Hitting a target moving faster than the missile

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armedupdate

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Unread post14 Jun 2017, 00:38

Most missiles need to much faster than target be able to hit them. For example, a Patriot cannot bring down ICBMs, even within terminal phase range. Is this mostly a sensor resolution problem of errors? I imagine radar technology advancing enough is able to get perfect sensitivity it can hit a non-manuvering target without manuvering(just intercept). I believe an AEGIS SM-3 was able to hit a sattelite which usually flies Mach 20, despite it being limited to Mach 10.

What is the practical speed difference a missile can hit something moving faster than it?

kinda-off topic question: Also what is harder target to hit? An normal standard Mach 2 fighter or MiG-25?
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Unread post14 Jun 2017, 01:41

armedupdate wrote:Most missiles need to much faster than target be able to hit them. For example, a Patriot cannot bring down ICBMs, even within terminal phase range. Is this mostly a sensor resolution problem of errors? I imagine radar technology advancing enough is able to get perfect sensitivity it can hit a non-manuvering target without manuvering(just intercept). I believe an AEGIS SM-3 was able to hit a sattelite which usually flies Mach 20, despite it being limited to Mach 10.

What is the practical speed difference a missile can hit something moving faster than it?

kinda-off topic question: Also what is harder target to hit? An normal standard Mach 2 fighter or MiG-25?

Velocity is relative, so the limit involves how much time the interceptor has to observe the target, predict its course, and maneuver to intercept. This can be literally impossible if the target's course is outside of the range the interceptor can get to, or if the target is capapable of dodging.
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Unread post14 Jun 2017, 07:10

I think the problems with Patriot or any other regular SAMs to shoot down ICBMs or other similar extremely fast targets are these:

- They need their own radar(s) to track the target to be able to shoot it down. Most radar systems are totally incapable of handling targets that fast and would require very specialized radar to track such a target. For Ballistic missile protection there usually is specialized radar which only looks in some fairly narrow sector for very fast targets. It's very difficult to make a radar which can track both slow and fast targets at the same time. Even more difficult when they have totally different flight profile.

- Even if radar was capable of tracking such a target, there would be very little time from target detection to it detonating. Regular SAM radars could even theroretically give time to react which would be measured in seconds. This means the system would have very short range and altitude coverage against such a target, making them basically useless against such extremely fast target.

I don't think missile needs to be faster than target necessarily. Against receding or most crossing targets that woud be the case naturally. But against incoming targets, missile can hit even if target is faster. Naturally the faster the missile is, more energy it has to maneuver and thus increase chace of hitting the target. Problem with older missiles has been inefficient guidance laws and systems which meant they followed inefficient trajectories bleeding speed and energy. This is an area where huge improvements has happened and newer missiles have much better guidance systems. For example AIM-120D has far longer range than AIM-120A. Some of that is because of somewhat larger rocket motor with more fuel, but most of it is because of better guidance system.
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Unread post14 Jun 2017, 20:03

It seems speed and radar tech is a main contributor. Since modern radars are not accurate enough to get 100% resolution and accuracy, by terminal intercept the missile still has to make a good adjustment to find the target and that can need lot of energy. The AEGIS shot against the sattelite was of course of exception since in space there is no drag when turning, the seeker can look everywhere and not loose energy and it is much easier to loiter one area with the thrusters.
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Unread post15 Jun 2017, 00:33

Radar is used to detect and track the target, but, as far as I know, all of the kill vehicles use IR cameras to accomplish the final intercept.
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Unread post15 Jun 2017, 05:04

The original post is wrong. Dont need for missile to move faster than target. As long as the missile can reach target, it can hit it. For an inbound target, its possible that a sam is slower than target. For a chase, the missile will need to be faster than target.

The issues for ballistic missiles was previously trajectory rather than speed.
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Unread post15 Jun 2017, 08:26

The problem is even in head on intercept the missile can still be off before terminal engagemnt due to sensor accuracy, having good speed is practical so there is speed saved when the turn happens.
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Unread post15 Jun 2017, 10:47

Thats why there are high powered illuminators to manage sensor accuracy. Nothing to do with shooter missile speed. The ossue for earlier illuminators was, as i understand, trajectory.
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Unread post16 Jun 2017, 01:31

Speed gives you the ability to hit the incoming target sooner, higher and farther away. That in turns permits you to look at the debris post hit and fire again if needed. They call it: Shoot Look Shoot. I have yet to find on the net anything that tells me what speed an interceptor needs to be to take out an ICBM or any other missile. The best blog site, and it's fascinating a read is: https://mostlymissiledefense.com/ You'll spend hours reading the posts.
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arian

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Unread post18 Jun 2017, 23:56

The main problem is time, which translates into range, which translates into speed. Speed determines the range at which you can intercept the incoming missile, and that's why it matters.

In essence, once you detect a ballistic missile launch (wither it is a tactical or ICBM doesn't matter, other than of course for the closing speed issue, and hence the greater range needed), the computer of the interceptor battery needs to calculate a point of intercept: that is it needs to predict where the target ballistic missile will be at the time when the interceptor reaches it.

Doing so comes with lots of error, and how much error is allowed in the point of intercept prediction is going to be a factor of how fast the interceptor can correct its trajectory and on the range of its on-board sensors (whether it is some sort of terminal IR guidance or terminal radar guidance etc). On board sensors have a limited range, so by the time they activate, the interceptor needs to be close enough to the target ballistic missiles for the sensor to pick it up. And of course the angle at which the two are moving, and whether the interceptor has enough fuel and energy to correct its trajectory in time to intercept.

So basically, the ballistic missile is detected. Its trajectory is calculated with a predicted flight path. That flight path is corrected as time goes by to become more accurate. But it needs to be pretty accurate, as it's not unlikely you'll be off several kms initially, and then dropping to several hundred meters, and hopefully several dozen meters by time of the final kill phase.

All this takes time. Updating predicted point of intercept, getting the interceptor in position, giving the interceptor enough energy to maneuver into position as the point of intercept is updated etc.

Since all this takes time, that translates into range. You may need to...start...your engagement when the target ballistic missile is several thousand miles away in the case of an ICBM, in order to intercept it at several hundred km range. Which means you need a really long-ranges interceptor to reliably be able to engage an ICBM.

The same applies to tactical ballistic missiles, but since they are much slower, the engagement range and time is also much smaller. Or some interceptor missiles (like PAC-3) can have a lot more maneuverability due to their thrusters, and hence the engagement zone can be much smaller.

The main reason a vanilla Patriot (not PAC-3) can't engage ICBMs is because it doesn't have enough time to get into the engagement zone, and the missile doesn't have time to maneuver into position. Not sure being faster would help it here.

Yes perhaps increasing the sensitivity of the radar or the computing power to better predict a point of intercept may help in gaining better probability of intercept. But maybe we're over-estimating the ability of radars or computers to actually do this. And even if you had all the computing power in the world to do it, that doesn't mean that you can predict a good point of intercept because what determines that is what the target ballistic missile does, which you can't know.

None of these senors are instantaneous. It takes several seconds, depending on the closing and lateral speeds, to get a good enough "fix" on where to hit the target with the on-board sensors of terminal kill vehicles (I'm guessing, of course I don't know). And at the speeds involved, several seconds is a long range. So just on that, a Patriot couldn't engage it because even if you had the physical ability to get into position, you may not have enough time to actually calculate an accurate enough position. A 100-200km max-range missile, which translates to maybe a 20-30km range engagement, just isn't anywhere near enough time for engaging an ICBM.

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