Re: Ariane Failure

["Marin David Condic" <dont.bother.mcondic.auntie.spam@[acm.org>]

"Steve O'Neill" <oneills@top.monad.net> wrote in message
news:3CB4DD65.99F17199@top.monad.net...
>
> Agreed... except when the potential result may be raining down flaming
> pieces of a billion dollars worth of satellite.  As I recall the photos
> were very impressive.
>
Well, I'm impressed by the photos too. It can be very educational to
engineers to look over the videos and photos of various engineering
disasters. There are plenty to choose from.

I'll still disagree that dual-redundant identical systems are a bad idea in
rocket technology and that they are somehow inherently less safe than
dissimilar systems. Having worked in that field I know some of the thinking
that goes into these sorts of designs and lots of highly reliable identical
systems have been built. "Dissimilar" only protects you from common design
errors - maybe. It also increases the probability that there *will* be a
design error. When considering the potential designs for a given piece of
avionics, you need to look very carefully at all the possible failure modes
you can think of and look at the probabilities of those failures occurring
and ask how well a given design strategy will minimize the risk. Dual
redundant, identical systems can and do function very well and at very high
levels of reliability and it isn't automatically clear that for a given
application a dual redundant dissimilar system is going to improve
reliability. In fact, quite the opposite might be the case.

MDC
--
Marin David Condic
Senior Software Engineer
Pace Micro Technology Americas    www.pacemicro.com
Enabling the digital revolution
e-Mail:    marin.condic@pacemicro.com