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From: thomas@mvac23.UUCP (Thomas Lapp)
Newsgroups: sci.space.shuttle
Subject: 100% criticality systems (WAS: Re: Board appointed to...)
Message-ID: <313.UUL1.3#5131@mvac23.UUCP>
Date: 4 Aug 90 17:37:53 GMT
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drd@siia.mv.com (David Dick) writes:
> If every part must work perfectly every time, it's a wonder
> the shuttle hasn't failed more often.  I would say that
> any engineered system in which "every part is critical" is
> rather badly designed.

I would guess it depends on the use of the term 'critical'.  It may
be critical that all of the parts perform to specifications, but
does it also mean that every part must perform?  Maybe the specs
say that a system contains two components, of which at least one
must work each time.  So although the system is a critical one,
you can tolorate a failure of one of the components.

If I design a part for some value of extremes which will never be
reached, and test it to those extremes, than I would have a pretty
good idea that as long as the specs are less than the extremes, that
I would be pretty well assured that my part would work every time
under normal conditions.  Doesn't seem like too poor a method of
design to me.  Am I missing something here?
                         - tom

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