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From: dnwiebe@cis.ohio-state.edu (Dan N Wiebe)
Newsgroups: sci.military
Subject: Re: Tank killing crowbars
Message-ID: <1991Feb13.032640.27454@cbnews.att.com>
Date: 13 Feb 91 03:26:40 GMT
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From: dnwiebe@cis.ohio-state.edu (Dan N Wiebe)


	*** PLAUSIBLE HEARSAY WARNING ***

The way I heard it, these orbital crowbars were based on the concept of
hypervelocity.  They were intended to hit the target at a speed faster
than the speed at which sound travels in whatever material the crowbar is
made of--so that the bar is "fed" into the target faster than the deforming
impact shock wave can climb back out.  In effect, or so I hear, while this
phenomenon is in progress (the bar slows down rapidly, of course, once it
hits the target), the bar can be considered infinitely hard--that is, harder
than the armor against which it is being used.  My source used the familiar
"knife through butter" phrase.

The problem lies in accelerating the rod to hypervelocity speeds in the
first place; I think that's probably why they're put in orbit (18 miles
per second or some such ungodly speed) and then deflected onto a target,
rather than being dropped from a B-52.  I don't know what the speed of sound
in steel is, but I'd guess it's more than 400 m/sec.

Another problem would be guidance.  Unless you used one heck of a shove to
deflect the thing from orbit, it'd come in at a pretty flat angle, following
a trajectory probably several hundred miles long.  Acquiring a tank-sized
target through several hundred miles of atmosphere while you're moving
eighteen miles every second would be challenging, to say the least, without
even bothering with reentry ionization problems, which, due to the required
speed, would probably continue pretty much up till impact.

If you could solve those two problems, though, tacking an explosive charge
on the rod would seem to be gilding the lily, so to speak.

Disclaimer: the stuff in the first paragraph is pretty much a paraphrase of
things I heard from somebody who has a doctorate in physics and ought to know.
The rest of it is personal speculation on my part.

Plug: Footfall is a wonderful book, as is Lucifer's Hammer and most of the
other Niven/Pournelle books.  (Other than being a Niven freak, I'm not
connected with either of them in any way.)

Shalom,
Dan Wiebe
dnw@rsch.oclc.org