System and process for controlling spacecraft attitude

摘要

This process for controlling spacecraft attitude uses one or more reaction wheels or inertia wheel. The viscous friction (dependent on speed) in the wheel bearings reduces the actual torque which is communicated to the spacecraft in response to a torque demand signal. Friction compensation is effected by applying the torque demand signal to a model of a frictionless ideal wheel, and by calculating the speed attained by the ideal wheel in response to the torque demand. An error signal is generated from the difference between the ideal wheel speed and the actual wheel speed. The error signal is added to the torque demand signal to produce the wheel drive signal. This results in a closed-loop feedback system in which the actual wheel speed tends to the ideal wheel speed, thus giving rise on the spacecraft to a torque which is substantially equal to the demanded torque.