Stealth in space

[Idobox]

Although proper stealth would be almost impossible, decoys and blinding could be rather easy.

The whole argument is that hiding your IR signature is almost impossible, unless you're actually a rock, and even then, you might be detected. But launching a few hundred very hot but small decoys would be a viable strategy. The enemy would know you're up to something, but they would have a lot of trouble identifying the actual target. Of course, unless you're very close, they will also have lot of time to find out which one is the relevant target, and also send a counter-attack weeks, months or even years before you reach them.

The other option is to blind their detectors. A focused beam of strong IRs targeted at your enemy's bases would blind its telescopes while you do your burn. If you can emit it continuously, or at least quite frequently, they couldn't know when you did your burn, or even if one happened.

The weaponized version of that uses a stronger IR beam, possibly pulsed, to deplete the coolant used on their telescopes, rendering them unusable.

The blinding solution of course works only for burns close to your emitter, logically close to your planet/base or main fleet. You will still need to find a way to hide your waste heat during the actual transfer.

The only type of mission it would make sense for would be spying/infiltration. For actual warfare, shooting first from far away would be a safer option, especially if you have access to lasers, particle beams or relativistic projectiles (basically weapons that give only seconds or minutes between the moment firing is detected by the target, and the moment the target is rendered unable to detect anything ever again, even less retaliate).

[Fel]

You are forgetting something very important: Triangulation.

If your exhaust is JUST above the noise floor; (To note, while I am not a specialist in IR, I can say that the noise floor in RAW (not camera phone post-processing faking) sensor data has GREATLY improved over the years; yielding low light high ISO shots that are still passable without post-processing. So the technology talked about is extremely outdated.) [And technically, some of this could have been done with even bigger sensors with low pixel density (i.e. specialty bodies)].

So let's again say your exhaust is JUST above the ever lowering noise floor, maybe it would go by unnoticed until you have two cameras getting that same blip. A sensor-net isn't going to use just one camera which means that your attempts to be extremely stealthy are for naught.

While we'll often clamp off the noise floor and some, in a single system design to prevent false positives; but when you're confirming with independent data from multiple sources, and verifying each agrees with the expected location via triangulation; you can delve much deeper in there and get data that would have been lost. Technically, you could have a signal slightly buried in noise; with noise occasionally dropping low enough to show the signal. It's possible to get false positives, even with the whole triangulation... but on a per-pixel analysis it may find that one area is continually slightly "hotter" than pure Gaussian noise. This is more so if you're JUST a little bit below the noise level, hot spots occur all the time which should show how much this is pushing things; but due to data verification is still possible.

http://deepimpact.umd.edu/gallery/T1_1983.html (Random search for "Thermal Image of a Comet")

[Fel]

The other option is to blind their detectors. A focused beam of strong IRs targeted at your enemy's bases would blind its telescopes while you do your burn. If you can emit it continuously, or at least quite frequently, they couldn't know when you did your burn, or even if one happened.

The weaponized version of that uses a stronger IR beam, possibly pulsed, to deplete the coolant used on their telescopes, rendering them unusable.

We have a massive ball of IR that still doesn't prevent us from using our telescopes, what is a little feeble IR Beam going to do? With digital cameras, raw provides MUCH more information than you would ever need which makes it significantly harder to actually create an unrecoverable image. (Ugg... and I can't find a good example of using lightshop to recover a completely blown out image.) Let's just assume that the IR Camera lacks basic adjustment software to compensate for the increased exposure; your "data" of your ship is still there even if you can't see it! If you adjust contrast, brightness, evs, and rebalanced blacks (all of which can be "somewhat automated" [your cellphone will do this automatically, but it doesn't always do it how you, the photographer, wants it])... and of course, just adjusting for the condition is much better. (Close your aperture more, take shorter shots, lower iso rating, etc...) [and again, cameras do this... but not the way you, as a photographer, may want it].

Eitherway, point is that even if you detonate a nuclear bomb near your ship, your ship will still absorb some of the blast... [and, quite frankly, if it wasn't showing up on IR before it probably would now XD]; this means that you can still detect the original object.

[gooddog15]

You could always build a ship that looks like a big asteroid.

Probably wouldn't work though.

[tater]

If the crew is at normal human temps inside (20 degrees), then the ship itself is that temp, and visible. Stealth is not possible, period. Decoys are obvious, too. Their movement and acceleration give them away compared to signature.

[meve12]

This topic has been done to death so much on rec.arts.sf.science, SFCONSIM-L, Rocketpunk Manifesto, Atomic Rockets, and basically anywhere else concerned with hard sci-fi.

Here's a link to a Rocketpunk Manifesto article + comments on the subject. I suggest you all read it before continuing this debate, since it's highly unlikely you'll be able to come up with something that hasn't already been thought of. Link. I also recommend that you read the linked articles/threads, especially the SFCONSIM one.

I've read through all of those too. You know what they don't mention?

Magsails. Four websites (and Atomic Rockets includes it in the engine list, even) and not a single mention of magsails for stealthy, no exhaust plume movement. Or directional radiators, or any power state other than full combat stations, or how many sensor outposts would be needed to reliably cover an area, or any mention of decoys more advanced than silvered balloons, or the use of the local star or planetary body as a background to dump heat(away from the star, of course) in order to avoid being detected, or even the difference between stealth(less likely to be detected, usually facilitated by proceeding in a secretive and cautious manner) and total invisibility(the inability to be detected whatsoever, which, as the detractors correctly if misleadingly argue, is impossible.)

Seriously? One wonders if they rejected the notion going in and came up with reasons why later, to counter the inevitable counterarguments.

[GreenWolf]

I've read through all of those too. You know what they don't mention?

Magsails. Four websites (and Atomic Rockets includes it in the engine list, even) and not a single mention of magsails for stealthy, no exhaust plume movement. Or directional radiators, or any power state other than full combat stations, or how many sensor outposts would be needed to reliably cover an area, or any mention of decoys more advanced than silvered balloons, or the use of the local star or planetary body as a background to dump heat(away from the star, of course) in order to avoid being detected, or even the difference between stealth(less likely to be detected, usually facilitated by proceeding in a secretive and cautious manner) and total invisibility(the inability to be detected whatsoever, which, as the detractors correctly if misleadingly argue, is impossible.)

Seriously? One wonders if they rejected the notion going in and came up with reasons why later, to counter the inevitable counterarguments.

In fact, these things are covered. Now, to be fair to you, they are mostly covered in the comments of Rocket Punk manifesto and SFCONSIM, but they are covered.

[jrphilps]

I've read through all of those too. You know what they don't mention?

Magsails. Four websites (and Atomic Rockets includes it in the engine list, even) and not a single mention of magsails for stealthy, no exhaust plume movement. Or directional radiators, or any power state other than full combat stations, or how many sensor outposts would be needed to reliably cover an area, or any mention of decoys more advanced than silvered balloons, or the use of the local star or planetary body as a background to dump heat(away from the star, of course) in order to avoid being detected, or even the difference between stealth(less likely to be detected, usually facilitated by proceeding in a secretive and cautious manner) and total invisibility(the inability to be detected whatsoever, which, as the detractors correctly if misleadingly argue, is impossible.)

Seriously? One wonders if they rejected the notion going in and came up with reasons why later, to counter the inevitable counterarguments.

Great minds think alike. Those are exactly some of the things I mentioned in this thread. These are plausible and original ideas which everyone shoots down without even bothering to demonstrate why they won't work. Thats not their job, granted, but if your going to say that something is debunked, you should at least copy/paste some article proving it.

As one example, chemical rockets are quite stealthy compared to electromagnetic engines: With a very small rocket and some concessions to future scientific advances, you could propose an environment where warships can secretly burn along until they get within a few million km of a suspected enemy position. Is that actually possible in the real world? Who knows.

Some of the more math literate people here could easily come up with a chart determining how far away engine x or y can be detected, but they don't bother. If they want to shut down the debate on stealth warships, they need to do more than just say 'nah uh!'

Edited April 2, 2015 by jrphilps

[cryogen]

Hiding IR signatures is a lot easier than has been suggested. You don't need to reduce thermal radiation; only emit it in the opposite direction as the observer. You can do this passively.

One way is by choosing surface materials with different emissivities (i.e. "black" on the radiating side, "white" on the stealth side).

Another way is to stack layers of surfaces, with vacuum in between. At each surface, thermal radiation is as likely to go backwards as forwards, so heat flow through the whole stack is greatly reduced (by a factor of 1/N). This is the idea behind multi-layer insulation (the gold foil on spacecraft), and on a larger scale, the "sunshield" on the James Webb telescope:

http://jwst.nasa.gov/sunshield.html

The cold side is 40 Kelvin!

With enough layers, you could probably vanish into the CMB noise.

Reflected radiation (like radar) is particularly bad at interplanetary distances, since reflected signals fall off as 1/R⁴, not merely 1/R².

[Kibble]

Just 40 Kelvin! That's impressive.

[tater]

You cannot know where the enemy is ahead of time. The more directional you imagine radiators, the less you can also know about enemy dispositions. Such a universe results in distant observation sats looking all around.

If you are talking science fiction warships, you are talking about a 293 K crew compartment as a minimum. How big are those radiators for the telescope? How big would they need to be for a larger crew compartment at room temp? Any power production for propulsion or weaponry must radiate 100% of the energy produced.

[Kibble]

If you are talking science fiction warships, you are talking about a 293 K crew compartment as a minimum. How big are those radiators for the telescope? How big would they need to be for a larger crew compartment at room temp? Any power production for propulsion or weaponry must radiate 100% of the energy produced.

If you're not talking science fiction warships, you don't need a habitat for astronauts, or very much power - for most purposes an RTG would suffice to power your quietly-inserted robotic probe. If you can minimize the chance that the spacecraft is detected en transfert, you also minimize the amount of time the bad guy's planet has to react to it.

[tater]

RTG probe to another planet? In another star system? If you have stealthy craft, they have stealthy sensors platforms someplace, and you have to radiate away, not isotropically. This was eliminated on usenet groups before most people here knew what the internet was (or were born), heck, before the web was a thing. Back then the price of entry for the discussion was being a science or engineering person (the only people on the net, basically).

Any weaponry requires loads of power (directed energy weapons), or loads of kinetic energy (a huge exhaust plume). Pick one.

If we are talking near future, there is still no hiding, as the craft have been observed since launch. Sensors might be placed all over using sails, perhaps (though you then must be careful do to reflect light the wrong way), but all sides can do this, scattering sensors… of course any sensors between (or behind) the home planets can capture any broadcasts them make of detections. And again, what possible weapon can be stealthy, and still effective?

Posit a stealthy system, and sensors use it, and there is a sensor arms race until they are scattered all over, eliminating directional radiators as useful.

The next issue is of course KE weapons as WMD (also beaten to death on the net before 99% of the people on this forum were born, I imagine ).

[Kibble]

Another WHAT? I'm talking about the Solar System, that we Homo sapiens live in.

You can't launch an infinite number of infrared space telescopes. Generally you'll want them inferior to the orbit of both your and the bad guy's planet, hunting the sky for little stuff, looking outward with their back to the (telescope-frying, helium evaporating) Sun, like how you find asteroids. You also want some at their Sun-El-Wun to observe any local activity at close range. While kept in a Lissajous orbit there, you always have your back to the Sun, and are staring Badguyville in the face.

[GreeningGalaxy]

I've read through all of those too. You know what they don't mention?

Magsails. Four websites (and Atomic Rockets includes it in the engine list, even) and not a single mention of magsails for stealthy, no exhaust plume movement. Or directional radiators, or any power state other than full combat stations, or how many sensor outposts would be needed to reliably cover an area, or any mention of decoys more advanced than silvered balloons, or the use of the local star or planetary body as a background to dump heat(away from the star, of course) in order to avoid being detected, or even the difference between stealth(less likely to be detected, usually facilitated by proceeding in a secretive and cautious manner) and total invisibility(the inability to be detected whatsoever, which, as the detractors correctly if misleadingly argue, is impossible.)

Seriously? One wonders if they rejected the notion going in and came up with reasons why later, to counter the inevitable counterarguments.

Magsails still have that problem where you require a ton of power. No, solar energy won't be enough (and even if it were, the panels would get very hot and easy to see). You'll need a nuclear reactor, and with a reactor comes glowing hot radiators, and with radiators come huge, brilliant heat signatures that you can detect from three stars away. Also, even if you somehow managed to get ahold of a perfectly-efficient source of electricity, the charged particles being redirected by your magnetic field are probably going to give off synchrotron radiation, which will be pretty easy to pick out by enemy sensors. The short and easy answer to the problem is that there isn't (and never will be) a propulsion system capable of providing any amount of thrust without also lighting up your ship like a Christmas tree; there are just too many steps in the energy conversion process and the efficiencies necessary to avoid transmitting detectable amounts of waste heat just aren't possible with any known or theoretical mechanism.

Atomic Rockets discusses in very good detail why decoys won't work - they're too easy to see through (thrust power is easy to measure from long distances, and they'll appear from your ship's position, so your enemy will easily be able to follow their little trails of bread crumbs straight back to you. With the added expense of hauling the things around, you might as well just send more ships.

As for directional heat radiation, Atomic Rockets also lays that one pretty much to rest - There just isn't a way to reflect thermal radiation with enough efficiency to prevent the back of the mirror from heating up, and even if there were, the losses in radiator efficiency would be very substantial and liable to make your ship so large that you could see it just by waiting for it to transit a planet or star.

Believe me, nobody here wants to believe that stealth in space is impossible, it's just that nobody so far has come up with an idea for it that would work.

[meve12]

Magsails still have that problem where you require a ton of power. No, solar energy won't be enough (and even if it were, the panels would get very hot and easy to see). You'll need a nuclear reactor, and with a reactor comes glowing hot radiators, and with radiators come huge, brilliant heat signatures that you can detect from three stars away. Also, even if you somehow managed to get ahold of a perfectly-efficient source of electricity, the charged particles being redirected by your magnetic field are probably going to give off synchrotron radiation, which will be pretty easy to pick out by enemy sensors. The short and easy answer to the problem is that there isn't (and never will be) a propulsion system capable of providing any amount of thrust without also lighting up your ship like a Christmas tree; there are just too many steps in the energy conversion process and the efficiencies necessary to avoid transmitting detectable amounts of waste heat just aren't possible with any known or theoretical mechanism.

A magsail design postulated by this article:http://casa.colorado.edu/~danforth/science/magsail/magsail.html

seems to draw 1,000,000 Amperes; the SAFE-400 generates 400,000 watts of thermal power, and coverts 100,000 watts to electrical power. So a SAFE-400 can power the magsail with 0.1 volts(since it's a superconducter loop,thus with no resistance at all, voltage is unimportant), with 300,000 watts of thermal power left over. This can be radiated by a radiator with an area of 1190 meters squared, operating at 273 kelvin, with an emissivity of .8(ranges from 0.0(perfect insulation) to 1.0(perfect black-body).

Note that this is a very inefficient radiator. This is by design; the lower the operating temperature of the radiator, the less likely it is to get picked up if you point it at an IR scope accidentally. It's still much less area than the magsail, which has a radius of 10 kilometers, so an "area" of 314.5 kilometers.

Now we can calculate the acceleration that this magsail would provide. The average force for this magsail design, according to the study, perpendicular to the solar wind(the point of sail would be "running") is 4.15 newtons. While they don't provide a direct force measure, deriving from the other figure for acceleration they give, the average force for facing edge on to the solar wind("beam reach") increases to 324 newtons(I'm not sure this is right, can you double check?). Both are for average particle density and velocity at Earth orbital radius.

The mass for the magsail is 36 metric tons, and the reactor itself is half a metric ton. Since the radiator operates at the freezing temperature of water, let's make it just that: a thin, circular sheet of water, dyed black and mixed with antifreeze, held in by a sheet of acrylate polymer, and spun to cause centrifugal 'gravity' and thus cause convection currents. A sheet a centimeter thick and 1190 meters wide would weigh around 11 metric tons. We'll assume for the sake of rounding that pumps, transformers and such are another half ton.

The total mass for our stealth propulsion bus is 48 metric tons.(Neglecting James Webb style radiator shield, because no information on mass of such could be found) Using the maximal possible thrust at Earth orbit average conditions (324 newtons), it can accelerate itself at 48,000,000 grams/ 324 newtons = 0.00000675 m/s^2.

You can't go anywhere particularly quickly, but you can get there relatively quietly.

Atomic Rockets discusses in very good detail why decoys won't work - they're too easy to see through (thrust power is easy to measure from long distances, and they'll appear from your ship's position, so your enemy will easily be able to follow their little trails of bread crumbs straight back to you. With the added expense of hauling the things around, you might as well just send more ships.

It discusses in good detail why building your decoy along the lines of the ship doesn't work. No mention is made of using IR spotlights on booms to simulate a ship of larger size than the decoy, or of, again, using magsails as above to maneuver your ship without getting spot so the decoy doesn't lead right back to you.

As for directional heat radiation, Atomic Rockets also lays that one pretty much to rest - There just isn't a way to reflect thermal radiation with enough efficiency to prevent the back of the mirror from heating up, and even if there were, the losses in radiator efficiency would be very substantial and liable to make your ship so large that you could see it just by waiting for it to transit a planet or star.

I do believe that problem of heat dissipation was solved for the James Webbs telescope. See this article:http://jwst.nasa.gov/sunshield.html

Granted it's a sun shield and not a radiator shield, but the tech is there, now.

Believe me, nobody here wants to believe that stealth in space is impossible, it's just that nobody so far has come up with an idea for it that would work.

We have, actually. Multiple times. It's just that I've only seen a few of the participants, pro or anti-stealth, backing up their words with numbers, so it devolves into a green-purple civil war pretty quickly.

A ship like the one described above would probably point its' radiator away from the sun, for two reasons: to prevent solar radiation from heating the radiator, defeating its' purpose, and because to prevent being blinding by the sun, IR scopes on lookout duty would be in low solar orbits, looking out. The magsail can twist on two "extension cables" to any heading necessary, so orientation is unimportant.

The nice thing about a magsail is, as described in the article, the fact that it's a propellant-less drive allows for some weird maneuvers that reaction drive ships would be hard pressed to emulate, such as hovering or gliding at a constant altitude but at suborbital or escape velocities. Though space weather would give it some trouble.

[tater]

Another WHAT? I'm talking about the Solar System, that we Homo sapiens live in.

You can't launch an infinite number of infrared space telescopes. Generally you'll want them inferior to the orbit of both your and the bad guy's planet, hunting the sky for little stuff, looking outward with their back to the (telescope-frying, helium evaporating) Sun, like how you find asteroids. You also want some at their Sun-El-Wun to observe any local activity at close range. While kept in a Lissajous orbit there, you always have your back to the Sun, and are staring Badguyville in the face.

If you are talking about a combat situation, you can certainly launch a lot of them. Remember that the goal for a sensor is not an HST, but wide angle scans. You also need to describe what a warship (drone or otherwise) looks like, what the role is. It needs to have directed energy weapons, or it needs to impact the target. The former generates vast amounts of power (you need ~2 MJ/cm^2 to burn through a single cm of steel), the latter requires loads of dv (for energy delivery, as well as actually hitting the target (even should it disperse shrapnel)). Nuclear weapons require near contact hits to be a problem (nuke-pumped x-rays are another option here).

If you stick with realistic weapons (note that some nuclear drive options ARE weapons), then engagement ranges are going to be pretty short, well under 0.1 light second. At some decent multiple of this engagement range, any ship you care to posit is visible, IMO.

If you are talking about spotting it in orbit around Jupiter at opposition from Earth, then sure, you might hide a stealthy ship… but it's not like you can engage it, and if you try to get there before its crew dies of old age (via sails, etc ), it will see you coming.

That's really what needs to be defined, at what range is hiding impossible under a particular set of assumptions, and how does that compare to ranges where weapons systems can be employed.

[Kibble]

You also need to describe what a warship (drone or otherwise) looks like, what the role is. It needs to have directed energy weapons, or it needs to impact the target. The former generates vast amounts of power (you need ~2 MJ/cm^2 to burn through a single cm of steel), the latter requires loads of dv (for energy delivery, as well as actually hitting the target (even should it disperse shrapnel)).

The energy of a hyperbolic escape orbit is plenty to shatter a spacecraft - your Killer Bus can just bee a regular probe.

If you stick with realistic weapons then engagement ranges are going to be pretty short, well under 0.1 light second. At some decent multiple of this engagement range, any ship you care to posit is visible, IMO.

That's true. But is that enough time to react?

If you are talking about spotting it in orbit around Jupiter at opposition from Earth, then sure, you might hide a stealthy ship… but it's not like you can engage it, and if you try to get there before its crew dies of old age (via sails, etc ), it will see you coming.

Why do you need astronauts on board?

That's really what needs to be defined, at what range is hiding impossible under a particular set of assumptions, and how does that compare to ranges where weapons systems can be employed.

Exactly! Istrebitel Sputnik was supposed to have been able to - once it detonates its charge - smash a satellite within one km. So its a question of whether you can hide long enough such that once they detect you, you are still able to rendezvous to 1 km within your budget for course corrections.

[GreeningGalaxy]

[snip]

A ship like the one described above would probably point its' radiator away from the sun, for two reasons: to prevent solar radiation from heating the radiator, defeating its' purpose, and because to prevent being blinding by the sun, IR scopes on lookout duty would be in low solar orbits, looking out. The magsail can twist on two "extension cables" to any heading necessary, so orientation is unimportant.

The nice thing about a magsail is, as described in the article, the fact that it's a propellant-less drive allows for some weird maneuvers that reaction drive ships would be hard pressed to emulate, such as hovering or gliding at a constant altitude but at suborbital or escape velocities. Though space weather would give it some trouble.

A few raisins I have with your proposed stealth ship design:

1). Liquid water (even liquid water spiked with antifreeze and cooled below 0 C) is still quite a lot warmer than the cosmic background, and it's going to show up on thermal scans pretty easily.

2). No matter how you cut it, 400 kilowatts of thermal power made into 100 kilowatts of electricity means you're radiating 300 kilowatts of infrared into space. if your radiators are gigantic enough for you to dissipate that without your radiator surface getting hot enough to be seen against the cosmic background, you're going to show up just by eclipsing stars.

3). Even if that magsail ship could remain discreet with its waste heat, it won't be very useful in combat. Once it's detected, its tiny maximum acceleration will leave it a sitting duck to the first missile fired, and its low mass budget will severely limit the amount of armaments it can carry. (more mass will require more power to push it around, which requires miles more radiator mass to keep it cool enough to stay invisible, which in turn requires more power to push around...) I suppose you could always strap an entire fusion torch assembly to the back which you can boot up as soon as you're detected and the jig is up, but those aren't renowned for being very light, either.

Other notes:

-Attaching spotlights to booms and whatever other smoke and mirrors you care to pull isn't going to fool your enemy. They're still going to see different types of radiation coming from the decoys than from you, and their telescopes will probably be able to resolve pretty good images of the decoys to tell that they're just spotlights on booms and not real fusion torches. In any case, the multiple viewpoints afforded by the sensor beacons the enemy has no doubt been launching are going to see through you pretty fast. The problem is just that the enemy can make too many measurements that you don't have good ways to fool, other than by using the real thing.

-Webb telescope-style radiation shielding won't work to hide a heat radiator. The sun would only be providing the telescope with a few kilowatts per square meter at that distance from the sun, and a radiator would be putting out hundreds of kilowatts at the very least, and if it's a true combat-capable ship, probably hundreds of megawatts. It doesn't matter how many layers you use on your mirrors; you'll still either have hot backsides or gigantic unwieldy things that can be spotted from Mars.

Believe me, nobody here wants to believe that stealth in space is impossible, it's just that nobody so far has come up with an idea for it that would work.

We have, actually. Multiple times. It's just that I've only seen a few of the participants, pro or anti-stealth, backing up their words with numbers, so it devolves into a green-purple civil war pretty quickly.

I'd interject that none of the numbers you just provided make a particularly good case for stealth, and do a rather good job of making one against it - you have atrociously low acceleration, huge amounts of waste heat, and impractically large radiators that still don't spread it out thin enough to be stealthy. Also, no, nobody on this thread has made a case for stealth in space that isn't full of rather serious holes yet.

But:

If you want to really argue on this topic, I'd advise you to cut out the middle man and go directly to rec.arts.sf.science and lay your case out before the experts.

Even if you don't do that, I'd recommend reading that page. It does pretty exhaustively cover the arguments for stealth in space, and if you find anything you disagree with in their reasoning, Atomic Rockets makes it sound like you might be able to get them to explain it to you better than anyone here could.

If you do have an idea that would actually work, though, please share it over there, because it would be pretty cool if stealth in space were a thing.

Edited April 3, 2015 by GreeningGalaxy

[meve12]

A few raisins I have with your proposed stealth ship design:

1). Liquid water (even liquid water spiked with antifreeze and cooled below 0 C) is still quite a lot warmer than the cosmic background, and it's going to show up on thermal scans pretty easily.

True-if against the cosmic background. The reason I can safely point my kilometer-wide radiator away from the sun is because in order to find that radiator, any IR scopes would have to be in a higher orbit, looking insystem. Which means they'll have to pick it out from the background of the Sun, which is somewhat untrivial even if you could make an IR scope that could operate while pointed at the Sun.

2). No matter how you cut it, 400 kilowatts of thermal power made into 100 kilowatts of electricity means you're radiating 300 kilowatts of infrared into space. if your radiators are gigantic enough for you to dissipate that without your radiator surface getting hot enough to be seen against the cosmic background, you're going to show up just by eclipsing stars.

See above.

3). Even if that magsail ship could remain discreet with its waste heat, it won't be very useful in combat. Once it's detected, its tiny maximum acceleration will leave it a sitting duck to the first missile fired, and its low mass budget will severely limit the amount of armaments it can carry. (more mass will require more power to push it around, which requires miles more radiator mass to keep it cool enough to stay invisible, which in turn requires more power to push around...) I suppose you could always strap an entire fusion torch assembly to the back which you can boot up as soon as you're detected and the jig is up, but those aren't renowned for being very light, either.

Who said it's useful for combat? Of course you don't use it for combat. You use it for long-term reconnaissance, or as a remote launch platform for strategic WMDs or antiship weapons. (Unmanned, of course. It's either a long wait or a suicide mission.)

Other notes:

-Attaching spotlights to booms and whatever other smoke and mirrors you care to pull isn't going to fool your enemy. They're still going to see different types of radiation coming from the decoys than from you, and their telescopes will probably be able to resolve pretty good images of the decoys to tell that they're just spotlights on booms and not real fusion torches. In any case, the multiple viewpoints afforded by the sensor beacons the enemy has no doubt been launching are going to see through you pretty fast. The problem is just that the enemy can make too many measurements that you don't have good ways to fool, other than by using the real thing.

Who said we had to make the decoy emulate a torch ship? We need it to emulate a coasting ship, which a ship using a magsail would look like at first glance, and would effectively be so in combat...Oh, right. Ok, I concede that argument, decoys would be superfluous.

-Webb telescope-style radiation shielding won't work to hide a heat radiator. The sun would only be providing the telescope with a few kilowatts per square meter at that distance from the sun, and a radiator would be putting out hundreds of kilowatts at the very least, and if it's a true combat-capable ship, probably hundreds of megawatts. It doesn't matter how many layers you use on your mirrors; you'll still either have hot backsides or gigantic unwieldy things that can be spotted from Mars.

Ah, but remember the operating temperature of our stealth ship's radiator is, in fact, the temperature of freezing water. We wouldn't be using the exact Webb solar shield in any case, it's too small. We would use a similar shield upscaled to our kilometer wide radiator.

In any case, it's not a combat ship, any more than a ballistic missile sub or a spy sat is; see above.

I'd interject that none of the numbers you just provided make a particularly good case for stealth, and do a rather good job of making one against it - you have atrociously low acceleration, huge amounts of waste heat, and impractically large radiators that still don't spread it out thin enough to be stealthy. Also, no, nobody on this thread has made a case for stealth in space that isn't full of rather serious holes yet.

I do believe I've filled in those holes-see above.

In any case, it's rather rude to arbitrarily say that each case is full of holes without pointing out those holes, or backing them up with sufficient math.

But:

Even if you don't do that, I'd recommend reading that page. It does pretty exhaustively cover the arguments for stealth in space, and if you find anything you disagree with in their reasoning, Atomic Rockets makes it sound like you might be able to get them to explain it to you better than anyone here could.

If you do have an idea that would actually work, though, please share it over there, because it would be pretty cool if stealth in space were a thing.

I think I will, then!

Edited April 3, 2015 by meve12

[Dausuul]

If the crew is at normal human temps inside (20 degrees), then the ship itself is that temp, and visible.

I refer you to a weird technobabble device called a "thermos." Yeah, I know, totally violates thermodynamics. It's physically impossible to carry a container of hot coffee without burning your fingers. Can't be done.

This is why I find the "STEALTH IN SPACE IS IMPOSSIBLE" arguments hard to credit. It may well be that the engineering problems involved make stealth impractical. But the naysayers feel it necessary to resort to absurdities like the above. Really? It's physically impossible to keep a ship from radiating IR for the duration of a mission? Hogwash. You don't have to be stealthy till the end of time--just long enough to get where you need to go and do what you need to do. As long as you can keep the outer hull cool and shunt your waste heat into an internal sink, and finish the mission before the heat sink warms up, you're good. Then you can sit there happily radiating IR all over the wreckage of your hapless enemy.

As I said, this may turn out to be impractical, or may be practical only for unmanned ships and/or short missions. Fine. That's a reasonable debate to have. But impossible? Come on.

[Scotius]

If you want to go somewhere fast in space, you must burn a lot of energy. Lots of energy = lots of heat to disperse or contain inside heatsinks. Besides, if someone noticed your ship accelerating on high-energy trajectory, he will most likely be able to calculate where you're going anyway - and how much time it will take you. Cue enemy ship(s) waiting for you with weapons armed. Of course you will detect them, but to avoid the ambush you will be forced to burn even more fuel\energy et ceatera, et ceatera.

[tater]

I refer you to a weird technobabble device called a "thermos." Yeah, I know, totally violates thermodynamics. It's physically impossible to carry a container of hot coffee without burning your fingers. Can't be done.

This is why I find the "STEALTH IN SPACE IS IMPOSSIBLE" arguments hard to credit. It may well be that the engineering problems involved make stealth impractical. But the naysayers feel it necessary to resort to absurdities like the above. Really? It's physically impossible to keep a ship from radiating IR for the duration of a mission? Hogwash. You don't have to be stealthy till the end of time--just long enough to get where you need to go and do what you need to do. As long as you can keep the outer hull cool and shunt your waste heat into an internal sink, and finish the mission before the heat sink warms up, you're good. Then you can sit there happily radiating IR all over the wreckage of your hapless enemy.

As I said, this may turn out to be impractical, or may be practical only for unmanned ships and/or short missions. Fine. That's a reasonable debate to have. But impossible? Come on.

You cannot keep the ship from radiating IR, period. Failure to do so cooks the crew, period. How do you radiate inside, exactly? That's where the heat already is.

The only reason FOR stealth is presumably war, right? Your spacecraft cannot be moving fast, as that would take a visible burn. As a result, the weapon is not a KE weapon. Any directed energy weapon requires massive power inputs… all of which power, must be radiated. All. Megajoules per cm^2 worth for directed energy weapons. This has been beaten to death by space warfare gaming geeks for ages on the net, very possibly since before you were born (we had long discussions about it on USENET in the 1980s, back when the ante to be on the net at all was to be in science or engineering at the university level). The answer has not changed.

Edited May 28, 2015 by tater

[SciMan]

It's impossible to be invisible in the IR spectrum in all directions with current technology.

However, stealth isn't about being invisible! It's about appearing the same, without being the same.

Invisible is impossible, stealthy is NOT impossible. Of course, it imposes severe design constraints.

Here's an unconventional approach to being stealthy in space. Optimize for low power usage, and build the weapons into an asteroid in the asteroid belt.

If you don't use a lot of power, you don't radiate a lot of power, and a few extra watts radiated from the entire surface of a mid-size asteroid is probably within sensor noise margins.

All asteroids are heated by the sun, so we don't even need to cool down to the cosmic microwave background. That's a very large haystack to find a hay shaped, hay sized, hay colored, very nearly hay temperature, needle.

Missiles are a good weapon choice, because you can design them to have all the "hot stuff" (like guidance, tracking, and propulsion) in the missile itself, pushed out the launch tube by cold gas like a torpedo, only firing up its own propulsion once well clear of the launcher.

So, if you put a battery of cold-launched fully internally-guided missiles on an asteroid in the main belt, its hard to find it until it's already launched its missiles.

But you can't make the missiles themselves stealthy.

[oriramikad]

But you can't make the missiles themselves stealthy.

Supercooled coilgun slugs, mebbe? o_O

Edited May 27, 2015 by oriramikad