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Re: The Olympics - satellite positioning



At 12:17 PM -0700 9/25/00, Michael Edmiston wrote:

I've never designed a guidance system before, so I am speculating... but it
seems there would be a couple ways to deal with this.

I've never done so either, but I've heard a little about this matter
from one of my kids. The gyros on spacecraft are simply reference
devices for gross pointing adjustments. Star sensors are used for
the final references. One does not turn the spacecraft *against* the
gyromechanical moment of a gyroscope, one typically uses "reaction
wheels" which act as reservoirs for angular momentum which is built
up unintentionally by the interaction of the spacecraft with the
vagaries of space - atmospheric drag, electromagnetic drag, etc. The
reaction wheels are eventually despun by means of vernier rockets or
else (in the case of Earth orbiting satellites) by torquing against
Earth's magnetic field. I don't know how commonly they are used
(they may only be in design stages now), but ring lasers can replace
mechanical gyroscopes in these applications.

Leigh