H∞ control of the V132 X-38 lateral-directional axis

Presents the design of an H_∞ controller for the X-38 V132 lateral-directional axes flight envelope. Linear fractional transformation (LFT) models of the lateral-directional axes of the X-38 crew return vehicle are constructed for six flight conditions within the flight envelope. These models include nine uncertain aerodynamic coefficient variations. The objective is to design a single controller for all flight conditions that robustly stabilizes the closed-loop system and achieves desired performance objectives for predefined aerodynamic variations within the flight envelope. Worst-case performance and gain/phase margins of the H_∞ controller are compared with the baseline gain-scheduled classical control design. Analysis and nonlinear simulation results show that the H_∞ controller achieves performance objective and robustness