reported HARM tracking when enableEmission false, setOnOff false, or Alarm State green after HAS launch

[MartinCo]

Hi ED,

With the most recent patch HARMs are pin point accurate even when the radars are set to enableEmission false, setOnOff false, or the alarm state green after a launch.

I have rolled back to DCS 2.9.17.12034 and this behavior was not present.

I believe this is true in the 18 as well (based on earlier thread) and a general HARM issue.

DCS Version: DCS 2.9.18.12722

Reproduction:

* Set up HAS for BB, SD, P, HK
* Launch one harm at each target at > 30nm
* setEmission Off via F10 menu
* Note that RWR indications are removed as they are off
* HARMs continue and precisely hit all 4 targets

It seems the HARMs have the precise coordinates immediately and INS rather than radar homing

Video: 

Please find mission/track:
 

Mission: harms.miz

Track File: harm-emission-off-tracking.trk

 

Thanks,
MartinCo

 

Edited Sunday at 06:28 PM by MartinCo
added info on rollback not showing this issue

[EricJ]

I don't fly the F-16 but the HARM is designed to remember the location of the emitting radar if it goes off. That was a feature added to real world HARMs due to experience with the Vietnam War when SAM radar operators turned off their radars due to a Shrike or Standard ARM attack and confuse the missile. If I'm reading right then that's intended behavior.

[MartinCo]

It was the AGM-88D that got upgraded to have GPS and ability to engage targets after turning off their radar - not our AGM-88C (which to my knowledge only used radar homing)

Just tested in POS/EOM just toggle launch too - ripple them all within a few seconds and then turn off the emitters - still precise hits from 35+nm

This does make all IADS systems / Skynet etc. a bit pointless (since if the harm will hit anyhow, no point going silent) - and didn't used to be the case (else these projects wouldn't have existed!)

Edited Sunday at 03:00 PM by MartinCo

[EricJ]

I just googled it and it says the C can still engage if the radar is shut off, and isn't as accurate, The D model is more accurate though, through the GPS/INS and so on.

Edited Sunday at 03:44 PM by EricJ

[MartinCo]

Right - but this is pin point accurate after turning them off immediately after launch from more than 30nm without much time to evaluate and refine the target and reduce the CEP

I just downgraded to the previous patch (DCS 2.9.17.12034) and they all missed, both in HAS, POS/EOM etc. which is very different to the current patch

 

Edited Sunday at 06:33 PM by MartinCo

[DSplayer]

This month's patch included some changes to the HARM that were not included in the changelog. Now, a HARM upon target loss will attempt to hit the last known INS position of the target while attempting to search for the signal. The HARM is not laser pinpoint accurate in INS, but can still get close enough to kill the targets as is in your case. I will note that if you were to make the radars stop emitting even earlier in flight, the miss area would increase further.

In previous patches (like the June patch), the HARM after target loss basically didn't fallback to its INS and continued the last command it had before target loss. That behavior was not correct.

There are also some other HARM changes like I said, but they're slightly unrelated to this specific case.

[Skarp]

9 hours ago, DSplayer said:

This month's patch included some changes to the HARM that were not included in the changelog. Now, a HARM upon target loss will attempt to hit the last known INS position of the target while attempting to search for the signal. The HARM is not laser pinpoint accurate in INS, but can still get close enough to kill the targets as is in your case. I will note that if you were to make the radars stop emitting even earlier in flight, the miss area would increase further.

In previous patches (like the June patch), the HARM after target loss basically didn't fallback to its INS and continued the last command it had before target loss. That behavior was not correct.

There are also some other HARM changes like I said, but they're slightly unrelated to this specific case.

The harm is hitting the point exactly. Its only variation of the hit is because it’s guided by INS not GPS. So it’s a bug from the patch  

Edited 15 hours ago by Skarp

[okopanja]

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[okopanja]

19 hours ago, EricJ said:

I just googled it and it says the C can still engage if the radar is shut off, and isn't as accurate, The D model is more accurate though, through the GPS/INS and so on.

Super precise INS for this missile would mean that it does not need expensive seeker, once the position of the target is determined (e.g. pre-launch on carrier), it would simply be enough to use it's INS without GPS if this was a real thing.

Sadly, this is not the case and even the later version you mentioned had to have GPS updates for this particular reason.

Depending on the mode the trajectory can be calculated based on the rough distance or without it in which case only the angular position can be used. 

Furthermore range/azimuth estimation is very rough at the start and requires to be constantly updated with the corrections based on the seeker readings. E.g. firing HARM at long distance and loosing signal earlier would result in much higher miss distance than e.g. firing it from just 5km away. 

As the distance at which the HARM is fired is longer, the time required to reach the target is also longer, and the drift of the INS will be progressing and cumulative. At the current state in DCS you can fire HARMs for 100-ish km away and still get it to hit the target with accuracy, simply this is not realistic.

One additional note: thanks to this change HARM now also hits objects that move. This involves e.g. Tor (features ability to move and shoot), but e.g. very maneuvering Su-27 while it is jamming. 

To conclude this change was half baked and results in yet another departure from realism.

[EricJ]

I mean I can't say you're wrong but overall I don't do anything whatsoever with the kinematics of an AGM-88C, but I do know it's not a silver bullet that's for sure, at least in the sim. As for real life we'll have to have somebody who actually fired them to weigh in, because I'm not that guy.

[[ED]Ben]

Thanks all - reported for investigation.