Newsgroups: sci.space.shuttle
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Question : Why does the shuttle roll inverted after lift-off?
Date: Mon, 6 Mar 2000 00:55:30 GMT

In article <1e6otpf.mo8qobm9l7jpN@ppp273.wcta.net>,
David Buchner <buchner@wcta.net> wrote:
>Oh, and also -- somebody mentioned that the Apollo rockets rolled after
>takeoff, too. What difference would it make, with a big long symmetrical
>pointy cylinder like that, which way it was "rolled"? And it wouldn't be
>too obvious to look at, either.

Guidance was considerably simplified if the pitch axis of the guidance
system was perpendicular to the orbit plane (and hence the other two axes
were in the orbit plane).  That turned the ascent to orbit into a mostly
two-dimensional problem, which considerably simplified the programming,
and limited the load on the rather slow computers of the day.

Actually, this is still a useful tactic even with modern computers.  There
isn't any shortage of computing power now, but simplifying the programming
is still helpful, especially when it makes error detection easier.
--
Computer disaster in February?  Oh, you |  Henry Spencer   henry@spsystems.net
must mean the release of Windows 2000.  |      (aka henry@zoo.toronto.edu)