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> The HAWC vehicle operates best in oxygen-rich atmosphere, where speed and maneuverability make it difficult to detect in a timely way. I'm reasonably sure th

by jhgb 5y ago

> The HAWC vehicle operates best in oxygen-rich atmosphere, where speed and maneuverability make it difficult to detect in a timely way. I'm reasonably sure that the infrared trace of a hypersonic vehicle doesn't make it difficult to detect. Likewise existing approaches to radar stealth are hard to reconcile with hypersonic speeds, which doesn't help avoid radar detection either.

sudosysgen 5y ago
Plasma stealth is an existing approach to radar stealth that is made easier by hypersonic speeds. Infrared targeting of multiple hypersonic missiles is easier said than done. The missile you're hitting them with is going to be heating up the air around the camera probably at the same temps as the missile it's intercepting, and a base station wouldn't have enough resolution to guide a missile accurately from 100+km away while being alert for other missiles.
- jhgb 5y ago
  > The missile you're hitting them with is going to be heating up the air around the camera probably at the same temps as the missile it's intercepting That would only apply if it were to hit it at comparable speeds. That's not necessary in many cases, especially in point defense when the target is heading towards you. Furthermore the limited time of flight of the interceptor might also allow for active cooling of the IR window in that brief period. Also, even detection from a fixed ground base (or from space - see SpaceX's newest missile detection project) is still detection in the first place, which is what I was commenting on. Wasn't even going to veer into interceptor guidance, but I'm sure there's multiple ways to do it.
  - deleted 5y ago
    [deleted]
  - sudosysgen 5y ago
    Interception against an actively manoeuvring target is a question of kinetic energy. If the intecepting missile is smaller all the hypersonic missile has to do is zig-zagging randomly and you're toast. If you're going to wait for the hypersonic missile to be close enough that this isn't a problem, you have the issue that your missile won't be able to manoeuvre right and might still be building up velocity. Plus there won't only be one! > the interceptor might also allow for active cooling of the IR window in that brief period. The issue isn't the IR window, it's the air directly in front of the interceptor missile, which has to target from the frontal aspect. >Also, even detection from a fixed ground base (or from space - see SpaceX's newest missile detection project) is still detection in the first place, which is what I was commenting on. Wasn't even going to veer into interceptor guidance, but I'm sure there's multiple ways to do it. Detection is not enough. We can already detect missiles from satellites even. The issue is calculating their velocity accurately and locating them at +- 10m from 100km+ away is not feasible without really large apertures and pretty long focal lengths. You wouldn't be able to accurately track more missiles than you have optics and the optics would be mind-boggingly expensive. Besides that, the target acquisition radar to maintain a feasible or even physically possible relative aperture for target acquisition would be unable to resolve any detail about the missile, so it would have no way of telling the difference between a missile and a flare of the same brightness and color.
    - jhgb 5y ago
      > Interception against an actively manoeuvring target is a question of kinetic energy. If the intecepting missile is smaller all the hypersonic missile has to do is zig-zagging randomly and you're toast. What you're describing is not a matter of kinetic energy (clearly if it were about kinetic energy, this would be defeated by making the interceptor weigh 30 tonnes) but a matter of transverse acceleration. On that matter, as far as I understand it, current AAMs/SAMs are somewhere in the 50g region. I strongly suspect that hypersonic vehicles due to their lower L/D are nowhere near that -- hell, many of them seem to have a hard enough time flying straight, if US military's experience is of any relevance here. Also, due to low L/D ratio in the high Mach region, if your missile is zig-zagging randomly, it won't stay fast for long. And if it's not zig-zagging randomly, then the question is how it gets the information how to zig-zag, since the nose of a hypersonic vehicle seems to be an extremely poor sensor platform -- which you admitted yourself. It's virtually certain that it won't be able to see the interceptor. > The issue isn't the IR window, it's the air directly in front of the interceptor missile, which has to target from the frontal aspect. It seems unlikely that the interceptor will have to fly at a comparable speed in a frontal aspect interception situation (considering that it doesn't need to catch up). But as for terminal interception, I suspect that here the inverse-fourth-power-of-distance operation of an active radar homing solution might help you if all else fails -- at a small enough distance this will work even better than the inverse square applicable to passive optical/IR detection. > would be unable to resolve any detail about the missile, so it would have no way of telling the difference between a missile and a flare of the same brightness and color. It would seem that the easiest way to distinguish a flare would be to look if it's in a controlled flight? Unlike a flare, the hypersonic vehicle will continue flying, and the difference is readily apparent. Besides, you can't have that many flares on it, so you can't keep firing them continuously -- again, the only thing that's available to you if you can't see the incoming interceptor.
      - sudosysgen 5y ago
        >What you're describing is not a matter of kinetic energy (clearly if it were about kinetic energy, this would be defeated by making the interceptor weigh 30 tonnes) but a matter of transverse acceleration. On that matter, as far as I understand it, current AAMs/SAMs are somewhere in the 50g region. I strongly suspect that hypersonic vehicles due to their lower L/D are nowhere near that -- hell, many of them seem to have a hard enough time flying straight, if US military's experience is of any relevance here. Not so. AAMs/SAM can only pull anywhere close to 50g at gigantic cost in drag and can only do that once and briefly. It is a question of kinetic energy because the missile that can regenerate kinetic energy and that loses the least kinetic energy relative to it's mass is at a massive advantage. >Also, due to low L/D ratio in the high Mach region, if your missile is zig-zagging randomly, it won't stay fast for long. And if it's not zig-zagging randomly, then the question is how it gets the information how to zig-zag, since the nose of a hypersonic vehicle seems to be an extremely poor sensor platform -- which you admitted yourself. It's virtually certain that it won't be able to see the interceptor. Traditional aerodynamic designs suffer from poor L/D ratios, yes. Waverider designs probably have much fewer issues. Given the advent of HGVs, which are made to turn multiple times without any engine to back them up, we can be fairly confident that this is not the case. As far as being a poor sensor, this is an oversimplification of a complex mechanism. Plasmas block radar up to a certain frequecy depending on their temperature. So you make it so that the radar is somewhere where the air is slightly colder and make its frequency higher. You don't even have to put the radar in the nose if the target you're trying to hit is sluggish and large enough. It doesn't need to maneuver in response to the interceptor. The missile knows when it is in LOS to the target, and knows that the interceptor will be fired soon after. So it already knows when the missile will be fired and thus when the missile would hit. The window for interception is pretty short. It would have to do evasive maneuvers at maybe 4G for maybe 30 seconds, all the while gaining back Ke from reducing in altitude in combination with engines. >It would seem that the easiest way to distinguish a flare would be to look if it's in a controlled flight? Unlike a flare, the hypersonic vehicle will continue flying, and the difference is readily apparent. Besides, you can't have that many flares on it, so you can't keep firing them continuously -- again, the only thing that's available to you if you can't see the incoming interceptor. This is a REALLY hard problem, and it's the reason why imaging infrared guidance was invented. It takes a lot of time to be certain that a flare in a ballistic trajectory at high speed is different from a missile coming towards you! Those are precious seconds you can't afford. Remember that you have no way of estimating distance.
- dotancohen 5y ago
  > Plasma stealth is an existing approach to radar > stealth that is made easier by hypersonic speeds. Does a vehicle traveling at such speeds that it compresses the air into a plasma have much aerodynamic control? I am aware that the space shuttle orbiters would roll during the plasma stage to control their rate of decent (less lift vector in the "up" direction) but could a missile maneuver to a target? Assuming that the sensors-through-plasma issue were resolved (which is another issue that I do not believe can be easily resolved).
jack_pp 5y ago
Isn't the point of these weapons that even if you can detect them they are too fast to intercept?
- JumpCrisscross 5y ago
  > even if you can detect them they are too fast to intercept? No. They still travel far slower than ballistic missiles. Their advantages are in being able to fly low and (theoretically) manoeuvre to avoid interceptors. They’re an evolution of cruise missiles, not strategic ballistic missiles.
  - jhgb 5y ago
    But maneuvering at high velocities won't be that easy. As far as I understand it, your lift/drag ratio decreases appreciably with increasing Mach numbers. So either you'd have to limit your maneuvering, or you'd have to have a propulsion unit with ridiculous amounts of thrust - at a situation when any amount of useful thrust is hard to obtain, since we still don't know really well how to do propulsion in this regime.
    - JumpCrisscross 5y ago
      As a former aerospace engineer, I’m sceptical of the strategic value of hypersonics. Tactical? Sure. They’d have a better chance of taking out SAMs, light radar, et cetera. But the talk about these being carrier killers is, based on everything we’ve seen, off the mark. (Spending the cost of one hypersonic on a swarming attack would probably do more damage.)
      - sudosysgen 5y ago
        The biggest difference between hypersonics and swarms of slow missiles is that the hypersonics can get there fast enough that you might not need high-quality targeting information. That's definitely a strategic advantage! Also the 3M22 is estimated to only cost around 2 million dollars.
nradov 5y ago
Sure hypersonic missiles will be detectible by infrared sensors. But those sensors have limited range, narrow field of view, and don't work well through clouds. And IR sensors can't give precise range data so they're less useful for targeting interceptors.

by jhgb 5y ago

sudosysgen 5y ago

Plasma stealth is an existing approach to radar stealth that is made easier by hypersonic speeds. Infrared targeting of multiple hypersonic missiles is easier said than done. The missile you're hitting them with is going to be heating up the air around the camera probably at the same temps as the missile it's intercepting, and a base station wouldn't have enough resolution to guide a missile accurately from 100+km away while being alert for other missiles.

jhgb 5y ago
> The missile you're hitting them with is going to be heating up the air around the camera probably at the same temps as the missile it's intercepting That would only apply if it were to hit it at comparable speeds. That's not necessary in many cases, especially in point defense when the target is heading towards you. Furthermore the limited time of flight of the interceptor might also allow for active cooling of the IR window in that brief period. Also, even detection from a fixed ground base (or from space - see SpaceX's newest missile detection project) is still detection in the first place, which is what I was commenting on. Wasn't even going to veer into interceptor guidance, but I'm sure there's multiple ways to do it.
- deleted 5y ago
  [deleted]
- sudosysgen 5y ago
  Interception against an actively manoeuvring target is a question of kinetic energy. If the intecepting missile is smaller all the hypersonic missile has to do is zig-zagging randomly and you're toast. If you're going to wait for the hypersonic missile to be close enough that this isn't a problem, you have the issue that your missile won't be able to manoeuvre right and might still be building up velocity. Plus there won't only be one! > the interceptor might also allow for active cooling of the IR window in that brief period. The issue isn't the IR window, it's the air directly in front of the interceptor missile, which has to target from the frontal aspect. >Also, even detection from a fixed ground base (or from space - see SpaceX's newest missile detection project) is still detection in the first place, which is what I was commenting on. Wasn't even going to veer into interceptor guidance, but I'm sure there's multiple ways to do it. Detection is not enough. We can already detect missiles from satellites even. The issue is calculating their velocity accurately and locating them at +- 10m from 100km+ away is not feasible without really large apertures and pretty long focal lengths. You wouldn't be able to accurately track more missiles than you have optics and the optics would be mind-boggingly expensive. Besides that, the target acquisition radar to maintain a feasible or even physically possible relative aperture for target acquisition would be unable to resolve any detail about the missile, so it would have no way of telling the difference between a missile and a flare of the same brightness and color.
  - jhgb 5y ago
    > Interception against an actively manoeuvring target is a question of kinetic energy. If the intecepting missile is smaller all the hypersonic missile has to do is zig-zagging randomly and you're toast. What you're describing is not a matter of kinetic energy (clearly if it were about kinetic energy, this would be defeated by making the interceptor weigh 30 tonnes) but a matter of transverse acceleration. On that matter, as far as I understand it, current AAMs/SAMs are somewhere in the 50g region. I strongly suspect that hypersonic vehicles due to their lower L/D are nowhere near that -- hell, many of them seem to have a hard enough time flying straight, if US military's experience is of any relevance here. Also, due to low L/D ratio in the high Mach region, if your missile is zig-zagging randomly, it won't stay fast for long. And if it's not zig-zagging randomly, then the question is how it gets the information how to zig-zag, since the nose of a hypersonic vehicle seems to be an extremely poor sensor platform -- which you admitted yourself. It's virtually certain that it won't be able to see the interceptor. > The issue isn't the IR window, it's the air directly in front of the interceptor missile, which has to target from the frontal aspect. It seems unlikely that the interceptor will have to fly at a comparable speed in a frontal aspect interception situation (considering that it doesn't need to catch up). But as for terminal interception, I suspect that here the inverse-fourth-power-of-distance operation of an active radar homing solution might help you if all else fails -- at a small enough distance this will work even better than the inverse square applicable to passive optical/IR detection. > would be unable to resolve any detail about the missile, so it would have no way of telling the difference between a missile and a flare of the same brightness and color. It would seem that the easiest way to distinguish a flare would be to look if it's in a controlled flight? Unlike a flare, the hypersonic vehicle will continue flying, and the difference is readily apparent. Besides, you can't have that many flares on it, so you can't keep firing them continuously -- again, the only thing that's available to you if you can't see the incoming interceptor.
    - sudosysgen 5y ago
      >What you're describing is not a matter of kinetic energy (clearly if it were about kinetic energy, this would be defeated by making the interceptor weigh 30 tonnes) but a matter of transverse acceleration. On that matter, as far as I understand it, current AAMs/SAMs are somewhere in the 50g region. I strongly suspect that hypersonic vehicles due to their lower L/D are nowhere near that -- hell, many of them seem to have a hard enough time flying straight, if US military's experience is of any relevance here. Not so. AAMs/SAM can only pull anywhere close to 50g at gigantic cost in drag and can only do that once and briefly. It is a question of kinetic energy because the missile that can regenerate kinetic energy and that loses the least kinetic energy relative to it's mass is at a massive advantage. >Also, due to low L/D ratio in the high Mach region, if your missile is zig-zagging randomly, it won't stay fast for long. And if it's not zig-zagging randomly, then the question is how it gets the information how to zig-zag, since the nose of a hypersonic vehicle seems to be an extremely poor sensor platform -- which you admitted yourself. It's virtually certain that it won't be able to see the interceptor. Traditional aerodynamic designs suffer from poor L/D ratios, yes. Waverider designs probably have much fewer issues. Given the advent of HGVs, which are made to turn multiple times without any engine to back them up, we can be fairly confident that this is not the case. As far as being a poor sensor, this is an oversimplification of a complex mechanism. Plasmas block radar up to a certain frequecy depending on their temperature. So you make it so that the radar is somewhere where the air is slightly colder and make its frequency higher. You don't even have to put the radar in the nose if the target you're trying to hit is sluggish and large enough. It doesn't need to maneuver in response to the interceptor. The missile knows when it is in LOS to the target, and knows that the interceptor will be fired soon after. So it already knows when the missile will be fired and thus when the missile would hit. The window for interception is pretty short. It would have to do evasive maneuvers at maybe 4G for maybe 30 seconds, all the while gaining back Ke from reducing in altitude in combination with engines. >It would seem that the easiest way to distinguish a flare would be to look if it's in a controlled flight? Unlike a flare, the hypersonic vehicle will continue flying, and the difference is readily apparent. Besides, you can't have that many flares on it, so you can't keep firing them continuously -- again, the only thing that's available to you if you can't see the incoming interceptor. This is a REALLY hard problem, and it's the reason why imaging infrared guidance was invented. It takes a lot of time to be certain that a flare in a ballistic trajectory at high speed is different from a missile coming towards you! Those are precious seconds you can't afford. Remember that you have no way of estimating distance.
dotancohen 5y ago
> Plasma stealth is an existing approach to radar > stealth that is made easier by hypersonic speeds. Does a vehicle traveling at such speeds that it compresses the air into a plasma have much aerodynamic control? I am aware that the space shuttle orbiters would roll during the plasma stage to control their rate of decent (less lift vector in the "up" direction) but could a missile maneuver to a target? Assuming that the sensors-through-plasma issue were resolved (which is another issue that I do not believe can be easily resolved).

jack_pp 5y ago

Isn't the point of these weapons that even if you can detect them they are too fast to intercept?

JumpCrisscross 5y ago
> even if you can detect them they are too fast to intercept? No. They still travel far slower than ballistic missiles. Their advantages are in being able to fly low and (theoretically) manoeuvre to avoid interceptors. They’re an evolution of cruise missiles, not strategic ballistic missiles.
- jhgb 5y ago
  But maneuvering at high velocities won't be that easy. As far as I understand it, your lift/drag ratio decreases appreciably with increasing Mach numbers. So either you'd have to limit your maneuvering, or you'd have to have a propulsion unit with ridiculous amounts of thrust - at a situation when any amount of useful thrust is hard to obtain, since we still don't know really well how to do propulsion in this regime.
  - JumpCrisscross 5y ago
    As a former aerospace engineer, I’m sceptical of the strategic value of hypersonics. Tactical? Sure. They’d have a better chance of taking out SAMs, light radar, et cetera. But the talk about these being carrier killers is, based on everything we’ve seen, off the mark. (Spending the cost of one hypersonic on a swarming attack would probably do more damage.)
    - sudosysgen 5y ago
      The biggest difference between hypersonics and swarms of slow missiles is that the hypersonics can get there fast enough that you might not need high-quality targeting information. That's definitely a strategic advantage! Also the 3M22 is estimated to only cost around 2 million dollars.

nradov 5y ago

Sure hypersonic missiles will be detectible by infrared sensors. But those sensors have limited range, narrow field of view, and don't work well through clouds. And IR sensors can't give precise range data so they're less useful for targeting interceptors.