Xref: utzoo sci.space:12158 sci.space.shuttle:3338
Newsgroups: sci.space,sci.space.shuttle
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: Re: space news from May 15 AW&ST (replacing computers)
Message-ID: <1989Jul2.210944.15387@utzoo.uucp>
Organization: U of Toronto Zoology
References: <1989Jul2.054432.5054@utzoo.uucp> <3827@phri.UUCP>
Date: Sun, 2 Jul 89 21:09:44 GMT

In article <3827@phri.UUCP> roy@phri.UUCP (Roy Smith) writes:
>> the Atlantis crew replaced one of the orbiter's five general-purpose
>> computers after it failed ...
>
>	I don't understand.  I thought that the various computers were all
>constantly checking each other and if one failed, it would be taken off line
>automatically and the others would continue to operate without it.  Why the
>need to rummage around behind the furniture for 4 hours?

Almost certainly they could have completed the mission without doing so.
However, having one computer dead *before* reentry means having that much
less redundancy available against the possibility of further failures.
So shuttle mission rules say that if time and parts are available, the
repair will be done.  If you were aboard, would *you* vote for reentering
with one computer dead if you could avoid it?

The real botch here is that the computers are so inaccessible that it takes
four hours to replace one.
-- 
$10 million equals 18 PM       |     Henry Spencer at U of Toronto Zoology
(Pentagon-Minutes). -Tom Neff  | uunet!attcan!utzoo!henry henry@zoo.toronto.edu