reported AIM120 odd behaviour (Target selection on pitbull)

[falcon_120]

Mission: F18 AIM 120 Amraam (Base game mission)

 

Behavior: Target locked on stt, Amraam on pitbull goes for totally different target (original target is turning to my right, while the target the AIM120 decides to engage is flying straight and slightly to the left. This happens on the second launch approx 1.30 min after track starts.

 

Expected behaviour (could be totally wrong): Since the Aim120 is being supportef in STT all the way (and maintained prior and after TTA), and given differences in target  aspects, the AIM120 should have an easy time discerning between those targets based on velocity gates and target aspect. This is considering this has been implemented in the last patch as advertised.

 

Please review to see if its normal behavior or maybe any of the parameters used to discern targets is not working as expected.

 

EDIT: Attached second track, this time happens on the first launch.

Amraam bug.trk

Amraam bug 2.trk

Edited October 21, 2021 by falcon_120

[nighthawk2174]

Odd with the datalink now that shouldn't happen, even post pitbull datalink updates are sent to the missile and would prevent this.  This is why shooting into furballs with 120's is a thing that can be done IRL.

[Cmptohocah]

4 hours ago, nighthawk2174 said:

Odd with the datalink now that shouldn't happen, even post pitbull datalink updates are sent to the missile and would prevent this.  This is why shooting into furballs with 120's is a thing that can be done IRL.

How's the missile's and/or airplane's radar supposed to discriminate targets in a fur-ball? Positions and speeds are dynamically changing all the time.
 

[Harker]

How's the missile's and/or airplane's radar supposed to discriminate targets in a fur-ball? Positions and speeds are dynamically changing all the time.
 

Maybe they're not in a turning fight, but just close to each other. IRL, assuming that your radar can differentiate them, it can communicate this information to the missile, even after it goes active, in order to help it locate the correct target.

In DCS, once a FOX3 goes active, the datalink is severed and the missile goes to the first/closest target it sees. I haven't tested it yet with the new implementation for the AMRAAM, maybe that changed.

[Cmptohocah]

1 hour ago, Harker said:

...

In DCS, once a FOX3 goes active, the datalink is severed and the missile goes to the first/closest target it sees. I haven't tested it yet with the new implementation for the AMRAAM, maybe that changed.

Pardon my ignorance, but isn't this how it's supposed to work? From what I understand, DL is there to give the missile mid-course guidance until it's own seeker can pick up the target and guide autonomously.
 

[Harker]

Pardon my ignorance, but isn't this how it's supposed to work? From what I understand, DL is there to give the missile mid-course guidance until it's own seeker can pick up the target and guide autonomously.
 

No, the DL remains active throughout the entire engagement (if possible). This means that, once active, the missile correlates datalink data with its own seeker data for optimal tracking.

This means that even if you, for example, somehow manage to notch the missile's radar, it'll still be able to guide via datalink updates and get close enough for a proximity detonation. And vice versa. This is one of the things that make such missiles extremely dangerous - it might be possible to notch the fighter or the missile, but it is almost impossible to notch both at the same time, since their radars usually paint you from different directions.

[Cmptohocah]

59 minutes ago, Harker said:

No, the DL remains active throughout the entire engagement (if possible). This means that, once active, the missile correlates datalink data with its own seeker data for optimal tracking.

This means that even if you, for example, somehow manage to notch the missile's radar, it'll still be able to guide via datalink updates and get close enough for a proximity detonation. And vice versa. This is one of the things that make such missiles extremely dangerous - it might be possible to notch the fighter or the missile, but it is almost impossible to notch both at the same time, since their radars usually paint you from different directions.

I see, that's interesting.
I could be totally wrong on this one, but I doubt DL will be accurate enough to get the missile close enough to the target without homing, but I guess it supplements the missile's radar.

[nighthawk2174]

2 hours ago, Cmptohocah said:

Pardon my ignorance, but isn't this how it's supposed to work? From what I understand, DL is there to give the missile mid-course guidance until it's own seeker can pick up the target and guide autonomously.
 

From various manuals we have 1-F15C-34-1, HAF1-F16C-34, MLU, a1-f18ac-nfm-700c, and a few others the datalink updates are not severed at pitbull they continue until missile timeout.  What your saying is how it used to work in DCS (well hopefully used too), but that was not accurate.  As was said by Harker this allows the missile to have an extra layer (ontop of the already op monopulse stuff) of countermeasures to notching and CCM teqniques. 

1 hour ago, Cmptohocah said:

I see, that's interesting.
I could be totally wrong on this one, but I doubt DL will be accurate enough to get the missile close enough to the target without homing, but I guess it supplements the missile's radar.

It should be more than good enough to get it close enough that the seeker will be able to get that last little bit of terminal guidance.  But yes if your in a 6 bar scan updates will be slow to be sent and it may not be enough if some really lucky (for the bandit) situations.  Hence why they often train for STT shots on closely grouped bandits according to the navy's BVR manual that's out there the update rate from STT should be well beyond adequate to get it close enough.   Plus getting it close is all that really counts at some point its going to become impossible to notch the amraam's seeker the S/N ratio will be too high and it will be too hard to stay in the notch, in theory this should occur at a few miles from the bandit.  Which is more than enough time for the amraam's seeker itself  to find/reacquire the target.  Monopulse seekers like the one on the amraam should have amazing range and azimuth resolution so getting it close should be well beyond good enough.   

[SgtNathan]

Please excuse me if this is not the same issue, or even an issue at all, however, on my very first engagement this patch I had multiple of my 120's miss their targets. On further investigation while watching the Tacview recording I found that were switching targets when nearing the locked aircraft, which happened to be STT locked the entire time.

Link to Tacview replay

Follow the second missile fired by me "JEDI 1-1 | Noot" in a F-16 at +3:19:54, and notice how when it nears the locked aircraft, it stops tracking the Su-27 and instead starts tracking my first fired missile.
Later, at +3:20:36, I fire my third missile, and while initally tracking the still STT'd Su-27, it then suddenly targets the R-73 fired by the Su-27 instead.

Edited October 28, 2021 by SgtNathan

[GGTharos]

On 10/27/2021 at 11:18 AM, Cmptohocah said:

I see, that's interesting.
I could be totally wrong on this one, but I doubt DL will be accurate enough to get the missile close enough to the target without homing, but I guess it supplements the missile's radar.

Not accurate enough for a direct hit in either TWS or STT, but accurate enough to choose a target among many (hereto referred to as 'the correct target').

In the -34s it is mentioned that the 120 Pk does not change whether it is supported or not once pitbull, which implies that the 120 stops processing the DL once locked on.  It may start listening to it again if it loses the target (the phoenix certainly does) but otherwise it's on its own.

No missile should be shot into a furball, as it can be aimed at the wrong target to begin with or it can switch to the wrong target under certain circumstances (the former demonstrated so well in SATAL ) regardless of the guidance being used (SARH, ARH, IRH).

 

But the other caution here is that despite what's written in these almost 3-decade old manuals in some cases, with the 120 this is all mostly software.  All of this behavior could change with a software update, subject only to the missile's hardware limitations.

[KenobiOrder]

53 minutes ago, GGTharos said:

In the -34s it is mentioned that the 120 Pk does not change whether it is supported or not once pitbull, which implies that the 120 stops processing the DL once locked on.  It may start listening to it again if it loses the target (the phoenix certainly does) but otherwise it's on its own.

It states that it does, listen that is, even after pit bull for the purpose of maintaining track or reacquiring. And in STT I would think the tracking would be more than adequate to guide the missile to impact if necessary.

 

[GGTharos]

23 minutes ago, KenobiOrder said:

It states that it does, listen that is, even after pit bull for the purpose of maintaining track or reacquiring.

It doesn't.   I mean you can call it listening or processing, it's largely irrelevant.  The DL has no impact while the missile is homing.

23 minutes ago, KenobiOrder said:

And in STT I would think the tracking would be more than adequate to guide the missile to impact if necessary.

No it isn't, which is why the missile must home on the target.

[KenobiOrder]

1 hour ago, GGTharos said:

It doesn't.   I mean you can call it listening or processing, it's largely irrelevant.  The DL has no impact while the missile is homing.

I didnt say the datalink had a overrides the homing, but the missile continues to receive updates via link in case it loses track or needs to sort a bandit. This is stated unambiguously.

1 hour ago, GGTharos said:

No it isn't, which is why the missile must home on the target.

why exactly? STT locks guide missiles all the time.

Edited October 28, 2021 by KenobiOrder

[nighthawk2174]

2 hours ago, GGTharos said:

It doesn't.   I mean you can call it listening or processing, it's largely irrelevant.  The DL has no impact while the missile is homing.

No it isn't, which is why the missile must home on the target.

We have multiple manuals from the F15/F16/F18 that all make it explicitly clear that DL continues after pitbull and is referenced by the missile in case of multiple targets in close proximity or if the target fades.

[GGTharos]

I didn't say it doesn't continue, I said that the missile does not process it while homing.

44 minutes ago, KenobiOrder said:

why exactly? STT locks guide missiles all the time.

They do not.  They illuminate the target, the missile guides itself - ie. homing.

[KenobiOrder]

11 minutes ago, GGTharos said:

I didn't say it doesn't continue, I said that the missile does not process it while homing.

Yes, thats also what I said. And my orginal post was just meant to affirm what you were saying since you said "may." So I dont think you understood my meaning.

 

11 minutes ago, GGTharos said:

They do not.  They illuminate the target, the missile guides itself - ie. homing.

Based on? All of the information available states that if the missile loses track it reverts to the link. Where is are sources that says that link cant guide the missile to the target if the missile never recovers track?

3 hours ago, KenobiOrder said:

It states that it does, listen that is, even after pit bull for the purpose of maintaining track or reacquiring.

 

Edited October 28, 2021 by KenobiOrder

[Cmptohocah]

8 hours ago, nighthawk2174 said:

We have multiple manuals from the F15/F16/F18 that all make it explicitly clear that DL continues after pitbull and is referenced by the missile in case of multiple targets in close proximity or if the target fades.

Would be great if you could share some of the material in its original form.

Also very interestingly, what happens if there are multiple targets in close proximity and the launching platform that is providing the DL suddenly switches to the wrong target, while the AMRAAM is tracking the correct one? Should it follow the DL or ignore it?

 

7 hours ago, KenobiOrder said:

Based on? All of the information available states that if the missile loses track it reverts to the link. Where is are sources that says that link cant guide the missile to the target if the missile never recovers track?

 

 

If the DL alone could guide the missile to the target, there would not be any need for homing.

[KenobiOrder]

34 minutes ago, Cmptohocah said:

If the DL alone could guide the missile to the target, there would not be any need for homing.

Lots of missiles are guided via command. Active guidance adds launch and leave capability and a slew of other things.

[Cmptohocah]

3 hours ago, KenobiOrder said:

Lots of missiles are guided via command. Active guidance adds launch and leave capability and a slew of other things.

From what I know 100% of A2A missiles in DCS use some sort of homing - IR, active radar, semi-active radar.

DL is used to bring the missile to the point where it's seeker can pick up the target and after that home in onto it, with the exception of IR ones of course.

ARH missiles are only "fire and forget" if their radar already is in range, which in DCS is I believe 13-15km (could be wrong on the actual numbers). They only true "fire and forget" A2A weapons are IR missiles.

Note: I am not talking about A2A passive guided radar missiles as we don't have those in DCS.

Edited October 29, 2021 by Cmptohocah

[GGTharos]

5 hours ago, Cmptohocah said:

Also very interestingly, what happens if there are multiple targets in close proximity and the launching platform that is providing the DL suddenly switches to the wrong target, while the AMRAAM is tracking the correct one? Should it follow the DL or ignore it?

Once the missile is homing it ignores the DL data.  The statement is that the Pk is not affected by loss of DL at that time.

4 hours ago, KenobiOrder said:

Lots of missiles are guided via command. Active guidance adds launch and leave capability and a slew of other things.

They aren't.  Receiving target position is not 'command'.   Command is a specific type of guidance used by a bunch of SAMs.

The closest that we know AAMs have come to it is the Phoenix missile where the sensor is commanded to look in a certain direction - but actual command guidance literally steers the missile, and the missile itself needs no sensor beside the fuze.

[dundun92]

11 hours ago, Cmptohocah said:

Also very interestingly, what happens if there are multiple targets in close proximity and the launching platform that is providing the DL suddenly switches to the wrong target, while the AMRAAM is tracking the correct one? Should it follow the DL or ignore it?

The missile does not use the DL if it has a stable track itself, only if it has "difficulty acquiring or maintaining a track", or for a "reference if missile seeker sorting of multiple targets is required" (exact manual wording). In other words, it uses DL if it has trouble in initial acquisition (either from multiple close targets or poor SNR on a single one), and if it looses/has trouble holding a lock and needs to reacquire.

Edited October 29, 2021 by dundun92

[nighthawk2174]

13 hours ago, Cmptohocah said:

Would be great if you could share some of the material in its original form.

All of them are ITAR and a few I was given by people who asked me not to share the files.  I wish I could share everything but I can't.  I know that the MLU and F16 stuff is easy to find and the F18 radar manual is somewhere out there.

13 hours ago, Cmptohocah said:

Also very interestingly, what happens if there are multiple targets in close proximity and the launching platform that is providing the DL suddenly switches to the wrong target, while the AMRAAM is tracking the correct one? Should it follow the DL or ignore it?

In close proximity the seeker will use the datalink updates to compare and track on the desired target.   From my current understanding of what's said is that the missile will select the target that best matches the host radars updates in terms of position and speed.  So if you have a two ship in a blue angles tight figertip and one suddenly breaks out right as the missile is going active  as far as i'm aware the missile should continue on to track the one that went straight.  It's less clear what happens after the initial sorting as these specific manuals really only talk about the moment the seeker is searching for the target and if the target is lost due to notch/ECM.  This exact situation though probably wouldn't happen at all as the host radar itself probably wouldn't switch onto the new target breaking away as it itself would be able to see there are two targets and that one has a now very different position and Vc while the other matches the predicted location and Vc of the tracked target, simple it would just build a new track/ignore the breakaway contact.  In short I don't think this is really an issue.

13 hours ago, Cmptohocah said:

If the DL alone could guide the missile to the target, there would not be any need for homing.

DL could probably get it a lot closer than I think you imagine it would but not close enough to 100% reliably trigger the proxy fuze to not need terminal homing.  Plus if contact is lost by the main radar the missile would be just as trashed as a SARH having a seeker on the target eliminates this weakness.  If the amraam's warhead was bigger this probably would be a lot more effective but since its a smaller warhead you need to get closer to the target which you need terminal radar homing for.  So regardless of how accurate the DL is terminal homing is needed otherwise you might as well just make a sarh missile.

7 hours ago, GGTharos said:

Once the missile is homing it ignores the DL data.  The statement is that the Pk is not affected by loss of DL at that time.

Both the F15 and F18 manuals are pretty clear in that datalink updates continue till missile timeout and will be referenced if needed.

 

Edited October 29, 2021 by nighthawk2174

[GGTharos]

49 minutes ago, nighthawk2174 said:

Both the F15 and F18 manuals are pretty clear in that datalink updates continue till missile timeout and will be referenced if needed.

Yeah I didn't say anything different.  The missile ignores it once homing.

Edited October 29, 2021 by GGTharos

[Santi871]

The range at which it starts ignoring DL updates is variable and depends on "several parameters". This implies that after a certain point in certain conditions, the 120's seeker can get a much better track than a radar further away could hope to achieve.

It also implies like GGTharos said that incorporating more updates makes the Pk no better (possibly even worse). Here's a public source that isn't ITAR controlled and so can be posted here.

https://trace.tennessee.edu/cgi/viewcontent.cgi?article=6680&context=utk_gradthes

Quote

AMRAAM performance is most sensitive to the last data link it incorporates into its guidance solution²². Usually the last data link used by the missile is one of the last data links sent to the missile, but not necessarily the last data link. At a specific range based on several parameters, the AMRAAM stops incorporating data links received into its guidance solution. The aircraft can estimate, but does not know when the AMRAAM will stop using data link information in its guidance solution. Variation in data link errors during later data links in particular could potentially impact AMRAAM performance.

Edited October 29, 2021 by Santi871

[Gianlc]

What is the logic that the missile uses on pitbull to choose a contact? If you shoot and don’t maintain Rdr lock until pitbull and don’t have the target on DL, what will tell the missile which contact it should lock on to? How will it choose it’s target?