R. Shaw "Fighter combat", some questions

[Maximus_G]

Although the gimbal limit may be bumped in a hard-turning intercept with a maneuvering target when the missile's turn capability cannot quite stop the target LOS drift, this situation more often leads to exceeding the seeker's tracking-rate limit. Missile seekers are usually gyro-stabilized to point along a fixed line in space, much like the needle of a magnetic compass. The body of the missile is then free to turn about the "fixed" seeker. Such motion causes little problem and generally is limited only by the missile's turn capability and the seeker's gimbal limits. If the seeker's LOS must be changed, however, because of changing target LOS, its gyro must be precessed. The rate at which this can be accomplished (known as the target's maximum gyro tracking rate) is limited, and it is often dependent on the target's signal-to-noise ratio.

Please pay attention to the text. Theres a portion quoted in bold. What did he mean?

 

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This page in the book

[Groove]

http://en.wikipedia.org/wiki/Signal-to-noise_ratio

[Maximus_G]

Thank you, though the problem is not in snr definition, but rather in the statement about "target's maximum gyro tracking rate", which is said to be dependent somehow on the target's signal-to-noise ratio. I'm trying to understand - HOW. Where is that dependency, when we presume that the gyro movement is purely of mechanical nature.

I guess mr. Shaw could be wrong here, or he simply said not what he meant to say.

 

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Target movement -> electrical command to change seeker direction - physical gyro movement. If the gyro moves too slow, target gets past sensor limits and disappears.

 

If the target is so hardly seen, that its movement loses lock, then there would be no command to change seeker direction. So, it has nothing to do with the seeker's movement speed limits. It's the different situation.

Edited May 15, 2009 by Maximus_G

[59th_LeFty]

I think I got an idea which MAY be the one you're looking for :)

 

If a signal-to-noise ratio is too low (which means harder target tracking) the effectiveness of the missile's LOS can be truly degraded - which let's say would be 15°, it became 10 or less due to electronic conditions. This is enough to keep target taracking, but in combination with target LOS change, it can really cause lose of sigth on a target.

 

On the other hand, if we're talking about SNR, it means existence of active jamming, which is easily defeated by modern ARHMs like amraam. So the discussion must keep stick to SAR missiles.

 

EDIT - correction: SNR is mentioned with actve jamming in the source? :) 'Cause the source of noise don't have to come from JAM, it can be other clutter :smartass:

Edited May 15, 2009 by 59th_LeFty

[Maximus_G]

The SNR here is simply a means of defining how good a target is seen. It does not involve jamming necessarily, it's about target signal strength compared to the background signal and seeker sensitivity.

 

LOS cannot be worse or better by itself, so it cannot degrade. It's an angle to the target.

Concerning this seeker question, LOS can be within seeker gimbal limits - or out of these boundaries. And it can move so fast that seeker would not be able to keep tracking it because of its maximum angular speed limit, say 60° per second for a certain missile type.

If the target is hardly seen, seeker's maximum target tracking rate can degrade - and get less than 60° per second. But that obviously would be not because of mechanical gyro limits, as the gyro itself can still turn at 60° per second. That's it.

[Maximus_G]

Just as [my] missile left the rail the MiG [-21] executed a maximum G, tight turning, starboard break turn. He couldn't have seen me. Either his wingman called a break or his tail warning radar was working. I had an instantaneous plan view of him and he was really hauling.... The missile couldn't handle it, exploding out of lethal range.

 

Commander Randy "Duke" Cunningham, USN

 

What's the meaning of "really hauling" here? I'm having a language problem.

[104th_Crunch]

Really hauling = really moving or moving very fast.

 

Hauling = carrying a load, like a truck driver or moving a load by hand for example. Really hauling means you are carrying your load very fast. Another expression you might hear is, "hauling ass" :) which also means the same thing, to move fast.

Edited October 20, 2009 by Crunch

[kaiserb_uk]

Re the SNR ratio - missile seekers use analogue feedback mechanisms, and if you think about the way a Sidewinder's seeker 'growls' and the way the growl varies depending on the strength of the heat source, it's not unreasonable to assume that a stronger heat source will also translate to a stronger force applied to the seeker's gyro.

 

I just made that up but it sounds convincing no?