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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?

rshowalter - 05:47pm Jul 7, 2001 EST (#6747 of 6750)
Robert Showalter showalte@macc.wisc.edu

I do have some things to check -- like the wavelength incoming - reflectivity of a moulton metal layer at that wavelength -- things like that.

You're talking about enough energy, if it is all absorbed, to boil away about a 2.4 cm layer of water over the surface hit by the lasar -- quite a lot of energy -- if the beam, when it gets there, is that intense, has that time on target --and if all the energy in the beam is absorbed.

If you do have pictures, or data, that show that the lasars really can do impressive damage - under particular conditions -- that would be interesting.

rshowalter - 07:26pm Jul 7, 2001 EST (#6748 of 6750)
Robert Showalter showalte@macc.wisc.edu

Emissivity, not reflectivity, is the term I was looking for. It is the amount of incident radiant energy absorbed -- and without being too fancy, for solid surfaces, it varies over a ratio of more than 50:1 . From close to 1 (though nothing's perfectly black) to less than .02 . Being a little fancy, you can get a ratio of 100:1.

And figuring the emissivity (especially of a well designed surface built with MD in mind) -- isn't easy. If a surface melts -- is the emissivity of the moulton layer that of mercury (about .09) or more or less?

That's not the only thing, and not the only class of thing, that matters, when you're judging the destructiveness of the lasar.

What about absorbtion by metal vapor boiled off the surface? Are there losses there, and are they important? If the vapor gets very hot, it could dissipate a LOT of energy - sheilding the surface. (In moving air, and higher up, in vacuum, the effects of this vapor layer would be different.)

How about the conduction velocity of the heat wave in the material subject to the incident light (as gun designers know, that conduction wave velocity's not infinite -- so twice the intensity, for half the time, sometimes buys you less than you think.)

These things mean that reasonable checking takes some time and wariness.

There other details, too, even making the assumption (by no means clear) that the 1 kw/cm^2 can be delivered for five seconds.

rshowalter - 07:28pm Jul 7, 2001 EST (#6749 of 6750)
Robert Showalter showalte@macc.wisc.edu

It takes impressive tracking to deliver that beam on the "spot" -- because the spot is moving.

The missile may be traveling at 10,000 meters/ second -- so that hitting the "spot" means tracking the spot over a distance of 50,000 meters.

Not all that easy to track, maybe.

rshowalter - 07:32pm Jul 7, 2001 EST (#6750 of 6750)
Robert Showalter showalte@macc.wisc.edu

gisterme , these calculations aren't so easy . . not for me, not for anybody -- and they take some guessing, because data isn't always there -- and ingenuity of defenders (who can spend a few thousand bucks to get fine advice) . . can't always be anticipated.

Even if you have data -- the data can mislead you badly. The assumptions built into a specific experiment can be misleading.

If the experiment is set up by an engineering team desperate to make the results look good the results can be terribly misleading.

An engineering team, on something like this, could make just one "non-obvious mistake" , one that everybody involved really wanted to make, to keep funding coming in . . . and the country could be stuck with a very expensive defensive system that wasn't any defense at all.

Sorry it takes me time to check these things -- but the easy calculations aren't always the ones that count. And so I'm at it.

But now, I'm going to get sweaty - - and then get back to it.

If, perchance, you have data that shows how damaging these lasars can be under "realistic" conditions -- it would be interesting, if you'd be able to release it.

Not definitive, necessarily, but interesting.

HAS a congressman actually witnessed what one of these fearsome monster lasars can do at close range?

(without, I notice, wiping out the mirror that aims the beam.)

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