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    Missile Defense

Russian military leaders have expressed concern about US plans for a national missile defense system. Will defense technology be limited by possibilities for a strategic imbalance? Is this just SDI all over again?

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dirac_10 - 07:59pm Mar 29, 2001 EST (#1738 of 1745)

The 20cm is an estimate based on light relay times, as you said.

I did it from memory, but I think that's about right

...if a designer included (relatively cheap) auxilary rockets designed purely to fire randomly in half-second intervals. Although the angle of deflection of the missile's path will be minuscle, we can resolve the sideways and forward components of the rockets motion independently. If a 7000kg rocket had a 1400N rocket thrust applied for 0.1 seconds,...

I think this is the simplist way to look at it. Light goes 3x10**8 m/s. At 100 km. light takes less than 1/1,000,000 of a second to make the round trip.

Think about it intuitively. How much can you make anything heavy move in 1/1,000,000 of a second from a standing start? A Saturn V couldn't do it.

At shorter distances (1km, etc.), it would be easily possible,...

We just sold Israel some that will shoot down an old Katuska rocket at 10 km. It's been in the news. Jerusalem Post for one. I suppose I'm gonna have to look it up.

Visible, 95% ...UV or greater...IR

Well, there is of course x-rays which you left out which we use no to see through the clouds.

To start with we would have to use something higher than radio since it can't be focused smaller than it's wavelength. And there are often special frequencies, such as the very narrow band of blue-green light that is the only electromagnetic stuff that will penetrate seawater. (Other than VLF).

And, what is the effect on the atmosphere of such a large energy density? Does the air get more or less opaque? What about modulation? Is the effect the same for a continuous burst as it is for pulses of some modulation? Lots of things for an engineer to sink her teeth into.

But x-rays? No problem.

And an important point needs to be made. Knocking one down at 50 km is better than nothing. Good chance the little toad in N. Korea won't know precisely the effective range. Would have to make a guess.

eurocore - 08:03pm Mar 29, 2001 EST (#1739 of 1745)

If the planes can already deal with very high temperatures over extended periods on much of their contact faces, why would a laser (with the slight inevitable correction errors) be able to do significant damage? If the wings have a 4mm protective layer from the heat now, why not double that to protect against lasers?

The space shuttle, heading back into earth orbit, endures ten of thousand of degrees C - couldn't the same (admittedly expensive!) materials be used to cover an ICBM?

Best Wishes,


rshowalter - 08:06pm Mar 29, 2001 EST (#1740 of 1745) Delete Message
Robert Showalter

rshowalter 3/29/01 7:58pm

dirac_10 - 08:09pm Mar 29, 2001 EST (#1741 of 1745)

rshowalter - 07:26pm Mar 29, 2001 EST (#1729 of 1738) Robert Showalter

Recall that the accelleration from the earth is 1 g -- .01 g, perpendicular to path, for a short time, throws things out A LOT

We have been able to predict the path of the ICBM since Kepler. We have known why (the .1g part) since Newton.


If gravity is the only force acting on the warhead, and we got a velocity doppler reflection, two or three. Otherwise more.

But all this assumes that we are going to shoot some time after we get the information from the data points. Two, or even one will do if we shoot fast.

rshowalter - 08:09pm Mar 29, 2001 EST (#1742 of 1745) Delete Message
Robert Showalter

George Johnson -- I'm just about sure it is you -- you don't know any mathematics. You don't have any engineering background. You're a superb writer, but we're dealing with an issue that can be tested and right answers should be morally forcing.

dirac_10 - 08:12pm Mar 29, 2001 EST (#1743 of 1745)

rshowalter - 07:40pm Mar 29, 2001 EST (#1734 of 1741)

dirac - on the top of the wing, pressures are lower by a few percent -- it is nothing like a vacuum.

I never said it was a vacuum. I said that the kinetic energy of the air above was not slight as stated. That it moved fast. I did say something about the missle would hopefully be out of the atmosphere. Perhaps that is the misunderstanding.

eurocore - 08:13pm Mar 29, 2001 EST (#1744 of 1745)


I'm sorry to correct you, but 100km is 10^5m, therefore it takes 10^5/(3*10^8) seconds to travel the distance.

This is 0.33*10^-3 seconds, or 33ms. The round trip takes 66ms therefore.

Your suggested time of 1/(1000000) second is 1 microsecond. 66ms is 66,000 times longer.

I agree with the X-rays, but they pass through thin sheet metal - the heating would not just occur at the surface and so would be more defuse than visible which has very low penetration. You'd have to up the power, correspondingly, as you'd be heating a large amount of metal at once.

You could of course, sterilise a pilot, but that's just being malicious...

Best Wishes,


rshowalter - 08:13pm Mar 29, 2001 EST (#1745 of 1745) Delete Message
Robert Showalter

rshowalter 3/29/01 7:58pm

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