4.37.3 AIM120 AQUISITION MODEL
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@Mav-jp Thank you for the info. Was a good read
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@Mav-jp very interesting. So it boils down to the Amraam knows where it is because it knows where it isn’t
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That is an impressive piece of research
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Nice.
It is not clear to me the followings:
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How is modeled the radar scan of the missile? Scan rate (angle sec/bars?) If the FRQ of the radar is known based on the size is is an easy calculation to determine the beamwidth. We can assume 10 GHz, almost every ARH uses the FRQ. Is it / will be modeled the scan?
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Where came the info that the AIM-120 is able to operate both with HPRF and MPRF? I have no idea about the modes of the AIM-120. But even the huge R-37M has only HPRF mode based on its detection distance against incoming / receding targets. (~3 times difference. between incoming and receding target of the R-37 could perform both HPRF and MPRF the distance would be only half against receding targets.)
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@molnibalage said in 4.37.3 AIM120 AQUISITION MODEL:
Nice.
It is not clear to me the followings:
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How is modeled the radar scan of the missile? Scan rate (angle sec/bars?) If the FRQ of the radar is known based on the size is is an easy calculation to determine the beamwidth. We can assume 10 GHz, almost every ARH uses the FRQ. Is it / will be modeled the scan?
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Where came the info that the AIM-120 is able to operate both with HPRF and MPRF? I have no idea about the modes of the AIM-120. But even the huge R-37M has only HPRF mode based on its detection distance against incoming / receding targets. (~3 times difference. between incoming and receding target of the R-37 could perform both HPRF and MPRF the distance would be only half against receding targets.)
nowhere in the document it says that the AIM120 operates both HPRF and MPRF in the same time,
first there is a HPRF search , THEN a MPRF, never in same time
As far as the SCAN of the missiles radar is concerned, there is no scan modeled , it’s purely algorithmic at that stage. I dont think modeling scanning time will bring anything on the table considering the small size of the UV. It might in edge case reduce the PG a bit, but it’s really really a level of detail that is not worth the effort IMO (it’s already complex enough LOL )
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@Mav-jp Thank you so much for this implementation And for the doc that comes with it.
Really interesting read! -
@Mav-jp According to you, there should be an interdependence between radar mode and submode regarding accuracy of data exchange, and this hasn’t been modeled yet, right?
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@suhkoi69 said in 4.37.3 AIM120 AQUISITION MODEL:
@Mav-jp According to you, there should be an interdependence between radar mode and submode, and this hasn’t been modeled yet, right?
i dont understand what you are talking about
please provide an example of what you want to say
what is Radar mode for you ? and what is Radar Submode for you ?
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@Mav-jp you wrote “One big question mark is: should the UV coverage be dependent on the FCR SubMode as well (i.e. 2.5 x σ of each submode ) ?. It would make sense because that would increase the selectivity without impacting the Probability of guidance at all. However, at that stage, the UV coverage (and thus size) is
independent of the FCR Submode i.e. the selectivity in all FCR Submodes is the same.It might be changed in future release to increase selectivity of STT vs TWS.”could you please explain more?
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@Mav-jp said in 4.37.3 AIM120 AQUISITION MODEL:
@suhkoi69 said in 4.37.3 AIM120 AQUISITION MODEL:
@Mav-jp According to you, there should be an interdependence between radar mode and submode, and this hasn’t been modeled yet, right?
i dont understand what you are talking about
please provide an example of what you want to say
what is Radar mode for you ? and what is Radar Submode for you ?
I meant: should there be a change if we switch to STT according to the TWS or SAM mode?
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@suhkoi69 said in 4.37.3 AIM120 AQUISITION MODEL:
@Mav-jp you wrote “One big question mark is: should the UV coverage be dependent on the FCR SubMode as well (i.e. 2.5 x σ of each submode ) ?. It would make sense because that would increase the selectivity without impacting the Probability of guidance at all. However, at that stage, the UV coverage (and thus size) is
independent of the FCR Submode i.e. the selectivity in all FCR Submodes is the same.It might be changed in future release to increase selectivity of STT vs TWS.”could you please explain more?
The UV size , i.e. the volume that will be searched is not dependant on the Radar Submode (it’s always 2.5 * Sigma of TWS) , the Error distribution is.
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@suhkoi69 said in 4.37.3 AIM120 AQUISITION MODEL:
@Mav-jp said in 4.37.3 AIM120 AQUISITION MODEL:
@suhkoi69 said in 4.37.3 AIM120 AQUISITION MODEL:
@Mav-jp According to you, there should be an interdependence between radar mode and submode, and this hasn’t been modeled yet, right?
i dont understand what you are talking about
please provide an example of what you want to say
what is Radar mode for you ? and what is Radar Submode for you ?
I meant: should there be a change if we switch to STT according to the TWS or SAM mode?
i understand your question, STT lock / SAM lock and TWS lock are three independant Radar submode, every one has a different distrubution error model, but how you go there to STT (from RWS or SAM or TWS ) is not playing any role
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Thanks for that interesting post.
Could you add some words on what the AIM-120C sees in terminal phase and why we see some strange behavior from time to time?
Example:
Last week we had an AIM-120C doing things that we can not explain. It pulls too much lead (it probably cant even see the target any more) and reacts rolls of the target that didn’t really change its vector.
Where in your article can we find some words that explain what happened here?
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@Razor161 said in 4.37.3 AIM120 AQUISITION MODEL:
Thanks for that interesting post.
Could you add some words on what the AIM-120C sees in terminal phase and why we see some strange behavior from time to time?
Example:
Last week we had an AIM-120C doing things that we can not explain. It pulls too much lead (it probably cant even see the target any more) and reacts rolls of the target that didn’t really change its vector.
Where in your article can we find some words that explain what happened here?
Unrelated with aquisition model
This is about guidance model ,
Bsically the guidance model is a lead pursuit model , as you can see in your ACMI, the AIM120 always lead pursuit to try to reach you and “cut the corners”
There is a special code that makes it limit it’s lead pursuit in order to keep the Target in his FOV. dont forget that the aim120 antenna can be moved, therfore in this ACMI , the target is CLEARLY still in its FOV.
As your speed was very high at first turn, the guidance model had to pull a LOT of G to catch up, loosing speed.
Then after , In this case here, your speed and the sped of the AIM120 is very close, it can’t simply not reach you , and your constant trajectory changes makes it loose energy every time
At some point i tried to switch to Pure Guidance in Terminal stage, but as a matter of fact, then you can find other scenarios where then the missile fails as well because of that. THe amount of lead in each stage can be adjusted in the Data file of the missile. The 4.37.3 is the best compromise we could find in many scenario.
Another point is in MP there is a DEad Reckogning model on top of this , which can make the AIM120 pull more lead than in SP
it is clear though that a full rewrite of the Guidance model would maybe help as it seems we might have computation bugs lurking in there
(the guidance model is from Microprose era, we just limited the pursuit according to the FOV / Antenna movement)
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@Mav-jp said in 4.37.3 AIM120 AQUISITION MODEL:
Another point is in MP there is a DEad Reckogning model on top of this , which can make the AIM120 pull more lead than in SP
it is clear though that a full rewrite of the Guidance model would maybe help as it seems we might have computation bugs lurking in there
(the guidance model is from Microprose era, we just limited the pursuit according to the FOV / Antenna movement)
Well then I hope for future updates and improvements in the guidance.
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@Mav-jp said in 4.37.3 AIM120 AQUISITION MODEL:
@molnibalage said in 4.37.3 AIM120 AQUISITION MODEL:
Nice.
It is not clear to me the followings:
-
How is modeled the radar scan of the missile? Scan rate (angle sec/bars?) If the FRQ of the radar is known based on the size is is an easy calculation to determine the beamwidth. We can assume 10 GHz, almost every ARH uses the FRQ. Is it / will be modeled the scan?
-
Where came the info that the AIM-120 is able to operate both with HPRF and MPRF? I have no idea about the modes of the AIM-120. But even the huge R-37M has only HPRF mode based on its detection distance against incoming / receding targets. (~3 times difference. between incoming and receding target of the R-37 could perform both HPRF and MPRF the distance would be only half against receding targets.)
nowhere in the document it says that the AIM120 operates both HPRF and MPRF in the same time,
first there is a HPRF search , THEN a MPRF, never in same time
As far as the SCAN of the missiles radar is concerned, there is no scan modeled , it’s purely algorithmic at that stage. I dont think modeling scanning time will bring anything on the table considering the small size of the UV. It might in edge case reduce the PG a bit, but it’s really really a level of detail that is not worth the effort IMO (it’s already complex enough LOL )
Of course they are in sequence. But imagine the impact of scan time when the detection range of an ARH seeker is just 1/3 against a receding target if the missile is only HPRF capable. The missile in case of loss of track simply can fly-by the target because of the scan time and scanned volume of airspace.
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@suhkoi69 said in 4.37.3 AIM120 AQUISITION MODEL:
@Mav-jp you wrote “One big question mark is: should the UV coverage be dependent on the FCR SubMode as well (i.e. 2.5 x σ of each submode ) ?. It would make sense because that would increase the selectivity without impacting the Probability of guidance at all. However, at that stage, the UV coverage (and thus size) is
independent of the FCR Submode i.e. the selectivity in all FCR Submodes is the same.It might be changed in future release to increase selectivity of STT vs TWS.”could you please explain more?
yes
There are two things separate to really understand
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we need to model in the sim the Error in positioning of the DLPP vs Target. In real, it is is naturally coming from the errors build in the system. In order to simulate this, we had to create an error model and position the DLPP according to this model. SO at the end of this process, the DLPP is placed somwhere around the Target, depending on conditions and of course randomized following the gaussian laws.
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then we need to define which UV will be search by the seeker, this UV is for now defined at 2.5 sigma of all the stochastics parameters of TWS error model. we could envisage to make this UV depends on each Radar Submode , this means that in STT the UV could be 2.5 sigma of STT error model while in TWS the UV could be 2.5 sigma of the TWS error model.
In essence that will not change the PG for a complete mid course tracking, but it will likely improve the selectivity of the STT compared with TWS.
It would however degrade very much the PG of STT in case midcourse track is lost (because the UV would be much smaller then) and i believe it would mean a PG close to zero in STT in those case whereas it would be higher in TWS.
When saying that it sounds weird isnt it ? that’s why we chose to stick to the wider one anyway for the UV search and this modeling makes things looks reasonnable
Maybe the real has a very narrow UV when mid course is complete (for better selectivity) but if Track is lost widens its UV search automatically ? … the possibilities of modeling are huge and certainly the missiles are clever to chose what’s the best option …
it could be done like that, reduces UV if track is maintained , but widens to 2.5 sigma TWS is track is lost ? …interesting idea…but in essence it wont change anything at the end in term of gameplay
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On another hand do we have solid info that regaining a lost lock is impossible? Or is it based on the D/L info you have?
(or am I completely wrong and getting the lock back is improving the DLPP position?)It’s seems weird to me, especially since in TWS as I understand you can loose a track and the system will interpolate the enemy position for a few second giving you time to get the lock back.
Since we are not loosing the connection with the missile but only with the enemy it would make sense that the missile would prefer to take the guidance from the interpolated track rather than going ballistic to the DLPP.
Really talking out of my ass here, no idea how that really works. But currently, against a good jamming enemy we are loosing a lot of lock and trashing a lot of missiles
Thanks!
Mike
