Re: ARIANE-5 Failure

[clodius@hotspec.lanl.gov (William Clodius)]

The association of the Venus probe failure with Fortran has long been
identified as an urban myth.  The Venus probe software that failed was
not written in Fortran and the softare failure had nothing to do with
misreading a statement of the form

DO 10 I=1. 10

as is commonly reported.  The Venus probe failure was caused by a
typographical error that caused the instantaneous velocity to be used
in the guidance system (rather than the required running average
velocity) resulting in an instability in the system.  The language
used in the software allowed the use of special typographical symbols,
and the person who entered the code failed to notice that the quantity
should be entered with a "bar" above it, which indicated that it was
an average quantity.

On the other hand a (non-fatal) software failure in the Mercury flight
system was identified with the misreading of a statement of the form

DO 10 I=1. 10

as the assignment

DO10I = 1.10

For short orbits this error had no observed effects, but on longer
orbits a consistent error in the reentry position was discovered to be
due to this error.





-- 
William B. Clodius		Phone: (505)-665-9370
Los Alamos National Laboratory	Email: wclodius@lanl.gov
Los Alamos, NM 87545