This paper studies three-axis attitude control problems of a class of flexible spacecraft having elastic appendages. A Linear Quadratic Regulator (LQR) associated with a state estimator is designed to control its attitude and the appendage vibration, simultaneously. In order to evaluate and demonstrate the controller performance, ground-based control experiments are conducted, using a ETS (Engineering Test Satellite)-VI laboratory model supported on a single-axis air-table. The evaluation is made concerning mainly with (a) LQR realization by using a thruster and a reaction wheel, and (b) stability robustness against the truncated vibration modes of flexible appendages.
