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 autolearn=ham autolearn_force=no version=3.4.4 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: 103376,583275b6950bf4e6 X-Google-Attributes: gid103376,public X-Google-ArrivalTime: 2003-06-01 10:17:05 PST Path: archiver1.google.com!news1.google.com!newsfeed.stanford.edu!logbridge.uoregon.edu!arclight.uoregon.edu!wn13feed!wn12feed!worldnet.att.net!204.127.198.203!attbi_feed3!attbi.com!rwcrnsc53.POSTED!not-for-mail Message-ID: <3EDA34F7.8010007@attbi.com> From: "Robert I. Eachus" User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.0.2) Gecko/20021120 Netscape/7.01 X-Accept-Language: en-us, en MIME-Version: 1.0 Newsgroups: comp.lang.ada Subject: Re: Saturated Math References: <3ECFF541.1010705@attbi.com> <3ED0B820.5050603@noplace.com> <3ED2096F.3020800@noplace.com> <3ED353BE.40605@noplace.com> <3ED4A323.3000909@noplace.com> <3ED5EA28.2040703@noplace.com> <20619edc.0305290913.31006f83@posting.google.com> Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit NNTP-Posting-Host: 24.62.164.137 X-Complaints-To: abuse@attbi.com X-Trace: rwcrnsc53 1054487824 24.62.164.137 (Sun, 01 Jun 2003 17:17:04 GMT) NNTP-Posting-Date: Sun, 01 Jun 2003 17:17:04 GMT Organization: AT&T Broadband Date: Sun, 01 Jun 2003 17:17:04 GMT Xref: archiver1.google.com comp.lang.ada:38287 Date: 2003-06-01T17:17:04+00:00 List-Id: Mike Silva wrote: > Would've saved Ariane 501's hindquarters too! It might have, but then Ariane 502 would have destroyed itself, or Ariane 503 or whatever. The beginning of the error cascade that started the destruction of Ariane 501 was an overflow treated as a hardware error--which it would have been on Ariane 4. But what actually destroyed Ariane 501 was that the guidance computer sent commands to the engines to deflect beyond the structural limits of the entire stack. This was another facet of reusing the Ariane 4 code with out checking it against the Ariane 5 requirements. The physical parameters in the control system were wrong. For very small deflections, using the wrong parameters was not harmful. But the first time Ariane 5 hit wind shear it would have destroyed the stack. The control loop was not stable if the required engine deflections were significant. This would have lead to oscillations that eventually deflected the engines beyond what the stack could tolerate, and things would fall apart. Even if it didn't, any resemblance between the result orbit and the intended orbit would have been accidental. This was, IMHO, the real Ariane 5 code reuse disaster. Not that unanticipated overflow could destroy the stack, but that it would have happened for any significant engine deflection. The mass, thrust and stack moments for the Ariane 5 were so different from the physical parameters for the Ariane 4 that disaster was inevitable.