To: Dave Jackson
I quote, “We also know that some aircraft instruments maintain an orientation in space by the use of two gyroscopes that rotate in opposite directions, on a common axis. The requirement for two counter-rotating gyroscopes is to cancel the 90-degree precession, of course”.
I am not aware of any aircraft instruments that have two gyro rotors rotating in opposition to each other to cancel out precession. The very nature of a gyroscopic type instrument is to precess when the aircraft attitude changes. It is the precession that causes the needle or little airplane to move showing the direction of movement.
Some satellites have gyros that rotate about a fixed axis. These gyros have a high moment of inertia and if there is any perturbing force the tendency to precess will impart a turning moment into the satellite structure causing it move in the desired direction.