Re: ARIANE-5 Failure (DC-X works)

[Ken Garlington <garlingtonke@lmtas.lmco.com>]

Robert Dewar wrote:
> 
> Eugene says
> 
> "vehicles have problems.  The DC-X flight control software is in Ada and
> is all computer generated.  You would not want to maintain this code by
> hand."
> 
> Sounds bogus, ultimately the code is maintained by humans, we do not yet
> have robots that can write and maintain code. Sure the code may be in
> some other language than Ada and then generate Ada (if the Ada is not
> maintained, but is just used as an intermediate language, it is
> essentially irrelevant that it is Ada). So the question is: what
> language WAS the software written in? And what is the argument that
> this code is easier to maintain than properly written Ada?

Based on various reports, MatrixX was used to develop the DC-X flight control
laws using standard control law notation, and then the System Build module
was used to generate Ada code for the control laws. MatrixX has had the
ability to generate Ada and C code for some time.

The main reason this code could be considered easier to maintain is that,
usually, control law engineers have limited experience coding software.
So, being able to "program" with control law notation makes it easier for
them. Also, by eliminating the manual translation of the control laws to
code, there would presumably be fewer errors in the final product.

I don't know if it is fair to say that generating code in Ada vs. C is
"irrelevant" in this context, since you will still get the benefits of
strong typing, etc. when the code is compiled. On the other hand, assuming
that MatrixX eliminates some of these errors during the control law design,
perhaps this extra support is less important.

I've noticed that a lot of flight control system (and engine control
system) developers are going to this approach of auto-generating code from
the control law design. Some generate FORTRAN, some C, and some Ada. It
would be interesting to find out if there are any inherent advantages in auto-
generating in one language vs. the others.

Anyway, with respect to the Ariane 5, I'm not ready to say that this was a
software failure yet. If it is, it will be interesting to see if the language
choice was a factor in the failure.