Broke up on launch

[Fred]

><forwards broke up on launch>
>
>You can read the report on the causes of the Ariane 5 rocket crash, which
>is available at:
>        http://www.esrin.esa.it/htdocs/tidc/Press/Press96/ariane5rep.html
>
>To summarize what happened:
>
> - An overflow occured in the Inertial Reference System (SRI) computer
>   when converting a 64-bit floating point to 16-bit signed integer value. 
>
> - There was no error handler for that specific overflow.  The default
>   handler (wrongly) shut down the SRI unit.
>
> - The standby SRI unit had previously shut itself down for the same
>   reason.  The hot SRI and the standby were running the same software.
>
> - The shutdown caused the SRI to output a core dump on the bus.  The main
>   computer interpreted the core dump as flight data, causing such a
>   violent trajectory correction that the rocket desintegrated.
>
> - The SRI software had been ported from the previous generation rocket
>   Ariane 4.  The original software designers made a deliberate decision
>   not to protect the conversion because overflow could not occur due to 
>the
>   physical characteristics of Ariane 4.
>
> - The program that failed was a pre-flight program, and should not have
>   been running during the flight.  (In the Ariane 4 design, this program 
>was
>   allowed to run during flight to guard against some rare condition, but
>   this was a poor decision in the first place; when the software was 
>ported
>   to Ariane 5 all justification for it was gone but nobody bothered to 
>turn
>   it off.)
>
>The investigation team concluded that the designers of the computer system
>put in protections against hardware faults but did not take into account
>software faults.  Furthermore the SRI had not been tested with realistic
>Ariane 5 flight data, and there had been no integration tests of the SRI
>with the rest of the new rocket.
>
>
>------- End of Forwarded Message
>
>


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