gas or plasma through a nozzle, but they are possible.

[Strider]

The assumed target has an atmosphere, which the iceballs are too small to survive reentry in. That's how there are so many.

Then compact them together. Or cover them with a layer of something that won't burn away as fast.

Compacting them together sort of defeats the point of having a lot of them. Covering them with something that is exceptionally resistant to burnup is exceptionally expensive, because the raw material we have to work with is ice. The plan is relatively dependent on the cheapness of the approach: all you need is some sort of rocket you can use to alter the trajectory of a big ice ball and some explosives to blow it into a ton of difficult to manage pieces once it's on its way. You get an instant power law distribution of dummy particles, a random few of which have the expensive weapons platforms concealed inside.

For example, if you take a 10 km Kuiper object, and you have a 20 m weapons platform you need to hide in a small iceball, you can break that Kuiper object into ~500^3 = 100 Million iceballs. If you plant 5 high cost high effectiveness weapons platforms among these iceballs, then the target must destroy virtually ALL of them in order to be safe. If you want to just use the things as bludgeons, remember the Dinosaur extinction was caused by a rock (much denser than an iceball) that was about 10 km in diameter. So essentially, you can have, at best, a couple vulnerable bludgeons, or you can have 100 million bits of cover to hide in.

[Admiral Valdemar]

This is not correct. At the very least, mass drivers (throwing cold slugs) have negligable signature. Photon drives have virtually zero signature; unless you're directly in the thrust axis all you can see is backscatter from any space dust present. Ion drives can have zero signature if the ions are thoroughly neutralised before ejection; as I understand it existing ion drives have such insignificant signature that they're practically undetectable. Of course all of these drives are less practical (at least for combat maneuvering) than drives based on exhausting hot gas or plasma through a nozzle, but they are possible.

Negligible here is still detectable. You are focusing on the exhaust and not the fact that the machinery powering the basic ship systems will be producing tremendous heat, to say nothing of throwing mass out by mass drivers or running a particle accelerator. You can't avoid the thermodynamic side-effects here without just not producing the energy in the first place.

[Ender]

What about a different version of this idea? Set up shop way far out in the system, in the Kuiper Belt (or in a very long term scenario, Oort Cloud even). Grab lots of biggish iceballs, mount rockets on them, and shoot them all at the planet, in a slow, ugly stream. Once they're already on the correct orbit, blow them up with proper energy so that the smallish pieces of them will separate but all intersect the target's eventual position within a light-second radius or so. Among this giant stream of crap, hide some weapons platforms buried in rocks that will activate when near the target and attempt to destroy it.

You don't naturally have any cover in space, but that doesn't mean you can't generate some. Of course, this strategy presumes you can get enough of a foothold out in the Kuiper Belt to create a big enough stream of debris that it can't all be mopped up before it reaches the target (This debris *should* be small enough to burn up in atmosphere since many little pieces gives them more to clean up). Remember, you can generate many tiny rocks for the target to deal with for the cost of one set of iceball rockets and some well planted explosives.

How about because this is hard Scifi and you are envisioning magic super engines that let you hurl bodies dozens of kilometers in diameter around like they are pool balls. Does that poke a sufficient hole in this idea, or should I go through the very detailed reasons that this is dumb?

[Ender]

This is not correct. At the very least, mass drivers (throwing cold slugs) have negligable signature. Photon drives have virtually zero signature; unless you're directly in the thrust axis all you can see is backscatter from any space dust present. Ion drives can have zero signature if the ions are thoroughly neutralised before ejection; as I understand it existing ion drives have such insignificant signature that they're practically undetectable. Of course all of these drives are less practical (at least for combat maneuvering) than drives based on exhausting hot gas or plasma through a nozzle, but they are possible.

Negligible here is still detectable. You are focusing on the exhaust and not the fact that the machinery powering the basic ship systems will be producing tremendous heat, to say nothing of throwing mass out by mass drivers or running a particle accelerator. You can't avoid the thermodynamic side-effects here without just not producing the energy in the first place.

There is also the fact that all those drives would carve out radio plumes in the ISM (and even more so in the denser intrastellar medium)

[Beowulf]

Ion drives can have zero signature if the ions are thoroughly neutralised before ejection; as I understand it existing ion drives have such insignificant signature that they're practically undetectable.

The ions from the drive still have a temperature and will radiate until reaching ambient. Most ion drives right now don't have much signature simply due to the low power used (<150kW vs the aforementioned 30 GW). If you up the power (and thrust) to something useful, they'd have just as much of a signature). And of course, none of this makes a dent in the previously mentioned power generation heat signature.

[Admiral Valdemar]

How about because this is hard Scifi and you are envisioning magic super engines that let you hurl bodies dozens of kilometers in diameter around like they are pool balls. Does that poke a sufficient hole in this idea, or should I go through the very detailed reasons that this is dumb?

Apparently you can throw masses out of a ship and not have the ship incur heat transference too. That'd be great, if only it weren't for the fact that modern mass drivers have a huge problem to do with thermal ablation conducting to the rails and gun assembly. Or that a photon drive lighting up a trail of interplanetary dust leading straight back to your ship is somehow a stealthy idea.

[Starglider]

You are focusing on the exhaust

Yes I was, because you were talking about exhaust plumes.

and not the fact that the machinery powering the basic ship systems will be producing tremendous heat,

That can be managed with heat sinks, screening mass and directional heat dumps. It is quite possible to have a plate covering the front of your ship chilled to liquid helium temperatures if the back side is covered in radiators, and this could still be tactically valuable if you know the (general) location of the enemy sensors.

You can't avoid the thermodynamic side-effects here without just not producing the energy in the first place.

You are assuming passive thermal management when a realistic spacecraft is anything but.

Or that a photon drive lighting up a trail of interplanetary dust leading straight back to your ship is somehow a stealthy idea.

Interstellar dust is so ridiculously sparse (on the order of a few atoms per cubic metre) that the radiation is literally undetectable. I confess I don't know the average density within a solar system, but I'd be surprised if it was opaque enough to detect the backscatter from even a terawatt laser from significant distances. If you think this is detectable please prove it.

The ions from the drive still have a temperature and will radiate until reaching ambient.

Maybe I'm missing something here but AFAIK ions do not have a 'temperature' in the conventional sense. In a bulk material, temperature is the kinetic energy implied by the difference between the velocity vectors of the individual atoms and the mass as a whole. Individual ions are effectively indivisible for thermodynamic purposes; physicists occasionally talk about them having 'temperature', but that's only relevant in the case of them actually hitting something. Collisions between ions in the exhaust will be insignificant for most acceleration schemes. That only leaves electrons that are already excited when the ion goes out the back of the drive to power thermal radiation, which is where neutralisation comes in. If you can neutralise the ions such that the electrons settle into the ground state before the ion exits the back of the drive, then you can minimise the exhaust plume signature. I don't know how practical this is, but even for poorly neutralised ion drives, the massive KE of the particle relative to its electron excitation energy (and relative homogenity of velocity vectors in the plume) makes it a much colder plume than any sort of thermal expander drive.

[Admiral Valdemar]

Yes I was, because you were talking about exhaust plumes.

We've been talking about far more than that.

That can be managed with heat sinks, screening mass and directional heat dumps. It is quite possible to have a plate covering the front of your ship chilled to liquid helium temperatures if the back side is covered in radiators, and this could still be tactically valuable if you know the (general) location of the enemy sensors.

Never said otherwise, but the heat is still being radiated and still readily detectable. You would need to have a 60 degree conical radiator behind the ship to focus any excess heat away, and that is assuming the enemy is focused entirely directly in front of you. You would not be able to attain any thermal equilibrium, because space isn't in equilibrium.

You are assuming passive thermal management when a realistic spacecraft is anything but.

No, I'm not. Waste heat will still be radiated. Just because you copy the shuttle or Soviet satellites and have an active coolant unit doesn't change the fact that you will radiate heat very noticeably.

Interstellar dust is so ridiculously sparse (on the order of a few atoms per cubic metre) that the radiation is literally undetectable. I confess I don't know the average density within a solar system, but I'd be surprised if it was opaque enough to detect the backscatter from even a terawatt laser from significant distances. If you think this is detectable please prove it.

Interplanetary dust particles are quite readily observed in visible and IR spectrums. The density is on an order of magnitude or more than the ISM (depending on actual location within the system), which would be thousands of atoms per cm^2. For a laser of any real benefit here, you'd need a large aperture and a lot of radiators to deal with the heat output. Even if the beam itself were to be practically transparent to all detectable spectrums, the cost would come from such a large investment in an otherwise useless drive that would better serve as a weapon, just as with the mass driver.

Maybe I'm missing something here but AFAIK ions do not have a 'temperature' in the conventional sense. In a bulk material, temperature is the kinetic energy implied by the difference between the velocity vectors of the individual atoms and the mass as a whole. Individual ions are effectively indivisible for thermodynamic purposes; physicists occasionally talk about them having 'temperature', but that's only relevant in the case of them actually hitting something. Collisions between ions in the exhaust will be insignificant for most acceleration schemes. That only leaves electrons that are already excited when the ion goes out the back of the drive to power thermal radiation, which is where neutralisation comes in. If you can neutralise the ions such that the electrons settle into the ground state before the ion exits the back of the drive, then you can minimise the exhaust plume signature. I don't know how practical this is, but even for poorly neutralised ion drives, the massive KE of the particle relative to its electron excitation energy (and relative homogenity of velocity vectors in the plume) makes it a much colder plume than any sort of thermal expander drive.

The drive would still produce heat radiated from the ship, only now you've got a truly useless drive system dispersing particles that will be taking likely 10% of the waste heat from the drive, assuming 90% efficiency (which will appear as fluorescence, so who needs IR detectors?). A diffuse cloud doesn't change the fact that it is going to be detectable against the background, since all we're talking about here is thermal differential here, not nominal temperature. The source of the emissions itself is the big giveaway, and for a ship along the order of mass we're talking about here, you're going to need one beefy ion drive to get anything done in any time and make it worth it. All the while, the enemy can be out there moving without such limitations and even using active sensors that would pick up a large cloud of ions with ease.