SAGG, TVM and GAI The Today's Modern SAM Guidance

Greetings to all readers and passerbys


Well since this group is about missiles and basically anything related to it.. i think it's appropriate to share some of my little stuff that i know but seems unpopular in both Art related or general military forum. How do i know ? simple ..i see no one making SAM's here using titlementioned techniques  and in military forum.. there almost no mention or discussion about SAM guidance..unless one great person that i know. Mr Sean O Connor (nick : SOC in secretprojects, keypublishing and russian military forum) mention it and honestly he's the one who clear my confusion and raise awareness toward the differences between SAGG and TVM guidance.

In this short entry i will describe some history and how those three guidance system works as well as what makes them so deadly and able to resist jamming that expensive inrastructure that supports them are simply justified for. And of course i will also describe some inherent limitations to these guidance techniques.  


Well let's start anyway.

TVM (Track Via Missile) and SAGG (Seeker Aided Ground Guidance).

These two guidance method shares the same place as they're virtually identical in terms of the infrastructure that support them. However there are also differences that makes both of them deserve abbreviations of their own and i'm here to describe it .

The TVM or Track Via Missile as far as i know started its inception during 1950's decade from braichild of US Navy's RIM-50 Typhoon-AN/SPG 59 naval SAM system to repel Soviet mass bomber raid. The idea was to put away the most expensive part of the missile which is the processing part to the radar and only to provide the missile with autopilot, semi-active seeker and datalink channel and have the missile to transmit its raw engagement data its "see" from her seeker to the engagement radar where most of the heavy lifting start.

The radar who tracks both the missile and target received the data and make use of it (and other set of data from his own tracking) to generate a set of guidance command and uplink it to the missile. The missile which do not have the capability to process its own guidance command will now act according to the received data.

The result from abovementioned scheme is simpler and cheaper missile which have long range accuracy of Semi Active RADAR Homing (SARH) guided missile while having fast response to target movement as good as command guidance/beam rider guidance scheme.

Most of the costs and complexities however are burdened to radar which now have to be capable to act both as Radar and datalink receiver as well as to track multiple targets (both missiles and the intended target) which limit antenna selection type (more like hardcoded though..)to Phased array as conventional antenna cannot handle multiple task simultaneously. That is why SAM System make use of TVM System like abovementioned RIM-50 Typhoon and MIM-104 Patriot use phased array and huge processing system. Despite the cost, use of phased array antenna often accompanied by large power aperture product and secure datalink system make the system relatively very difficult to jam as the jammer must be able to compete with the radar's processing which obviously can carry larger computing power than aircraft's onboard jammer.

Now onto the SAGG (Seeker Aided Ground Guidance) scheme. All characteristics of TVM that i mentioned above applies to SAGG. However there is one important difference that make it have its own terminology separated from TVM namely processing system. The SAGG missile have processing part that are not exist in TVM missile thus able and do process its own guidance command from raw engagement data received from her seeker. However that guidance command is not acted upon.. but instead downlinked back to the Radar which like TVM also generate its own set of guidance command. Both set is later compared and in Russian S-300/400 SAM System combined with data originated from other sources like the battery's air surveillance radar (like ST-58U "Tin Shield" or 64N6E "Big Bird") The result is final guidance command which uplinked back to the missile which is acted upon.

So in a nutshell .. SAGG is a more complex and expensive "offspring" of the TVM. However the payoff of increasing resistance toward ECM simply justified the mass production of the system like what we seen in Russian S-300 family starting from S-300PS in 1980's and so on until the S-400 that begin testing in 1993.

One may question why it's more difficult to jam SAGG Missile ? the reason lies within the missile which can act "on its own" if needed. In TVM scheme if the radar is jammed then the missile will be a dead meat as it can't act on its own unless the Radar can "realize" that she's being jammed and switch to HOJ (Home on Jam) mode or any other appropriate modes that are not jammed.

For SAGG however it will have at least one nifty trick that if the Radar is jammed.. it can order the missile to go on its own like SARH guided SAM's while the Radar only act as a SARH Illuminator (assume jamming like RGPO,VGPO which does not generate tracking error by artifically generated glint which will deflect the antenna away from the real target) If the missile is being jammed..The RADAR can order the missile to go HOJ (Home on Jam) or "manually" guide it like command guidance missile.. although this may not give desired accuracy for long distances (in excess of 50-60 Km) due to radar beam pointing error.

There are other reasons too but i would describe them in the closing passage as GAI (Ground Aided Inertial) guided SAM's also share that anti-jam characteristics.

Well since i'm already mention GAI..i think it's the time to jump on it now


GAI (Ground Aided Inertial)

This is yet another very similar girl as previously mentioned SAGG and TVM by having similar radar and other infrastructure as datalink. GAI however take place only during mid-course phase of the flight where the missile is "on its way" to its target and often not yet to activate her seeker. In terminal phase however another form of guidance take over.

So what's being datalinked to the missile ? Target's position (and possibly something else like the missile's position or another guidance command) which will be used in conjunction with the missile's own inertial guidance system to generate mid-course guidance command. The result of this is very accurate guidance command which would means that once the seeker lights up.. it won't take too long for her to acquire target. Thus the seeker can be activated or illuminator directly pointed to target only in very last moment.

For example in Russian S-300V/SA-12 Giant/Gladiator the transition between GAI to Semi Active Radar Homing command take place only in 3-10 seconds before impact.  Reducing possibility of enemy to jam the missile seeker or its associated radar/illuminator. It may also provide some protection against Anti Radiation Missile (ARM) as the emitting components of the SAM's like Radar's or illuminator is only "pointed" to target at the very last moment thus possibility of detection by enemy RHAWS/RWR set can be "delayed" to the point when the RWR lights up the missile is already too close to evade.  How about the Radar ? RWR can detect it's emission too right ? Yes but that's not all of the truth. Another reason on why the SAGG,TVM and GAI system are so expensive are phased array radar antenna. The payoff however is that this antenna's radiation pattern can be controlled in a manner to reduce sidelobe and produce very complex waveform to make life difficult for RHAWS/RWR/ESM as well as their associated jammer and anti radiation missiles to pick its emission or in other word LPI (Low Probability of Intercept) capability.

Back to GAI guidance.. the history of this system is kinda sketchy but i think it's originated somewhere in 1970's where Russians were developing their S-300 version for army unit (S-300P/SA-10 is for Air Defense Unit while S-300V/SA-12 is for army) The result was the nefarious S-300V/SA-12 Giant-Gladiator which as far as i know was the only user for this GAI system.


So that's all i know about the SAGG, TVM and GAI system.. now as i promised before i will go into the "other reason" why jamming life is difficult for those three sisters of SAM guidance.

Readers alike may aware that those systems shares similar traits of having datalink channel connecting the missile and the associated radar's and this channel is of course can be jammed. However jamming of the datalink are complicated in two ways :

First is the nature of the datalink antenna and associated system.
Since the SAGG, TVM and GAI relies heavily on datalink channel to provide their superior accuracy the designer of the system will obviously use every piece of knowledge to make it less vulnerable to enemy actions.  It can be achieved by providing complex waveform having encryptions or even use of separate datalink antenna as the MIM-104 Patriot's PADIL (Patriot Data Information Link) to transmit and receive data to and from the missile.

As for how encryption and complex waveform can complicate jamming process is that they get in the way of the ESM which may have limitations to process complex waveform (i may treat this in separate subject but not now or in the near time as i'm also still studying design of ESM system..and unfortunately it took time) Thus there are nothing to feed to the jammer. It may attempt to spuriously jam all frequency (Barrage jamming) However this might just attract trigger happy SAM operator to switch on the HOJ mode and passively track the jammer so in turn..the jammer essentially become a beacon to the missile.

The second reason related to geometry.

So OK ..i can't jam the datalink antenna.. but it think i can jam the missile's own datalink. Good point as the missile datalink antenna usually closer, less sophisticated and may have less ERP (Effective Radiated Power) so it can't burn through the jamming The last but not the least the antenna is usually a low gain design having broad radiation pattern..thus i can inject jamming signal to it from other direction.

Problem with this however is that the SAGG,TVM and GAI guided missile in their long range trajectory often will fly a loft-glide trajectory. This is trajectory where the missile will soars up as high as her propellant can allow then from that altitude she will glide down all the way to target. In this trajectory the missile will essentially gain energy from the gravity that pulls her down.. and her speed will produce just enough body lift (ever seen Patriot missile ? or S-300's missile ? they lacked large strakes or other large control surface because body lift is all they need to glide) So it will head to target from above.

Problem with this is that typical aircraft jammer suite or MAWS (Missile Approach Warning System) often lack coverage to the top side of the aircraft..thus make jamming or early warning difficult. Padded with LPI Radar and often high performance missile (9M82 missile of SA-12 Giant have speed of Mach 7,8 and some 20-30 G Maneuverability) it will severely cut reaction time to creep contributing to "lethality" point of the SAM's.

Well that's all related to the datalink jamming scenario problem.

And are there any "downside" of those systems ? yep cost.

SAGG,GAI and TVM are costly due to their Radar and associated supporting system thus making this system  to be only found on "high echelon" of air defense where they will protect highly vital installation or center of gravity of their owner's army.

One less told factor of Soviet falldown in 1991 was because they  mass produced SAGG and GAI guided SAM's like the S-300PS, PM, upgrading already existing S-300PT to S-300PT-1A and developing S-400 (in 1985) in response to US's cruise missile program as well as buying over 500 MiG-31 inteceptor. That measure uncotrollably bloated the PVO budget contributing to the fall of the Union in 1991.

However their SAM's remain the benchmark for today's air defense capability and has become a base for other nation like China's HQ-9 (but this seems more like patriot than S-300 though).


Well that's all i can describe for now.. gotta rest.

Best regards.

Dhimas Afihandarin.