Experimental verification attitude control techniques for flexible spacecraft slew maneuvers.

Abstract

The experimental verification of attitude control designs for flexible spacecraft is essential for reliable operation in space. The Flexible Spacecraft Simulator (FSS) at the Naval Postgraduate School is designed to test a variety of control designs. The experimental setup simulates pitch axis motion of a flexible spacecraft consisting of a rigid central body and a flexible appendage connecting a reflector. The primary actuators are a reaction wheel and thrusters. Angular position information is obtained with a rotary variable differential transformer (RVDT) and angular rate information is obtained by a solid state rate sensor. Two analytical models are derived: one based on cantilever modes, the other based on system modes. Both are the result of linearized equations of motion which assume small flexible displacements and rates. Slew maneuvers are conducted using four separate controllers. They are proportional-derivative (PD), torque profiles, bang-bang and optimal controllers. Techniques for state estimation are explored for the optimal controller since the standard estimation methods prove to be unsatisfactory. The sinusoidal torque profile delivers the best performance overall with the PD a close second. Momentum wheel desaturation with thrusters and thruster slew maneuvers are also performed. In all cases, experimental results are in close agreement with analytical predictions.