Re: The Olympics - satellite positioning

[Leigh Palmer <palmer@SFU.CA>]

At 6:50 AM -0700 9/27/00, Michael Edmiston wrote:
> I think Leigh and I are saying the same thing and we are just using
> different words to say it.  Leigh says there is a gyrocompass fixed to the
> stars, plus there are "reaction wheels" acting as "reservoirs" for angular
> momentum.

Not quite. What I'm suggesting is that a large angle orientation
error signal can be seen in real time from the gyros, but refined
pointing relies on a more time consuming star finding procedure.

> The different thing I said was to label the "reaction wheels" as another set
> of gyros.  I described two sets of "gyros," one gimbaled for maintaining a
> position reference, and another larger set not gimbaled for use as an
> angular mometum reservoir.

There's an important difference between the reaction wheels and
gyros. The reaction wheels have, at times, very small angular
momenta (perhaps even zero). Gyros, on the other hand, must be
spinning to function. While reaction wheels are "reservoirs" of
angular momentum, perhaps they are better looked upon as sinks
for unwanted angular momentum.

Leigh