Re: Ariane 5 Failure from 1996

[John McCabe <john@nospam.assen.demon.co.uk.nospam>]

jonathan <johnscpg@googlemail.com> wrote:

Jonathan

>Any program that met the requirements would have destroyed the flight
>at exactly the same time and in exactly the same way. It could
>have been written in C, Ada, or assembly and if it met the
>requirements
>exactly it would have destroyed flight 501 the same 37 seconds
>after liftoff.
>
>Post-flight analysis described the problem as a requirements failure .
>
>(That's my memory of the event.)

I don't want to get into another discussion on the failure itself, I'd
just like to know if there's any known information about this claim
that's been made about C.

FWIW though, if, as someone else has said, the SRI for  A5 used a
MIL-STD-1750A processor then, as I remember that chip, there is a way
for arithmetic overflow (i.e. x + y = z where x and y are both
positive and z is negative) to cause a machine fault interrupt. I
imagine that this would be disabled in C as it's not a check that
should be made by the language (forgive me if my memory of
MIL-STD-1750A is hazy, I haven't used them since 1997). The point this
guy was making was that, in C, the machine fault would not have
occured as the overflow would have been allowed to happen and 3 or 4
seconds later the SRI would have shut down as expected (well, as
required for Ariane 4!) and all would have been well.

Sounds like nonsense to me though.

John