Air bearing table mechanization and verification of a spacecraft wide angle attitude control system.

The problem of controlling the attitude of a space vehicle slewing through large angles in three dimensions is experimentally investigated. The investigation is based on a control system synthesized from Euler's theorem on rotation which states that any attitude change of a rigid body may be accomplished by a single rotation about a properly chosen axis. A theoretical analysis showed that a system using the control law has global stability. The investigation was carried out using an air bearing table to simulate the spacecraft, twogimbaled star trackers as position sensors, rate gyroscopes to provide damping information, and reaction wheels as control torquers. An on line digital computer acts as a real time controller which determines the control axis orientation from star tracker gimbal outputs, and generates simultaneous commands to the three torquers. The experimental results show that the control system was stable while slewing through large angles and had excellent pointing accuracy.