Stealth

[BD Cerridwen]

Howdy folks. For the longest time, I've tended towards speed (acceleration) and maneuverability as a ship's best defense. However, here's an argument for Ion Drives.

-> Invisible to Energy Sensors

-> Creates a Radar Window - jamming radar

Taken alone, these should make a ship invisible to the sensors available. But it all depends on how weapons track targets. Are they purely aimed on sensor control or is there a visual tracking element as well? If the second is true, would a black hull coating make targeting, or at least pinpoint targeting, more difficult? What are your opinions - how would you adjudicate this in a game that you referee?

[cliff]

I would think if a ship has cameras that there would also be some visual tracking as well. Painting a ship black would probably help with this, but I think it would reduce or cancel the effects of a reflective hull. I think a gloss black would help maintain some of the reflective hull atributes.

I was wondering myself though, that if you have a reflective hull, is it a mirror finish? if so, then wouldn't reflect your surroundings? making nearly invisible to begin with?

[BD Cerridwen]

Interesting point on the mirror finish, I hadn't considered that.

Of course I don't expect to make the ship invisible, regardless of the hull finish. I just want to make the attackers waste time trying to find it. Assuming that an ion radar window is a sphere with a radius of 5000km, one engine can create 523,333,333,333 cubic km of space to search visually. Even on a two dimensional planar search, that's 78,500,000 square km - for just one engine! Since each additional engine can add another 10,000 km hex to the window, you can multiply these numbers by the number of engines to get the additional amount of space to eyeball.

Given the fact that Energy Sensors cost 200,000cr, one can assume that most ships won't have them. Now if we adapt a Decoy to carry a holographic projector ... Or, to cover all bases, piggy-back a small robotic HS1 ship with an ion drive and a holographic projector ...

[BD Cerridwen]

Hold on a second with the mirrors. If you're in a star system, accelerating towards a jump or decelerating after one, wouldn't the reflective hull still reflect the light of the star, thus making you more visible? I think I'll go back to the black hull.

Oh, and regarding the black hull canceling the reflective hull, yes that's true. Basically my 'stealth' ship would not have the reflective hull defense. However, the cost of it might well be transferred to making the hull low visibility.

[Will]

Of course, any ship can be a stealth ship if it shuts down their engines(after using maneuvering thrusters to put themselves on their desired course), coast on inertia, kill most of its nonessential systems, and rely on passive sensors only.

Space is big, and spaceships, especially ones radiating as little EM noise as possible, are very small...

[BD Cerridwen]

I certainly agree, Will. Any ship will be difficult to find visually in space. A ship that is "running silent" will still be visible to radar (although it might be mistaken for debris). Which brings me full circle to the radar window. The window itself is not invisible so the hunter will have a limited, but still huge, area of space to search. So my question essentially boils down to, how difficult is finding a ship in the window? How much more difficult is it if the ship is painted in a low-observable scheme? Basically my intent is to make ion drives viable in the Star Frontiers Knight Hawks genre.

My opinion is that it would in part depend on the systems used to search. We can assume that astrogation and weapons systems are very likely to have some sort of optical component with the range and sensitivity to scan space tens of thousands of kilometers away and across. Astrogation optics could probably be used anywhere within radar range (and probably energy sensor range, but then ion windows are invisible to energy sensors so I ignore them for this purpose). Deluxe Astrogation gear would likely give a bonus due to better optics or better optical processing systems associated with this high quality gear. Weapon optics are probably limited to the maximum range of the weapon. Of course, getting in close enough to use weapon systems in the search also means that the hunter may become the hunted, although a "cloaked" ship that fires would likely increase its chance of being found.

I would probably start with a 2% chance per optics system per turn minus the number of hexes in the window. For example, a corvette using its astrogation gear only looking for a six engined ship casting a window would be 2 (chance per optics system) * 1 (number of optics systems employed) * 1 (turns spent searching) - 6 (windowed hexes) = -4 in the first turn. The second turn would be 2 * 1 * 2 - 6 = -2. The third turn is 2 * 1 * 3 - 6 = 0%.

If I were to use such a system, a low-observable ship would cut the chance perhaps in half. Adding ships would likely mean that each ship would have to calculate search checks individually, unless they had a computer link to coordinate the effort.

Anyway, that's my opinion. Let me know if you have other ideas.

[cliff]

What about creating multiple masking screens with different vectors. You create your first screen and then create a second one with a different vector from within the first one. Now the searcher has multiple clouds to search. The creator of the screens can choose to stay with the first or glide away with the second.

Also, what about HS size of the ship creating the screen. a HS20 would be easier to detect than a HS1 (remember one hex is 10,000km across, thats a lot of space to search). To put this into prospective, a HS20 ship is 0.6km long and 0.1km in diameter, how long would it take to scan one hex to find a ship this size? Now what if the ship is half this size, or half this size again? the smaller the ship, the more difficult it would be to see visually. Personally, I do not think that 1 turn (ten minutes) would be enough time to properly scan one hex of 10,000km. I guess what I am getting at is, you are searching for a needle in a haystack but the haystack is the size of the planet earth, you could be searching for a very long time. I would suggest to just wait your quarry out, sooner or later they have to emerge from the cloud (remember the screen will work both ways so if you have Ions as well, they can't see you either).

[Will]

I certainly agree, Will. Any ship will be difficult to find visually in space. A ship that is "running silent" will still be visible to radar (although it might be mistaken for debris). Which brings me full circle to the radar window. The window itself is not invisible so the hunter will have a limited, but still huge, area of space to search. So my question essentially boils down to, how difficult is finding a ship in the window? How much more difficult is it if the ship is painted in a low-observable scheme? Basically my intent is to make ion drives viable in the Star Frontiers Knight Hawks genre.

My opinion is that it would in part depend on the systems used to search. We can assume that astrogation and weapons systems are very likely to have some sort of optical component with the range and sensitivity to scan space tens of thousands of kilometers away and across. Astrogation optics could probably be used anywhere within radar range (and probably energy sensor range, but then ion windows are invisible to energy sensors so I ignore them for this purpose). Deluxe Astrogation gear would likely give a bonus due to better optics or better optical processing systems associated with this high quality gear. Weapon optics are probably limited to the maximum range of the weapon. Of course, getting in close enough to use weapon systems in the search also means that the hunter may become the hunted, although a "cloaked" ship that fires would likely increase its chance of being found.

I would probably start with a 2% chance per optics system per turn minus the number of hexes in the window. For example, a corvette using its astrogation gear only looking for a six engined ship casting a window would be 2 (chance per optics system) * 1 (number of optics systems employed) * 1 (turns spent searching) - 6 (windowed hexes) = -4 in the first turn. The second turn would be 2 * 1 * 2 - 6 = -2. The third turn is 2 * 1 * 3 - 6 = 0%.

If I were to use such a system, a low-observable ship would cut the chance perhaps in half. Adding ships would likely mean that each ship would have to calculate search checks individually, unless they had a computer link to coordinate the effort.

Anyway, that's my opinion. Let me know if you have other ideas.

All valid points, BD.

As for ion windows,they might work if the window itself can be confused for solar wind activity, background ionization due to the effects of the local sun, planets, etc. I leave that one up to our resident science guy.

I do know that non-ion engine ships could use chaff to throw off radar and lidar(ladar). Simply fire off rockets full of metallic strips(and possibly water as well) in every direction(as cliff has mentioned) and then go silent. Your low EM signature would be confused with stellar background noise, while radar/lidar "pings" off the crud.

As for visual ranges in space, I would think they'd be practically unlimited(there being no horizon, atmosphere, &c.), but useful up to a point, before the speed of light conspires to make such information almost worthless.

Same with conventional radar/lidar systems...at a range beyond 30 hexes(300,000 K)the time lag makes their telemetry unreliable(which is why I introduced subspace radar systems in my game, but, that's just a shameless plug....)

[Will]

Taken alone, these should make a ship invisible to the sensors available. But it all depends on how weapons track targets. Are they purely aimed on sensor control or is there a visual tracking element as well? If the second is true, would a black hull coating make targeting, or at least pinpoint targeting, more difficult? What are your opinions - how would you adjudicate this in a game that you referee?

Gun weapons in my game rely on radar and passive EM information(including the old Mark I Eyeball) to track their vectors through space and calaculat firing solutions based on that information.

My missiles and torps, on the other hand, are self-guided, with fully selective seekers and the ability to correct their own courses in mid-flight.

I would rule that a black hull would impose a penalty(say -20%) to detection chances, but it would more likely be offset by the bonuses for Hull Size(which, in my game, is an abstraction of not just how big the ship is visually, but how much electromagnetic noise it puts out, as larger ships generate more emissions than smaller ones).

Also, if a ship's been damaged(especially its engines), its chances of being detected would increase, as it would be making more noise in the EM spectrum than normal.

[BD Cerridwen]

Excellent feedback Will! I like your inclusion of generic EM emissions. You all have given me plenty to consider and have helped clarify my idea for a 'steath' ship. Thanks!

[Aethelwulffe]

Black hulls emit more heat...more visible in the infrared spectrum as it is creating some heat even if the engines are not going. If the engines ARE going, you can presume...ion drive or whatever, that it will be lit up like a christmas tree and a refec hull in a non-issue.

[Will]

Black hulls emit more heat...more visible in the infrared spectrum as it is creating some heat even if the engines are not going. If the engines ARE going, you can presume...ion drive or whatever, that it will be lit up like a christmas tree and a refec hull in a non-issue.

Duhhh...completly overlooked that small fact.

[BD Cerridwen]

Black emits heat simply because it absorbs light energy, unless I'm badly mistaken. As one journeys further from a star, the light energy that is available is reduced. At some point, the heat that a black hull would collect from star light would be negligible when compared to the heat generated to keep the beings aboard her alive. Where exactly this point is, I wouldn't have a clue, and I don't think it really matters. According to the Alpha Dawn rules, the only race capable of seeing beyond the human visible spectrum is the Vrusk, and they're at the ultra-violet end. Therefore, consideration of infrared emissions are likely not relevant to the basis of my question. Especially in the presence of these two words: Masking Screen.

For the most part, my question relates to the visible spectrum. The Ion Window is already clouding radar signals and is invisible to energy sensors, so what is left according to the rules? We have the generic Astrogation Equipment, the assumed optics associated with weapons systems, and windows. Astrogation gear is described as telescopes and such. I think it's safe to assume that a basic astrogation setup would include a typical stargazer's telescope and perhaps a radio telescope type of thing. The radio telescope would be about as useful as the ship's radar for finding a windowed ship, and the telescope is limited to the visible spectrum. If you want all of the filters and/or spectrometry equipment attached to your telescope, that would require the Deluxe equipment set - and require an astrogator with the experience to use it! And even then, what are the effects of the ion cloud on this equipment? Or, more accurately, what are the effects on the heat energy particles emitted by the ship? Will they collide with the ions and diffuse widely while in the ion cloud thus creating a giant heat blob? For that matter, will photons themselves become confused in the ion cloud and thus render the hull color/type moot ?

[simplymenotu]

I read this a few days ago and thought it might be of interest.

STEALTH DOESN’T WORK: Space is vast, but mostly
empty. Space is also dark and cold; the average
background temperature of space is 2-5 Kelvin. Ships
with habitable life support sections, even with the
engines off, will have a surface temperature of at least
200 to 250 Kelvin (ice melts at 273 Kelvin). For a typical
habitable section of a ship, the radiated heat signature
is in the range of a few hundred kilowatts, which is
generally detectable out to 30,000 km in under a day
using a full spherical search pattern with a broad-field
IR-band telescope with an aperture of 3 meters.
In addition to the waste heat generated by life support,
a ship’s power generation system generates heat. A
perfect Carnot heat engine produces 2 watts of waste
heat for every watt of electricity it produces, where
waste heat dissipation is free (like in an atmosphere).
In space, waste heat has to be radiated. Minimizing
radiator size (to make them retractable in combat, and to
make them mass less) means running them at a higher
temperature, which reduces the efficiency of the Carnot
cycle. Each radiator in AV:T is roughly a 25m x 25m
surface radiating from both sides at around 1600 K.
Each radiator disposes of roughly 44 GJ of waste heat
in 128 seconds, for a signature strength of roughly 340
megawatts, which is detectable (easily) out to around
10 light seconds (3 million kilometers) under the same
conditions as the crew’s waste heat. (The distance from
the Earth to the Sun is 500 light seconds, as a point of
comparison.)
Beyond that, for a 5,000 ton ship using a reaction drive,
even in cruise mode, it’s producing a minimum of a
340 gigawatt signature at about 2800 K, which gives a
1 day spherical search pattern “guaranteed” detection
radius of a bit over 1,000 light seconds, or roughly 2
AU. In low thrust fuel economy mode, it takes roughly
10-16 weeks to cross 1 AU. During this entire time, the
people attempting detection need only look for a 14th
magnitude star with measurable proper motion. (A ship
in combat thrust puts out drive signatures 10 times as
bright, and would be easily detectable out at roughly
triple the ranges listed above, or around 6 AU)
Finally, any ship using a reaction drive reveals its mass
by the correlation between observed rate of thrust and
the temperature and brightness/mass spectroscopy of
the exhaust plume.

[BD Cerridwen]

That's darn good info. I appreciate your contribution.

Counterpoints to Attack Vector: Tactical:
A. A windowed ship has 0 thrust.
B. The possible effect of the ion cloud confusion is not addressed.
C. All of the search times are given in terms of a day of searching (20 hrs./day * 6 turns/hr = 120 or a 1 in 120 cumulative chance per turn of finding the ship by the means presented).
D. A 'reaction drive' = Atomic or Chemical Drives (from what I can find of them on the internet), a non-factor for an Ion Driven ship making longer range detection a moot point.
E. The 'power generation system' can be shutdown provided that a sufficient battery back up is available for key systems.

For a typical
habitable section of a ship, the radiated heat signature
is in the range of a few hundred kilowatts, which is
generally detectable out to 30,000 km in under a day
using a full spherical search pattern with a broad-field
IR-band telescope with an aperture of 3 meters.

30,000 km is 3 hexes, easily within range of every spacecraft weapon and close enough for a very good probability of hits. I take this to also mean that searching from further away will be more difficult and likely take longer. If my assumption of the difference in 'astrogation equipment' is correct, a 'broad-field IR-band telescope' would fall into the Deluxe category.

Stealth doesn't have to provide perfect invisibility, it just needs to make detection and targeting difficult enough to give the stealthed ship enough time to do it's job, escape, or to summon help. Without the Ion Drive's ability to provide a degree of stealth, it has virtually no use on star ships. The only benefit for traveling beyond a single star system with an ion drive would be deep space exploration as finding fuel would be easy.

So here is my conclusion from this discussion. The hull covering is a non-factor. Visually spotting a ship in the vastness of space is extremely difficult regardless of the hull color. The effectiveness of the search is dependent on the definition of Astrogation Equipment vs. Deluxe Astrogation Equipment, something I assumed from the beginning.

Thank you all for participating. I found this to be a useful exercise.

[Aethelwulffe]

If you don't run your engines, you don't create heat (as much) and you give off less IR. If you have a black hull, you will get rid of heat more quickly than any other color or specular quality hull. Assuming for a moment that the ship's drives throw mass that includes an incredibly high percentage of the total heat you produce out with the exhaust, you are still gonna need radiators to get rid of the heat. Let's see how this affects you:

1. A warship trying to be stealthy with likely use directional radiators that have been aligned opposite the local star, and have reflective "blinders" so that they emit heat in mostly only one direction: away from the star. This let's them try to hide their signature by blending in with the star when viewed from a larger orbit around the star, and not at all or very little from inside a smaller orbit.

2. The ship will likely use angled radiation-reflective materials in the hull. This will help with battle damage, act as a angled scattering reflector of radar, and help insulate the hull to prevent unwanted emissions. This covering will mean that the ship will certainly need radiators just to get rid of heat from life support systems and sensors, much less weapons or engines. A high albedo (like white) DOES mean that you are easier to spot visually, but if the object is truly reflective, it will appear either very bright (reflecting back directly from a flat surface), or you won't see it at all.

3. An alternate is a superconducting covering that are linked to heat coils/sinks and or capacitors that can be dumped to prevent damage when hit. White or black, this coating will get rid of heat more rapidly than anything else. It would allow you to control the signature of the ship by instantly changing temperature when you link it to heat sinks (connected through insulation by even a tiny wire). What insulation you have between the real ship and the exterior coating makes a large difference in how all that works.

4. An insulated object will tend to convert all of it's emissions into one wavelength of light, such as IR, as it overheats. Eventually, the internal heat build-up will make a insulated object show more brightly in the IR spectrum than an uninsulated one that emits in a wider band.