Re: Papers on the Ariane-5 crash and Design by Contract

[john@assen.demon.co.uk (John McCabe)]

nouser@nohost.nodomain (Thomas) wrote:

>In article <332B5495.167EB0E7@eiffel.com> Bertrand Meyer <bertrand@eiffel.com> writes:

<..snip..>

>I think the lesson to be learned from this is that projects should
>choose hardware that is sufficiently powerful to let the software
>engineers implement their software without making dangerous
>compromises and without having to spend a lot of their time on
>worrying about how to squeeze complex algorithms into inadequate
>hardware.  With more powerful hardware, you don't have to disable the
>runtime checks in a language like Ada in the first place, and you can
>afford to add adequate exception handling code.  While on a rocket
>every gram and watt counts, we are talking maybe 10-20% more memory
>and performance.  More powerful hardware might also have permitted a
>simpler, more easily tested and maintained design overall.

That's far easier said than done. It's not necessarily cost/power/mass
that's the problem with computers used in the space industry, it's
availability of radiation tolerant or hardened processors and memory
and so on. Memory is generally too much of a problem, you can easily
get hold of Radiation Tolerant memories from Harris and Honeywell or
MHS, however hardly any microprocessor manufacturers build devices
specifically for the space industry, and those that do generally don't
build very fast devices.

The most commonly used device in the european space industry at the
moment is the GPS MA31750 (probably), a MIL-STD-1750 implementation
that runs at 10MHz and gives a performance of 1.3 MIPS. It is,
however, available radiation hardened. 200MHz Pentium Pros are not.

>Of course, those hardware costs might have been noticeable, resulting
>in either lower payload or noticeably higher overall project costs.
>But if you want your rockets to fall out of the sky less often, that's
>the price you have to pay.

Given a higher performance version of the same processor, the extra
hardware costs are unlikely to be significant, the MA31750 we've been
using costs aroun $13000 (Thirteen Thousand Dollars - 1.3 MIPS, 10MHz
- Value for money?), and 8kx8 RAMs are around $2500 a piece. However
as I said, in the Space Industry, you are probably using the highest
performance device available to you anyway so cost is irrelevant
(unless of course you want to use hundreds of millions of dollars of
project money to package and qualify a new processor!).


Best Regards
John McCabe <john@assen.demon.co.uk>