AIM-54 guidance

[Andrei]

If 18km to the target, the missile switches to infrared [in case of the A variant] or active radar [C and later] seeker.

 

Sorry, where did you get the infrared capability of seeker from?

[Dudikoff]

Don't understand your point Dudikoff - I don't see how being in a look-down situation should help with seeker acquisition range(rather the opposite I would think).

 

You wrote:

 

The AIM-54 is a long range missile and the small antenna of the SARH seeker obviously cannot home directly on target reflected energy from 100+ miles distance, so the only explanation I can see for the "SARH midcourse guidance" reference would be some combination of inertia/"periodic beam riding".

 

My point was that for the long range launches, the mid course corrections phase probably doesn't begin from the launch, but after the missile has been lofted to within a certain range of the target. Since the primary target at those long ranges would be bombers on a strike pattern, they won't veer of course enough from the missile's calculated intercept point for this to be a problem.

Edited April 19, 2016 by Dudikoff

[red_coreSix]

What we really mean when we say "mid-course SARH" is 'bi-static radar reception'. The AIM-54 isn't homing in on the target like a AIM-7 or R-27. But it is using

the radar reflections off the target to update the targets relative azimuth and elevation from the missile during mid-course flight.

 

Okay, I get that. But this still doesn't explain how the AIM-54 gets range to target information. I'd guess some sort of frequency modulation as was stated in another post, but then how would the radar differentiate between multiple missiles if not with different channels or frequencys for each missile.

Which is actually pretty close to a datalink again :)

[Dudikoff]

Okay, I get that. But this still doesn't explain how the AIM-54 gets range to target information. I'd guess some sort of frequency modulation as was stated in another post, but then how would the radar differentiate between multiple missiles if not with different channels or frequencys for each missile. Which is actually pretty close to a datalink again :)

 

Datalink means sending target data updates directly to the missile. How are different SARH-like channels which illuminate the target "pretty close to a datalink" exactly?

Edited April 19, 2016 by Dudikoff

[microvax]

Sorry, where did you get the infrared capability of seeker from?

 

German wikipedia says so in the section about the guidance process. Iirc I did also read it elsewhere but to long ago to remember where... As I said, I do not have enough source material To claim what i wrote is 100% correct. :D Its all a bit hazy around the AIM54, since it hasnt been really used.

[Dudikoff]

German wikipedia says so in the section about the guidance process. Iirc I did also read it elsewhere but to long ago to remember where... As I said, I do not have enough source material To claim what i wrote is 100% correct. :D Its all a bit hazy around the AIM54, since it hasnt been really used.

 

First time I've heard of such a claim, but I'd expect an IR sensor would be clearly visible on the missile.

 

Perhaps there were referring to some sort of target handoff by the F-14A IRST system which was used on the earliest F-14 blocks?

Edited April 19, 2016 by Dudikoff

[red_coreSix]

Datalink means sending target data updates directly to the missile. How are different SARH-like channels which illuminate the target "pretty close to a datalink" exactly?

 

I know what a datalink is, but if you are sending modulated signals with different modulation for each missile to provide range information you might as well code other information with it. So yes it is pretty close to a datalink...

 

Also it's just a theory, I don't know how the AIM-54 gets range. But if you know better, please.

[microvax]

First time I've heard of such a claim, but I'd expect an IR sensor would be clearly visible on the missile.

 

Perhaps there were referring to some sort of target handoff by the F-14A IRST system which was used on the earliest F-14 blocks?

 

That is very probably, yee probably so. Which would imply datalink. I dunno what kind of Info the IRST could provide. But sounds reasonable to me.

 

 

Yee found a pic of a AIM54a, probably some kind of IRST handoff then. https://upload.wikimedia.org/wikipedia/commons/c/c9/AIM-54A_(left)_on_F-14_at_NAS_Pax_1984.JPEG

[Beamscanner]

Okay, I get that. But this still doesn't explain how the AIM-54 gets range to target information.

Exactly what I stated in my first post

 

I'd guess some sort of frequency modulation as was stated in another post, but then how would the radar differentiate between multiple missiles if not with different channels or frequencys for each missile.

Which is actually pretty close to a datalink again :)

 

Yup, this was my conclusion in the post I linked from another topic.. Though its not RF modulation, its Pulse Position Modulation (modulating the pulse timing) for the range information.

 

Datalink means sending target data updates directly to the missile. How are different SARH-like channels which illuminate the target "pretty close to a datalink" exactly?

The theory is that the PRF of the AWG-9 is slightly modulated every so often, with the embedded data providing target range to the missile which sees the PRF modulation reflected off the target. This technique is known as Pulse Position Modulation or PPM, and is not considered a "datalink" in the engineering world as it is mechanic of the radar itself and not a dedicated 'datalink'. Just like a flashlight is not considered a 'datalink' even though it can be used to relay information if modulated. Similar to the flashlight, the AWG-9 wouldn't be able to embed that much information into the signal as compared to a traditional "datalink".

 

PPM was a common technique used during this period of history. What engineers typically refer to today as a 'datalink' (be it a cell phone connection or Wifi, etc) is a signal dedicated to transmitting information. Usually via RF shift keying or Phase shift keying from a CW signal, not a pulse one.

 

That is very probably, yee probably so. Which would imply datalink. I dunno what kind of Info the IRST could provide. But sounds reasonable to me.

Nope. The F-14a didn't have an IRST, it had TCS. TCS range was about 10 miles. At that range the AIM-54 seeker could lock the target itself, and thus not need a datalink..

Edited April 19, 2016 by Beamscanner

[Dudikoff]

I know what a datalink is, but if you are sending modulated signals with different modulation for each missile to provide range information you might as well code other information with it. So yes it is pretty close to a datalink... Also it's just a theory, I don't know how the AIM-54 gets range. But if you know better, please.

 

Ah, I see what you mean. Sorry, I was looking at it from a viewpoint where the target range is not transmitted via the TWS pulses at all as it was just a theory.

 

IMHO, it sounds rather complex for the time period and I would expect some simpler solution like e.g. signal strength of the reflected pulses received by the SARH antenna for mid-course guidance. I think that could be pretty well matched to the strength of the radar seeker head to ensure that the target could be locked by it.

Edited April 19, 2016 by Dudikoff

[Dudikoff]

Nope. The F-14a didn't have an IRST, it had TCS. TCS range was about 10 miles. At that range the AIM-54 seeker could lock the target itself, and thus not need a datalink..

 

The early F-14A blocks had an IRST system. It had proven unreliable and was thus later replaced by the TCS.

[Beamscanner]

IMHO, it sounds rather complex for the time period and I would expect some simpler solution like e.g. signal strength of the reflected pulses received by the SARH antenna for mid-course guidance. I think that could be pretty well matched to the strength of the radar seeker head to ensure that the target could be locked by it.

 

Determining range based only off signal strength is infinitely more complicated... No radar that exists uses that.

 

PPM was pretty common before digital processing came around. A lot of old SAMs used PPM for missile guidance.

Here is a radar book from 1959 that explains the use of pulse modulation as a means of command guiding missiles..

https://books.google.com/books?id=a0TxaTq2rQIC&pg=SA1-PA48&lpg=SA1-PA48&dq=pulse+position+modulation+missile&source=bl&ots=3TL9fQKJyN&sig=TRF66iWT19c0rL9B6w3xFXQqlVk&hl=en&sa=X&ved=0ahUKEwjC1PfRn5zMAhUB5mMKHVGODKEQ6AEIJDAB#v=onepage&q=pulse%20position%20modulation%20missile&f=false

 

The early F-14A blocks had an IRST system. It had proven unreliable and was thus later replaced by the TCS.

Semantics

 

The point I made remains. The range for the optical system on the F-14A and F-14B was short enough for the AIM-54 seeker to get a lock immediately after launch. Indicating that a datalink would not like be required in order to perform this short range engagement.

Edited April 20, 2016 by Beamscanner

[BlackLion213]

Afaik the AIM54 guidance worked as follows:

 

There are two main modes for the Missile to be guided until 18km to the target, INS, which makes it fire and forget or SARH. If 18km to the target, the missile switches to infrared [in case of the A variant] or active radar [C and later] seeker. If the Seeker detects jamming, it directly switches to HOJ, if the jammer is turned off again, it directly switches back to active radar. Since HOJ only happens in final approach, after the missile has climbed to 30km in case of the C and is falling to the target, it should not be that much of an range reduction. [speed is somewhat hard to get, but its said to be mach 5 when its at the highest point of its trajectory.]

 

 

Sorry, where did you get the infrared capability of seeker from?

 

I have never heard of the AIM-54 having an infrared system, but this paper references "Both missiles use the Hughes AWG-9 Doppler radar fire control system, with an infrared subsystem. "

 

First line on page 2 of the PDF under control and guidance.

 

http://www.forecastinternational.com/archive/disp_old_pdf.cfm?ARC_ID=1066

 

I'm not sure what "infrared subsystem" means exactly, is this referring to a back-up guidance/tracking system?

 

Of note to the original quote, both the AIM-54A and AIM-54C use the same basic system of guidance so I don't think the statement about the AIM-54A using infrared while the AIM-54C uses active radar is correct.

 

This PDF is an interesting read, seems that the overall hit rate for AIM-54 shots for the USN during testing and fleet training was 88%. BTW, I don't know if that is a good or bad number for testing and fleet aircrew training shots. Anyone know what it was for the AIM-7 or AIM-9 (or even AIM-120)?

 

Also, the PDF states that the command-inertial system of the Phoenix's was directly integrated into the AMRAAM. Perhaps this is why AIM-54 data remains classified and finding good information is so difficult?

 

Also, here is another overview PDF for the AIM-54 that discusses the missiles development timeline, internal testing, and fleet integration till retirement.

 

http://www.navair.navy.mil/index.cfm?fuseaction=home.PrintNewsStory&id=2943

 

-Nick

[captain_dalan]

 

 

The theory is that the PRF of the AWG-9 is slightly modulated every so often, with the embedded data providing target range to the missile which sees the PRF modulation reflected off the target. This technique is known as Pulse Position Modulation or PPM, and is not considered a "datalink" in the engineering world as it is mechanic of the radar itself and not a dedicated 'datalink'. Just like a flashlight is not considered a 'datalink' even though it can be used to relay information if modulated. Similar to the flashlight, the AWG-9 wouldn't be able to embed that much information into the signal as compared to a traditional "datalink".

 

Exactly what i read. And as these are essentially analogue computers, each missile is mechanically coded before mission launch, thus responding to only one "code". You can't reprogram them or reassign a new modulation to them.

[Beamscanner]

Nick, as always, nice work!:)

 

Dalan, do you still have that resource?

 

Mircovax, I believe you are thinking of the AIM-47, the precursor to the AIM-54. The AIM-47 was supposed to get an IR seeker for terminal homing but they couldn't meet the size requirements with the addition of the IR receiver. Also, the AIM-47 never went operational..

Edited April 20, 2016 by Beamscanner

[Dudikoff]

I'm not sure what "infrared subsystem" means exactly, is this referring to a back-up guidance/tracking system?

 

Since it says "Both missiles use the Hughes AWG-9 Doppler radar fire control system, with an infrared subsystem.", I think it refers to the IRST as part of the FCS.

[Dudikoff]

Determining range based only off signal strength is infinitely more complicated... No radar that exists uses that.

 

That's not what I've said. I've said using the strength of the received reflected signal as means of roughly determining the sufficient RCS of the target for the missile's own radar to achieve lock. E.g. when a certain signal strength is received, activate the radar. It's just a simple idea on how to solve this problem with analogue electronics. I'm not saying this is how it works as there would be some issues with the radar signal strength degradation with range, etc.

 

PPM was pretty common before digital processing came around. A lot of old SAMs used PPM for missile guidance.

Here is a radar book from 1959 that explains the use of pulse modulation as a means of command guiding missiles..

 

Yes, for missile guidance where the guidance commands are sent directly to the missile as both the missile's and target positions are known. Here we assume there is no typical datalink, but SARH mid-course guidance. Encoding target range from the carrier into the radar signal so the missile would decode it from a reflected signal just sounds overly complicated as I don't see what good would this range from the launching aircraft information do to the missile? The target may have changed course, velocity, etc. and the same goes for the launching aircraft.

 

IIRC, the F-14 doesn't have any TTA indications on the HUD (?) which might indicate that the FCS was not aware of the missile's location or when it would activate the radar. On the other hand, if the FCS was calculating all this, then it could just send the encoded activate command via these pulses and not some vague range information, no?

 

Semantics. The point I made remains. The range for the optical system on the F-14A and F-14B was short enough for the AIM-54 seeker to get a lock immediately after launch. Indicating that a datalink would not like be required in order to perform this short range engagement.

 

You might consider it semantics, some might consider the IRST as basic F-14A knowledge. You know, semantics.. :)

 

The datalink was mentioned by another poster. All I said was that the infrared reference was probably referring to the IRST and assumed that it might have been integrated into the FCS to hand-off IRST target data to the Phoenix inertial system (obviously, lofting would not be used in such an engagement).

 

Exactly what i read. And as these are essentially analogue computers, each missile is mechanically coded before mission launch, thus responding to only one "code". You can't reprogram them or reassign a new modulation to them.

 

But these would be radar channels for SARH mid-course guidance corrections or SARH guidance (e.g. similar to how these channels are set for monopulse SARH missiles) as IIRC the Phoenix could be launched in SARH mode as well (which would probably require an STT lock).

 

Did you actually read that the *target range* is encoded and sent within these TWS pulses?

Edited April 20, 2016 by Dudikoff

[captain_dalan]

But these would be radar channels for SARH mid-course guidance corrections (e.g. similar to how these channels are set for monopulse SARH missiles). Did you actually read that target range is encoded and sent with these TWS pulses?

 

It didn't say precisely what data were encoded, only the vague "telemetry needed for missile guidance".

 

 

Dalan, do you still have that resource?

 

 

Unfortunately no. It was some time ago, and my folder structure is a mess. I'll try again today after work, but i'm not very optimistic about finding it.

[microvax]

Nick, as always, nice work!:)

 

Dalan, do you still have that resource?

 

Mircovax, I believe you are thinking of the AIM-47, the precursor to the AIM-54. The AIM-47 was supposed to get an IR seeker for terminal homing but they couldn't meet the size requirements with the addition of the IR receiver. Also, the AIM-47 never went operational..

 

yee probably mixed up aim 47 and 54 in my memory and the wiki does that as well or does mean the IRST. Yee, makes sense.

[Beamscanner]

That's not what I've said. I've said using the strength of the received reflected signal as means of roughly determining the sufficient RCS of the target for the missile's own radar to achieve lock. E.g. when a certain signal strength is received, activate the radar. It's just a simple idea on how to solve this problem with analogue electronics. I'm not saying this is how it works as there would be some issues with the radar signal strength degradation with range, etc.

 

You said "IMHO, it sounds rather complex for the time period" referring to PPM. It's not. It was in fact the method of choice for that period.

 

Additionally, using the amplitude of a multi-path signal from a separate transmitter to queue seeker activation is entirely more complex then determining range via target position updates using PPM. It is also unreliable to use this method because the indicated RCS at any given moment will vary.

 

The target's RCS varies when:

-The target changes aspect (showing its belly vs it's nose)

-The target opens it bomb-bay

-The target's radar changes it's aspect (scanning vs. fixated)

-The target's control surfaces are in motion

 

Additionally, the perceived RCS will change when:

-Another larger aircraft in the distance is in the AWG-9's beam

-Another aircraft exists between you and the intended target (potentially, an ally)

-The target or any of his wingmen start jamming on the same freq.

-The target releases chaff

 

Furthermore, the S/N ratio will continuously vary due to background noise, sidelobe jamming, chaff clouds, ground clutter, etc..

 

If this was the way it worked, the missile's seeker would easily be activated well outside of it's detection range, and likely run its battery dry prior to impact as well as inform the target of it's existence prior to the seeker detecting the aircraft, allowing the target to escape.

 

Finally, this method wouldn't allow the missile to fly a lead pursuit, as it cannot deduce target range.

 

Yes, for missile guidance where the guidance commands are sent directly to the missile as both the missile's and target positions are known. Here we assume there is no typical datalink, but SARH mid-course guidance. Encoding target range from the carrier into the radar signal so the missile would decode it from a reflected signal just sounds overly complicated as I don't see what good would this range from the launching aircraft information do to the missile? The target may have changed course, velocity, etc. and the same goes for the launching aircraft.

The AIM-54 doesn't use missile tracking+command guidance AFAIK.. I linked that book simply to highlight that PPM was a common technique during that time frame.

 

What I think is happening is that the AIM-54 receives data on the targets position via coded PPM messages embedded the AWG-9's radar pulse set. The AWG-9 embeds this data in it's PRF when it's beam sweeps the target.

 

The AIM-54, having an Inertial Sensor Assembly (ISA), tracks it's own position and data on the targets position relative to where the missile was launched (which the F-14 could measure) is passed to the missile to determine the targets current range from the missile.

 

Another question that I brought up was to how the individual missiles knew which reflection was their intended target. If I'm right and PPM is used, a sequence start code could be used to tell the missile which of the reflection's pertained to their specific target when multiple missiles were launched. Thus allowing the missiles to ignore reflections that didn't have the proper sequence code embedded in the PPM (i.e. ignore the reflections and positional data of targets the other missiles were going after). A code such as this, would be set up between the AWG-9 weapon system and the missile prior to launch(maybe even prior to take off?). This would match up with what captain_dalan had read.

 

You might consider it semantics, some might consider the IRST as basic F-14A knowledge. You know, semantics.. :)

 

It's semantics because it didn't change the point I was making, and has no direct relation to the overarching question on whether the AIM-54 uses a datalink.. Also, because were not getting an F-14 with an IRST, and most F-14A's didn't end up with an IRST.

 

The datalink was mentioned by another poster. All I said was that the infrared reference was probably referring to the IRST and assumed that it might have been integrated into the FCS to hand-off IRST target data to the Phoenix inertial system (obviously, lofting would not be used in such an engagement).

The document that nick found indicated that the TCS was used to hand off (bore sight) the AIM-54 seeker onto a target. No data needs to be sent to the AIM-54 in this case because the AIM-54 seeker's detection range is probably better then the TCS's detection range.

 

Meaning the seeker is told where to look just prior to launch, and activates immediately after launch. no link required

 

http://forums.eagle.ru/showpost.php?p=2748679&postcount=7

Edited April 21, 2016 by Beamscanner

[Dudikoff]

You said "IMHO, it sounds rather complex for the time period" referring to PPM. It's not. It was in fact the method of choice for that period.

 

Please quote where I said that. I said that the concept of sending some vague range from the target aircraft to the missile encoded in the TWS illuminating pulses sounds unnecessarily too complex for the time-period as in analogue processing electronics in the missile which has to process and store that range information.

 

Additionally, using the amplitude of a multi-path signal from a separate transmitter to queue seeker activation is entirely more complex then determining range via target position updates using PPM. It is also unreliable to use this method because the indicated RCS at any given moment will vary.

 

The target's RCS varies when:

<cut>

Furthermore, the S/N ratio will continuously vary due to background noise, sidelobe jamming, chaff clouds, ground clutter, etc..

 

Good points, but they also work against your range theory. At which range would you switch to active radar as the potential lock depends on the target RCS and would vary for differently sized targets?

 

If this was the way it worked, the missile's seeker would easily be activated well outside of it's detection range, and likely run its battery dry prior to impact as well as inform the target of it's existence prior to the seeker detecting the aircraft, allowing the target to escape.

 

You know the time its radar can run on batteries or this is just a biased assumption? I don't think they used an AA set there. Also, the active radar and the SARH seeker might continue to work in sync after it goes pitbull till the active radar detects the target it guides towards or the missile loses its kinetic energy.

 

Finally, this method wouldn't allow the missile to fly a lead pursuit, as it cannot deduce target range.

 

It's for the midcourse phase, not the terminal so it might have been acceptable given it's intended targets (bombers and cruise missiles). They always mention the improvements made on the AIM-54C for engaging fighters so it seems that the initial model wasn't ideal for those.

 

The AIM-54, having an Inertial Sensor Assembly (ISA), tracks it's own position and data on the targets position relative to where the missile was launched (which the F-14 could measure) is passed to the missile to determine the targets current range from the missile.

 

Well, that assembly is there for tracking the missile's flight parameters (angle, etc.) to control the missile after launch and fly it. That it's also used to keep track of its movement and at high speed in 3D space, store that data and then processes the positional updates received from the F-14 to just determine the range seems very complicated, especially since presumably it already guides towards the target using the SARH pulses.

 

Another question that I brought up was to how the individual missiles knew which reflection was their intended target. If I'm right and PPM is used, a sequence start code could be used to tell the missile which of the reflection's pertained to their specific target when multiple missiles were launched. Thus allowing the missiles to ignore reflections that didn't have the proper sequence code embedded in the PPM (i.e. ignore the reflections and positional data of targets the other missiles were going after). A code such as this, would be set up between the AWG-9 weapon system and the missile prior to launch(maybe even prior to take off?). This would match up with what captain_dalan had read.

 

This is not an issue since e.g. monopulse seekers are tuned for the specific set of frequency channels used by the launching platform and for the AIM-54A it seems to have been done on the ground. But, it has nothing to do with the embedded PPM.

 

It's semantics because it didn't change the point I was making, and has no direct relation to the overarching question on whether the AIM-54 uses a datalink.. Also, because were not getting an F-14 with an IRST, and most F-14A's didn't end up with an IRST.

 

Yes, but you charged in with a definitive "F-14A never used an IRST" which was quite a bold statement if some posts before mention that it did in fact exist.

 

The document that nick found indicated that the TCS was used to hand off (bore sight) the AIM-54 seeker onto a target. No data needs to be sent to the AIM-54 in this case because the AIM-54 seeker's detection range is probably better then the TCS's detection range.

 

Meaning the seeker is told where to look just prior to launch, and activates immediately after launch. no link required

 

The data needs to be sent to the missile by the FCS prior to launch, that's what I said and also that the old IRST might have also been integrated in the FCS in the same way as TCS later was. You keep implying that some datalink was mentioned here.

 

 

 

In any case, we need someone with the -1A weapon employment manual to know more. Hopefully, LN have access to those.

Edited April 21, 2016 by Dudikoff

[Alicatt]

Please quote where I said that. I said that the concept of sending some vague range from the target aircraft to the missile encoded in the TWS illuminating pulses sounds unnecessarily too complex for the time-period as in analogue processing electronics in the missile which has to process and store that range information.

I was training as a radar technician back in the early 70s for commercial marine radars though not military ones, and we were making radars that had digital computers in them for analysing range, bearing, and speed for anti collision, it was on the training course for these radars that I built my first digital computer.

 

[D4n]

Wow wow wow guys thanks for the comprehensive answers/participating in the discussion! xD Anyone here who read all posts/pages in this thread and can tell me what the answers are on my questions on page 1:

 

"What's TCS? And I wonder at which range the radar (F-14A) can burn through ECM (from Su-27 for example)...

 

And HOJ mode for Phoenix will probably reduce range to 50-100 km I guess... (because in HOJ the missile will fly straight towards the target...)" right?

[red_coreSix]

I iAnd I wonder at which range the radar (F-14A) can burn through ECM (from Su-27 for example)...

 

And HOJ mode for Phoenix will probably reduce range to 50-100 km I guess... (because in HOJ the missile will fly straight towards the target...)" right?

 

We'd have to know the power output of the Su-27 jammer and that of the AWG-9 so calculate the burn through. But since we don't have that we can only guess. Since the AWG-9 is the second most powerful radar employed on a fighter I'd guess ranges of 30-50 miles.

 

HOJ will definitely decease the range, as the missile has no range and velocity information and thus can't calculate a perfect proportional navigation curse (or loft), it can however still fly on collision course using the jammer as a reference and zeroing the line of sight rate. Missiles in DCS don't do that for some reason so don't hold your breath on that.

Edited April 21, 2016 by red_coreSix

[gospadin]

Well wouldn't it make sense to home in on strongest reflection? Probably Leatherneck will get information, as this missile isn't in service anymore in the US Navy... (Officially at least)

 

Given that Iran still has some AGM-54s, I doubt the US will ever release any "hard" technical information to the public. The risk is too high.

 

That being said, I'm personally okay with accepting this is a simulation, and the fidelity will be variable by functional area.