Stealth in space

[jrphilps]

This is a topic that may or may not have been covered already, but since I couldn't find any direct hints of it, I'll take a chance and post it anyway. Some of you have undoubtedly seen this page at the atomic rocket website, and been sorely disappointed by what you read. Back in the day, I was a fan of the stealth warship archetype that was defined by the USS sulaco. When I read that page several years ago, I couldn't believe that something as weak the space shuttles OMS engines (which have a thrust of just 26,700 newtons) could be detected past the orbit of mars! This didn't seem intuitively possible to me, so I pushed it out of my mind.

Recently, though, I've started to look back on this topic and realize that I brushed it aside too quickly. The ability to detect the exhaust plume of a rocket at tens or hundreds of millions of km with an infrared telescope is a major problem if nations are ever planning to wage war in space. I looked at "]the math by john schilling which claims to prove this, and discovered that a 2 meter IR telescope is so sensitive, it can detect a single RCS on the space shuttle firing at a range of 15 million km. I don't have the talent to verify whether this is true or not, but again, it seems pretty unbelievable!

One thing thats not clear is whether john is referring to the primary RCS (thrust of 3870 newtons) or the vernier RCS (thrust of 106 newtons). Does anyone know the math behind how infrared telescopes work? Is it just a linear equation, I.E, you half the heat signature and decrease the detection range by half, or is it something more complex? Also, would using a very cold jet of gas forced out by mechanical pressure be more stealthy than a chemical rocket using superheated propellent? I will appreciate any answers you can give!

Edited March 29, 2015 by jrphilps

[VirtualCLD]

IR light follows the same maxwell equations as visible light. It just has a longer wavelength. Therefore there are a lot of similarities with visible optics, but there's a lot of gotchas. In visible, you tend to spot objects based on reflections from a light source (such as the sun). In IR, everything emits lights, so you are looking for the light source itself. Since everything emits lights, your telescope focal plane is typically cooled... cryogenically. Sometimes parts of the optics themselves have to be cooled to, so as not to "blind" your camera (equivalent to visible optics that have black parts where you don't want to see light reflections).

All that being said, both visible and IR sensors can be very sensitive. So the slightest change in signal, be it visible light or temperature, can be detected.

[Jovus]

Just spitballing from the WISE specs, but that sounds about right.

Stealth in space would involve hiding behind other bodies and blowing up enemy detectors, not designing ships that can't be seen. Though to be frank, I doubt stealth will be much used if we ever have fusion torch battles. (As opposed to some FTL or other science fantasy paradigm, which of course can't at all be predicted.)

[Kibble]

Without assuming crazy future technology, spacecraft will bee exactly as stealthy as minor planets. They have a lot of things in common - they're small, dark, pretty cold, and on unpredictable unstable orbits.

[jrphilps]

Just spitballing from the WISE specs, but that sounds about right.

So you can confirm that the 15 million km detection range is accurate? If so, which of the shuttles reaction control system was john schilling referring to, the primary RCS or vernier RCS? Theres a big difference between the two.

Stealth in space would involve hiding behind other bodies and blowing up enemy detectors, not designing ships that can't be seen. Though to be frank, I doubt stealth will be much used if we ever have fusion torch battles. (As opposed to some FTL or other science fantasy paradigm, which of course can't at all be predicted.)

Thats why we need more exact figures on how sensitive the IR telescopes are. If they can detect the vernier RCS at that distance, then all attempts at stealth are pretty much screwed. But if its just the primary RCS they can detect, you might have some wiggle room. In theory, your ships could use small chemical engines to burn for a long time and then coast, without being detected. The only way for an astromilitary to counter this would be to field literally thousands of space telescopes like WISE. The inner solar system has a radius of 450 billion meters, and a volume of 3.82 × 10 35 meters. Thats quite alot of space to cover.

[meve12]

I don't know the mathematics, but...

The basic problem is that since you always have too much waste heat, and the only way to get rid of it in a vacuum is to radiate it as IR light, you end up being an IR emitter with a non-emitting background, with little to no clutter to sort through. If the enemy has IR telescopes that are any good, you're definitely going to get spotted at some distance even without the engine.

That being said, how close you can get and not get spotted can make all the difference, especially if there's any bodies you can make a burn behind. Don't need to close within a kilometer if you've got megawatt lasers, see? Or reasonably fast missiles or boarding shuttles.

[DaveofDefeat]

Thanks to black body radiation, stealth in space is impossible. Just like warfare today, it will come down to who spots who first. That is barring some crazy technology.

Also just a gripe about the whole hiding behind planets and stuff. To hide behind a planet you would already need to know pretty much exactly where the enemy is in order to determine where behind the planet is, and if you know that you would probably be better off blowing him up.

Edited March 29, 2015 by DaveofDefeat

[Nibb31]

What would be the purpose of stealth in space anyway? The distances are so huge and the travel times are so long that a surprise attack hardly makes sense anyway.

[Scotius]

Spying missions perhaps. Either by a fly-by of small independent craft, or by covertly placing a spy-sat at your enemy doorstep. It could be done (probably) by preparing a stone half-sphere looking like a small asteroid, with fake impact pockmarks etc. All equipment generating heat would be concealed behind the stone cover. This satellite would need some sort of control authority to always keep the stone facing the target and a narrow beam laser communicator sending packets of data only during the periods when beam would be impossible to detect. When placed in exotic enough orbit, such satellite could be pretty hard to detect. After all, we do not track all small space boulders in Earth's vicinity. Until we actually decide we need to actively looks for such obiects, then it's only a matter of time and luck.

[Pixel of Life]

*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.

Edited March 29, 2015 by CaptainKorhonen

[magnemoe]

Without assuming crazy future technology, spacecraft will bee exactly as stealthy as minor planets. They have a lot of things in common - they're small, dark, pretty cold, and on unpredictable unstable orbits.

Unless then under trust, remember its multiple level of stealth/ camouflage. You have tactical stealth where you tries to get as close to enemy as possible before getting detected, this will be very hard and you can forget trusting. Then you have strategic camouflage here you want to hide something far away and you can use various tricks as burning then behind a body. Say you are at Mars and want to reach earth without showing that you are underway to earth.

[lajoswinkler]

The only way I see it would be to pump the heat from the part of the ship facing the enemy and radiating it in opposite direction. Crazy insulators wouldn't work for long - heat creeping is unstoppable. You'd need a system which would keep your enemy-facing side at background temperature of the space.

[maltesh]

Unless then under trust, remember its multiple level of stealth/ camouflage. You have tactical stealth where you tries to get as close to enemy as possible before getting detected, this will be very hard and you can forget trusting. Then you have strategic camouflage here you want to hide something far away and you can use various tricks as burning then behind a body. Say you are at Mars and want to reach earth without showing that you are underway to earth.

Only really works if /everyone/ you're planning to go after, and all their satellites, and all their allies are sitting on Earth.

If there's a sufficient space population in the Solar System that /having/ a warship at Mars is feasible, /and/ you're not operating under various sci-fi genre conventions, you have to assume that someone, somewhere, either on Mars or elsewhere in the solar system is going to be sufficiently motivated and in the right position to see the burn you've gone through the trouble of hiding from Earth.

Rocks also generally do not race from one planet to another at speeds exceeding solar escape velocity, so if you are pretending to be a rock, you're going to have to pretend to be a rock for a long time, with all the cooling problems that entails.

Your best bet is to not pretend to be a rock, but to pretend to be a spacecraft of a different type that has a legitimate (or at least plausible and distracting) reason to be doing what your spacecraft just did.

[Technical Ben]

Is there a sailing analogue to this (avoiding subs for the obvious reason)?

We would only be able to hind behind local obstacles, and use extreme distances on occasion. Perhaps burning while behind the moon? But then you'd need to hope no satellites in other positions or base stations on the moon can see you.

[Scotius]

Stealth on sea =\= stealth in space. Seagoing warship can have its radar profile decreased, noise generating equipment sound-proofed. Magnetic field neutralised by demagnetisation of the hull. It can be painted in camouflage pattern, and in extreme cases partially submerged. And yet all those measures only delay detection - which is critical to the mission anyway. The moment one of the ships will open fire, it will be detected immediately. First side scoring a solid hit will win anyway, because modern warships are rather fragile.

Space is much more unforgiving environment. There is not many places where you can actually hide, and if there are any in vicinity, you can be sure they will be watched by the enemy 24\7. You can go to great lenghts to appear as a inert rock - but the moment you need to move you will be detected.

[Bill Phil]

There is stealth in space. Just not in the normal way...

If you minimize the heat given off to what an asteroid has, than it looks like a chunk of rock.

Plus, you can use pressurized gas. Or just burn near very hot celestial bodies...

The usefullness isn't all that much in the end, though.

Edited March 29, 2015 by Bill Phil

[Kibble]

It's also worth noting that infrared space telescopes can't look in the vicinity of very bright objects, or else they blast thru their liquid helium supply and burn out their optics. Remember WIRE!

But discussions of stealth in space always end up very vague and strawman-y, because people don't agree upon (or even discuss) the nature and strategy of space combat.

[sta7ic_matt]

I can think of four common ways to track space objects: visually, with radar, thermographicly, and gravitationally.

Visual: If it's not black, it reflects light. If it's black, it'll absorb sunlight, making it invisible to telescopes, but will both "look hot" and require dedicated cooling systems.

Radar: The classic, with all the usual modern stealth technologies being applicable.

Thermographically: Paint it white and avoid 'hot' propulsion (ie everything but pressurized air), to minimize black-body radiation and thermal spikes.

Gravitationally: If it's big enough, it'll perturb the orbits of other objects. If it's big enough to perturb other objects, "stealth" is something of a joke.

I want to mention that the STS's RCS units were hypergolic AJ10 thrusters, which means that the bi-propellant combination immediately reacted upon mixing in the combustion chamber. "Visible from Mars" wouldn't surprise me much.

[Bill Phil]

Actually, those AJ10s were the OMS engines. Not RCS.

[GreenWolf]

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.

Seriously, this topic is has been beaten to death so much that it's not even a corpse anymore.

[DaveofDefeat]

The only way I see it would be to pump the heat from the part of the ship facing the enemy and radiating it in opposite direction. Crazy insulators wouldn't work for long - heat creeping is unstoppable. You'd need a system which would keep your enemy-facing side at background temperature of the space.

That still means you would have to know the general location of the enemy, which limits its effectiveness.

[lajoswinkler]

That still means you would have to know the general location of the enemy, which limits its effectiveness.

At least you could use it to come close to the enemy which location you know, but as soon someone comes around, they will see the glow.

[jrphilps]

*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.

If you are launching warships from a space station, it might be possible for the base to offer some concealment: When the ships initiate a burn and head out to their objective, the station could use some kind of broad spectrum IR back lighting to disguise the ships engine exhaust. The people watching via telescope would know that ships had been launched, but they wouldn't know how many or where they were going.

Another interesting possibility: If you equip warships with a photon sail, you could use the stations lasers to boost them to their target without being detected. There might be some waste heat released by the beams interaction with the sail, but probably not enough to pick up via IR telescope.

[Scotius]

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.

Seriously, this topic is has been beaten to death so much that it's not even a corpse anymore.

But such brainstorming is fun Even if we only reaffirm that stealth in space is impossible, we will have used our imagination for a bit, someone will learn something new. That will be a positive outcome from a negative outcome Sorry, it's 5 in the morning and i'm still finishing my first cup of wakey-juice

[Slam_Jones]

Obviously you just strap an Alcubierre device onto anything you want to move. No exhaust!

(I think. I really don't know much about the Alcubierre)