Path: utzoo!attcan!uunet!seismo!sundc!pitstop!sun!amdcad!ames!elroy!jpl-devvax!jplpro!leem
From: leem@jplpro.JPL.NASA.GOV (Lee Mellinger)
Newsgroups: sci.space.shuttle
Subject: Re: Shuttle computer reprogramming
Message-ID: <3000@jpl-devvax.JPL.NASA.GOV>
Date: 6 Oct 88 19:53:14 GMT
References: <6689@nsc.nsc.com> <6980@ihlpl.ATT.COM> <1938@kalliope.rice.edu> <2993@jpl-devvax.JPL.NASA.GOV> <2994@jpl-devvax.JPL.NASA.GOV>
Sender: news@jpl-devvax.JPL.NASA.GOV
Reply-To: leem@jplpro.JPL.NASA.GOV (Lee Mellinger)
Organization: Jet Propulsion Laboratory, Pasadena CA.
Lines: 50

In article <2994@jpl-devvax.JPL.NASA.GOV> david@beowulf.JPL.NASA.GOV (David Smyth) writes:
|-In article <2993@jpl-devvax.JPL.NASA.GOV> leem@jplpro.JPL.NASA.GOV (Lee Mellinger) writes:
|->In article <1938@kalliope.rice.edu> phil@Rice.edu (William LeFebvre) writes:
|->|In article <6980@ihlpl.ATT.COM> knudsen@ihlpl.ATT.COM (Knudsen) writes:
|->|
|
|Probably you saw the patches for existing code.  As far as I know, the initial
|implementation of all routines was done in HAL/S, and modifications then done
|in AP-101 machine code.
|
|->The computers are 4Pi/AP-101's which are esentially ruggedized IBM
|->360's in a small box.  That is the four prime computers, the fifth is
|->a Rockwell/Autonetics machine.  All four are online during launch and
|->landing on a synchronized bus.  They all vote on the solutions, and if
|->one dissagrees, the others vote it out and it is taken offline.  The
|->Autonetics machine is there in case there is a generic HW or SW
|->failure that would take out all four prime machines.
|
|When was this change implemented?  Originally, all 5 machines were AP-101s.
|The four primaries ran IBM developed PASS Primary system, and the one
|back-up was an identical AP-101 running an Intermetrics developed BFS
|Backup Flight System.  All 5 online at launch on the synchronized bus,
|the fifth watching for anytime the primaries disagree, and annunciating the
|errors to the pilots.  The pilots can manually disable any of the 4 primaries
|which are failing, but the standard procedure (was - still is?) to switch
|to the BFS and abort.
|
|The backup was an afterthought to take care of generic SW failures.  The
|SW architecture of the BFS is completely different from the PASS in case
|there is some bizarre architectural problem nobody found during testing:
|for example, loss of synch at boot, which was only discovered (well, correctly
|diagnosed) following the launch hold at T-12 minutes on the first flight!
|
|I do not believe the backup computer is in any way different from the
|primaries.

Mea Culpa.  They tell me the first thing to go is ... I forgot.
Anyway, you are correct about the hardware being the same, but
sometime back, Aviation Week reported that the code for the backup
machine was written by Autonetics.

Lee

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|Lee F. Mellinger                         Jet Propulsion Laboratory - NASA|
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