What are the advantage of Semi active laser homing (SAL) over Laser beam riding (SACLOS)?

[Ronny]

With laser beam-riding SACLOS, the sighting device emits a laser signal directed toward the target. A detector in the tail of the missile looks for the signal. Electronics in the missile then keep it centered in the beam.


With Semi active laser homing (SAL), a laser is kept pointed at the target and the laser radiation bounces off the target and is scattered in all directions, a laser seeker on the head of the missile detects which direction this energy is coming from and adjusts the projectile trajectory towards the source.


SACLOS key advantage over SAL is that it can use much weaker laser source and harder to detect by laser warning system, it is also less effected by things like smoke cover countermeasure. But it seem like SAL guidance are far more popular. So what are the advantage of SAL over SACLOS?

 

[TomS]

The most obvious advantage of SALH is that it allows third-party designation, from another aircraft or a ground-based controller. Beam-riders require illumination from the launch platform.

 

[overscan (PaulMM)]

Also with SALH the nearer the missile gets to the target, the higher power the reflected signal and the more concentrated, while for SACLOS the light source is ever further away and more and more diffused.|

Its analogous to the argument for SARH over beamriding for AAMs.

 

[Ronny]

The most obvious advantage of SALH is that it allows third-party designation, from another aircraft or a ground-based controller. Beam-riders require illumination from the launch platform.

That also mean the launching platform can't move significantly from original position in case of beam riding missile? and it probably less effective against fast moving target?

 

[Dilandu]

So what are the advantage of SAL over SACLOS?

The main advantage is that missile isn't forced to fly along the beam all time. The straight-flight trajectory is generally not optimal for many kind of engagements. With SACLOS, the missile is forced to fly more or less straight along the beam (or you need a much more complicated targeting device, capable of tracking the target and moving the guidance beam separatedly), spending much more energy to stay in air. With SAL, the missile could fly at optimal trajectory - usually semi-ballistic - reach longer range, have more energy for maneuvering, and, for example, dive on target from above.

 

[Dilandu]

Also with SALH the nearer the missile gets to the target, the higher power the reflected signal and the more concentrated, while for SACLOS the light source is ever further away and more and more diffused.|

Its analogous to the argument for SARH over beamriding for AAMs.

Must point out, that - assuming the same beam power - the emitted signal would always be much more powerful than reflected, no matter how far the missile is. The emitted beam is tightly focused and powerful; the reflected beam is unfocused and part of it always get absorbed.

So no, the problem is not the intensity of the beam; the problem of beam-riders is widening of the beam with distance, so the guidance became less accurate.

 

[timmymagic]

One advantage for laser beam riding SACLOS on LMM that has been mentioned by the RN is that it performed better than SAL on 'low emissivity' targets like RHIBS. That might be true for some of the smaller UAV as well.

 

[overscan (PaulMM)]

Must point out, that - assuming the same beam power - the emitted signal would always be much more powerful than reflected, no matter how far the missile is. The emitted beam is tightly focused and powerful; the reflected beam is unfocused and part of it always get absorbed.

So no, the problem is not the intensity of the beam; the problem of beam-riders is widening of the beam with distance, so the guidance became less accurate.

I wasn't directly comparing the two power levels, SAL seeker will always see a lower signal strength compared to a beamrider given same power laser for self-illumination at least. I just meant the closer the SAL gets to the target, the stronger and more accurate the signal it sees, while for beam riding the opposite is true - the further it flies, the lower the power signal it receives and the more spread out it is. So guidance accuracy may decrease at long range.

 

[stealthflanker]

and SALH rationalize volume distribution inside the missile. Can put all the electronics up-front, while maximizing rear volumes for propellant.

Beamrider, kinda tricky especially for tactical missiles like say, Kornet and Refleks as they have to put the motor at middle of the missile, making nozzle design and size kinda tricky. This is so that the rear receiver and optical beacon for the missile are clear from missile's own exhaust.

 

[timmymagic]

and SALH rationalize volume distribution inside the missile. Can put all the electronics up-front, while maximizing rear volumes for propellant.

Beamrider, kinda tricky especially for tactical missiles like say, Kornet and Refleks as they have to put the motor at middle of the missile, making nozzle design and size kinda tricky. This is so that the rear receiver and optical beacon for the missile are clear from missile's own exhaust.

LMM's receivers are in 'pods' on each fin facing backwards. It doesn't preclude an exhaust at the rear of the missile.

This is also an additional beneft to laser beam riding SACLOS. The target will get no warning of being 'painted' by a laser, and also a DIRCM system will have no effect on a seeker head...

 

[TomS]

LMM's receivers are in 'pods' on each fin facing backwards. It doesn't preclude an exhaust at the rear of the missile.

This is also an additional beneft to laser beam riding SACLOS. The target will get no warning of being 'painted' by a laser, and also a DIRCM system will have no effect on a seeker head...

There will still be warning, since the laser will (eventually) impinge on the target. We've seen video of Ukrainian Skif ATGM operators holding the guidance laser off the target until part way through the flight to minimize warning time.

 

[timmymagic]

There will still be warning, since the laser will (eventually) impinge on the target. We've seen video of Ukrainian Skif ATGM operators holding the guidance laser off the target until part way through the flight to minimize warning time.

The main reason for Stuhna H operators doing that was to clear obstacles and cover that they'd fired behind, the missile also has a noticeable tendency to slightly dip following launch, which Stuhna operators have remarked on. Possibly the only targets where that wasn't the case was the 2 x KA-52 kills that 'may' have had LWR (not all do), but its noticeable that both kills had trees in the foreground that needed to be cleared (incredibly it was the same location/FARP and same Stuhna team on both occasions..).

 

[Dilandu]

I wasn't directly comparing the two power levels, SAL seeker will always see a lower signal strength compared to a beamrider given same power laser for self-illumination at least. I just meant the closer the SAL gets to the target, the stronger and more accurate the signal it sees, while for beam riding the opposite is true - the further it flies, the lower the power signal it receives and the more spread out it is. So guidance accuracy may decrease at long range.

Ah, then I misunderstood you. My apologies.

 

[Zoo Tycoon]

Modern beam riders don’t have a single beam pointing at the target;- they project a cone or grid of beams. Because these don’t fall on the target, laser sensors on the target won’t be triggered. As the missile nears the target, the size of the beam cone is constricted down gather the missile into the target, so the target will only detect the beam when it’s to late to do anything. One advantage is the ability to fly optimally trajectory to maximise range I.e the missile seeks the top limit of the cone . Another is the fragile laser sensor are pointed in the opposite direction to the target so will not be interfered by countermeasures on the target. Yet another is the target doesn’t need to be reflective.

One disadvantage is SALH, when illuminated from the launch location is the missile can cast a shadow over the target so breaking lock, that’s why you see these spiralling around the beam.

 

[Ronny]

also a DIRCM system will have no effect on a seeker head...

I don't think DIRCM system work on SAL seeker either, it purely against infrared sensor

 

[Ronny]

To sum up: This is correct?

 

[Dilandu]

To sum up: This is correct?

Quite good summary!

 

[Zoo Tycoon]

To sum up: This is correct?
View attachment 738917

Some of these systems are not comparable due to range and fire support.-

Corrections;-
-a cone or grid laser beam riding allows optimal trajectory (semi ballistic extended range).
- a cone or grid beam rider is immune to laser detection and countermeasures
- a cone or grid based beam rider won’t need a terminal manoeuvre because the target will be unaware it’s being fired upon
- Active radar guidance only works over relatively short ranges. Hence it needs mid flight updates so it’s not fire and forget. The same is also true for the longer range infra red systems.

No idea what passive anti radiation is? Looks to good to true.

 

[timmymagic]

No idea what passive anti radiation is? Looks to good to true.

A HARM for example is passive anti radiation, i.e. it homes in on the targets radar emissions. AARGM can be, but also has an active radar seeker for the terminal attack.

 

[timmymagic]

To sum up: This is correct?
View attachment 738917

I would split out immunity from flares and dircm into 2 categories. A forward facing SAL seeker head, like IR, IIR or optical, is still vulnerable to DIRCM. Particularly the more modern systems. If the seeker is blinded it cannot guide.

I'd also add in 2 additional categories for traditional IR and Optical. A decent IIR seeker 'should' not be affected by flares. But it can be affected by a modern IR smoke countermeasure.

As @Zoo Tycoon says Active Radar could need 'third party designation' in a way i.e. a data link for a longer range engagement. All depends how close and what sort of target set. For example Brimstone is active radar and doesn't require a data link, but engages a different target set and closer than say an Amraam or Meteor.

For Laser Beam Riding the question around the launch platform moving significantly would depend on what you mean by 'move'. The platform could advance by flying forward (say a Wildcat firing LMM i.e. Martlet). It probably wouldn't be moving significantly to the side though...

 

[Archibald]

Also with SALH the nearer the missile gets to the target, the higher power the reflected signal and the more concentrated, while for SACLOS the light source is ever further away and more and more diffused.|

Its analogous to the argument for SARH over beamriding for AAMs.

A debate somewhat similar to the three original Sparrow AAMs : the I, the II and the III. The I was beam ridding, and a total waste of missile. The II tried to pull an AMRAAM in the 1950's "fire and forget, I have my own internal radar, thank you" - and failed. In the end the III with SARH was the most "workable" of the three AIM-7 guidance systems, albeit by a very low margin, as shown in Vietnam. AIM-7F in the early 1980's finally got a decent success rate. It only took 30 years since 1950... 1982 was turning point for both AIM-9L and AIM-7F. They worked at last !

Air-to-ground weapons got the same harrowing guidance issue lasting over decades. Case in point: first guided munition attack ever, May 10, 1972 on Vietnam bridges. Laser worked, if barely. Electro-optical failed miserably.

In France AS-30 and AS-30L were world aparts, despite having mostly similar airframe and name. Took more than two decades to get a workable guidance system.

 

[Ronny]

I would split out immunity from flares and dircm into 2 categories. A forward facing SAL seeker head, like IR, IIR or optical, is still vulnerable to DIRCM. Particularly the more modern systems. If the seeker is blinded it cannot guide.

As far as I understand it, current DIRCM doesn't physically blind the seeker but more or less shine the bright laser light and make it hard for the seeker to see. But when I search up, there is no DIRCM system advertised capability to deal with SAL sensor, they all seem to deal with infrared seeker

 

[Ronny]

Corrections;-
-a cone or grid laser beam riding allows optimal trajectory (semi ballistic extended range).

I honestly not aware of any beam riding missile with semi ballistic trajectory, I guess it might be possible if you manually point the laser beam at higher elevation than target then slightly walk it down to target. But I don't think the targeting system will do that physically

- a cone or grid beam rider is immune to laser detection and countermeasures

How come?, the laser beam will eventually have to point at target right?, and besides, if enemy deploy a smoke screen , then the laser can penetrate that either right?

View: https://www.youtube.com/watch?v=CjlJi4l0cBs&ab_channel=TankNutDave

- a cone or grid based beam rider won’t need a terminal maneuver because the target will be unaware it’s being fired upon

Not really, on a ship CIWS for example detect target using its own radar, so it will detect the missile even if the missile use beam rider guidance.

On aircraft, missile warning system either use UV to detect the missile exhaust plume (for example: AAR-60 used on F-16) or they use imaging infrared to detect missile exhaust plume and the friction of missile nose (for example: AAQ-37 used on F-35) or they can also use mini pulse doppler radar sensor to detect the missile (for example: PVS2000 used on Eurofighter)

On tank, most active hard kill protection system use MMW pulse doppler radar to detect projectile

- Active radar guidance only works over relatively short ranges. Hence it needs mid flight updates so it’s not fire and forget. The same is also true for the longer range infra red systems.

I disagree, depend on target, the detection range of active radar seeker can be even higher than max kinematic range of most laser beam riding missile
Same can be said about IR sensor

 

[Zoo Tycoon]

I honestly not aware of any beam riding missile with semi ballistic trajectory, I guess it might be possible if you manually point the laser beam at higher elevation than target then slightly walk it down to target. But I don't think the targeting system will do that physically.

There’s no manual beam pointing in a modern system, the beam or beams are electronically steered;- the ability of a single laser to electronically paint a cone has been around since the late seventies, just look at a Jean Michel Jarre concert. Modern systems use an image tracker to precisely paint the beam relative to the target, so the operator just has to keep both target and missile within the field of view.

 

[Zoo Tycoon]

How come?, the laser beam will eventually have to point at target right?, and besides, if enemy deploy a smoke screen , then the laser can penetrate that either right?

View: https://www.youtube.com/watch?v=CjlJi4l0cBs&ab_channel=TankNutDave

The laser cone or grid is deliberately not projecting in direct line of sight to the target at initial launch, its projected as a cone wide enough to gather the missile. As the missile flys down range the cone constricts (gets smaller in diameter). The missile only encounters the beam at the cones perimeter and turns away from it towards the cone centre. As the engagement reaches its terminal phase the cone is now a circle just wide enough to circle the target and the missile is in the centre of the cone.

 

[Zoo Tycoon]

Not really, on a ship CIWS for example detect target using its own radar, so it will detect the missile even if the missile use beam rider guidance.

On aircraft, missile warning system either use UV to detect the missile exhaust plume (for example: AAR-60 used on F-16) or they use imaging infrared to detect missile exhaust plume and the friction of missile nose (for example: AAQ-37 used on F-35) or they can also use mini pulse doppler radar sensor to detect the missile (for example: PVS2000 used on Eurofighter)

On tank, most active hard kill protection system use MMW pulse doppler radar to detect projectile

I disagree, depend on target, the detection range of active radar seeker can be even higher than max kinematic range of most laser beam riding missile
Same can be said about IR sensor
View attachment 738939

Defeating any type of close in protection has nothing to do with the guidance, it everything to with engagement velocity and terminal kinetic energy.

Millimetric radars are inherently short range due to atmospheric attenuation, especially when matched to a small diameter emitter;- it’s in the physics, a 4 inch diameter radar can’t track a target at 100km All variants of the R27 are “Initial phase Inertial navigation with radio command updates” followed by an infra red or millimetric radar guided terminal phase. I think something has got lost in translation with the example presented.

 

[Ronny]

Defeating any type of close in protection has nothing to do with the guidance, it everything to with engagement velocity and terminal kinetic energy.

Different kind of guidance allow for different kind of terminal maneuver though. IIR and Active radar seeker allow for pretty aggressive terminal maneuver because they can reacquire target quickly, and they don't have a corridor they needed to fly within

Millimetric radars are inherently short range due to atmospheric attenuation, especially when matched to a small diameter emitter;- it’s in the physics, a 4 inch diameter radar can’t track a target at 100km All variants of the R27 are “Initial phase Inertial navigation with radio command updates” followed by an infra red or millimetric radar guided terminal phase. I think something has got lost in translation with the example presented.

Atmospheric attenuation probably affect laser way more than RF wave
Anyway, R-27T (the one with IR seeker) is a Lock on before launch missile, it must lock on target before launch. I don't think it is very surprising that 36T seeker can lock on an aircraft from 16-18 km in head on direction though. Aircraft are hot when they fly at high velocity, another example is the ancient AGM-65G, its IIR seeker can lock on a building from 18.5 km.


Regarding R-27R, it is a semi active radar missile, basically a sensor that rely on aircraft radar, so it definitely not millimeter wave, more like X-band. The range is around 25 km against average fighter.


For Ku band active radar seeker such as 9B-1103M, the range is roughly 20 km against average fighter

 

[Ronny]

The laser cone or grid is deliberately not projecting in direct line of sight to the target at initial launch, its projected as a cone wide enough to gather the missile. As the missile flys down range the cone constricts (gets smaller in diameter). The missile only encounters the beam at the cones perimeter and turns away from it towards the cone centre. As the engagement reaches its terminal phase the cone is now a circle just wide enough to circle the target and the missile is in the centre of the cone.

Wouldn't the laser warning system literally able to see the laser beam like this whether the laser hit the vehicle directly or not?

 

[Zoo Tycoon]

Different kind of guidance allow for different kind of terminal maneuver though. IIR and Active radar seeker allow for pretty aggressive terminal maneuver because they can reacquire target quickly, and they don't have a corridor they needed to fly within


Atmospheric attenuation probably affect laser way more than RF wave

As for your assertion”don’t have corridors”;- 24hours ago you didn’t know these existed but now you’re an expert on their terminal accuracy? As someone trying to help you with your initial request, is showing a little respect to much?

I never made any claims on laser atmospheric attenuation compared to other technologies

Sure an IR system can track a fighter sized target at up to 20km, but with that sensitivity it can’t acquire it. It’ll find all sorts of other sources especially when looking down. At one talk I attended, the pilot speaker noted his Sidewinder wanted to lock onto a a field where cows had recently been and left various warm patches. A system of many times the complexity of the missile seeker is required to tell it “look at this micro rad lat/long to see this thermal pin prick” among all the distracting thermal clutter. If you have such a supporting system just pass the targets position to the missile IINS…. Be rude not to. Just because some salesman say make me rich, it doesn’t translate into practical capability.

 

[Ronny]

As for your assertion”don’t have corridors”;- 24hours ago you didn’t know these existed but now you’re an expert on their terminal accuracy? As someone trying to help you with your initial request, is showing a little respect to much?

Umm I'm not sure why you would think I disrespected you?. My tone is pretty calm and I don't think I throw any insult?
I'm not talking about the terminal accuracy of laser beam riding missile. I meant it obvious that laser beam riding missile have to always keep its tail/sensor toward the launch platform laser transmitter (since it basically bounce around inside the laser beam /laser grid whatever).


So it quite obvious that a laser beam riding missile is not capable of these evasive maneuver of IIR or Radar guided missiles:

I never made any claims on laser atmospheric attenuation compared to other technologies
Sure an IR system can track a fighter sized target at up to 20km, but with that sensitivity it can’t acquire it. It’ll find all sorts of other sources especially when looking down. At one talk I attended, the pilot noted his Sidewinder wanted to lock onto a a field where cows had recently been and left various warm patches. Just because some salesman say make me rich, it doesn’t translate into practical capability.

Oh because you said IR and active radar seeker are short range system, so I was under the assumption that you were comparing them with laser beam rider. Of course, with any system, their range is affected by target type and also background clutter