Re: ARIANE-5 Failure

[Dale Stanbrough <dale@goanna.cs.rmit.EDU.AU>]

Robert Dewar writes:
But it would be nice to find out, anyone on this list have a REALLY
AUTHORITATIVE first-hand source for the truth on this one (it is one
that many people "know" the answer to, but as Jim pointed out, they
disagree and can't all be right!)


Robert Eachus posted this one a few years back now. Although it doesn't
quote anyone, its level of detail lends an air of credibility. Maybe
we should ask Mr Eachus where he got his info from...

Dale

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Subject: FORTRAN bug(was Re: C++ vs. Ada -- Is Ada loosing?)
From: Robert I. Eachus, eachus@oddjob.mitre.org
Date: Mon, 7 Dec 1992 23:47:34 GMT

     Nice to get some facts in here.  As I remember it, there were two
bugs involving Venus probes.  One was code that assumed that an
uninitialized variable always start life equal to zero. When this code
was rerun after several months in space... The FORTRAN bug which
resulted in the destruction of the first Venus probe was that in:

     DO 20 I = 1,10
 
the comma was replaced by a period:

    DO 20 I = 1.10

of course in FORTRAN (in particular FORTRAN 66) the spaces are
ignored, and this was interpreted as:

    DO20I = 1.10

    (Implicitly declaring a real variable DO20I and assigning to it.)
This had not caused a problem on earlier launches as the loop was to
refine the amount of correction for wind, and a single repetition was
usually enough.  But when a gust hit, the inaccurate calculation
resulted in an oscillation, and the RSO destroyed the missile.