Newsgroups: sci.space.history
From: henry@spsystems.net (Henry Spencer)
Subject: Re: Could the shuttle be converted?
Date: Thu, 29 Jul 1999 02:33:01 GMT

In article <379F8216.E7735F11@psu.edu>, Greg Bondar  <ghb1@psu.edu> wrote:
>Do they still use variants of analog computers for control systems?
>(reprogrammed by re-wiring...

Not for a long time.  The Saturn V was almost all digital, controlled by
software; so was the Block II Apollo spacecraft.  (It is questionable
whether the Apollo LM could have been controlled satisfactorily by an
analog computer at all.  Even the "manual" control mode made heavy use
of multiple modes and nonlinear algorithms.)

Analog computers rapidly dwindled in importance as digital computers got
better and faster.  Analog computers are costly to build and cranky to
adjust, and both hardware cost and accuracy loss limit the complexity of
the calculations they can do.  Nowadays they're pretty much restricted to
"legacy"  applications where it's not worth the development cost to go
digital -- for example, the Concorde engine/intake control system is still
analog, and the maintenance crews hate it because it has a zillion
adjustments and they all interact, but the Concorde fleet is too small to
justify development and certification of a digital version.
--
The good old days                   |  Henry Spencer   henry@spsystems.net
weren't.                            |      (aka henry@zoo.toronto.edu)