From: jbh55289@uxa.cso.uiuc.edu (Josh 'K' Hopkins)
Subject: Re: SDI update
Organization: University of Illinois at Urbana
Date: Wed, 8 Apr 1992 21:19:32 GMT

gabriele@aero.org (Mark Gabriele) writes:

>>>... What steps are being taken now to ensure this system
>>>doesn't accidently shoot down a shuttle?

>>About the same ones taken to make sure that Patriot doesn't accidentally
>>shoot down an airliner.

>Which isn't really correct.  You see, when you have an independent
>space-based system comprised of several thousand autonomous pieces all
>whizzing around 100+ miles up, it's rather difficult to pull the plug
>on them.  You rely on controls, certainly.  But these controls are NOT
>(no way, no how, can't be) as good as the very simple control of
>having the device under your physical control.

	I don't know the details of BP (does anybody?) but it would seem rather
likely that they won't be "armed" a fair portion of the time.  When tensions
get high or there is a terrorist threat, then you would turn it on.  (just
speculation of course)

>I will provide a simple example.  Say that a hypothetical space-based
>system consists of a thousand units, which have a mean time between
>failure of 100 years.  Then we can expect that some of them will begin
>to fail soon.  More than that.  It could be that some of them choose
>to fail in an unsafe fashion.  The odds of this might be very poor -
>call it 1 in a million per year - but again, you're still gambling,
>and people get (un)lucky all the time.  Careful design cannot prevent
>that.  Unfortunately, if one of these things decides that the shuttle
>is an Enemy Attacker, nobody can do much to stop it from going off and
>killing the thing - it's not like you can walk up and pull out the
>plug.
	Fair enough.  Systems do fail.  But can you explain a failure that
leaves the Pebble in operable shape, yet also overrides all safegaurds, and
convinces it that the shuttle (which doesn't look or act much like a missile)
is an ICBM? I'd willing believe that several BP's will be lost to power 
failure, orbital debris damage and what have you.  But it take's a fairly
impressive failure (if it's possible) to have this kind of accident.

>The moral is that strategic weapons should *always* be kept under
>physical control.  Proposals to do otherwise are just dangerous.

	Why does a general have less control of BPs with good saftey features
than he/she does of a missile in a silo?  Either way there are concievable 
fail points (which would probably involved premediation by a human) that can
override the central control.  The important issue is to make leave as few
fail points as possible and make them unlikely to fail.
	The assumption that putting weapons of distruction under human control
makes them safer is a questionable one.  Rather than the example of the Patriot
we might consider the Ageis radar system (do I have the right one?) and the
ship Vincennes.  Human beings had complete control of the launch system, and
they still managed to shoot down an Iranian airliner.  
	The most serious problem with weapons of mass destruction is that they
can be used.  I'm much less worried about them failing than that they might
work.
			Josh Hopkins
Xref: sparky sci.space:7486 sci.physics:6739