Controlling attitude maneuvers of flexible spacecraft based on nonlinear model using combined feedback-feedforward constant-amplitude inputs

Attitude maneuvers of rigid main body with two large solar panels spacecraft are studied. Equations of motion of the spacecraft are derived using Lagrange´s formulation and the solar panels are supposed as flexible substructures. To discrete the solar panel motions, the finite element method is used. The solar panels are modeled as rectangular bending plate elements. The complete equations of motion resulted are a nonlinear differential equations. The system showed rich physical phenomenons caused by nonlinear couplings between the rigid and flexible substructures those are not uniform in roll, pitch, and yaw motions. Input shaper is the known feed-forward method for fast maneuvers of flexible systems while reducing their residual vibrations. The method is very powerful and effective for the linear systems. When this method is applied to maneuver the studied spacecraft, which is the nonlinear system, the desired attitude displacements and velocities cannot be achieved anymore. To solve the above problems, a combination of feedback and feed-forward inputs are proposed. The feedforward input is based on the input shaper, while the feedback input is formulated basing on the known proportional-derivative (PD) controller. Under the combined feedback-feedback proposed method, the maneuvers can be performed efficiently. The comparison of maneuver results between the proposed method, the PD control, and other feed-forward controls will be presented and discussed.