reported Aim120 can not see targets against the sky

[Hobel]

tracks show the problem

Aim120C.acmi Aim120C blind.trk

[nighthawk2174]

Yeah seems this is part of the notch behavior discussed before:

my thoughts on the matter are layed out in this thread.

[Маэстро]

There is no notch in look up conditions. It's a part of antichaff logic - lock on targets with extremely low radial velocitiy is forbidden. Will think about this problem, maybe will add some trajectory shaping.

[Mad_Shell]

1 hour ago, Маэстро said:

 It's a part of antichaff logic - lock on targets with extremely low radial velocitiy is forbidden.

Mmmmh, not sure it's the right approach. Once the target is locked and if target signal is not rejected (no notch or look-up condition), the range/angular/speed gates should remain on target even when its radial velocity is small. Also, methods to reject chaff are more based on the missile predicting target position, and chaff falling out of that position (chaff quickly loses speed and ends up way slower than the target), thus out of the lock gates. Maybe the missile won't at first lock a target with slow radial velocity, but once a target is locked, it should hold the lock even with low radial velocity if in look-up condition. I can't imagine the designers making a system where the missile will lose lock each time a target hits low radial velocity, no matter the intercept geometry...

[okopanja]

11 minutes ago, Mad_Shell said:

Mmmmh, not sure it's the right approach. Once the target is locked and if target signal is not rejected (no notch or look-up condition), the range/angular/speed gates should remain on target even when its radial velocity is small. Also, methods to reject chaff are more based on the missile predicting target position, and chaff falling out of that position (chaff quickly loses speed and ends up way slower than the target), thus out of the lock gates. Maybe the missile won't at first lock a target with slow radial velocity, but once a target is locked, it should hold the lock even with low radial velocity if in look-up condition. I can't imagine the designers making a system where the missile will lose lock each time a target hits low radial velocity, no matter the intercept geometry...

There is a document for this?

[Mad_Shell]

21 minutes ago, okopanja said:

There is a document for this?

There is indeed a patent by the AMRAAM manufacturer, written just when the missile deliveries began, that states that the lock gates will continue to follow the predicted target position and speed for a few moments, even if the lock is lost. Also, it seems rather logical to keep the lock on a target even if the radial velocity is small if the missile can see that target  has already locked it, and that the target is alone. 

[nighthawk2174]

5 hours ago, Mad_Shell said:

There is indeed a patent by the AMRAAM manufacturer, written just when the missile deliveries began, that states that the lock gates will continue to follow the predicted target position and speed for a few moments, even if the lock is lost. Also, it seems rather logical to keep the lock on a target even if the radial velocity is small if the missile can see that target  has already locked it, and that the target is alone. 

Yeah and this is just how feedback loops can work in general.  I fully agree with your inital post as the target would not have to compete against clutter and would stick out.  So when the speed and range gates are run through the return spectrum they should just grab the target.  Lookdown would be harder but still possible for MPRF, HPRF would rely entirely on S/N being high enough.

[NineLine]

Thanks guys, this is now reported.