From: bmac@astro.ucla.edu (Bruce Macintosh)
Newsgroups: sci.military
Subject: Thor crowbars energy (was re: Offensive applications of SDI)
Date: 15 Apr 92 04:38:09 GMT
Organization: AT&T


From Bruce Macintosh <bmac@astro.ucla.edu>

>dasher!patter@uunet.UU.NET (24224-guthrie) writes

>In article <1992Apr11.002344.19476@cbnews.cb.att.com> 
>v064lnev@ubvmsb.cc.buffalo.edu (Avatar) writes:

>>       Could someone please explain to me how this is possible?  Am I to
>>understand that the Thor (aka Crowbar) weapons system has an impact explosion 

>That is correct. That statement is based on the assumption that these
>"crowbars" will be traveling fast enough to vaporize on impact with
>little penetration. 
Fine.
>Essentially you wind up with a partial conversion of mass to energy.

No. (Hopefully, this is just poorly phrased, and isn't trying to suggest that
matter is actually being converted into energy . . . 

What you end up with is a conversion of kinetic energy (8 km/s of orbital
velocity) into heat. No mass is converted into energy whatsoever. Not a scrap.
A 400kg crowbar travelling at 8km/s has a *lot* of energy. If it's shaped
right, I assume it can punch through a lot of atmosphere without losing
too much mass. If not, the velocity should be scaled down appropriately,
or the mass. (Energy will scale as velocity squared and linearly with mass.)

There is also a small amount of gravitational potential energy, but for a 200km
orbit that only adds about 10% to the total energy release.

Which leads us to another point about the whole Thor concept. Where does the
energy of impact come from? Kinetic energy of the orbiting crowbar, see above.
Where did *that* energy come from? Chemical energy of the booster that carried
it into orbit. So Thor is just a mechanism for storing chemical energy and then
applying it at the moment and place of your choice. Unless you're getting the
THOR launches free (spare room in shuttle flights, and at current launch rates
that would take rather a long time to get many of the things in orbit), 
you might as well just leave your THORs on the ground, in (say) ICBMs; the
re-entering sub-orbital ICBM would have about as much kinetic energy as the
orbiting THOR satellite, and you don't need to fill low earth orbit up with more
junk.

That's *if* the whole thing (suitably accurate sensor package that can work
through an 8km/s reentry plasma) is technically feasible - which I still doubt -
and *if* either concept is politcally feasible - which I *really* doubt. 
(Putting offensive weapons in space is *not* a trend that the US should start,
in my opinion.  You certainly couldn't use  these - especially the ICBM version-
against any nuclear power, because the incoming THOR satellite/ICBM would be
indistinguishable from a nuclear weapon satellite/ICBM, and certainly 
wouldn't inspire steady nuclear-trigger fingers in the intended target.

I sent the original poster a copy of my calculation of the 16 tons TNT figure;
it's irrelevant to the list as a whole, but I'll send copies to anyone who
wants it. In calculating it, I found that I couldn't remember the conversion
from Joules to kg of TNT; I remembered "about 10^6 joules/kg TNT", but I would
appreciate it if anyone on the net could remind me of the more accurate number.


Bruce Macintosh				bmac@astro.ucla.edu
UCLA Department of Astronomy		Infrared Imaging Detector Lab