Active Disturbance Rejection in Large Flexible Space Structures

The design of an active control law for the rejection of persistent disturbances in large space structures is presented. The control system design approach is based on a deterministic model of the disturbances and it optimizes the magnitude of the disturbance that the structure can tolerate without violating certain predetermined constraints. In addition to closed-loop stability, the explicit treatment of state, control and control rate constraints, such as structural displacement and control actuator effort, guarantees that the final design will exhibit desired performance characteristics. The technique is applied to a simple two bay truss structure and its response is compared with that obtained using a Linear Quadratic Gaussian/ Loop Transfer Recovery (LQG/LTR) compensator. Preliminary results indicate that the proposed control system can reject persistent disturbances of greater magnitude by utilizing most of the available control, while limiting the structural displacements to within desired tolerances.