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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 - 06:02pm Feb 8, 2002 EST (#11367 of 11370)

rshow55 2/8/02 3:26pm

"...Do we agree that there is no feedback loop good enough for ABL to work? (It seems to me that we should agree about this.)..."

gisterme 2/8/02 3:06pm

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

"....Or should we work through the argument in detail?...'

There's plenty of detail in the link referenced above to show that optical resolution is not a problem.

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. At their best they'll still reflect back about 2% of incident "light". Light is in parenthesis because that really means electromagnetic waves at any wavelength, not just the visible spectrum that we perceive as light.

So even with just 2% of illumination energy reflected back to the detector an object can still be seen. Increasing the power of the target illumination source will increase the target's visiblity and increasing sensitivity of the detector will also increase visibility. If a tuneable free electron laser similar to the one described in:

http://www.space.com/businesstechnology/technology/fel_001023.html

were used as the illumination source, it's frequencey could be swept to one where the target was not so reflective. That would mean a much larger percentage of the illumination signal would be reflected back, ragardless of the surface material. That signal would be used to close the feedback loop.

Remember, Robert, that this illumination beam is not being used to locate the target. The target is already announcing its line-of-sight (LOS) location by being positioned at the very tip of a huge hot trail of rocket exhaust. A passive infrared sensor operating open-loop could aim the illumination beam plenty well enough to get it onto the target. Then if the return signal was too weak to close the loop because the target was too reflective at the illumination beam's frequency, well, you'd just tune the illumination beam until a frequency was reached where the target wasn't reflective and the loop could close.

The references given show that that is not impossible, in fact that is is possible using an integration of existing technology.

So we know that we're within bounds in those departments. Since we don't have a clue as to the true specifications of the ABL (no doubt that would be classified) about all we can do is specualte about how it might work. Let's do.

If you know LOS just where the ICBM is (right at the end of the rocket exhaust trail) and you have optics with enough resolution to see see just where the end of that trais is, why would you need a closed feedback loop to be able to hit it with the "big" laser? Why not just aim a few meters ahead of the end of the exhaust tral and let 'er rip? The rocket can't be anywhere else whether you can see it or not. The answer to that is the answer to another of your questions, Robert, and may clarify for you some earlier specualtion that you seem to have missed. Your question was, "how do you get enough energy onto the target to do any damage?" You need the closed loop for two reasons:

1. To get the realtime feedback necessary for the adaptive optics to make the necessary corrections to offset effects of atmospheric turbulance. Remember, that that's why ground based telescopes are beginning to rival the HST. It really works.

2. To get the exact range to the target. We know that very precise time-bases exist and given that, lasers can be used to measure distance very precisely.

The first one you should know. The second you mignt wonder about. Why would you need the range to target f

gisterme - 06:07pm Feb 8, 2002 EST (#11368 of 11370)

gisterme 2/8/02 6:02pm

continued...

The first one you should know. The second you mignt wonder about. Why would you need the range to target for a speed-of-light weapon? Only reason I can think of would be to enable adjustment of beam convergence for the "big" laser such that it's incident energy is concenterated to a very small point on the target. So my speculation is that the adaptive optics could be used for more than just correcting the beam to compensate for atmospheric turbulence. They could also focus the beam to a small point on the target to increase the effective energy density delivered. Don't forget that electromagnetic waves follow the rules of superposition.

Only a small hole in the missile body is required to destroy it.

A closed loop system like that would be very difficult to defeat because there are no materials that are reflective at all wavelengths. That fact is the basis for the science of spectrometry.

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