AIM-54 guidance

[SinusoidDelta]

Not sure if this has been posted. I haven't had a chance to read it yet:

https://www.dropbox.com/s/w2hfx90ttk1iz5e/BergenMark1975.pdf?dl=0

Edited June 17, 2016 by SinusoidDelta

[lunaticfringe]

Where is the price from? Is there a list on the internet with the prices?

 

Attached.

 

Folks tend to think that because it is called "Freedom of Information" that getting ones hands on documents, even in this case a thesis, is at no charge. Not even close to being true.

 

Generally speaking, one pays if the document requested hasn't been released prior, and doesn't qualify for a "public good" waiver; even identifying as an amateur historian doesn't always get qualified, based on the point that they expect you at some point to attempt to monetize the material. Which, because of the fees I've paid in the past, I tend to do just that.

 

So at that point you're not getting a waiver, you're paying at quarter of an hour prices, plus copies (or digital media). The MDR process gets expensive because, rather than unclassified documents simply not issued prior, the material must be reviewed line by line whether or not all, part, or none of the document in question can be released to the general public.

[punk]

Attached.

 

Folks tend to think that because it is called "Freedom of Information" that getting ones hands on documents, even in this case a thesis, is at no charge. Not even close to being true.

 

Generally speaking, one pays if the document requested hasn't been released prior, and doesn't qualify for a "public good" waiver; even identifying as an amateur historian doesn't always get qualified, based on the point that they expect you at some point to attempt to monetize the material. Which, because of the fees I've paid in the past, I tend to do just that.

 

So at that point you're not getting a waiver, you're paying at quarter of an hour prices, plus copies (or digital media). The MDR process gets expensive because, rather than unclassified documents simply not issued prior, the material must be reviewed line by line whether or not all, part, or none of the document in question can be released to the general public.

 

So is there a way of using foia to track down the blue prints for the cockpit layouts?

[Hadwell]

Attached.

 

Folks tend to think that because it is called "Freedom of Information" that getting ones hands on documents, even in this case a thesis, is at no charge. Not even close to being true.

 

Generally speaking, one pays if the document requested hasn't been released prior, and doesn't qualify for a "public good" waiver; even identifying as an amateur historian doesn't always get qualified, based on the point that they expect you at some point to attempt to monetize the material. Which, because of the fees I've paid in the past, I tend to do just that.

 

So at that point you're not getting a waiver, you're paying at quarter of an hour prices, plus copies (or digital media). The MDR process gets expensive because, rather than unclassified documents simply not issued prior, the material must be reviewed line by line whether or not all, part, or none of the document in question can be released to the general public.

 

 

 

the difference between being allowed to do something, and being allowed to do something for free lol

 

freedom of speech is the former...

 

isn't that one of americas things? "freedom isn't free"?

 

 

lol

[Dudikoff]

Re: CW operation with embedded FM ranging.

 

One can be quite certain that the same technique applied with the AIM-7 is used between the AWG-9 and AIM-54 as described in both STT and TWS; all that changes is the rate of update.

 

The described technique (where a reference FM-modulated CW signal received by the missile's rear antenna is compared to the one reflected off the target to determine the target range) might have been used for the PDSTT mode on the Tomcat which is using the CW illumination I presume and in which Phoenix seems to be using a semi-active mode only and flying a direct path to the target (e.g. like the E or F Sparrow). But, I don't see how it could possibly be used for the TWS launch where the missiles are lofted and no CW illumination is present and a datalink is used instead (e.g. like on the AMRAAM) as described in the document posted by SinusoidDelta.

Edited June 19, 2016 by Dudikoff

[Beamscanner]

Not sure if this has been posted. I haven't had a chance to read it yet:

https://www.dropbox.com/s/w2hfx90ttk1iz5e/BergenMark1975.pdf?dl=0

 

Nice find..

 

As per that document, the AIM-54 may be fired one of 3 ways.

 

Air Combat Maneuvering: A short range Launch and forget mode that does not require the AWG-9 to maintain track on the target. In this mode the missile is given a guidance command and told to go active immediately. No Illumination signal is used, and up to 6 targets can be engaged simultaneously. (page 20)

 

Single Target Track: In this mode the AWG-9 maintains track on one target and may launch a AIM-54 in Semi-active mode while the AWG-9 illuminates the target. The AWG-9 will also send track data and steering commands to the missile via coded messages in the radar pulse.(just as I speculated) As per the document, the missile will not ever go active in this mode of operation.(page 20-21)

 

Track While Scan: During a TWS shot, the missile is first given preset instructions for an optimal flight path. The missile then flies out and at a point starts receiving track data and command messages from the AWG-9 radar. Eventually, the AWG-9 will transmit a missile message known as the Active Transfer Command (ATC) which tells the missile seeker to go active. Missile Messages are still transmitted from the AWG-9 until the track is lost, just in case the missile seeker fails to find the target. Up to 6 targets may be engaged in this mode. (page 21)

 

Nothing in the document mentions the illumination or Semi-active guidance during a TWS engagement (or any engagement involving more than one missile). That's not to say that this doesn't happen, but the lack of input in this detailed description tells me that no illumination is used. At the very least, we know that data is transmitted from the radar to the missile which would alleviate all of the ambiguities that would have arose from a theoretical system that only used intermittent semi-active homing against six simultaneous targets.

 

The reason so little information exists on the datalink, is because the its not a formal "datalink". But rather just missile messages from the AWG-9 radar itself. Likely in the form of Pulse Position Modulation, a common technique of that time frame.

 

So, we should not expect to detect an AIM-54 launched in TWS. Though, our RWRs will see the AIM-54 seeker when it goes active.

 

On an entirely unrelated note, it appears the AWG-9 uses a combination of PRF modulation and pulse group RF Modulation (FM ranging) to acquire unambiguous range on its targets.

 

Thanks Delta!

Edited June 20, 2016 by Beamscanner

[lunaticfringe]

The described technique (where a reference FM-modulated CW signal received by the missile's rear antenna is compared to the one reflected off the target to determine the target range) might have been used for the PDSTT mode on the Tomcat which is using the CW illumination I presume and in which Phoenix seems to be using a semi-active mode only and flying a direct path to the target (e.g. like the E or F Sparrow). But, I don't see how it could possibly be used for the TWS launch where the missiles are lofted and no CW illumination is present and a datalink is used instead (e.g. like on the AMRAAM) as described in the document posted by SinusoidDelta.

 

1. The AIM-7F functions in either CW or PD; all that is required is the selection of SP PD on the MSL OPTION selector.

 

2. The WCS, when Phoenix operates in NORM mode from the MSL OPTION selector instructs the missile to function for CW if the AWG-9 is in a Pulse STT mode, or as appropriate for Doppler otherwise.

 

The radar is designed to perform FM modulation for the AIM-7F in either function mode- CW or PD. Do you legitimately think it wouldn't feed the AIM-54 that same data- especially when the missile works in the same modes, plus TWS?

 

As to the document SinusoidDelta provided, it details next to nothing as to the contents of the data transmitted. Further, AIM-54 is specifically designated, and functions, as a semiactive *radar midcourse guided* weapon; it's listening to all sorts of data, not just the DL. And with regards to the loft profile, the Phoenix antenna has a 60 degree gimbal limit- radiated energy is going to get there.

[lunaticfringe]

So is there a way of using foia to track down the blue prints for the cockpit layouts?

 

Try it.

 

https://foiaonline.regulations.gov/foia/action/public/request/publicPreCreate

 

Sub agency will be Navy Air Systems Command.

[Beamscanner]

And with regards to the loft profile, the Phoenix antenna has a 60 degree gimbal limit- radiated energy is going to get there.

 

I think what he meant was, how does the receiver on the missile determine range when the transmitters location is unknown and the receiver does not sit inside the direct path between the target and the transmitter.

 

Here is a simple diagram

 

Forgive me if I missed something.

[D4n]

Wait, you pay for what you believe sb. else can accomplish in 1/4 h of work?!

[GGTharos]

IMHO the target location data is transmitted on the M-Link.

The missile can then perform the calculation based on its own INS. Given that most of the (practical) loft algorithms that I have seen reduce the glide angle in inverse proportion to the target distance, it would seem that the missile needs to be receiving this data.

 

The M-Link is transmitted by the radar antenna; I would expect it to be picked up even if the missile is sitting in the sidelobes. IMHO.

 

 

I think what he meant was, how does the receiver on the missile determine range when the transmitters location is unknown and the receiver does not sit inside the direct path between the target and the transmitter.

 

Forgive me if I missed something.

[Dudikoff]

I think what he meant was, how does the receiver on the missile determine range when the transmitters location is unknown and the receiver does not sit inside the direct path between the target and the transmitter. Forgive me if I missed something.

 

Not exactly. I was wondering how would the technique of comparing the reference CW signal to the FM modulated one reflected from the target work in TWS mode which doesn't use CW transmitter, but a datalink is used instead (which as GGTharos suspects is probably transferring positional target data updates to the missile).

 

Now, this is for the normal AIM-7F mode. I have no idea how the guidance works when the AIM-7F is launched in the PD mode (as mentioned by lunaticfringe) exactly since AFAIK the AIM-7F has a conical scan seeker (rather than a monopulse one as on the AIM-7M). Is the radar pulse frequency increased to such a level that a similar effect to CW is achieved or what? In that case, why would this require a special mode selector control so there must be something specific here (unless it's some launch procedure or guidance optimizations for the different mode).

Edited June 21, 2016 by Dudikoff

[D4n]

What are sidelobes?

[Beamscanner]

IMHO the target location data is transmitted on the M-Link.

The missile can then perform the calculation based on its own INS. Given that most of the (practical) loft algorithms that I have seen reduce the glide angle in inverse proportion to the target distance, it would seem that the missile needs to be receiving this data.

Potentially, we just need hard conformation.

 

Keep in mind that it would need more than just target range from the AWG-9.. As the AWG-9 (the jet) can move around in space. Thus the missile would need to know 3 things

 

-it's own location (we are all certain it has this)

-The location of the AWG-9 (perhaps from the "datalink")

-The target's range from the AWG-9 (presumably from the "datalink")

 

The M-Link is transmitted by the radar antenna; I would expect it to be picked up even if the missile is sitting in the sidelobes. IMHO.

without a doubt, the missiles aft antenna will pick up the side lobes of the AWG-9(certainly for data reception purposes, and potentially for bi-static FM ranging).

 

Not exactly. I was wondering how would the technique of comparing the reference CW signal to the FM modulated one reflected from the target work in TWS mode which doesn't use CW transmitter, but a datalink is used instead (which as GGTharos suspects is probably transferring positional target data updates to the missile).

 

 

You can use FM in pulsed operation as well.

 

For instance, you may transmit pulse group RF agility. As an example, the pulse train may look like

 

A__A____A___B__B____B___C__C____C

 

The example above shows a 3 element 3 position stagger with embedded FM for ranging. (each letter representing a different RF and the spacing the various PRFs, in this case 3 different RFs and PRFs being used)

 

Because we've colored our pulse groups, we've effectively tripled our maximum unambiguous range. Using the aforementioned PRF modulation also increases our maximum unambiguous range and using at least 3 different PRF/PRIs allows us to remove "ghost" returns.

 

(The downside of this, is that it becomes difficult to integrate pulse groups of different frequencies for Pulse Doppler processing.)

 

So, hypothetically, the missile could associate a pulse and reference it against it's reflected counterpart and use the time difference to determine a distance.

 

What are sidelobes?

 

Sidelobes represent the radiation of Electromagnetic energy outside the focus of the main beam(weak beams offset from the main powerful beam). These areas are a fundamental product of all practical antennas. Even our flashlights have sidelobes that surround the powerful center of your flashlights beam. The amplitude, shape and position of sidelobes depends on the antenna shape and frequency emitted.

 

Below you can see a generic radiation pattern of a directional antenna, take note of the main beam and it's sidelobes and back lobe.

 

It is important to note that no practical antennas are perfectly directional, and thus they all produce sidelobes to some degree. Keep in mind that radiation patterns also represent the reception pattern of EM energy.

 

This is important, because it means that even if a signal isn't in the main beam (or beamwidth) of your antenna, if it's powerful enough (or close enough) it will still come through your receive assembly.

 

 

I made a thread on this awhile back, because I had been shot down with a radar guided missile that never populated into my RWR, presumably because it was directly below my jet and not in my RWR antenna's main beam. (which isn't a realistic outcome)

Edited June 21, 2016 by Beamscanner

[GGTharos]

Potentially, we just need hard conformation.

 

Keep in mind that it would need more than just target range from the AWG-9.. As the AWG-9 (the jet) can move around in space. Thus the missile would need to know 3 things

 

-it's own location (we are all certain it has this)

-The location of the AWG-9 (perhaps from the "datalink")

-The target's range from the AWG-9 (presumably from the "datalink")

 

 

Going from documents on what happens with AMRAAM, and suggesting that the same is done with AIM-54:

 

The information is sent to the missile in two parts:

- ID+Target position

- ID+Target vector

 

No need to know anything about the AWG-9's position.

[Beamscanner]

Going from documents on what happens with AMRAAM, and suggesting that the same is done with AIM-54:

 

The information is sent to the missile in two parts:

- ID+Target position

- ID+Target vector

 

No need to know anything about the AWG-9's position.

 

Target position relative to what?

 

Perhaps a fixed reference point is created and provided to the missile at launch, and the target position is based off that reference point rather then the relative position from the jet(which is ever changing).

[Dudikoff]

Perhaps a fixed reference point is created and provided to the missile at launch, and the target position is based off that reference point rather then the relative position from the jet(which is ever changing).

 

Yeah and the missile then probably keeps track of it's position via an INS as mentioned by GGTharos.

 

I'd still love some details on what the PD mode does exactly in relation to the AIM-7F. I suppose it sets some guidance optimizations for the target being illuminated by a pulse doppler mode (from the main antenna rather than the CW illuminator part I presume?) which seems to be supported for conical scan seekers, but more prone to jamming according to the Kopp page.

Edited June 22, 2016 by Dudikoff

[punk]

I am not sure if this has anything to help or even whether it just restates what is already posted , but I received a new book the other day; Grumman F-14 Tomcat by Doug Richardson; (reprint 1987)" and began reading through the Weapons Systems and Sensor chapter, pages 64-69, though I haven't finished the chapter or any of the rest of the book yet, I came across the following;

 

"[...] Phoenix is steered by tail-mounted control surfaces... [offering] lower drag and higher manoeuvrability ... at 17G. [...] After launch, the weapon can use three types of guidance. For long range shots, during the first stages of flight, the missile flies a pre-programmed course under autopilot control. In mid-course flight, the nose-mounted seeker takes over, operating in semi-active mode. If the launch aircraft's AWG-9 radar is set for Track-While-Scan operation, the target is not continually illuminated, so the Phoenix guidance system receives only samples of radar data.

 

"Long missile range demands that demands on missile energy (i.e velocity) be minimized. On maximum-range missions, Phoenix does not fly directly towards the target, but is lofted into a high trajectory to reduce interference between the AWG-9's powerful transmitter and the missile borne receiving system, and to minimize aerodynamic range. [...]

 

"When switched to active-radar mode the missile seeker has a maximum range of 9-11 nm. Once this has been done, the missile is independent of it's parent aircraft and will continue to home without outside assistance. If fired from aircraft at 11nm or less, the round will automatically carry out an immediate target-acquisition, flying all the way to impact as an active-radar "fire-and-forget" weapon.

 

"Some have suggested the existence of a "flyout" mode which would allow the missile to tackle stand-off jammers on which the AWG-9 cannot obtain lock. This presumes the missile could fly most of the way to the target under auto-pilot control, switching to it's built in seeker in the final stages."

 

Notes:

Bear in mind, some people question anything published by Osprey, but I am no SME.

The 17G manuever number comes from testing/training data, not real world battle condition data I believe.

I have just starting reading about the upgrades from A to C model AIM-54s, so have not gotten to anything on the other missile systems. If I find anything that seems to add to your discussion I will try and get something posted.

Sorry if my quotation skills are off, it has been awhile since I have had to worry about nit picky English teachers :/

 

<Salute>

[Basher54321]

Good stuff

 

People should ask questions about any source - especially if they have better information in a better source.

 

That doesn't stop Osprey being one of the best sources available though.

[punk]

Some additional exerts from an article by Forecast International Inc. Missile Forecast November, 1997:

 

AIM-54A/C/C+ Phoenix - Archived 11/98

 

Control & Guidance. [...] Missiles use the Hughes AWG-9 Doppler radar fire control system, with an infrared subsystem. The central processing computer is built by Control Data Corporation. The missile incorporates command/inertial guidance through the mid-course and active terminal guidance; the onboard guidance system is designated DSQ-26, the detection device is designated the DSU-28, and the safety fuze the FSU-10/A. Northrop Corporation Electronics Division supplies the inertial reference component. The AIM-54C features an all-new Digital Electronics Unit with all-digital processing and an ability to identify targets by individual characteristics through pre-stored computer simulations. The aerodynamic control surfaces are electro-hydraulically actuated with components supplied by Hydraulic Research and Moog. Borg Warner has developed a pneumatic actuation system for the AIM-54.

 

AIM-54C Improved Phoenix. To meet anticipated threats in the 1980s and beyond, the Navy initiated development of the improved AIM-54C Phoenix. This development was accelerated due to the compromising of -54A technology in Iran. The C version is optimized for use against multiple, close-interval cruise missiles and waves or streams of hostile aircraft. The C model of the AIM-54 is also capable of operating in a severe electronic countermeasures environment, and features upgraded target detecting devices, electronic units, receiver-transmitter units, and autopilots, as compared with the AIM-54A. The Naval Weapons Center, China Lake, CA, redesigned the target detecting device, which incorporates a pseudo noise feature. This improves the missile's kill probability over a wider threat spectrum, increases its capability in poor weather, and also enhances the missile's reliability in the electronic counter-countermeasures environment.

The improved electronics unit is of digital design and incorporates an autopilot function. This increases the Phoenix's capability against very fast targets at very high altitudes. The unit's autopilot includes an inertial reference system.

The new receiver-transmitter unit is of solid-state design, incorporating some classified features for enhancement against opening targets, cluster threats, and beam aspect situations. The strap-down inertial reference feature is designated a command-inertial function and makes Phoenix much more accurate immediately after launch. With this enhancement, control of the missile is maintained by the AWG-9 fire control system on the F-14 through the mid-course point of flight. This is the command part of the technique. During this time, the missile's radar is also active. For terminal homing, the missile is fully autonomous, the inertial part of this technique. The AIM-54C provides a four-fold increase in missile capability over the AIM-54A. The AIM-54 command-inertial technology has been proven in tests against BQM-34 and BOMARC target drones. The tests were termed successful, and the command-inertial technology has also been incorporated into Hughes' AIM-120 AMRAAM program.

 

<Salute>

[red_coreSix]

The Naval Weapons Center, China Lake, CA, redesigned the target detecting device, which incorporates a pseudo noise feature. This improves the missile's kill probability over a wider threat spectrum, increases its capability in poor weather, and also enhances the missile's reliability in the electronic counter-countermeasures environment.

 

Interesting, pseudo noise as in frequency hopping LPI? Or just resistance against noise jamming?

[GGTharos]

It might be something along these lines:

 

http://link.springer.com/article/10.1007/s13369-011-0123-z

Edited August 2, 2016 by GGTharos

[SinusoidDelta]

Interesting stuff. A quick google search turns up a lot of applications for pseudorandom noise (PRN). Punk's citation is intentionally vague in terms of how PRN was utilized. I'm guessing it's elementary stuff by today's standards.

 

Here is one source that mentions it for the Aim-54 and 120: http://calhoun.nps.edu/bitstream/handle/10945/41427/14Mar_Osborn_Adam.pdf?sequence=1

 

And a small excerpt from Missile Guidance and Control Systems by George M. Siouris. I think that is what he alludes to here. The only other mention of PRN is in regards to cruise missile GPS guidance signals which doesn't really apply here.

 

The fundamental effect of noise is to mask or hide the true value of dλ/dt. Noise can occur due to target effects or receiver (missile) effects. As we saw in the previous subsection, the radome contributes a bias error due to the diffraction effects of the radome, which is called boresight error. Receiver noise is generated within the missile receiver, and the target signal must compete with it. This noise has increased angular amplitude at longer ranges, where the signal-to-noise ratio∗ (SNR) of the target is the lowest. Receiver noise consists primarily of thermal noise generated by the antenna and receiver electronics on board the missile. The effective amplitude of this noise increases with increasing range, because of the corresponding decreasing SNR. There are, in general, three types of missile receivers that can be considered. These are:

Passive: The target supplies the radiated signal.

Semiactive: The target is illuminated by a source that is not on board the missile. Active: The target is illuminated by a source on board the missile.

Specifically, the receiver will generally include some type of automatic gain con- trol, which attempts to keep the receiver signal power nearly constant. As a result, theeffective noise level will change with received signal power relative to some reference level. Commonly, a normalized angular measurement noise model is defined that uses the variance (or power spectral density) of the indicated boresight error, measured at a range that yields an SNR of unity as the reference level.

[Beamscanner]

pseudo-random noise usually refers to phase noise (phase modulation).

 

Modulating the phase of a signal alters it's coherency in the frequency domain, and thus broadens the instantaneous frequency of the signal. (the bandwidth of the signal expands)

This is one method of generating a "spread spectrum" signal.

 

Most radars require velocity information, and thus need a coherent signal. That is, a signal that exists in a narrow band of the spectrum at any given instant(generally speaking, coherancy useally means a constant phase velocity, and thus a stable narrow frequency).

 

In order to perform Doppler processing with a pseudo-random phase noise spread spectrum signal, the receiver must be aware of the exact phase modulation used on each pulse so that it may perform a phase filter process (reversing the phase modulation) and extract the fundamental frequency of the signal. Thus making it a coherent narrow band signal, suitable for Doppler processing.

 

 

In terms of electronic protection.

 

This technique creates a wide instantaneous bandwidth, which spreads the power over the spectrum, making it more difficult for enemy receivers to pick up. It also makes it more difficult for enemy jammers to completely cover.

 

Additionally, deception jammers (like those used on fighter jets) wont be able to perform all of the techniques available to them against a signal using PR phase noise.

 

For instance, because the enemy jammer cannot know the fundamental frequency of the signal it wont have any control of the false tracks that it creates. (ie it wont be able to 'select' the velocity of its false tracks, because without a means to strip the signal of its phase modulation the fundamental frequency will remain ambiguous. In fact, the jammer may unintentionally emit on a frequency that is being filtered out with the ground clutter and could be completely useless.

 

Because of this, the jammer will likely chose to emit a spread spectrum signal as well with random phase noise in order to create sporadic variables in the return. another option being to simply repeat the phase modulation of each pulse and attempt to over power the skin return. But this wouldn't be deception jamming, its "coherent noise jamming".

 

EDIT: all of the above refers to radar transmissions. Phase coding is also used in communication signals as a means to filter out interference from other signals in the environment and as a means of encrypting embedded data.

Edited August 11, 2016 by Beamscanner

[lunaticfringe]

I stated previously that the Navy's terminology was precise regarding semi-active for a reason.

 

The missile data link provides the location for the antenna to look for an echo. Everything else was encoded in the pulse.

 

There's about 30 pages of redaction giving harder data on the AWG-9 and AIM-54 itself. I'm waiting to determine if an appeal is desired.