Question regarding naval air defence (illumination, missile guidance)

Hello all, after going through some naval threads lately I've began to wonder about the efficacy of the various guidance modes and air defense capability of various destroyers, and the exact way AAD work.

I'm going to lay out how (from what I've gathered over time) the basics of AAD works, and if any of this is off target (not sure if pun intended), please correct me.

For SARH (semi active radar homing) missiles, illuminators are required to guide missiles in the terminal phase (X band usually?), after a longer range but less precise radar such as SPY-1 (S band?) detects and vectors in a missile to the general location of the target.
Illuminators include SPG-62 onboard ticos and burkes, and onboard russian ships and 052B, 054A, it is orekh.
There is a limit to how many illuminators a ship carries (for instance 054A and ticos carry four, burkes carry three), and also there is a limit to how many missiles each individual illuminator can guide (2 for orekh, I believe?). Another limitation for the ship's overall air defence is that of the necessity of legacy illuminators to physically rotate towards the incoming threat.
These factors, combined, will be the big factors in determining a vessel's multi target engagement capability, yes/no (assuming everything else is as constant as possible)?

Okay, so depending on the answer to the above, I have further queries regarding the efficacy of ARH (active radar homing) SAMs versus SARH SAMs.

Now the difference between ARH and SARH, is that ARH missiles can guide themselves in the terminal phase, while SARH requires guidance from a different source (for naval warfare it would be illuminators as mentioned above, for A2A, it requires a fighter to keep its fire control radar illuminated on the target).
There are various ships equipped with ARH SAMs -- these include the eurofrigates+type 45 which are equipped with Aster 15/30, Type 052C equipped with HHQ-9 (and probably 052D too) (the lack of illuminators is quite telling, and dragon eye radar is already accepted as S band), and zumwalt/burke flight iii when they are equipped with the ARH SM-6 (currently SM-2 variants are SARH, I believe? ESSM is also SARH).

(ARH missiles are also less limited by the range of the illuminator, meaning two missiles of equal size, propellant, but carrying ARH versus SARH seekers, means the ARH missile can potentially engage a target at a greater distance and take full advantage of its kinetic range... but I digress)

Am I right in believing that ships equipped with ARH SAMs are less limited by the illuminator factor, and that it only requires the ship's volume/multifunction radar to vector missiles into the general area of the incoming target (usually in combination with inertial guidance) before the terminal phase is handed off to the missile itself? Putting it practically, do ships equipped with ARH SAMs offer potentially better multi target engagement capability than SARH SAM equipped ships?

Of course physical limitations of the VLS launch rate will limit both ARH and SARH equally, as well as the battle management systems of the various ships... But is the theory sound?


---

Finally, does anyone know how many missiles the US SPG-62 illuminator can guide at once (more than two I hope)? This entire post materialized when I noticed how burkes were equipped with only three illuminators and 054A were equipped with 4. I thought if SPG-62s were only capable of guiding two SARH SAMs each, that meant a burke can only guide six missiles against targets simultaneously, while an 054A can guide 8! That maths didn't look right to my head.


As a caveat, I'm not claiming ARH is inherently superior to SARH or that the latter should be abandoned for the former. zumwalt and burke flight iiis will still be equipped with X band AESAs capable of guiding a large number of SARH missiles due to the agile beam forming nature of AESA, I believe, and even SM-6 will still come with an SARH guidance mode.

(although if later posts could clarify the advantages and disadvantages of ARH vs SARH guidance more comprehensively I'm sure all will benefit!)


Thanks to anyone who replies and drops knowledge bombs!

Here's my opinion on the matter and questions posed. It's all been cobbled from publicly available data and interpreted by myself so I won't claim what I say is the only truth.

SARH guidance on AAW ships is indeed done almost exclusively by x-band radars, yes. Maybe there are examples of other bands but I don't know of any. SPY radar is indeed S band, as many radars of similar role are, though here there can be some ships with L or C band radars. Or both.

From what I gathered, the limit of how many missiles can an illuminator guide is purely arbitrary. In some literature one can read about two missiles per illuminator, sometimes it even states two targets are illuminated by one illuminator while guiding two missiles. But nowhere did i find a description of mechanics. People who claim to be in the know have told me (but i've no way of verifying that) it really boils down to this (and it makes sense to me): Every mechanically steered illuminator has a single beam for terminal interception. It is fairy focused, but over long distances (10-20 km) it spreads out enough that it is perfectly possible for that beam to illuminate two or even more incoming targets.

Some issues arise: Since those illuminator beams are continuous wave illumination, there is really no data about distance, range, heading itd. All that isn't so important anymore because we're talking about last few seconds of interception and one assumes distances are already quite small. If two targets are one next to another, missile has to know how to pick one target over another. If one target is closer than the other, then i *assume* the amount of emission that gets picked up by the missile can be interpreted in such a way that missile can pick the closer or farther targer.

Real issue is this: if two missiles are flying towards two targets and there is just one illuminator that paints both targets: how do those missiles know which one is supposed to intercept which target? One obvious solution is continued assistance by ship's other systems. Perhaps SPY radar can continue sending updates and keep each missile on path to each target. But that sort of defeats the whole purpose of guidance radar/illuminator radar combo.

I was told in reality the two targets per illuminator either isn't really used or isn't counted on OR it is used in specific situations where targets are sequential, not parallel. Meaning One target is for example 20 km from ship, other target is more or less in the same line and illuminator doesn't have to move, but is behind it, 25 km from the ship. Two (or more) missiles are fired, also sequentially. Then if the first missile brings down the first target, the illuminator just goes on with its job, the second missile just goes on flying and tries to down the second target.

While that mechanic doesn't seem terribly useful, it can be useful for older types of AAW systems where the number of midcourse update channels is small or when there is so many targets that even newer systems would welcome the relief and instead of them guiding the missiles in midcourse, the illuminator is used to, in effect, guide the second missile to second target. Of course, all this makes sense in very specific situations where distances between targets are just right and there's not much wastage time wise.

But, like I said, one really can't count on two or more targets being illuminated by a single beam. Enemies will perhaps make the attacks so it comes from sufficienly different angles or group them so the illuminator will have a hard time picking the right one. For all intents and purposes, burkes are often meant to really do target just three targets per cycle.

Number of illuminators can be misleading. 054a has 4. Sovremenny has 6! Those can be worth more than Burke's 3. But there are situations where they won't be worth any more. Illuminators on 054a are positioned so they can't all look at the same position. Most of the time only 2 will be able to illuminate same position. Perhaps in a very narrow segment of azimuth 3 will be able to illuminate the same point. With Sovremenny it's even worse. The positioning of its illuminators virtually prevents more than 3 illuminators to paint the same area.

Ships move and manouver. In falkland war British ships actively manouvered when missiles were flying towards them so the missiles would hit the least crucial part of the ship. I was told it is also a matter of normal procedure for ships to manouver so their radar signature is most perplexing for the missile, perhaps smallest or hardest for missile to actually see what part it's hitting, etc. In the same regard, ships manouver so their defense systems are optimally positioned to engage the threats.

That means that Burke, if it has a chance, will manouver so all three of its illuminators will target a group of incoming threats. If the threats are coming from opposite directions, that won't be possible but then we'll probably have a situation where one illuminator is dedicated for one side, the other for other side and there's one free illuminator to switch sides as the situation progresses and, perhaps, as targets on certain side are engaged with more luck than on the other side.

Why are there so few illuminators on burke? I've no answers to that, just an assumption. Previous ships had more. But I am assuming the technology enabled the terminal illumination phase to be shorter than before. In most literature one can read about "several seconds" of terminal illumination. Maybe before, in the 70s, it was 10 or 15 seconds. Maybe now SPY radars can have so many channels for so many interceptors and have enough precision to bring the interceptor so close to target that really no more than several seconds is needed to intercept the target.

There is also the matter of height of those illuminators. Burke ones are fairly high up. Ones on Sovremenny aren't as high up, especially the midship ones. All that means closer distances and less time to intercept targets thus perhaps requireing more illuminators.

Biggest factor in overall efficiency is, i'd say, number of channels targeting system handles and number of interceptor missiles in the air going for different targets. If ship illuminates 2 targets terminally but has enough midcourse guidance channels so there are 12 more missiles (on top of the 2 guided by illuminators) that are in the air and fly towards their respective targets - then that can be more efficient defense than a ship that manages to paint 3 targets, but has midcourse guidance channels only for 6 more missiles. In the latter case the first three missiles need to hit, thus freeing the illuminators, thus freeing the channels for 3 more missiles to be fired. By which time it may be too late to react.

Sadly, I have to go now and I don't know when I'll be able to write more. Maybe tomorrow or on Monday. But this is a very interesting subject that I'd love to converse more on. Will reply to the rest of the opening post later...

this is a very interesting thread

Your question is not limited to naval SAMs , but to SAMs in general . Basically , most SAMs use SARH for terminal guidance and command link for mid-course corrections . Target would be acquired with target acquisition radar which would give general coordinates (there are other methods of acquiring target but we would not dwell on them for now ) . Target acquisition radars usually operate on lower frequencies (S-band and similar) then engagement radars . Older acquisition radars were mostly mechanically steered , but modern ones are usually PESA (and in rare instances AESA ) .

After that missile could be launched at target . Missile itself needs to be tracked to correct its position relative to the target . This is particularly important for long range SAMs , because they need to travel longer in order to get near enough to acquire target themselves . Older SAMs had dedicated radars for tracking their own missiles because of the limitations of mechanically steered radars (they could usually track only one or two targets at the same time ) . Newer fire-control radars track multiple targets and their own missiles at the same time . Corrections to the missile course would be given over secure channel(s) sometimes by fire-control radar itself .

When the missile gets near the target it is time to illuminate it with fire-control radar . Of course , you could do that earlier , but well-trained SAM crews avoid to do that in order to give minimum response time to target (this of course doesn't apply if your target is a missile , and not a fighter plane armed with HARMs ) . Missile on-board seeker picks-up the target and steers missile towards it . When it gets close enough close enough proximity fuse is activated , or alternatively warhead could be detonated via command signal from SAM battery .

Separating targets flying close enough is not a easy task . Even if the SAM radar could do that , seeker on the missile usually could not . Common solution for this problem is automatic re-acquirement of the target , and launching missiles with a little time delay . It is not a perfect solution by any means and despite all the talk about AEGIS and similar systems if enemy manages to launch more then 10 ASM at single target there is virtually no chance to avoid being hit .

From this discussion I get the impression that the flight time of a missile is important. You want missiles with high speed. But what amount of manoevrability will the missile need when it reaches its target and how do you achieve that?

Thanks, all for the replies.

Clearly this confirms that the air defense capabilities of various ships cannot be simply reduced to the number of VLS they have, or even the range of the missiles but should also factor in everything from type of guidance, number and positioning of illuminators... as well as whether the attack is from a single axis or multi-axis.

Anyway, there was a great thread a few years back similar to the current subject, which shed quite a bit of info on the matter.
http://www.sinodefenceforum.com/wor...sonar-other-modern-military-sensors-4763.html

The "illuminator target sharing" question also seems to be answered by the fact that mechanically steered illuminators can only illuminate one target at a time, and that "simultaneous illumination" is really dependent on whether the type of attack allows for staggered target switching.


---

Is it fairly accepted that an ARH armed air defense ship is generally superior than SARH armed, given the former's extra effective range and multi target capability?

The coming of VLS virtually negated the launch rate as a serious factor. When they appeared and offered launch rates of less than a second for two or more launches, other things became the bottleneck.

Thunderchief touched upon a very important but oftentime neglected issue. To achieve better results, SAM systems need to be able to know where their own missiles are. While that isn't as important for short range engagements, even medium range interceptions benefit from it. I'm talking 20-30 km or more. Either the missile is self guided or it receives help for midcourse guidance. In order for those corrections and istructions to be precise, it needs to be precisely tracked. What also helps is data from the missile itself. Lots of missiles have inertial guidance. They can send their own data to the fire control while in flight. Fire control uses both the info about trajectory errors from the missile and its own tracking data from its own radar and makes up an even better, more precise tracking solution.

Sometimes the info from the missile can be more precise than the info from the fire control. Good example of that are new air to air missiles. Radars on fighter planes are not that great at tracking such small objects as missiles at the increasingly far distances of close to or even over 100 km. Plus they have other stuff to do oftentime, or they are better off not emitting all the time due to stealth reasons etc. Then we have the missile, which using gps updates, sends its own position back to the fire control (plane) and helps fire control know where it is, enabling fire control to send more meaningful course corrections. It isn't just a matter of precision, it enables more ballistic trajectories instead of flatter trajectories and increases range, in situations where such trajectories are a viable tactical option.

Some people sometimes don't understand why some missiles have stated short ranges, even if they're big. Trajectory is oftentime correctly identified as the culprit. But it's not just about the terminal guidance and illuminators. Without knowing where the interceptor missile is, even the midcourse updates can't be used as efficiently if the missile tries to fly a highly lofted path. Good tracking of own fired missiles at medium and long ranges is crucial for using up most of the missile's energy. missiles of kub family are a very good example of that issue. They could have theoretical ranges of over 70 or perhaps even close to 100 km, if their parent fire control systems are good enough.

I would say ARH definitely helps in ship's defenses. That's the reason why more and more navies are using such systems. It also helps at really long ranges, where even ship's powerful illuminators could be bested by low power ARH seeker at close ranges.

I would assume sarh offers added protection against jamming in certain situations.

When it comes to speed, it's definitly a must against certain kinds of threats. If a threat breaches horizon 30 km from the ship, one doesn't want a ballistic profile flightpath but the quickest way to reach that threat and try to neutralize it, so more missiles can be directed against it if the first interception try fails. Similarly, if one fires at a plane 200 km away, one doesn't want 3-4 minutes of flighttime during which all sorts of things could happen. Speed does negate manouverability but it also means said missile is harder to track and manouver against. To my knowledge, most big SAM systems kill with speed alone. Manouvering is mostly for midcourse in their case. Most targets don't know when exactly to manouver and evade. And they can't be performing evading manouvers blindly every second. Stuff like missile apprach warning sensors are a rather new development and so far not many planes have them, but they are so far passive and have to approximate the nature of threat, its speed and distance. Speedier missiles may still be fast enough to push through before the plane evaded enough to get out of the danger zone.

It's always a trade off between speed and manouverability. Long range missiles tend to accentuate speed, short range systems like ones for ship defense tend to accentuate manouverability. Salvo of missiles can somewhat replace manouverability as targets will not be evading all the time, they will only do preprogrammed manouvers.

Also, I don't think ARH increases range, versus SARH, unless we're talking about specific situation where there's a dedicated illuminator for sarh whose power is not sufficient to match performance of arh at really long ranges. In example of aegis system that may be true only for ranges of over 200 or even closer to 300 km.

@Totoro , in fact no SAM system that I'm aware uses GPS (or GLONASS , Beidou ... ) . SM-3 could be exception , but I doubt even that . You see , GPS is susceptible to jamming , especially because SAM tend to turn and twist a lot during flight , unlike lets say JDAM which could point GPS antenna upwards to reduce possibility of ground jamming .

What some systems use is track-via-missile . In this case , you would need two-way data link between missile and SAM battery . Being closer to the target , missile seeker (either SARH or ARH ) could potentially get better return from the target than SAM radar . That information is then passed down the link to SAM battery .But , even in this case , missile has no way of determining its own position . Instead , all it knows is a relative bearing and distance to the target . Computer in the SAM battery would need to calculate absolute position of both the target and the missile .



BTW , most of the long range SAMs would try to climb as high they could get and then swop down on the target using accumulated potential energy . This way they increase range and their own SAM system could keep track of them .

Only SAM I know of that uses GPS is SM-3. Raytheon's promotional materials aren't shy about it. That being said, while SM-3 is technically a SAM, it's not really meant for anti-aircraft roles. So we still may have to wait a bit to come to a conclusion there. Maybe SM-6 also uses GPS but that's pure guesswork on my part.

I was careful to point out GPS as an example for air to air missiles. Will we see proliferation of GPS aided INS systems on surface to air missiles remains to be seen.

It seems we disagree about susceptibility of GPS receivers to jamming and trajectories of SAM missiles but I'll leave it at that, as I've no desire for protracted forum arguments.

What is clear is that more and more SAM systems use active radar homing for end stage interception. TVM was popular in 70s, 80s and 90s, but now ARH is more popular across the spectrum. Both medium range and long range SAMs add ARH. Of course, two way datalinks are a given, so some functionality of TVM can still be retained.

What I wanted to point out boils down to this: Although Hq16 has the kinematics to achieve considerably longer ranges (against certain types of targets), it isn't easy to utilize those kinematics. Lofted trajectories are the end solution, but it isn't enough just to have a datalink sending corrections to the missile - one can't expect those lofted trajectories to work unless the missile itself is tracked very precisely in real time. Since 054a doesn't have a system which would track its own hq16 missiles several times a second, and since hq16 doesn't have GPS assisted INS (brochure for hq16 mentioned just INS) HQ16 can be guided with enough precision only through relatively short distances. Perhaps then the missiles use straighter trajectories and minimize opponent's reaction time.

I think the use of GPS on medium to long range SAMs, while useful, is unlikely to catch on.

The biggest benefit of GPS is in giving precise positional data on the SAM during the boost and cruise phase of the flight. This, coupled with a two way datalink, allows the missile to use predicted position of the enemy rather than having to constantly track the target throughout the engagement.

I believe the massive range increases from the SM1 to SM2 is largely down to this shift in tracking and the flight path the missile takes.

As others have pointed out, many modern long range SAMs, when engaging far away targets, will climb fast and almost follows a ballistic trajectory, which is the trajectory most efficient at maximising range. Compare that to the same missile having to keep its nose pointed at the target throughout the engagement and once can easily see how the effective engagement range of the same missile can be vastly improved.

While GPS is a great way to provide accurate positioning data on the SAM, and for the boost and cruise phase, a SAM typically not be pulling sharp turns, so there shouldn't be much of an issue in terms of GPS tracking accuracy until the engagement phase, but by then the GPS would have served its purpose already. However, in this day and age with massive phase array radars and advancements in computing processing making systems like Aegis almost standard on the newest warships, and with the radar and supporting targeting computers able to track thousands to tens of thousands or more targets at the same time in 360 degrees of the ship, having individual GPS transponders on the missiles seems a bit redundant, especially when those missiles will already be packing inertial navigation systems. And indeed, the transition from SM1 to SM2 without needing GPS transponders in each missile pretty much proves that predictive engagement does not require GPS in each missile.

This, while GPS can and will provide very accurate positioning data for predictive engagement, it suffers from being redundant, and are susceptible to jamming, and on a SAM were every square centre meter and ounce of weight is precious, I suspect most makers will choose to forgo installing GPS on the SAMs.