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From: ken@alberta.UUCP (Ken Hruday)
Newsgroups: can.politics
Subject: Re: problems with Star Wars #2 (part 2: the crux)
Message-ID: <590@alberta.UUCP>
Date: Wed, 17-Jul-85 16:18:57 EDT
Article-I.D.: alberta.590
Posted: Wed Jul 17 16:18:57 1985
Date-Received: Thu, 18-Jul-85 02:08:23 EDT
References: <1197@utcsri.UUCP> <5772@utzoo.UUCP> <1240@utcsri.UUCP> <5797@utzoo.UUCP>
Reply-To: ken@pembina.UUCP (Ken Hruday)
Organization: U. of Alberta, Edmonton, AB
Lines: 31

In article <5797@utzoo.UUCP> henry@utzoo.UUCP (Henry Spencer) writes:

>2. Even if complete effectiveness is required, this does not require that
>the software be perfect.  It only requires that it be good enough to stop
>all the warheads.  It really doesn't matter whether the software crashes
>six times in the first five minutes, *if* it has enough margin of capability
>that it nevertheless shoots down all the warheads.  Whether such margin is
>possible is a different issue; if it is, then perfect effectiveness does
>*not* demand perfect software.  Anything less than 100% correctness in the
>handling of my bank account is unacceptable to me, but I don't hide my
>money in a mattress just because I know the bank systems crash occasionally.
>They recover, and finish the job correctly.

I think we can all agree that the "benign" errors that you describe above
can be tolerated - but I think you've missed part of John's point. We
have no assurance that these are the type of bugs left in the system.
It is therefore necessary to insure that at least part of the system is
verifiably or proven correct. Without this assurance the system will have
a finite (and possibly measurable) probability of not working at all.

Additionally, even if the system is verified correct, this is no guarantee
that 100% of the warheads can be brought down. Effectiveness of the system
can only be estimated statistically since we don't know where all the warheads
are to be launched from, the cloud cover, etc. Once more, if we accept your
admission that a "pop-up" sort of system is unacceptable, then we must take 
the worst case scenario since (in an orbiting defence system) the Russians 
will know the positions of the satellites and launch to their maximum 
"advantage" so as to strain the defense system to it's limits.

						Ken Hruday
					  University of Alberta