Sparrow II active radar homing missile

[Dilandu]

I'm sorry if this is frustrating for you to explain why constantly.

No, not at all, honestly (besides, I like to explain, must confess).

I don't know if it's the insomnia or just a failure to understand why that is, but I'm just not getting it.

The problem is, that 1950s missile seekes aren't fast or reliable. They need time to acquire a target. Basically the seeker need to catch the target singal by rotating antenna, choose this particular signal amongst others by some mean, adjust the antenna angle so the target would be in the equisignal zone (i.e. directly on the axis), reduce the angle of antenna rotation so only the chosen target would be within the seeker field of view, set the range gate or Doppler shift parameter to filter all other signals. After that the seeker is "locked on" target.

If the missile seeker is locked on target before launch, it's usually not a problem; missile have time, while its seeker is pointed in right direction by either pilot (holding target in the sight) or fire control system (aligning seeker boresight line with the one of plane's radar). So when missile finally took off, the seeker is already tracking the target.

If the missile seeker must catch the target AFTER launch, it's much bigger problem. The seeker need to perform search, acquisition, filtering, gating, ect. by itself - and in a very short time available before the missile just fly past the target. And there is no one to tell seeker where exactly to search for the target or how far the target is. The seeker must figure it out all by itself, in a very short time window available.

To make this goal less unsurmountable, it would helps greatly if the missile more or less oriented toward target (and got a range/Doppler data from the plane) before seeker got activated. The "simple" gyro autopilot (it would likely not be exactly simple) can't do that, because target is moving, and missile flight is not perfectly stable. Any windage deviation that missile might need to correct could cause the situation that at the moment of seeker activation, the missile is not looking into the direction of the target. Or at least not looking precisely enough for seeker to lock on in limited time available.

 

[Archibald]

1950s missile seekes aren't fast or reliable. They need time to acquire a target.

Reminds of those interceptions where pilots mostly used AIM-9 seekers (!): trying to get them lock on the right IR source - the ennemy fighter nozzle... Scoop: it failed 95% of the time, if not worse. This was tried because the fighter carrying the Sidewinder had a radar that was too primitive, or no valuable radar at all. Let the IR seeker do the job, if it locks, fire !

 

[Dilandu]

Reminds of those interceptions where pilots mostly used AIM-9 seekers (!): trying to get them lock on the right IR source - the ennemy fighter nozzle... Scoop: it failed 95% of the time, if not worse. This was tried because the fighter carrying the Sidewinder had a radar that was too primitive, or no valuable radar at all. Let the IR seeker do the job, if it locks, fire !

And that's why AIM-4 Falcon was viewed as superior to Sidewinder (prior of its reputation being ruined by dumb Phantom FCS, of course). The Falcon fire control system could pre-lock the missile seeker automatically, aligning it with plane radar (or IR tracker) while the missile was still insilde the weapon bay. Essentially the whole acquisition was handled by plane fire control computer. At the moment of launch, the AIM-4 seeker was already locked on target - despite not actually seeing the target before launch - and spend no time trying to acquire on its own.

(basically it was the reason, why Falcon failed in Vietnam - the F-4 fire control computer could not pre-lock, forcing the missile to do it alone)

 

[fortrena]

Incidentally, the Canada Aviation and Space Museum, in Ottawa, has in its collection a life-size engineering model of the Sparrow II's radar.

Ingenium Collection - Objects - 2015.0589.001

Ingenium Canada Collections Online

collection.ingeniumcanada.org

 

[Archibald]

And that's why AIM-4 Falcon was viewed as superior to Sidewinder (prior of its reputation being ruined by dumb Phantom FCS, of course). The Falcon fire control system could pre-lock the missile seeker automatically, aligning it with plane radar (or IR tracker) while the missile was still insilde the weapon bay. Essentially the whole acquisition was handled by plane fire control computer. At the moment of launch, the AIM-4 seeker was already locked on target - despite not actually seeing the target before launch - and spend no time trying to acquire on its own.

(basically it was the reason, why Falcon failed in Vietnam - the F-4 fire control computer could not pre-lock, forcing the missile to do it alone)

Never realized this before. So, just like the interceptor was fully integrated into the SAGE GCI (to the point of almost making the pilot a passenger); the infrared Falcon was fully integrated into the interceptor IRST & radar.
The whole damn thing fully automatized and integrated all the way from SAGE GCI command centers to Falcon IR seeker. Impressive !

Ground-controlled interception - Wikipedia

en.wikipedia.org

This begs an interesting question. Once the Falcon IR seeker locked on a target [as you describe]; could SAGE directly fire the missile, that is fully bypass the pilot ? We are getting closer from BOMARC than F-106 by this point...

 

[Dilandu]

Never realized this before. So, just like the interceptor was fully integrated into the SAGE GCI (to the point of almost making the pilot a passenger); the infrared Falcon was fully integrated into the interceptor IRST & radar.

Exactly. It was a very high-tech system, with pilot role reduced to minimal (essentially choosing and confirming target & performing some operations during takeoff and landing). USSR have similar system for Su-9 interceptor (later for Su-11, Mig-25), the "Vozdukh" (rus. Air) system; less automated, but more transportable.

 

[Scott Kenny]

The problem is, that 1950s missile seekes aren't fast or reliable. They need time to acquire a target. Basically the seeker need to catch the target singal by rotating antenna, choose this particular signal amongst others by some mean, adjust the antenna angle so the target would be in the equisignal zone (i.e. directly on the axis), reduce the angle of antenna rotation so only the chosen target would be within the seeker field of view, set the range gate or Doppler shift parameter to filter all other signals. After that the seeker is "locked on" target.

If the missile seeker is locked on target before launch, it's usually not a problem; missile have time, while its seeker is pointed in right direction by either pilot (holding target in the sight) or fire control system (aligning seeker boresight line with the one of plane's radar). So when missile finally took off, the seeker is already tracking the target.

If the missile seeker must catch the target AFTER launch, it's much bigger problem. The seeker need to perform search, acquisition, filtering, gating, ect. by itself - and in a very short time available before the missile just fly past the target. And there is no one to tell seeker where exactly to search for the target or how far the target is. The seeker must figure it out all by itself, in a very short time window available.

To make this goal less unsurmountable, it would helps greatly if the missile more or less oriented toward target (and got a range/Doppler data from the plane) before seeker got activated. The "simple" gyro autopilot (it would likely not be exactly simple) can't do that, because target is moving, and missile flight is not perfectly stable. Any windage deviation that missile might need to correct could cause the situation that at the moment of seeker activation, the missile is not looking into the direction of the target. Or at least not looking precisely enough for seeker to lock on in limited time available.

Alright, got it.

Trying to get all that done in the ~5sec or less that a K-band missile has between "detect contact" and "at closest point of approach" is nigh-impossible and requires a couple of miracles.

And it seemed like a good idea at the time.

 

[Dilandu]

And it seemed like a good idea at the time.

1950s techno-optimism; if something theoretically worked, engineers immediately became totally sure that they would figure out the way to make it work on practice.

 

[P-STICKNEY]

Never realized this before. So, just like the interceptor was fully integrated into the SAGE GCI (to the point of almost making the pilot a passenger); the infrared Falcon was fully integrated into the interceptor IRST & radar.
The whole damn thing fully automatized and integrated all the way from SAGE GCI command centers to Falcon IR seeker. Impressive !

Ground-controlled interception - Wikipedia

en.wikipedia.org

This begs an interesting question. Once the Falcon IR seeker locked on a target [as you describe]; could SAGE directly fire the missile, that is fully bypass the pilot ? We are getting closer from BOMARC than F-106 by this point...

The short answer is no - once the flyout platform -- Interceptor or BOMARC, indicated that it had achieved a lock on the designated target,
SAGE dropped its guidance, and the attack was made by the aircraft's Weapons Control System. For BOMARCS, it's fully automatic, for the manned interceptors, depending on the particular aircraft, the attack can be made, as long as the Pilot has the Action Switch (Trigger) held down, automatically, with the aircraft's Fire Control System tied to the Autopilot, or the Pilot flying the aim dot into the center of the Allowable Steering Area circle, as it collapses, with the Fire Control System releasing the weapons at the computed correct point.

BOMARC had active seekers all along - Pulse Radars for the A Models, and Pulse Doppler for the B Models.

 

[P-STICKNEY]

No, not at all, honestly (besides, I like to explain, must confess).


The problem is, that 1950s missile seekes aren't fast or reliable. They need time to acquire a target. Basically the seeker need to catch the target singal by rotating antenna, choose this particular signal amongst others by some mean, adjust the antenna angle so the target would be in the equisignal zone (i.e. directly on the axis), reduce the angle of antenna rotation so only the chosen target would be within the seeker field of view, set the range gate or Doppler shift parameter to filter all other signals. After that the seeker is "locked on" target.

If the missile seeker is locked on target before launch, it's usually not a problem; missile have time, while its seeker is pointed in right direction by either pilot (holding target in the sight) or fire control system (aligning seeker boresight line with the one of plane's radar). So when missile finally took off, the seeker is already tracking the target.

If the missile seeker must catch the target AFTER launch, it's much bigger problem. The seeker need to perform search, acquisition, filtering, gating, ect. by itself - and in a very short time available before the missile just fly past the target. And there is no one to tell seeker where exactly to search for the target or how far the target is. The seeker must figure it out all by itself, in a very short time window available.

To make this goal less unsurmountable, it would helps greatly if the missile more or less oriented toward target (and got a range/Doppler data from the plane) before seeker got activated. The "simple" gyro autopilot (it would likely not be exactly simple) can't do that, because target is moving, and missile flight is not perfectly stable. Any windage deviation that missile might need to correct could cause the situation that at the moment of seeker activation, the missile is not looking into the direction of the target. Or at least not looking precisely enough for seeker to lock on in limited time available.

Falcons didn't really lock before launch. Yes, the Fire Control System pre-loaded the missiles with the appropriate data, but this told the missile where, exactly, to look when it was extended out of the bay. Whichever missile on the rack got the target aqcquired signal back from its seeker first got the firing signal.

The IR Falcons were expected to operate under these conditions, and never got that from the F-4. It wouldn't have been possible there until the implementation of SEAM (Sidewinder Extended Acquisition Mode), where the IR seeker was slaved to the airplane's radar.