Robust controllers for the Middeck Active Control Experiment using Popov controller synthesis

The purpose of this paper is to demonstrate robust compensators designed using Popov controller synthesis on the Middeck Active Control Experiment (MACE): a Shuttle program scheduled for flight in January, 1995. The experiment has been designed to investigate the extent to which the on-orbit behavior of a precision-controlled spacecraft can be predicted and controlled using analysis and ground testing prior to launch. Previous flight experiments indicate that, on-orbit, the structural dynamics can change significantly, and that these changes are very difficult to predict. Thus the need arises for robust control techniques that can guarantee on-orbit performance for flexible spacecraft even though the models have large parameter uncertainties. Such a technique is developed in this paper using the Popov stability criterion from absolute stability theory. A state space representation of the stability analysis test is combined with an ℋ₂ performance objective to provide a powerful technique for robust controller synthesis. A numerical algorithm for optimizing the controller gains and stability multipliers is discussed. Several experimental results on MACE are used to demonstrate that Popov controller synthesis guarantees robustness to real parameter variations and yields good performance with respect to the reference LQG designs