Stealth in space

[KerikBalm]

I read that post. Drifting in from another system seems pretty absurd, the great, great grandchildren of the "attacker" would be interested to discover the result, except they won't know, either, unless they send a craft for BDA, and maybe their GGGG grandchildren can find out.

Time dialation from relativistic speeds, cryostasis, etc.

Even if the journey is long , lets assume both ships were going at the same speed, and departed very close in time...

If ships have FTL, they need not contain themselves to the ecliptic, they can FTL out of plane, then use normal space if stealth were considered a thing (if you consider it real, then all reasonable countermeasures will also become a thing, so there will be sensors scattered all around, etc).

FTL involved even more handwavium... it allows time travel. If you can time travel, just detect your enemy and be detected by your enemy. Then before the battle starts, go back in time using your FTL, and have knowledge of where the enemy is without the enemy knowing where you are...

Unles the enemy uses FTL time travel too... and .... yea.... lets not introduce FTL to the situation.

Or if you have FTL that doesn't allow for time travel (but it would.... but lets say your sci fi universe has some limitation to prevent that).

"jump" In at 1 AU, detect your enemy...

You have 8 minutes 10 seconds until the enemy sees you.

You jump again to 0.1 AU away - you fire your hard X-ray laser.

The enemy is destroyed 49 seconds later, never having detected you.

-Sure your SF universe could prevent this with FTL sensors that detect the jumps... but if your sci-fi universe doesn't have such sensors, then stealth is allowed (like a ship jumps in to subspace/hyperspace to do FTL, and you would need a sensor in hyper/sub space to detect this - and the quarry ship is out of hyper/subspace, and won't detect the jump until the energy from that jump reaches it... 8 minutes after the jump)

A hard x-ray laser? What is pumping it, a bomb? If it is a reactor… all that energy has to be radiated.

Yup, which would be why you'd want your first strike to be all that you need.... you'd run into a wall very fast where your ship is all heat sinks and radiators and cooling equipment, and this super-laser is tiny in comparison.

You really have to jump through hoops to try and justify any sort of stealth in space, even in special cases. For what people think of generally as SF combat (we will assume FTL drive as the sole conscious attempt to violate physics), we have to have warships appearing in system, then finding the enemy (who is now also magically stealthy), maneuvering without being seen (impossible), etc.

Yes, I agree completely.

As I said, it is not absolutely impossible in all cases. In certain limited scenarios, it could work, yet still be very impractical.

Cloaked ships of startrek... F-117's over baghdad.... that sort of stealth... not going to happen.

More like a sniper in a ghillie suit that is revealed after firing.

Instead of a ghillie suit... you've got a supercooled facade, and directional radiators.

One of the guys we hashed this out with around 20 years ago is an IR astronomer (at the time he was at Mauna Kea). Even a comfortable crew compartment is a relatively bright IR source for an early 1990s IR telescope. He did the math on reasonable (current at the time) telescope systems, and whole sky surveys capable of detecting "player" sized starships were easy to do, as they could be very wide field. If the ship was actually powered up, it was "naked eye" visible in magnitude (except in IR) at a vast range.

We did this because we actually wanted stealth to work, but it just doesn't. With a lot of hand-wavium, we managed to get some sensor rules for a space combat game that allowed some mitigation of otherwise automatic detection at great range. At any sort of tactical range… all ships are easily visible.

Yea... but again, that's assuming radiation in all directions... presenting a supercooled side to Earth would block it.

Again, I'd stress that for a nitty-gritty discussion, you really need to nail down the specifics of the SF universe people are dealing with so we are all on the same page. If it is Earth vs Mars using nothing we don;t have now, that is different than having a space warship using FTL drive to go to a nearby system to attack.

Yes, it very much does matter what the situation is....

If we go to a SF universe that diverges from our own history back in the 70's... the USSR never collapses, both sides aggressively explore space in an extended cold war... probes are scattered all over the solar system, much the way sonobouys are to track submarines, etc... then there is no way to hide.

If you instead posit some alien spacecraft arrived in our solar system a century ago, and currently has a colony/base on a kuiper belt object (lets presume its core has enough heavier elements to support some manufacturing)... well then probes doing flyby's of Earth, stayng hidden using directional radiators... or just disguised as space debris, etc don't seem so far fetched (from a physics standpoint).

They could then do a lot of things without being detected by us, if they are willing to wait a long time (I'm assuming interstellar travel without FTL, so I'll assume that they are willing to wait).

Impractical/unworkable in most scenarios? Yes

Strictly impossible? No

Edited May 29, 2015 by KerikBalm

[tater]

Still, any stealth is functionally a special case. In a universe of initial starting conditions for a fight, stealth would be an exceedingly rare accident

Directional radiators cannot be a go-to answer, however. If that is the only made up tech (with supercooling the opposite side). You are still required to know the location of all enemy sensors. If this is our given, any enemy that you need worry about will simply throw passive sensors all around the system. The countermeasures are simply too easy, and stealth stops being a thing even if in special cases it is possible. Our aggressor appears, and is spotted on the hot side however many light seconds away the nearest sensor is on that side. That sensor likely gets spotted, but not before it sends a warning. If that sensor is a weapons system, the fight might be over as the x-Rays hit the target as the warning simultaneously flys by to "home." That's aside from the energy increase needed to actively cool one side.

If the enemy is not that advanced, you don't need stealth.

If relativistic flight is possible, stealth is the least of the target world's problems assuming a "total war" paradigm.

Edited May 30, 2015 by tater

[DerekL1963]

To detect something at this distance your field of view should be very narrow. I'm not saying that this is 100% reliable, but imagine I launch 2 thermonuclear warheads like this:

These two blasts will give me at least some time.

(Image snipped)

No, not really. 99.99% of the effects usually associated with a nuclear weapon are the result of the interaction between the energy released by the bomb and the surrounding environment (atmosphere, water, earth) or with the Earth's magnetosphere. In free space, none of these things are present. You'll get a flash maybe a few dozen nanoseconds long (with the peak being a dozen or two at best, rising and falling very sharply) as the energy released (mostly in the form of gamma rays and hard x-rays traveling at the speed of light) travel through the bomb debris (the physical remnants of the explosives in the primary, the weapons case, plus the delivery vehicle) and then it'll all be over. You could stare right at it with the naked eye from a dozen kilometers away and you'd never notice it. (Though you'd want to be further away or heavily shielded to escape the effects of prompt radiation.)

[Windspren]

What about ion engines?

[luizopiloto]

Thermonuclear weapons are not very effective in space vacuum, as they needs air to increase fission power and create a shockwave... Unless you make it explode inside the enemy ship...

Lasers are the best choice for attack weapons... And to lure enemies, Solid Rocket Fuel. It can burn for longer time...

[Wesreidau]

Thermonuclear weapon are perfectly effective in a vacuum, since they emit huge amounts of energy in x-rays.

[tater]

Or just kinetic energy, though lasers basically cannot miss within some large range.

- - - Updated - - -

Thermonuclear weapon are perfectly effective in a vacuum, since they emit huge amounts of energy in x-rays.

Huge by manmade standards. Small by astronomical standards. Nukes in space are little more useful than a slug. They have an area of effect, but it is tiny, if you can get an H-bomb close enough to damage a warship (that must be hardened for ambient space radiation threats), you might as well just hit it with a rock.

At 1 km from detonation, a 1MT bomb deposits ~1 megajoule of energy per square meter. Penetrating steel takes ~1-2 MJ/cm^2. That's about 1000x the insolation at earth. But the insolation at earth is ~1300J/m^2 every second. So 16 minutes in orbit worth of warming the hull. Meh.

If the detonation takes place at 5km? 8022 joules per meter. That's less than solar radiation at Mercury.

Edited May 30, 2015 by tater

[Wesreidau]

Modern air-to-air or surface-to-air missiles are not designed for skin-to-skin kills but proximity detonations, which are far easier to manage and spread the damage across more of the target. Hitting a ship with a rock sounds nice, assuming you hit the ship, but if a missile is about to miss by a kilometer it still can provide crippling damage. Achieve near-skin detonation and the ship is out-and-out vaporized.

Of course, those air-to-air missiles focus their explosive potential in ring of titanium rods to maximize the chance of a kill. To maximize the nuclear warhead, one makes it a nuclear shaped charge. These were examined in the 60's as the solution to problems in the Orion project and research persisted long after Orion itself was abandoned. Most of the details remain classified, save that they create core-of-the-sun hot spears of plasma moving at 3% of C, and that it would be quite simple to have our missile point toward the target and detonate once its nuclear directed-energy weapon warhead was in range.

[tater]

Like nuke-pumped x-ray lasers which SDI looked into as well. Yes. You said thermonuclear weapons were perfectly effective in a vacuum, however, which they are not even a little. They require specialized treatment, and need to point at the target, they are not area effect weapons. Throwing a rock was a joke (and a Heinlein reference). KE weapons would detonate a substantial distance from the target, and blanket the target area with shrapnel. Damage would depend upon the closing velocity, which varies depending on what sort of SF universe we are talking about, obviously. Fusion torch ships could easily be closing at 30+ km/s. Still, a proximity detonation, though perhaps many 1000s of km away (spread the ball bearings out such that there is a reasonable chance that a few hit a target of some cross sectional area).

[Wesreidau]

A kinetic-kill weapon can also be nuclear.

Velocities achievable with thermonuclear shaped charges are impressive. Unlike molten jets produced by conventional shaped charges, which are limited to about 10 kilometers per second (about four times the velocities of the gases resulting from chemical explosions), thermonuclear shaped charges can in principle propel matter more than two orders of magnitude faster. Since fusion temperatures reach 100 million K, the detonation front of a thermonuclear explosive travels at speeds in excess of 1,000 kilometers per second. Using a convergent conical thermonuclear bum-wave with a suitable liner, one could theoretically create a jet traveling at 10,000 kilometers per second, or 3 percent of the speed of light.

Perfectly effective.

[tater]

Your post didn't say nuke pumped x-ray lasers or plasma weapons. You said "thermonuclear weapons." This is becoming merely semantic, but the implication of the first post was nukes in general, not directed energy weapons pumped by nukes (plasma weapons are basically directed energy, as are particle beams). Regardless, for some readers at large here it might be instructive to be disabused of the idea that nuclear weapons need only detonate some distance from a target to be dangerous (which was certainly the context of the post right before yours).

What's the range of the plasma jet before it disperses, BTW?

A skin hit would be nasty regardless of nuke, plasma, or a the dead mass of a missile closing at 30km/s

The point with any intercept weapon is that the target cannot avoid being hit once the incoming weapon is within some range. If you can get within a few km, you can probably actually hit the target. The question with nukes becomes if it is worth the hassle of storing nuclear weapons if the same mass of nothing (or ball bearings) would result in a mission kill just as often. There might still be a stigma attached to nukes as well, dunno.

[Wesreidau]

A fourth-generation nuclear weapon is still a nuclear weapon. Since you are loading mass onto your ship, one may as well make that mass as potent as possible. And I can't tell you the range of the plasma jet. I see "two thousand kilometers" thrown around, and fractions of a radian. The program was never declassified after fifty years.

[Shpaget]

Why don't we look at the existing anti satellite weapons?

In the 1950s US did a test where they "intercepted" a satellite in LEO. The missile passed 4 km from the sat which, according to wikipedia is enough to disable it with a nuke.

More recently (2007), China successfully performed a destruction of a sat in a 860 km polar orbit with a kinetic projectile in a head on collision. I must say that is pretty impressive. Granted, that particular satellite didn't try to evade the collision and was a sitting duck, if being a tiny target and moving at thousands of km per second can be called being a sitting duck, impressive still.

[Heimdall5008]

Maybe to return to the stealth discussion...

I once read a sci fi book were capital war ships used a meter thick ice armor (you can grow it in space, "heal" it easily, it is reallatively light). In normal operations they actively cooled the armor to sustain it against the heat of the ship and used big radiators to bleed of the heat. But they could also use a stealth mode (for a limited amount of time) where they started to melt the inside of the ice to dispense their heat. The outside of the ice armor would stay at space temperatures for quite some time.

[GreeningGalaxy]

*Insert obligatory Elite: Dangerous comment here*

No, seriously, could the heat sink launcher thing could actually work? If you could cool the craft's hull enough, I doubt the telescope would be able to tell whether it's a spacecraft or not by just looking at the exhaust, especially if you managed to make the exhaust "cold" by using some form of electric propulsion. The hot heatsinks floating in space around the craft would make it even more difficult to detect it.

No, they wouldn't, they would make it far easier to detect you. The heatsinks would all be very close to you when they first appeared on the enemy's scopes (which you can bet they would, being as hot as they are), and no matter how fast you fired them, they'd stick around close to you when viewed from a long distance away. Worse still, after watching multiple launches, your enemy would be able to put together a great picture of exactly how fast your supposedly-stealthy ship is moving, and how much speed it's getting from each heatsink shot, thus revealing your mass and ship class. Plus, heatsinks are necessarily pretty heavy, which is going to make your ship either low in delta-V and acceleration or absolutely gigantic. Or both.

I once read a sci fi book were capital war ships used a meter thick ice armor (you can grow it in space, "heal" it easily, it is reallatively light). In normal operations they actively cooled the armor to sustain it against the heat of the ship and used big radiators to bleed of the heat. But they could also use a stealth mode (for a limited amount of time) where they started to melt the inside of the ice to dispense their heat. The outside of the ice armor would stay at space temperatures for quite some time.

Doubt it. Ice may seem cold, but it's still not as cold as the cosmic background by a longshot, and once you start melting it from one side, the other side is going to glow bright enough to see on an infrared telescope of the kind your enemy will be carrying. Ice isn't a superb conductor of heat, but it's also not that great an insulator, at least not enough for these purposes.

Ice also makes terrible, terrible armor because it has horrid flex strength and is very heavy, but I guess it could be sort of useful against interplanetary dust if you're planning on staying out a while.

Edited May 30, 2015 by GreeningGalaxy

[tater]

A fourth-generation nuclear weapon is still a nuclear weapon. Since you are loading mass onto your ship, one may as well make that mass as potent as possible. And I can't tell you the range of the plasma jet. I see "two thousand kilometers" thrown around, and fractions of a radian. The program was never declassified after fifty years.

Interesting. Next time I meet a plasma guy at LANL or SNL I'll ask about it (and see if they can answer without having to kill me ).

A couple thousand km is better than having to hit, for sure. Pointing error becomes critical, though. This points out a useful distinction between "stealth" (which is still not a thing ) and confusing specific sensors in certain situations. A missile needs its own sensor suite, and in the case of the nuclear-pumped plasma jet concept this becomes really critical as it is not constantly honing a solution as it approaches, it has to fire at range and hit a target that subtends a small angle. I suppose like the x-ray laser concept, you could design it as a "shotgun" firing multiple jets (or perhaps a mixture of jets and x-ray lasers). Anyway, the ship-mounted sensors might well be considerably more capable than the missile-mounted version (which needs to be cheaper as well), and might be more susceptible to countermeasures as a result (shorter integration times as well). In this regime mitigating your signature might have some benefit, forcing missiles closer before they can detonate. Of course if a missile can hit you at 2000+km, the target ship can easily hit the missile at that same range---or farther. This means missile systems will need to saturate defensive anti-missile systems.

It's all interconnected.

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Maybe to return to the stealth discussion...

Stealth in a meaningful sense is not a thing, period.

We can come up with a few special cases where it might be possible to sneak up on an adversary, but if we are talking about warships moving from A to B in some time frame measured in manageable fractions of a lifetime, then attacking, it is not possible. If you want to posit launching a weapon from another star system, then letting it drift to the target over 10000 years, that's another story.

[UmbralRaptor]

After spending far too long coming to grips with the WISE photometric system, I've come to the conclusion that not only can you see every burn, but you can easily spot hulls in the light-second range, and any radiator that isn't edge-on out to a light-hour or so with a clone of it. A 283 K blackbody 2 m in radius at the distance of the moon (well, 374000 km) is not only bright enough for WISE to spot, but to give you a rough idea of what its hull is made out of. In the warm phase.

https://drive.google.com/file/d/0Bxef3KjILrVrMUtXeFRnaEw1cFk/view?usp=sharing

WISE is a 0.4 m IR telescope in a sun-synchronous orbit that ran out of coolant back in 2010. The NEOWISE program uses the W1 (3.4 μm) and W2 (4.6 μm) passbands only. It uses passive cooling (sunshield plus pointing away from both the sun and earth) to get down to around 73-77 K. The W1 and W2 bands use 7.7 second exposures, though the system as a whole has an 11 second cycle for imaging. Images appear to be 1024x1024 at 2.75"/pix (47 arcminutes wide), with a resolution of ~6". (Confusingly, Atlas files are listed as 1.375"/pixel.) The limited field of view is actually the biggest problem, as it suggests that getting all-sky coverage will take at least 8.58 days with no overlap and 103 days with each point imaged 12 times as initially planned. Not that WISE entirely pulled that off...

The NEOWISE Single-exposure photometric measurements of point sources in unconfused regions have SNR=10 at W1=15.0 and W2=13.5 mag. If you just want detections, 90% completeness is achieved for NEOWISE Single-exposure detections in unconfused regions at W1=15.9 mag and W2=14.4 mag. (combined W1 and W2 SNR>3). (The spreadsheet defaults to assuming you want the photometry values, but that is easily changed.) The largest problems are bright backgrounds (being in the ecliptic and especially in the galactic plane hurt sensitivity. Ditto being near bright stars/planets)!

Relevant bits for breaking out of WISE's Vega magnitudes to Jy*Hz:

http://wise2.ipac.caltech.edu/docs/release/allsky/expsup/sec4_4h.html

http://wise2.ipac.caltech.edu/docs/release/allsky/expsup/figures/sec4_4ht2.gif

http://wise2.ipac.caltech.edu/docs/release/allsky/expsup/figures/sec4_4ht9.gif

I ended up getting object emissions for those temperatures (assuming 4800 K for K2V and 5780 K for G2K) via integrating Planck's Law with the bandwidth figures centered on 3.4 and 4.6 μm respectively. This may have been overly narrow. Assuming spherical cows emitters, lots of things cancel so at the detection limit, object radius is directly proportional to its distance. See the attached spreadsheet for my calculations.

Incidentally, WISE's catalog of astronomical objects is over half a billion, and NEOWISE detected over 10 thousand objects in its first year.

But all of this analysis is for a semi-broken spacecraft on a distinctly limited budget. Your space navy may well face HST/KH-11 class telescopes (2.4 m) with better detector band choices and lack WISE's bugs. So all those numbers can easily go 100x fainter. WISE can't see craft (aside from larger exhaust plumes) at Jupiter, but these would. And if you can get good enough detections of a craft's hull, you can do photometry to spot the difference between whatever its using and a rock. Which makes playing asteroid that much more problematic.

Edited May 31, 2015 by UmbralRaptor

[DerekL1963]

But all of this analysis is for a semi-broken spacecraft on a distinctly limited budget. Your space navy may well face HST/KH-11 class telescopes (2.4 m) with better detector band choices and lack WISE's bugs. So all those numbers can easily go 100x fainter. WISE can't see craft (aside from larger exhaust plumes) at Jupiter, but these would.

Your space Navy may well face such birds *at* Jupiter - and Mars, and Earth, and in carefully chosen Solar orbits. If you've got the money and technology to build a significant space Navy, the cost a fleet of a couple three dozen detector birds is essentially in the rounding error.

[tater]

I think that the Voyager RTGs are likely theoretically detectable now with an IR telescope and they are both more than 100 AU away. And tiny. At that scale size, what current telescopes really lack for this task is resolution because of the tiny size of the target. Of course resolution goes with aperture, and so does light gathering.