From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me X-Spam-Level: X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00,FREEMAIL_FROM autolearn=ham autolearn_force=no version=3.4.4 X-Google-Thread: a07f3367d7,f096ebb5dcac664d X-Google-Attributes: gida07f3367d7,public,usenet X-Google-NewGroupId: yes X-Google-Language: ENGLISH,ASCII Path: g2news2.google.com!postnews.google.com!k6g2000yqn.googlegroups.com!not-for-mail From: sjw Newsgroups: comp.lang.ada Subject: Re: Ariane 5 Failure from 1996 Date: Tue, 14 Jul 2009 13:50:37 -0700 (PDT) Organization: http://groups.google.com Message-ID: <984ccfb0-4da1-4c5b-af36-5d31505e13b1@k6g2000yqn.googlegroups.com> References: <851f477d-c5a4-4c87-b930-4a47ba508579@h8g2000yqm.googlegroups.com> NNTP-Posting-Host: 82.20.239.89 Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable X-Trace: posting.google.com 1247604637 31083 127.0.0.1 (14 Jul 2009 20:50:37 GMT) X-Complaints-To: groups-abuse@google.com NNTP-Posting-Date: Tue, 14 Jul 2009 20:50:37 +0000 (UTC) Complaints-To: groups-abuse@google.com Injection-Info: k6g2000yqn.googlegroups.com; posting-host=82.20.239.89; posting-account=_RXWmAoAAADQS3ojtLFDmTNJCT0N2R4U User-Agent: G2/1.0 X-HTTP-UserAgent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10_5_7; en-us) AppleWebKit/530.19.2 (KHTML, like Gecko) Version/4.0.2 Safari/530.19,gzip(gfe),gzip(gfe) Xref: g2news2.google.com comp.lang.ada:7054 Date: 2009-07-14T13:50:37-07:00 List-Id: On Jul 10, 4:04=A0pm, Martin wrote: > My understanding of the Ariane pretty slim but if Wikipedia is > accurate (http://en.wikipedia.org/wiki/Ariane_5) then it seems likely > that the same error would have occurred, as my reading is that it was > the deliberate removal of Ada checks that led to the 32-bit Float > being assigned to a 16-bit value, i.e. that part was C-in-Ada-syntax. In the Ariane 4 flight profile the float couldn't have overflowed the 16-bit target (I think the physical value concerned was the ground velocity) so they decided they could save cycles by not checking for potential overflow before assigning and/or not setting up an exception handler (these protections were retained elsewhere). In Ariane 5 the flight profile was such that overflow could, and did, occur, resulting in an exception (presumably a constraint error).. I don't exactly what is said to have happened after that, there was mention of a subsystem that shouldn't have been running after launch feeding diagnostic data in place of real data to a higher subsystem which shut itself down ... So, in C, the overflowed data might well not have resulted in the exception which doomed the rocket. As someone below has said, it's quite possible that something else would have gone wrong!