How AIM-120D uses GPS

[armedupdate]

I have a question on how the new AIM-120D works with GPS. How does the GPS influence its flight? Is it mainly datalink or can it use sattelites as sensors to guide it?

[hornetfinn]

GPS just gives the missile exact position (including altitude), speed and time information. It's always supporting INS (Inertial Navigation System) which measures and calculates the missile orientation, position and velocity. GPS is used to reset errors that always happen in INS process (calibrate). GPS, while very accurate, is by itself is too slow for missile guidance but combined GPS/INS gets benefits from both while mitigating the drawbacks of both.

GPS/INS gives more precise flight path and allows higher flight efficiency for missile (smoother flight). Along with two-way datalink this gives better control for guiding the missile against the intended target as both the missile and launching aircraft know more precisely where the missile is, where it's heading and the flight parameters of said missile. This gives higher accuracy and better ability to evade countermeasures.

[sprstdlyscottsmn]

It also could allow the missile to be guided to a target that is not being illuminated by radar. I am not normally one for speculation, but if two F-35s flying a ten(s of) miles apart and they each get a signature on DAS (azimuth and elevation only) and share that info automatically over MADL they will realize that there is only one point in space where those two tracks intersect. Since the F-35s have their own GPS locations and know relative Azimuth, Elevation, and Range to the target they know the targets GPS locations. They now have a 3-D position of the target. As that position changes over time they have heading and velocity info. This is all supposedly happening all the time in the F-35 computers. So the 2-way datalink and GPS assisted guidance allows accurate passive shots without radar lock. AIM-120D also features "improved HOBS capability". This seems like it fits. Given the kinematics of the AIM-120D, any aircraft in DAS range is in firing range, even behind the aircraft, unless it is running away at full AB and can thus be seen from 90+mi but is no longer a threat.

[deadseal]

It knows where it is because it knows where it isn't.

[sprstdlyscottsmn]

It knows where it is because it knows where it isn't.

Ug, just hearing that much of it re-broke my brain. It is where it wasn't and it will be where it isn't. If it is where it was we have a variation.

[SpudmanWP]

The GPS only needs to get it within a few miles of the target in order for the active seeker to take over. Knowing the precise location of itself and of it's target lets the AIM-120D achieve a greater range due to optimizing it's flight profile.

[hornetfinn]

The GPS only needs to get it within a few miles of the target in order for the active seeker to take over. Knowing the precise location of itself and of it's target lets the AIM-120D achieve a greater range due to optimizing it's flight profile.

It will also allow higher hit probability as the missile will likely need to maneuver less during end game as the missile is oriented more precisely towards the point where missile and target collide and also because missile retains energy better due to more optimized flight profile. Of course it also allows for missile seeker to look directly towards the intended target when it goes active saving time and allowing quicker target acquisition.