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SARH missiles guidance


85th_Maverick

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Sorry that I need to address the same question which I've put some 5+years ago (the initial thread got closed), but I'd like to ask again:

 

If you fire a SARH missile at a locked target and then you lose lock, then re-lock that target, shouldn't the missile re-acquire the target or simply follow the new reflected radar signals (be it a chaff or a real target, whatever)?

 

AFAIK the SARH missiles doesn't have an own radar, but only a radar signals receiver in it's nose and/or a sort of datalink for course updates that are given by the launching platform's (aircraft for instance) fire control computer inputs according to the radar signals detected by the launching platform in order to lock a target. In other words, the SARH missile's guidance should be slaved and listen to the info/inputs given by the plane's (or ground platform's) onboard radar whenever that radar will give info to the missile or follow a specific radar signal reflected from the target onto the missile's radar receiver.

 

Why does the SARH missile no longer listen to targeting info once the first lock has been lost? I would've thought that you could fire a SARH missile without an initial lock (using weapons launch override) towards a target and if you lock that target later, the missile would then start listening to the FCC and own plane's radar and go where it's continuously directed by the received radar's signals and not fall blind like a brick. Maybe some of us know about the technique that an SA-6 used to down an F-16. They've used their radar for 2-3 sweeps to determine the target's vector info, turned it off, fired the missile on an estimated intercept course, turned on the radar at a calculated time, the missile started listening to the radar's info after tracking the target and hit the F-16. What's different in DCS that this may not happen on any platform (aircraft or sam)?

 

Thanks!


Edited by 85th_Maverick

Good knowledge and common sense make the absurd run for defense.

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If you fire a SARH missile at a locked target and then you lose lock, then re-lock that target, shouldn't the missile re-acquire the target or simply follow the new reflected radar signals (be it a chaff or a real target, whatever)?

 

Maybe. Depends on the missile, on the entire system.

 

AFAIK the SARH missiles doesn't have an own radar,

 

Yes it does. Just because it doesn't have an emitter doesn't mean it's not a radar.

 

Why does the SARH missile no longer listen to targeting info once the first lock has been lost?

 

Depends on the system. Lots of missiles are capable of performing a search after the target is lost. How long they perform it for and with what parameters depends on the missile.

 

Maybe some of us know about the technique that an SA-6 used to down an F-16.

 

And some of us also know that SAM systems and AI systems are designed and operated differently. Don't expect stuff that works with SAMs to work with AI systems. In particular, don't expect your 27s to track if you launch them without a lock. The fire control system will assume you wanted to eject them and the seeker might not even power up.

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They've used their radar for 2-3 sweeps to determine the target's vector info, turned it off, fired the missile on an estimated intercept course, turned on the radar at a calculated time, the missile started listening to the radar's info after tracking the target and hit the F-16. What's different in DCS that this may not happen on any platform (aircraft or sam)?

 

Thanks!

I can't specifically answer your question with any accuracy, but the SAM encounter you mention sounds like it might have used a mode similar to FLOOD mode for the AIM-7 in DCS. I don't really use FLOOD much so I can't remember if you can turn off the radar at any point, but in the mode the missile doesn't follow a lock. However this also means that you have less control over what the missile does. The SAM operators may have used a specific mode that was advantageous in their situation, but might not always be the best choice. STT, which is used with most SARH missiles, is intended to track a single, specific target. It may be desirable (or just a consequence of design) for the missile to reject locks that don't correspond to the original STT target.

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I can't specifically answer your question with any accuracy, but the SAM encounter you mention sounds like it might have used a mode similar to FLOOD mode for the AIM-7 in DCS.

 

It's a ballistic launch, it may work in different technical ways for different SAMs, and we don't know anything about the tuning/operation of these SAMs. SAMs are better set up to give you the ability to do things more manually, whereas AI systems are deliberately set up to be very automated.

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As has been mentioned before this does depend a lot on the missile system in question, but one important thing is that usually between losing the lock and reacquiring it, everything has moved a considerable distance. The target moved a lot - even if it's just in a straight line - the missile probably darted off on a straight line and the radar emitter/launching aircraft has moved as well.

The thing is, chances are your new lock is already outside the 'field of view' of the missile after a few seconds. Varies with type, of course.

The deal with FLOOD mode (and its relatives) is pretty much saying to the missile: 'Look, I can't get a target lock for whatever reason, so I'll just illuminate a wide area as best as I can. If you happen to see a decent reflection off anything, just go with it!' It usually doesn't work well for longer distances, because the energy gets spread over too wide an area, so it might be as much about losing a lock as it is about just not having time to lock in a close engagement.

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Maybe. Depends on the missile, on the entire system.

 

Yes it does. Just because it doesn't have an emitter doesn't mean it's not a radar.

 

Depends on the system. Lots of missiles are capable of performing a search after the target is lost. How long they perform it for and with what parameters depends on the missile.

 

And some of us also know that SAM systems and AI systems are designed and operated differently. Don't expect stuff that works with SAMs to work with AI systems. In particular, don't expect your 27s to track if you launch them without a lock. The fire control system will assume you wanted to eject them and the seeker might not even power up.

 

Copy that Tharos! I really appreciate your answers!

 

As for the SARH, yeah, I meant it doesn't have an active emmiter as radar, has just a radar receiver receptor such as a signal gathering dish.

 

Kind regards!

Good knowledge and common sense make the absurd run for defense.

Flying has always been a great interest for mankind, yet learning everything about it brought the greatest challenge!

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I can't specifically answer your question with any accuracy, but the SAM encounter you mention sounds like it might have used a mode similar to FLOOD mode for the AIM-7 in DCS...

 

Just found it, this is what i was referring to:

 

 

Kind regards!

Good knowledge and common sense make the absurd run for defense.

Flying has always been a great interest for mankind, yet learning everything about it brought the greatest challenge!

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It's a passive radar, it does everything except emit the signal :)

 

For example, the sparrow has no data-link but, here's an idea of what it does:

 

When you press the trigger:

Tune missile to the radar if not already tuned

Spin up gyro and check BIT

Download target data - basically, the target vector but for the missile it's more long the line of 'turn in this direction for intercept, look at that direction with narrow doppler filter centered on this frequency'

 

So, the missile comes off the rail with all this info, fire the missile and executes the english bias turn (point seeker at target, point itself towards the intercept. Note the missile isn't even searching yet)

 

Once a little time has passed, the seeker starts looking in the desired direction for a radar signal centered on a certain frequency. This is the doppler signal center for your target, it's basically the closure component of your vector.

 

Note: This behavior is why pre-emptive CMs are a thing!

 

If it doesn't find a target, it'll throw the doppler filter open and continue the search.

 

If you launch without a lock, it performs this wide open search while your FLOOD horn illuminates as much stuff in front of the aircaft as possible.

 

In both cases, the missile picks up the launch radar's frequency on the rear antennas to use as comparison in order to determine the doppler shift (closure) of the target signal picked up by the seeker. This is why I keep saying it's a radar :)

 

Note the way the aircraft is designed here: If you don't launch in STT, FLOOD provides the STT signal automatically. The missile is tuned to pick up this signal. Launching with the radar off has the missile basically going off with nothing to look for.

 

There are other issues also, but let's go the SAM now.

 

A lot of SAMs have some sort of command back-up. That means you can have the missiles ready to launch balistically and still maintain some form of control over them, and wait to turn your radar on at the last moment. It requires you get data from somewhere else or a limited number of sweeps, and, it requires the target to cooperate.

 

So it's a neat ambush but it's not terribly useful in a large scale scenario. If you shut your SAM down like that you're unable to provide major defense and note that this method literally bagged one aircraft out of thousands of sorties.

 

 

Copy that Tharos! I really appreciate your answers!

 

As for the SARH, yeah, I meant it doesn't have an active emmiter as radar, has just a radar receiver receptor such as a signal gathering dish.

 

Kind regards!

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Now, about the SARH missiles: "Why does the SARH missile no longer listen to targeting info once the first lock has been lost?"

 

Maybe. Depends on the missile, on the entire system..

 

I admit that I've only looked on what wikipedia tells about SARHs in general, but, for example do you have any information about the capability of an AIM-7 or R-27 model which does just that? This way, no matter if the target has gone past the seeker's FOV, it will now receive mid-course commands via datalink or whichever form of data info (indeed, if the whole system is designed to support this also) from the "mother radar" and steer until it's seeker is again within the required FOV to track the reflected signals.

 

Kind regards!


Edited by 85th_Maverick

Good knowledge and common sense make the absurd run for defense.

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Sorry for going in so thorough into the subject, but it seems that the AIM-7 for instance does indeed use 2 signals for steering inputs: one from it's own receiving radar, the other as a backup from the launching aircraft's radar.

 

This is from wiki, indeed with little details, but probably just enough to confirm that the missile can start steering towards the target that is for a moment outside it's seeker's FOV:

 

"The missile detects the reflected signal from the target with a high gain antenna in a similar fashion and steers the entire missile toward closure with the target. The missile guidance also samples a portion of the illuminating signal via rearward pointing waveguides. The comparison of these two signals enabled logic circuits to determine the true target reflection signal, even if the target were to eject radar-reflecting chaff"

 

It is indeed talking about chaff discrimination from the real target by having the missile now "tell back" to the launching radar what it sees and the launching radar will tell: "no, that's not the right signal, that's a chaff", but may the same way it can also receive mid-course updates to steer towards the target that it's own radar receiver can't yet have in it's FOV. Idk, just a guess!


Edited by 85th_Maverick

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Can't tell that for sure, but keep in mind that having a rearward facing antenna that 'looks at the launch vehicle' isn't necessarily the same as some sort of datalink. The part you quoted at least doesn't say a thing about a report going back at all, which I believe isn't a thing a SARH missile is likely to do. The idea of that type of missile after all is that you do not have to lug along a bulky and heavy transmitter.

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Sorry for going in so thorough into the subject, but it seems that the AIM-7 for instance does indeed use 2 signals for steering inputs: one from it's own receiving radar, the other as a backup from the launching aircraft's radar.

 

It needs to know the reference signal from the launching aircraft for comparison with the signal reflected from the target to be able to extract the doppler shift (needed for e.g. the speed gate function and distinguishing targets from the ground clutter, I guess).


Edited by Dudikoff

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The AIM-7 has no datalink at all, while the R-27 data-link is only transmitted for a portion of the flight time. There's little information on when those missiles 'give up' after they lose track.

 

 

 

This way, no matter if the target has gone past the seeker's FOV, it will now receive mid-course commands via datalink or whichever form of data info (indeed, if the whole system is designed to support this also) from the "mother radar" and steer until it's seeker is again within the required FOV to track the reflected signals.

 

Kind regards!

[sIGPIC][/sIGPIC]

Reminder: SAM = Speed Bump :D

I used to play flight sims like you, but then I took a slammer to the knee - Yoda

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What dudikoff said.

 

 

The rear waveguides pick up the launching aircraft's radar signal, like I mentioned in my first response to you. It's used to get the doppler shift (closure) by comparing the frequency of this signal to the one received by the seeker. Nothing else is happening there.

 

 

The missile rejects chaff by itself - since chaff slows down quickly, its doppler shift will be different from that of the targets in no time at all.

 

 

 

It is indeed talking about chaff discrimination from the real target by having the missile now "tell back" to the launching radar what it sees and the launching radar will tell: "no, that's not the right signal, that's a chaff", but may the same way it can also receive mid-course updates to steer towards the target that it's own radar receiver can't yet have in it's FOV. Idk, just a guess!

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Ok, a question here. Let's say you launch an SARH missile which doesn't have a datalink. It uses INS to get to a point where it should start detecting radio returns from the launching aircraft's radar, and gets to tracking the target. The missile knows the radio frequency (which was sync'ed before launch) and thus would not go for reflections from other aircraft (on different frequencies).

Now, if the missile loses the reflections for x seconds, should it not be able to detect the reflections again if they are within its FOV, or within the software-defined timeout? Think of it like any other sensor with some software logic controlling the behaviour

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Sure, but that software was pretty 'hardcoded' back in the day.

 

 

A SARH AAM without datalink expects to detect a target right away. Right after the english bias maneuver, the seeker begins to search.

Shooter's waveform is received on the rear waveguides after launch.

 

 

 

Ok, a question here. Let's say you launch an SARH missile which doesn't have a datalink. It uses INS to get to a point where it should start detecting radio returns from the launching aircraft's radar, and gets to tracking the target. The missile knows the radio frequency (which was sync'ed before launch) and thus would not go for reflections from other aircraft (on different frequencies).

Now, if the missile loses the reflections for x seconds, should it not be able to detect the reflections again if they are within its FOV, or within the software-defined timeout? Think of it like any other sensor with some software logic controlling the behaviour

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It is indeed talking about chaff discrimination from the real target by having the missile now "tell back" to the launching radar what it sees and the launching radar will tell: "no, that's not the right signal, that's a chaff", but may the same way it can also receive mid-course updates to steer towards the target that it's own radar receiver can't yet have in it's FOV. Idk, just a guess!

 

As was stated in previous posts, no, it's not talking back to the launching aircraft, but internally comparing what it sees coming off the launching aircraft's radar (which has to be doppler shifted because the missile is travelling away from the aircraft at great speed) via the rear antenna with what it's seeing come off the target (which should be something other than zero) via the nose antenna. Chaff slows down quickly so that radar return is filtered out as doppler reaches zero, it then looks for one in the appropriate frequency range, hopefully finding the target again. The size of these doppler filters and how fast the missile can reacquire and how fast it scans it's detection cone etc. etc. are the super classified bits.

 

This is why you notch the launching aircraft/missile and dump chaff. Get the seeker off you and looking out into space and going away from you.

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See, that's the thing. The target's return signal is highly dependent on the geometry, the environment, the material, presence of any other EM radiation in the same frequency band (jammers, for instance), even multipath. So, the receiver logic already knows that the received echo could vary up to a certain extent. The SARH missile separates from the rail, looks for the target's return signal, essentially something which responds back above the required SNR margin.

 

 

 

Now, theoretically, shouldn't the logic be there to expect temporary loss of signal (perhaps not complete, but below the noise gate), but as long as it sees a reflection from the target in its field of view, shouldn't an SARH missile (at least the modern AAMs) be able to reacquire its target? This wouldn't require a datalink either.

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Now, theoretically, shouldn't the logic be there to expect temporary loss of signal (perhaps not complete, but below the noise gate), but as long as it sees a reflection from the target in its field of view, shouldn't an SARH missile (at least the modern AAMs) be able to reacquire its target? This wouldn't require a datalink either.

 

Considering the missile will generally continue in the same direction it was going when it lost signal, you don't really need a dedicated circuit for this logic, but you can put in delay circuits so that the signal drops off "slowly" instead of instantly throwing it into the search logic, so if you do reacquire "quickly" it's already looking in the best place.

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TO add to this, that missile's radar has a 6deg instantaneous FoV. It's not a lot, and if it loses its target for more than a very short time, that target will run right out of any reasonable search zone that the missile can implement in the short amount of time it has to do so ... that's assuming it even executes a search pattern, rather than staring in a specific direction.

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I've had it happen in the F-14B, that a target was lost after a BVR AIM-7M shot, but switching quickly enough to a WVR radar mode allows the missile to pick the target back up and intercept it :)

I was quite happy to see that, since the AWG-9 seems to be very prone to loosing lock when both the launching aircraft and the target are vividly manoeuvring...

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I always heard the 530D has this ability. But never flown the Mirage(yet). Anyone confirm?

 

It does, at least in DCS, IDK if it is realistic.

IRCC, the longest time I had a lost lock and the missile still hit was around 5 seconds, quite impressive :)

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