PDA

View Full Version : Why do missiles need to "lock-on"?


Whack-a-Mole
04-11-2009, 11:35 PM
I thought this may have been answered before here but my search turned up nothing and not waiting over and over to refine it.

In the movies you see pilots in a dogfight trying to achieve a target lock on the enemy plane. The beep-beep-beep-beep-beeeeeeeeeeeeeep, then shoot.

First off is this accurate? Never been in a fighter jet so only have the movies to inform me. While I grant movies take all sorts of creative license I assume they would not make this up out of whole cloth if it just did not work that way at all.

Second, does it matter if it is a radar guided or heat seeking missile?

Third, why? How can my heat seeking missile need to take time to identify that hot bloom in the cold sky ahead of it? What is it waiting for? "See that hot thing out there? Good...go to it!" Perhaps if there are multiple targets you want to designate one or another but should be easy enough to use a selector to "tag" a given target for your missile.

Fourth, what about targets you cannot see? Many missiles can engage well beyond visual range. Does the pilot still need to wait for a lock?

Johnny L.A.
04-12-2009, 01:08 AM
"See that hot thing out there? Good...go to it!"

[Talking missile]

Sure thing? Which one? That hot yellow ball up there? Or that big green area below us that's hotter than the light blue area above us?

[/TM]

IANA fighter jock, but it seems to me that the missile needs to 'know' which hot spot to aim for. Early heat-seeking missiles such as the Falcon had to use liquid nitrogen (?) to cool their sensors, which could take several seconds. (It also had to hit the target before the coolant ran out.) I remember watching a documentary on Vietnam dog fights, and it was mentioned that one pilot was at such an angle to the target that the missile could not get a lock. IIRC, the angle exceeded the missiles tracking and/or maneuvering parameters. So the pilot has to position the aircraft such that deflection is not too great. Heat-seekers such as the Sidewinder had (has) to 'lead' the target too, or else get into a tail-chase. I'm guessing that a lock helps to reduce the chance of the missile missing its target due to the deployment of countermeasures such as flares.

With radar-homing the missile has to lock on with its own radar (active homing), which is fairly small. The target aircraft might maneuver rapidly or deploy chaff or electronic jamming. With semi-active homing the attacking aircraft must illuminate the target with its own radar (larger than what the missile has) and the missile homes in on the reflected radiation. If the attacking aircraft has to turn away, then the missile will not have the radiation to track.

Whack-a-Mole
04-12-2009, 02:48 AM
[Talking missile]

Sure thing? Which one? That hot yellow ball up there? Or that big green area below us that's hotter than the light blue area above us?

[/TM]

IANA fighter jock, but it seems to me that the missile needs to 'know' which hot spot to aim for. Early heat-seeking missiles such as the Falcon had to use liquid nitrogen (?) to cool their sensors, which could take several seconds. (It also had to hit the target before the coolant ran out.) I remember watching a documentary on Vietnam dog fights, and it was mentioned that one pilot was at such an angle to the target that the missile could not get a lock. IIRC, the angle exceeded the missiles tracking and/or maneuvering parameters. So the pilot has to position the aircraft such that deflection is not too great. Heat-seekers such as the Sidewinder had (has) to 'lead' the target too, or else get into a tail-chase. I'm guessing that a lock helps to reduce the chance of the missile missing its target due to the deployment of countermeasures such as flares.

I would hope they have programmed the missiles to not fly to the sun. Would be absurdly easy to foil them otherwise.

I can see the point about the missile not "locking on" if it cannot maneuver to hit what it is after. That makes sense. More, "I see it but I won't be able to hit it" thing. So that said I presume the target lock can turn on and off as the planes maneuver.

Declan
04-12-2009, 03:08 AM
First off is this accurate? Never been in a fighter jet so only have the movies to inform me. While I grant movies take all sorts of creative license I assume they would not make this up out of whole cloth if it just did not work that way at all.

Every documentary and computer simulation released post Vietnam has mentioned this , so I am taking it as fact.

Second, does it matter if it is a radar guided or heat seeking missile?

Not a fighter pilot or weaponeer, but it used to be just heat seekers, but now with the new aim-120 it will also include radar guided.Previously Radar guided missiles were beam riders that had the aircraft radar iluminating the target and the aim-7 sparrow for example would home in on that, until a set distance from the target and boom.

Third, why? How can my heat seeking missile need to take time to identify that hot bloom in the cold sky ahead of it? What is it waiting for? "See that hot thing out there? Good...go to it!" Perhaps if there are multiple targets you want to designate one or another but should be easy enough to use a selector to "tag" a given target for your missile.

The target aircraft is maneuvering in relation to your fighter and the seeker head is small, so you have to give the seeker head enough time to identify the heat source.

Fourth, what about targets you cannot see? Many missiles can engage well beyond visual range. Does the pilot still need to wait for a lock?

I just played the games , but lots of targets came up on the hud and once you identified the one you wanted , the icon changed and said lock. Since its based on the actual systems , I can only infer that its close enough.

Problem with BVR missiles is that almost all of the time the rules of engagement has precluded its use in really long shots. Since over the course of an ACM engagement many miles can be traveled at high speed, you could concievably bring freindly or innocent air traffic into peril.

Declan

Stranger On A Train
04-12-2009, 03:24 AM
I would hope they have programmed the missiles to not fly to the sun. Would be absurdly easy to foil them otherwise.Older 'heat-seeking' missiles tended to lock onto the largest thermal source in the field of view, and yes, flying into the Sun was often an effective (if not entirely reliable) method of diverting them. Remember, this is before complex microprocessors capable of discrimination of large amounts of discrete data thousands of times a second. While newer generations of sensors and filtering systems have more capability to discern between genuine bogies and solar spectra, 'sun lock' is still a problem. As Johnny L.A. noted, the sensor has to be cooled by onboard coolant, which has a very limited operating span.

Radar guided missiles are another issue; they go wherever the guidance controller tells them to go. Of course, this means maintaining a radar lock on the target up to the point that onboard systems can take over. With networked AEW&C aircraft it is possible to do this in a fairly automated fashion so that from the perspective of the pilot it is a 'fire & forget' operation, but the initial capture still needs to characterize the signal before a guidance lock can be completed.

Stranger

Reply
04-12-2009, 11:44 AM
...With networked AEW&C aircraft it is possible...

Is that another term for AWACS?

JRDelirious
04-12-2009, 01:47 PM
Is that another term for AWACS?
Yes -- AWACS is not really a generic term, though it gets used as that, it refers to specific systems (or families of systems).


As mentioned, the homing devices are good, but not infinitely good. And to keep them from going off and following just anything that's around that's either hot or radar-reflective, it's better if while they're still connected to your fire control system you tell them which target to go after and verify that they can actually hit it.

UncleBill
04-12-2009, 09:31 PM
Former Missileer here. Surface to Air type. I assume the info on the Stinger is generally transferable to air-to-air heat seekers. If not, then this would be applicable for the ground guys only.

The missile has an "eye" in the seeker section, but the range of vision is very tight, needle-like. Well, an expanding needle. Once activated (and cooled, using Argon gas), it goes into a predetermined search pattern, physically moving the seeker head, scanning for the intended target. The scan has a larger, but still limited cone of vision it can see. So the fighter has to maneuver to get the target into the larger search cone, then activate and begin the scan. Since we have to objects moving very fast in three dimensions, I'm sure it doesn't make much for the target to depart the search cone from time to time. In the Stinger, the gunner has to listen for that "locked" tone, and "uncage" the seeker head, allowing for a much greater cone of vision so lock is not easily lost. I would imagine the Sidewinder does that uncaging automatically.

As for not shooting the sun, it looks for the IR (Infra Red) signature, wavelengths and such, and certain parts of the spectrum can be programmed so that if it DOES get "blinded" by the sun, it goes back into search mode, and it knows where the target was headed, so it has a pretty good chance of finding it again.

Reply
04-12-2009, 09:38 PM
Yes -- AWACS is not really a generic term, though it gets used as that, it refers to specific systems (or families of systems).


So AWACS is a specific family of AEW&C systems, though both acronyms mean roughly the same thing? Now that's confusing.

UncleBill
04-12-2009, 09:54 PM
The military needs to changes things around every so often. Makes the changer feel important. 3C's used to be Command Control and Communication. Now there is C4ISTAR (adding Computers, Intelligence, Search Targeting, Acquisition and Reconnaissance). What used to be AWACS is now AEW&C.

flyboy
04-13-2009, 11:18 AM
So, just to summarize here: There are three types of missiles: IR, Active, and Semi Active. IR is what Uncle Bill was talking about. No radar involved, just passive infrared tracking. Active missiles have their own on-board radar emitter and receiver so they can independently illuminate and track a target. Semi Active missiles rely on something else to light up the target--they only have a receiver.

All have their pluses and minuses. The beep-beep you hear in the movies is simply the fighter jock's radar threat system audibly pumping out what it hears: the missile's target tracking radar (whether it's on board the missile or some other platform) homing in on the plane--the radar is performing a pre-designed tracking function in order to narrow itself down to the plane only, and in the process it hits and then scans off of the target, each time hopefully narrowing in on the target. Thus the "beep..... beep.... beep... beep.. beep.beeb beeeeeep" you hear. You won't hear anything like this with an IR missile since there is no radar involved. If you're in a threat envelope, you'll be watching for missile launch flashes and smoke plumes and have your threat warning system on. Unless you're Scott O'Grady.

As far as the Vietnam-era missles go.... today's missiles are a whole 'nother breed. The problems of then are pretty much gone in today's systems, although you will find countries which use Vietnam-era weapons.

Does it matter which type of missile? You have to look at the user. How much does it cost? How much to maintain it? Train to use it? Is it portable? How high do you want to reach? There're a lot of factors going into what missile you'll be using (and seeing as a threat). Does the missile need a "lock" before firing? Most do, and depending on the type and sophistication of the missile, it can be a "fire and forget" missile, or it may require you to sit (exposed) straight and level as you continue to illuminate the target for the missile.

For BVR missiles, I imagine you'd have to have some sort of lock before launch, but again it depends on the type of missile and weapon system you're using. For the U.S., you'd definitely also have to meet certain basic criteria of a threat--seeing the blip on your screen will not be enough to launch. You'll need other corroborating information which I won't get into.

Kobal2
04-13-2009, 11:32 AM
So, just to summarize here: There are three types of missiles: IR, Active, and Semi Active.

Pssst, you forgot one : TV guided missiles. I don't blame you though : only the Russians have A/A TV missiles AFAIK. In the US and OTAN forces, I think the only one if the A/G Maverick missile.

It's pretty much what it says on the tin : a missile guided by a plain optic camera (which doubles as an IR missile, because said camera also has an IR and Night Vision modes). And they work just like IR missiles do : by tracking an object against its contrasted background. So dark plane on clear sky = target.

If I recall clearly, the Russian ones were developped to counter stealth planes, and also just in case the US managed to design airframes with perfectly concealed exhausts. Masking heat and radar echo is one thing, turning invisible is another ;)

flyboy
04-13-2009, 12:21 PM
Good catch. And I should specify that these are SAMs I'm talking about. Getting into other types of missiles and guidance systems will just confuse things.

UncleBill
04-13-2009, 12:48 PM
It's pretty much what it says on the tin : a missile guided by a plain optic camera (which doubles as an IR missile, because said camera also has an IR and Night Vision modes). And they work just like IR missiles do : by tracking an object against its contrasted background. So dark plane on clear sky = target.

If I recall clearly, the Russian ones were developped to counter stealth planes, and also just in case the US managed to design airframes with perfectly concealed exhausts. Masking heat and radar echo is one thing, turning invisible is another ;)I can neither confirm nor deny one search function that looks for the "shadow" cast by the target against the natural background IR spectrum. The HAWK SAM system had/has a Tracking Adjunct System (TAS) that used a TV camera with really good zoom to maintain the tracking radar's track of the target while the radar was not radiating.