Application of the LQG and feedforward controllers to the deep space network antennas

The controller development and the tracking performance evaluation for NASA's deep space network antennas are presented. A command preprocessor, LQG controller, feedforward controller, and their combination are designed, built, analyzed, and tested. The antenna exhibits nonlinear behavior when the input to the antenna and/or the derivative of this input exceeds the imposed limits; for slewing and acquisition commands, these limits are typically violated. A command preprocessor was designed to insure that the antenna behaves linearly, just to prevent nonlinear limit cycling. The estimator model for the LQG controller was identified from the data obtained from the field test. Based on an LQG balanced representation, a reduced-order LQG controller was obtained. The feedforward controller and the combination of the LQG and feedforward controller were also investigated. The performance of the controllers was evaluated with the tracking errors and the disturbance errors.