Re: Ariane 5 failure

["Marin David Condic, 407.796.8997, M/S 731-93" <condicma@PWFL.COM>]

Ken Garlington <garlingtonke@LMTAS.LMCO.COM> writes:
>Alan Brain wrote:
>> A really good safety-critical
>> program should be remarkably difficult to de-bug, as the only way you
>> know it's got a major problem is by examining the error log, and
>> calculating that it's performance is below theoretical expectations.
>> And if it runs too slow, many times in the real-world you can spend 2
>> years of development time and many megabucks kludging the software, or
>> wait 12 months and get the new 400 Mhz chip instead of your current 133.
>
>I really need to change jobs. It sounds so much simpler to build
>software for ground-based PCs, where you don't have to worry about the
>weight, power requirements, heat dissipation, physical size,
>vulnerability to EMI/radiation/salt fog/temperature/etc. of your system.
>
    I personally like the part about "performance is below theoretical
    expectations". Where I live, I have a 5 millisecond loop which
    *must* finish in 5 milliseconds. If it runs in 7 milliseconds, we
    will fail to close the loop in sufficient time to keep valves from
    "slamming into stops", causing them to break, rendering someone's
    billion dollar rocket and billion dollar payload "unserviceable".
    In this business, that's what *we* mean by "performance is below
    theoretical expectations" and why runtime checks which seem
    "trivial" to most folks can mean the difference between having a
    working system and having an interesting exercise in computer
    science which isn't going to go anywhere.

    MDC

Marin David Condic, Senior Computer Engineer    ATT:        561.796.8997
M/S 731-96                                      Technet:    796.8997
Pratt & Whitney, GESP                           Fax:        561.796.4669
P.O. Box 109600                                 Internet:   CONDICMA@PWFL.COM
West Palm Beach, FL 33410-9600                  Internet:   CONDIC@FLINET.COM
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