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Missile Defense

Technology has always found its greatest consumer in a nation's war and defense efforts. Since the last attempts at a "Star Wars" defense system, has technology changed considerably enough to make the latest Missile Defense initiatives more successful? Can such an application of science be successful? Is a militarized space inevitable, necessary or impossible?

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gisterme - 07:05pm Feb 8, 2002 EST (#11371 of 11376)

rshow55 2/8/02 6:12pm

"...If I've made a mistake here, what would it be?..."

It would be that the reference point for the ABL application of adaptive optics is the brightly illuminated target. That's a great reference point. And the reason for the 1 arc second resolution limitation for traditional ground-based telescopes noted Caisson's book is due to atmospheric turbulence. Adaptive optics compensates for atmospheric turbulence so that resolution of ground based telescopes can be improved. If you understood feedback loops, you'd realize that the difference between the reference and the "approximation" you mentioned is only the loop error. What that means in terms of apparent optical path correction depends entirely on loop gain and bandwidth of the mirror actuation system.

Think about your stereo amplifier at home. It is a closed-loop amplifier that takes a small signal and reproduces an amplified approximation of that signal. In such amplifiers, 0.01% distortion (or better) is common because they use a closed-loop feedback system that utilizes excess gain to continually correct the output signal to match the input signal x some gain factor. Without the feedback loop the distortion would be huge and the output would sound lousy. So the output is only an amplified approximation of the input no matter how low the distortion figure may be.

Likewise, the atmosphere-distorted waveface of starlight that enters a telscope is adjusted by the adaptive telescope mirror as it is reflected to the camera such that the camera sees a corrected approximation of what the waveface of the starlight was like before it was distorted by the atmosphere.

The mistake in the conclusion you draw is that you don't understand that the AO has the effect of eliminating atmospheric distortion thereby restoring the limits of telescope resolution to the design of the optics alone. Ideally it would eliminate all distortion. In reality, how much distortion is actually eleminated is a function of how good the system is. I'm sure that there are performance statistics available, Robert. Why don't you check if you're interested? Does the AO correct 90% of the distortion? 99%? 99.9%? That should be checkable, Robert.

The AO for a laser system would exploit exactly the same principles. It just uses the illuminted target as the reference "star" rather than something else. After all, the atmospehric turbulence you want to compensate for is that which exists along the LOS path between the target and the laser.

rshow55 - 07:13pm Feb 8, 2002 EST (#11372 of 11376)

For the COIL laser to do damage, you need resolution considerably BETTER than space telescope -- certainly that's true if the surfaces are reasonably reflective, as you've agreed before.

How is the system to get that resolution -- even if a feedback path did exist (and if the feedback path is to the missile exhaust -- the resolution isn't remotely good enough.)

You have your angles very wrong, gisterme - - I'll get back to this, but I'm responding to a previous posting of yours. Thanks.

rshow55 - 07:21pm Feb 8, 2002 EST (#11373 of 11376)

MD11337-11339 gisterme 2/8/02 6:02pm raises points worth attending to.

First, gisterme refers to gisterme 2/8/02 3:06pm and says

" That post shows why there's no physical reason that such a feedback loop couldn't work."

I look at the post, and don't understand what I'm being asked to see. What in the post shows that "there's no physical reason that the feedback loop couldn't work? What in the post shows that "the feedback loop could work?"

Could you help me see what you're referring to here, gisterme ? Some explicit sentences saying -- "the post shows that the feedback could work because . . . would be appreciated.

rshow55 - 07:24pm Feb 8, 2002 EST (#11374 of 11376)

MD11337-11339 gisterme 2/8/02 6:02pm goes on, and raises points about reflection.

The first point is about imperfections of reflection, and a related point concerns wavelengths.

gisterme says:

"The other issue you've raised, what happens if the missile body is a smooth mirrored surface, is also not a stopper. That's because even the best reflective materials are not perfect and are also not reflective at all wavelengths.

Well, light interacting with a material can either be reflected, absorbed, or transmitted. If it is absorbed or transmitted -- it does not go back to the detector, and can't be involved with feedback. Only reflected light (or other EM) radiation can be useful for feedback. Now, the reflection can be diffuse, or planar. If the reflection is planar, so that angle of incidence equals angle of reflection, or even approximately equals angle of reflection, then that is a stopper. Are you saying that the reflection from a mirror surface is partly diffuse? I don't believe that is true, or true enough to be quantitatively important. Perhaps you can correct me.

The other issue is that reflection is not the same at all wavelengths. But the COIL laser is a specific wavelength - - and it is the laser source on ABL .

Are other lasers possible? Sure. Any that are CHEMICAL will be in a narrow range of wavelengths (not more than an octave on frequency) where reflection isn't very variable for most reflectors. But the ABL deals with a specific kind of laser.

I don't have to say that no laser weapon can ever work -- though that may be true. For today, it is sufficient to say that the ABL system, on which billions of dollars are being spent, can't work.

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