[c914]

However, as was said earlier, stealth is always a relative term and I still say it would be possible to operate secretly within hostile space, with certain limitations, because no one is ever going to have arbitrarily good sensors.

I would add to this position of your ship and observer to system star and activity of that sun. Also how good observer knows star system and space object in it.

[Scotty]

Let me put it this way. The Ocean is a vast place and turbulent place, but it's possible to give an orbital satellite enough resolution to pick up the algae thrown up in the wake of a submarine and to track it's movement (despite being underwater).

And look once again at the relative ranges here.  A satellite orbits, call it 200 miles above the Earth.  The algae wake of a submarine is several kilometers long.

Not move the satellite 150 million kilometers out of the way and reduce the size of the target.

The longer you accelerate the longer the interval of time that the enemy has to detect you. Also you forget that going someplace in space requires you to stop as well which means you will be decelerating for an equally long time. Or maybe you just want to pass through the system, but if you're scouting that means you don't know what's there so you're throwing  yourself across a system hoping that you don't fly right into the enemy. (ie usually you're tracking his fleet movements and his fleet could be off doing who knows what. Patrols, wargames, logistic transport, etcetera). Of course space is big, you're unlikely to fly right through his formation but you don't necessarily have to.

In order:  Yes.  Yes, however, stopping at close range is not necessarily your goal; once again, space is flippin' HUGE.  Again, the odds of you flying into an enemy fleet in one of the 14 HEPTILLION cubic kilometers in one AU is so astronomical my calculator (TI-84) overflows with the numbers before it gets to it (past 9.99 x 10⁹⁹). 

Ships will still radiate excess heat and they will still use reaction drives.

1) yes, but maybe more effectively than you think.  Think aircraft.  Some of them are really hard to get a good look at on radar and manage to pass themselves off as BIRD SIZED.  What makes you think a spaceship won't be able to do the same thing, but as a bit of debris or as a sensor "ghost" instead?
2) You think so.  We have no real idea.  Maybe we'll have gravitic drives by then.  No one knows.

Main disadvantage for the same ship: They can only use passive sensors in order to not give their position away, and have also limited means of communication. On the other hand the other side can use active sensors (radar mainly) to locate objects in space.

I think something we're missing is the necessarily long-term missions that would go on, since accelerating too fast would be a Bad Thing.  We could be talking weeks without communications, almost like navies back before telegraphs.

I would go further, ans say that the smaller object is a sewing needle.

[NGTM-1R]

Let me put it this way. The Ocean is a vast place and turbulent place, but it's possible to give an orbital satellite enough resolution to pick up the algae thrown up in the wake of a submarine and to track it's movement (despite being underwater).

I assume you can prove this, because AFAIK non-acoustic ASW is, was, and forever shall be a load of crap.

[The E]

I think I read something like this in a Tom Clancy novel once.

Now, detecting a surface ship via its algae wake, that's certainly possible, but submarines?

[Thaeris]

Let me put it this way. The Ocean is a vast place and turbulent place, but it's possible to give an orbital satellite enough resolution to pick up the algae thrown up in the wake of a submarine and to track it's movement (despite being underwater).

I assume you can prove this, because AFAIK non-acoustic ASW is, was, and forever shall be a load of crap.

Well, the surface of the water the submarine is beneath will bulge a little... Detecting that in a rolling ocean, however, will not happen as far as I can tell.

[General Battuta]

Let me put it this way. The Ocean is a vast place and turbulent place, but it's possible to give an orbital satellite enough resolution to pick up the algae thrown up in the wake of a submarine and to track it's movement (despite being underwater).

I assume you can prove this, because AFAIK non-acoustic ASW is, was, and forever shall be a load of crap.

Well, the surface of the water the submarine is beneath will bulge a little... Detecting that in a rolling ocean, however, will not happen as far as I can tell.

Seriously? Seriously?

Go fill a bowl with water.

Put a pencil in it.

Do you get a pencil-shaped bulge? Huh?   This is an incompressible medium. It's really hard to produce local topological changes just by displacement.

Now, granted, there's propagation speed to be taken into account when the submarine moves.

[Thaeris]

My friend, you have taken that far out of context...

....Though I will admit that was a tremendously amusing response...

[General Battuta]

I really don't get what you were going for, then.

[NGTM-1R]

What, you mean the ocean will rise detectably because there's a submarine in it? o.0

[Thaeris]

I've seen it noted on several science programs on television before. I believe what I was (rather ignorantly) referencing was the "Bernoulli Hump." Of course, that might be the wrong reference as well. I may need to do a little more research. Here's an interesting site for this discussion:

http://www.behindbluelines.com/2009/07/22/what-is-state-of-the-art-in-submarine-detection/

[NGTM-1R]

I know all about this.

It's not practical. It only works for about 100 feet of depth. On a good day you can see that deep in shallow water with your naked eye. The stuff from '70s patent was pure fantasy. Nothing has really changed in that regard. So you deny everything down to 200 feet these days, maybe. Ultimately MAD is going to be the sensor system that eliminates the submarine if any does.

Acoustic detection and tracking is still king. You look for a Collins or a Gotland not by their noise, but by their lack of noise. (Yes, you can do that, much like you can see a car painted black on a starlit night because it's darker than the background.)

[General Battuta]

I've seen it noted on several science programs on television before. I believe what I was (rather ignorantly) referencing was the "Bernoulli Hump." Of course, that might be the wrong reference as well. I may need to do a little more research. Here's an interesting site for this discussion:

http://www.behindbluelines.com/2009/07/22/what-is-state-of-the-art-in-submarine-detection

The hump will only occur if the submarine is very close to the surface, as NGTM-1R said.

[Flipside]

I seem to recall talk of being able to detect 'knots' in the water caused by a submarine turning? It was developed, iirc, from a technique that was used to avoid torpedos, where a sub would make a sharp turn in the water, and the turbulence it created would confuse the torp?

[Akalabeth Angel]

Let me put it this way. The Ocean is a vast place and turbulent place, but it's possible to give an orbital satellite enough resolution to pick up the algae thrown up in the wake of a submarine and to track it's movement (despite being underwater).

I assume you can prove this, because AFAIK non-acoustic ASW is, was, and forever shall be a load of crap.

8 or 10 years ago a Canadian Firm was launching some sort of satellite but the US Government was like "no, it's too good. It can track our submarines" so I think they had to dumb it down a bit to appease the yanks. Or so the news told me.

[TrashMan]

If I have to choose between believing anything written here, or things written at projectrho, I'll go with the latter.

20 guys with degrees beats you guys here (that includes you too Herra, sorry, but quantity does matter too). If they say no stealth in space...then no stealth in space.

[NGTM-1R]

If I have to choose between believing anything written here, or things written at projectrho, I'll go with the latter.

20 guys with degrees beats you guys here (that includes you too Herra, sorry, but quantity does matter too). If they say no stealth in space...then no stealth in space.

Herra brings up issues they don't even address and you just assume they forgot them because they're awesome? wtf kind of logic is that?

[Akalabeth Angel]

Herra brings up issues they don't even address and you just assume they forgot them because they're awesome? wtf kind of logic is that?

I know what forum the two main guys frequent if anyone wants me to relay some counterpoint.

[NGTM-1R]

It's called "field of view". As anyone who's dabbled in astronomy can tell you if you wish to look deep, then you must also look narrow. The more magnification you apply, the less your field of view encompasses. To make matters worse, electronic instruments remain unable to simply look and instantly detect faint objects. (The human eye has them beat all to hell in this regard, amusingly.) Hubble and Chandra have to take long exposures for their shots, the fainter (and distance increases faintness exponentionally) the longer you have to look to detect it with your electronic eyes. (Using even very good 23" amateur equipment, faint objects take twenty or thirty minute exposures. Hubble and Chandra usually take longer ones looking for even fainter objects.) Even allowing for magical future tech, while there's very little possiblity you'd be sneaking up to within realistic shooting range of someone, at interplantary distances there's every reason to believe you could simply not be looked at for hours or even days while they try to sweep the whole sky.

Active sensors like radar are not viable objects for system surveillance due to range gate issues. The AEGIS's SPY-1 could probably get a radar return off the Moon, but by the time the Moon return got back to the receiver it would be arriving simulatanously with returns from other, much closer objects painted by radar pulses sent out much more recently. If you wish to track objects close-in, you must dial up your pulse rate to do so accurately. Slowing it down to the rates you would use to track objects at even mere interplanetary distances is not only impractical, but downright dangerous since someone could launch an attack in the time between your pulses. There are ways to get around this, like "chirp" radars that radiate each pulse on a slightly different frequency so the computer can distingush them, but even then there are limits that keep the range gate well below interplanetary, much less covering a whole solar system.

[Herra Tohtori]

Look, I'm not saying stealth in space is definitely possible or definitely impossible.

I'm just doing the maths in order to determine what kind of sensor equipment you need in order to pick up a ship like this and actually determine it is in fact a clever ruse and not an asteroid.

The requirements are:

-You have a radar system that has already registered and archived the orbits of all legitimate objects within it's range
-is able to scan the area in a reasonable time; this time is the minimum grace time for a stealth ship. No radar system can immediately track the whole sky. If it takes a week to do a full sweep of the space, then it can take up to a week to detect the new object. On average, based on probabilities, it takes three and a half days.


Radar echoes are easy to minimize, however. A system that is able to detect every particle in, say, Saturn's belt would be impressive indeed. There's also places with a lot of junk gathering to them with very chaotic orbits; trojan asteroid zones come to mind first and foremost. Determining these orbits would pretty much require solving +three body problem which is, for current mathemathics, rather impossible. You can get approximations, sure, but you would need arbitrarily small dt (time differential, for not-mathematically inclined) values to really approach the accuracy you need for this kind of thing.

It's also possible to do the Han Solo and simply attach the spy ship on some already existing object. Without getting a good look at the asteroid or comet or whatever the ship attached itself to with good old Mark I, it would be very, very difficult to determine that it's there at all.

Optical detection of one kilometre wide target at 1 AU distance, beyond detecting a point source of radiation of course, would require resolution beyond 0.000689396936 arc-seconds, and again the system has a certain time it needs to sweep the whole sky. It can't do it instantaneously. You can't really fit a fish-eye lense with large enough CCD cell to cover half the sky immediately; even if you could, image analysis would become a problem.

As far as thermal imaging goes, same limitations apply. Sure you can detect a point source of light, but without more detail you can't know what the surface material is and without that, you can't know what the emissivity rates are. Sure, you can get some hints out of spectrum analysis, but that just reveals the element if even that; and element alone can't give you exact knowledge of the surface's emissivity rates which is required in order to accurately determine the surface temperature, which is required to differentiate from non-ship targets. It would most likely be fairly easy to pass between the surface variations of asteroids as far as surface temperature of the ship goes.


However, the further the ship is from the green zone, the more difficult it is to remain hidden, because the average temperature gained from solar heating either drops or rises too low to sustain livable environment and active heating needs to be engaged.

Still, I'm just bringing up all the difficulties in first of all detecting a ship - even a big'un at that - at interplanetary distances. Moreover I'm concentrating on the difficulties on how to determine that a target is actually a ship, especially if it wants to pass off as an asteroid or other naturally occurring target.



Thus far my conclusion is you need insanely good sensor equipment in order to make stealth impossible within any sort of reasonable range. If you want to handwave efficient enough sensors into existence for your scifi universe, sure you can negate the possibility of stealth ships, but you should still remember to limit the range of absolute detection and remember issues like light speed that make simultaneous events not simultaneous at all.

[Ionizd]

Interesting discussion.  Here's my take;

1) It makes no sense to have manned fighters in space.  Providing for the pilot's safety while attempting to maximize maneuverability, acceleration, weapons capacity and spacecraft integrity would be a gross exercise in futility.  Just the environmental factors in space would put the pilots at unreasonable risk, let alone actual combat stresses.  I could certainly see unmanned, remote controlled armed drones with human pilots on nearby carriers connected via VR being much more effective in space ship-to-ship combat.  The fighters would be much more maneuverable and could accelerate/decelerate much more quickly without having to worry about the pilot's physical limits and the added mass necessary for life support, displays and controls.  No cockpit means no structural weaknesses due to the canopy and the required position of the pilot to maximize visibility.  Long range and reconnaissance missions would have to be manned, but larger, faster, lightly armed ships with the following characteristics would be used.

2) Heat signatures can't be masked, but they can be directed away from an enemy by using strategically placed heatsinks and an active heat management system that would radiate heat in the opposite direction.  It's also possible to store heat for short periods of time and radiate it later.  Well insulated hulls and/or cockpit environments would be a necessity for the safety of the crew, and nearby objects could be used to mask thermals effectively.

3) There are better ways of dealing with electromagnetic signatures than simply hiding them.  The real future of stealth technology isn't in minimizing radiation sources and surface area profiles, but in using electronic warfare techniques.  Any electromagnetic wave can be duplicated and emitted 180 degrees out of phase to cancel the original signal out.  Not only that, but it's possible (today our military uses this emerging technology with great success) to mask the original signal and emit a fake signal which will misdirect the enemy to another location kilometers away.  Minimizing radiation sources has its place, but active electronic warfare is much more tactically valuable.

4) Propulsion and thrust doesn't have to be employed in space like it does in an atmosphere.  The reason why atmospheric fighters must always employ forward or downward thrust is because it's used to generate lift and the craft's forward velocity is affected by drag.  In space, drag would be minimized, gravity fields would be minimal or at least distant enough not to immediately present a solid object/instant deceleration  hazard.  Short, high intensity bursts of thrust in the opposite direction of the desired course are all that's required to move an object along in space.  Stealth techniques could employ either tighter burn times or longer, low intensity burns to blend in with background noise would be the order of the day.