Anti-missile weapons

[locarno24]

Trav missiles are FAR too small to incorporate sub-munitions that are large enough, or powerful enough to damage a spaceship hull.

Aside, of course, from the Multi-Warhead Missile.

There is no ECM for the hot missile.

Without really thinking, three comments:

1) IR baffling to reduce the heat signature of the missile - you can't eliminate it but you can radiate as much as possible back towards the launching ship not the target. In addition, (pulling out Universal Traveller answer No. 3) It's A Feature Of Gravetic Technology - if a missile is using a grav system for acceleration then it needn't necessarily have a hot exhaust plume (which is what IR systems generally see rather than the missile itself).

2) Flare ejectors dispensing short-burn decoys on similar vectors.

3) Relatively low power, low-coherency (i.e. wide 'spot' angle) IR-frequency lasers which strobe back and forth over the target. Any time the laser sweeps over one of the ship's IR sensors, it will be temporarily blinded because the entire field of view will be saturated. Now multiply by one or two of these devices in the nose of each of a barrage of 100+ missiles....

Large Aircraft Infrared Countermeasures is a current equivalent of this technology.

http://www.globalsecurity.org/military/systems/aircraft/systems/laircm.htm

For example, several of the latest designs of anti-ship missiles
are much more like torpedoes, they submerge a long distance from the
enemy ship and then attack submerged, exploding under the ship

Interesting. I know ASROC, Ikara, etc, deliver torpedos, but they are short ranged (~20Km) anti-sub, not ship-to-ship weapons with the 70+ km stand-off range needed for that sort of fight. Which missiles did you have in mind?

 

[rust]

Interesting. I know ASROC, Ikara, etc, deliver torpedos, but they are short ranged (~20Km) anti-sub, not ship-to-ship weapons with the 70+ km stand-off range needed for that sort of fight. Which missiles did you have in mind?

No operational systems, just designs several countries are reported to be
working on, for example a French successor to the Malafon with longer
submerged range and a higher payload.

 

[locarno24]

Malafon is an anti-sub rocket, again - a longer range is one thing but unless it's going up by a power of ten it's not turning it into a SSM.

Surprised to hear that there's any work still going on on the concept, really. Most rocket-delivered torps got pulled from service about the same time that the SSGN concept came into being (ASROC, Ikara and Malafon have all been obsolete for a decade) and replaced by torp-carrying helos.



Aaaanyway. Back to something resembling the topic. [Sorry]

The small 50kg missiles in Traveller scream for swarm attacks. Even a turret can launch 3 at a time and the bays can launch even larger numbers.

True. A capital ship dedicating a significant proportion of its hardpoints to triple fixed mounts for missile launchers can put out a ridiculous amount of fire (assuming it has the magazine space for it as well!). One other thing you might consider for anti-missile-missile work, though, was a concept out of Honor Harrington - the 'triple ripple'. Designed to deal with missile swarms, this involved using a relatively small number of nuke warheads as counter-missiles.

They detonated in advance of the missile wave - not amongst them (where they'd catch one or two laterally in their emp/radiation pulse) but in front, where the missile's sensitive thermal/radar arrays are positioned, looking for the signature of the target ship. A ship's arrays are hardened but with the mass budget of the missile it's not possible. Result - missile's sensors cooked, resulting in a piece of ordnance that is (at best) ballistic and (at worst) going to self-destruct to prevent itself becoming post-battle UXO.

 

[DFW]

1) IR baffling to reduce the heat signature of the missile - you can't eliminate it but you can radiate as much as possible back towards the launching ship not the target. In addition, (pulling out Universal Traveller answer No. 3) It's A Feature Of Gravetic Technology - if a missile is using a grav system for acceleration then it needn't necessarily have a hot exhaust plume (which is what IR systems generally see rather than the missile itself).

Interesting but unworkable. The heat problem has noting to do with "plume".
Here's a good starting point: http://www.egglescliffe.org.uk/physics/astronomy/blackbody/bbody.html

 

[locarno24]

Any object radiates in the IR but that's dependent on temperature. Yes, it's going to be a lot hotter than the surrounding space but whether it's radiated output is enough to let the target ship's sensors lock onto it in a timely manner is a different matter.

As ever in space mechanics, if you're looking at an object you'll see it, if you're trying to scan a sizeable chunk of the night sky to find it first it can take some time - potentially time you haven't got.

Realistic missile engagements under the traveller rules have shots taking between 1 and 5 rounds to impact, which means between a 6 and 30 minute flight time. No signature reducing method is going to remain effective at point blank range, but the lower the signature, the closer the missile will get before your point defence fire control can pick it up, which means less time working out counter-fire. For lasers this is probably less important, but if you're bringing counter-missiles into the setting, it definitley is.

A rocket/fusion plume isn't the only 'hot' part of a missile (although there is at least no stagnation pressure heating on the nose in this case), but it's significant because it's 'outside' the missile - any part of a missile's skin can be cooled and the heat rejected by a heat sink radiating in a different direction (I don't have to be stealthy in every direction - just the one you're looking at me in!). A plume of exhaust gas/plasma can't.

 

[DFW]

Any object radiates in the IR but that's dependent on temperature. Yes, it's going to be a lot hotter than the surrounding space but whether it's radiated output is enough to let the target ship's sensors lock onto it in a timely manner is a different matter.

Like I said, START your study there. As you continue to study you will learn how easy it is to spot what in outer space, using IR only. Remember, your background is ~ -270°C. Absolute zero is −273.15°C

Here's a formula to use:

The maximum range a vesssel running silent with engines shut down can be detected with current technology is:

Rd = 13.4 * sqrt(A) * T2

where:
Rd = detection range (km)
A = spacecraft projected area (m2 )
T = surface temperature (Kelvin, room temperature is about 285-290 K)

Being generous the missile (using TL 7 detection tech) can be spotted at a range of ~59,000 km.

 

[Mongoose Pete]

Being generous the missile (using TL 7 detection tech) can be spotted at a range of ~59,000 km.

Likewise, using the same formula for a ballistic launched missile, with a very small profile and which was stored in an unheated missile bay/turret (i.e. the average missile in Traveller if dropped without a powered launch), you could easily get within a 1,000km before sensors would notice it.

I would imagine if heat is the principle signature then military vessels would cryogenicly cool munitions before launch, if the storage magazine couldn't be insulated against heat-bleed from the rest of the ship.

Of course if the missile needs to catch up with a target accelerating away from it, then it comes down to how much heat its own drive produces - which is handwave time since I don't think anybody has yet specified the energy efficiency of manoeuvre drives.

 

[DFW]

I would imagine if heat is the principle signature then military vessels would cryogenicly cool munitions before launch, if the storage magazine couldn't be insulated against heat-bleed from the rest of the ship.

Doesn't matter. If the missile has a power source, it'll radiate at that temp.

Of course if the missile needs to catch up with a target accelerating away from it, then it comes down to how much heat its own drive produces - which is handwave time since I don't think anybody has yet specified the energy efficiency of manoeuvre drives.

If it is at least room temp, see the detection range for TL 7 passive sensors above. Basically, the SOL hotline is the only recourse to detection at VERY long ranges.

 

[locarno24]

I'm aware of the scope of absolute temperature. But the fact that something is detectible with 'astronomic' sensors doesn't make it detectible by sensors which react with a useful timeframe (since we're talking about launching counter-missiles). A detector looking for single photons cannot scan a region of the sky quickly (quickly being minutes) without becoming saturated. TL doesn't enter into it.

Scanning a region of sky takes time, and the more cluttered a region of space is with bright point sources*, the harder it is to pick out a less energetic return. Add that to the fact that radiated power (and hence power per metre squared falling onto any putative sensor) is a function of temperature to the fourth power, then any reduction of the absolute temperature of the presented face of the missile by half is going to reduce your signature by a factor of sixteen.

Assuming liquid nitrogen cooling on the 'approach' face (rejecting the heat backwards via heat sinks that are not pointing towards the enemy), you have a leading face that's at about eighty Kelvin. Relative to a two hundred and ninety kelvin 'room temperature' round, you are dropping from four hundred W/m2 radiated power to two W/m2. Yes, that energy (and more, since you have to account for the energy used by the cooling system) has to be radiated away in some direction, but if it's being radiated away from the enemy ship, it doesn't matter because it's not helping you see the missile.

Unsure where you get that formula for detection range from, by the way? - giving the missile a projected area of a couple of square metres (not unreasonable for a head-on profile), then a detection range of 59,000 km (using your value for 'current tech' would need a surface temperature of nearly 500 degrees C. Is that correct, and if so, what method are you using to gauge the increase in ability?

Doesn't matter. If the missile has a power source, it'll radiate at that temp

No it won't. If a missile has a power source, then the sum of the energy radiated in all directions has to equal the energy generated in the same time increment. The big flaw if you model it as a black body is to assume it is uniform in all directions. Won't work for a ship (which could be detected from any aspect) but will work for a munition because it'll always be pointed at the enemy.


* like....say....a warship in combat with its drives, active sensors and particle weapons burning, and launching clutches of flares and decoys, more or less exactly on the same bearing as the missiles it's firing at you?

 

[DFW]

I'm aware of the scope of absolute temperature. But the fact that something is detectible with 'astronomic' sensors doesn't

I say this in all friendliness, you're going to have to get a lot more educated in this area of physics before you can argue the point further. Don't know what else to tell ya.

 

[rust]

By the way, IR sensors are not good at determining a distance to an ob-
ject with an unknown temperature, especially when the object is moving
straight towards the sensor - and without knowing the distance to the ob-
ject, it is not easy to determine quickly whether the point source is an ap-
proaching missile or one of dozens of stationary flares in the background.

 

[DFW]

By the way, IR sensors are not good at determining a distance to an ob-
ject with an unknown temperature, especially when the object is moving
straight towards the sensor - and without knowing the distance to the ob-
ject, it is not easy to determine quickly whether the point source is an ap-
proaching missile or one of dozens of stationary flares in the background.

That's why you use multiple sensors on the ship in order to "triangulate". The principle of triangulation is used as a basic method for range estimation. However, when the target directions are nearly collinear relative to the baseline, this method produces unacceptable results. The problem is solved by introducing the ratio of IR energy adsorbed at the end of a baseline in a measurement vector within the extended Kalman filter type target state estimator. Also, a recursive estimator for the extinction coefficient that describes the influence of the atmosphere is designed. This combination results in a new adaptive structure for simultaneous estimation of target kinematic states and atmospheric parameters. Such a structure performs much better than the standard triangulation method, yielding acceptable results even in the case where target directions are close to the baseline. Simulation and experimental results demonstrate the feasibility and limitations of the proposed approach. Of course when operating outside an atmosphere, this becomes simpler and more accurate.

N.B. - The Kalman filter is a mathematical method named after Rudolf E. Kalman. Its purpose is to use measurements that are observed over time that contain noise (random variations) and other inaccuracies, and produce values that tend to be closer to the true values of the measurements and their associated calculated values. The Kalman filter has many applications in technology, and is an essential part of the development of space and military technology

 

[DFW]

Who says that missiles use any sort of reaction drive? As far as we know they might very well use grav drives and batteries leaving little heat trails to detect.

Doesn't matter. I am assuming reactionless drives. Unless it is launched (and subsequently unpowered) it has a PP, drives, electronics, etc., ... and thus, heat that radiates.

 

[Mongoose Pete]

That's why you use multiple sensors on the ship in order to "triangulate". The principle of triangulation is used as a basic method for range estimation. However, when the target directions are nearly collinear relative to the baseline, this method produces unacceptable results. The problem is solved by introducing the ratio of IR energy adsorbed at the end of a baseline in a measurement vector within the extended Kalman filter type target state estimator. Also, a recursive estimator for the extinction coefficient that describes the influence of the atmosphere is designed. This combination results in a new adaptive structure for simultaneous estimation of target kinematic states and atmospheric parameters. Such a structure performs much better than the standard triangulation method, yielding acceptable results even in the case where target directions are close to the baseline. Simulation and experimental results demonstrate the feasibility and limitations of the proposed approach. Of course when operating outside an atmosphere, this becomes simpler and more accurate.

Nice piece of cut and paste of Djurovic's abstract by the way. :roll:

However that technique still does not satisfy the issues of sensor resolution over distance when the sensor is being washed out by a heat source multiple orders of magnitude greater than the missile. The exact same principle which prevents detection of objects in line with the sun for example.

As previously pointed out, the heat source of a battery is microscopic in comparison to say, a simple magnesium flare. Missiles with no drive engaged could operate on a tiny trickle of energy, just enough to power their passive sensors, comms channel (if picking up targeting telemetry from other missiles, and a processor to determine when to engage its drive.

Also as previously pointed out, the drive may have a very low IR signal. In addition, I think a standard missile almost certainly has a frontal cross section way less than a square meter. locarno24's directional radiators are also completely plausible, assuming you don't have a second ship/sensor platform positioned across system to send data to the attacked vessel.

 

[rust]

Hmm ... I was just thinking of a missile that starts with a high IR signature
and then steadily reduces the signature during its approach to the target
ship while the stationary flares in the background start with a low IR sig-
nature and then steadily increase it while the missile approaches the tar-
get ship ... could perhaps become a difficult task for a sensor ...

 

[Mongoose Pete]

Hmm ... I was just thinking of a missile that starts with a high IR signature
and then steadily reduces the signature during its approach to the target
ship while the stationary flares in the background start with a low IR sig-
nature and then steadily increase it while the missile approaches the tar-
get ship ... could perhaps become a difficult task for a sensor ...

Yep. There are plenty of ways to spoof the sensor. Take it a step further and have a slightly divergent spread of variable IR emitters which cut in and out randomly - guaranteed to screw any Kalman algorythm. Or far simpler, just target the ship/sensor with a low power laser every ten seconds which will overload the IR receptors and keep them saturated. :wink:

 

[DFW]

Nice piece of cut and paste of Djurovic's abstract by the way.

Thanks, as an Engineer you get to read a lot of stuff from your field.

However that technique still does not satisfy the issues of sensor resolution over distance when the sensor is being washed out by a heat source multiple orders of magnitude greater than the missile. The exact same principle which prevents detection of objects in line with the sun for example.

Of course. Put yourself directly between the target and the sun. I didn't state that as it is "stating the obvious". I try not to take up space by posting what everyone already knows.

As previously pointed out, the heat source of a battery is microscopic in comparison to say, a simple magnesium flare. Missiles with no drive engaged could operate on a tiny trickle of energy, just enough to power their passive sensors, comms channel (if picking up targeting telemetry from other missiles, and a processor to determine when to engage its drive.

Apparently you don't understand how a missile is going to get from launch ship to target over vast distances. Sure, have the missile floating for long periods of time while the target is accelerating away. Cool!

Also as previously pointed out, the drive may have a very low IR signal.

Power source please... The greatly avoided topic of those arguing for no IR.

In addition, I think a standard missile almost certainly has a frontal cross section way less than a square meter.

Which is why I used a smaller number. However, I used TL 7 sensor sensitivity. Would you like me to factor in probable TL 13-15 sensitivity and DSP? I don't think you do.

Locarno24's directional radiators are also completely plausible, assuming you don't have a second ship/sensor platform positioned across system to send data to the attacked vessel.

Again, not relevant. Unless you are now stating that standard ship missiles are refrigerated & insulated enough to basically be at close to absolute zero? Let me know.

 

[DFW]

Hmm ... I was just thinking of a missile that starts with a high IR signature
and then steadily reduces the signature during its approach to the target
ship while the stationary flares in the background start with a low IR sig-
nature and then steadily increase it while the missile approaches the tar-
get ship ... could perhaps become a difficult task for a sensor ...

Due to the missile onboard PP being fired up, the missile would grow hotter. If a flare is stationary it would quickly get out of line between the missile and the moving, maneuvering target. As to those who think the missile is going to have mounted lasers detecting and then shooting the precise locations of the small passive sensors on the target ship, I have a bridge or two to sell ya. At a high price.

 

[BP]

One aspect of MGT space combat I don't care for is the lack of effectiveness of anti-missile systems (at least against low tech missiles).

While one can debate the detectability and countermeasures capabilities of futuristic missiles, close-in defense should be able to take care of the vast majority of missile strikes. This would offset their low tech and low cost.

Inexpensive missiles have, in the RW, created a demand for effective countermeasures, especially for more vulnerable (in relation to dynamics), expensive assets like ships and tanks. Of course, this has resulted in ever more effective missiles - but at higher costs (and lower availability).

 

[DFW]

While one can debate the detectability and countermeasures capabilities of futuristic missiles, close-in defense should be able to take care of the vast majority of missile strikes. This would offset their low tech and low cost.

Especially considering the small size of the missiles (no armour) sand and/or laser fire would snuff them easily and quickly. In my game they are close to useless unless they are nukes as a starship hull is very tough and the missiles VERY low mass.