Re: Fortran or Ada?

[jbs@yktvmv.watson.ibm.com]

In article <36156677.7566@lanl.gov>,
 on Fri, 02 Oct 1998 17:49:11 -0600,
 William Clodius <wclodius@lanl.gov> writes:
>jbs@yktvmv.watson.ibm.com wrote:
>> <snip>
>>          The report I have says nothing like this.  What report are
>> you referring to?
>>                         James B. Shearer
>
>Robert Eachus's comments are "mostly" inferable from the report. He is
>correct that the report says (in equivalent words) that "the stack was
>destroyed when the engine deflection exceeded the physical stress limits
>of the stack (booster and payload)." He is also correct that this
>implies that the software did not properly check that such an engine
>deflection was safe at that thrust. I suspect that he infers from
>presummed best practices that the software would make such a check, and
>that it failed because the physical parameters were wrong, and that the
>most likely reason that they were wrong was because the Ariane 4
>parameters were used. However, the number of steps used in that
>inference are long and while the individual steps are plausible
>collectively they are less plausible. Further, whether any other system
>malfunction could have caused the software to command that that
>deflection is unknown.

         Actually what the report says is:

!    f) Approx. 0.05 seconds later the active inertial reference system,
!    identical to the back-up system in hardware and software, failed for the
!    same reason. Since the back-up inertial system was already inoperative,
!    correct guidance and attitude information could no longer be obtained and
!    loss of the mission was inevitable.
!
!    g) As a result of its failure, the active inertial reference system
!    transmitted essentially diagnostic information to the launcher's main
!    computer, where it was interpreted as flight data and used for flight
!    control calculations.
!
!    h) On the basis of those calculations the main computer commanded the
!    booster nozzles, and somewhat later the main engine nozzle also, to make a
!    large correction for an attitude deviation that had not occurred.
!
!    i) A rapid change of attitude occurred which caused the launcher to
!    disintegrate at 39 seconds after H0 due to aerodynamic forces.
!
!    j) Destruction was automatically initiated upon disintegration, as
!    designed, at an altitude of 4 km and a distance of 1 km from the launch
!    pad.

         I don't see anything in there about the engine deflection
being unsafe in itself, it just pointed the rocket in the wrong
direction.  Presumedly a less extreme deflection (error) would just
have delayed the accident a few seconds.
                   James B. Shearer