Tactical missile autopilots: Gain-scheduled H(infinity) control and dynamic inversion

Autopilot design for a bank-to-turn (BTT) tactical missile is inherently nonlinear, with highly coupled dynamics. These difficulties create a need for the use of multivariable and nonlinear control techniques. This dissertation studies the application of two distinct modern control methods, {dollar}{lcub}cal H{rcub}sb{lcub}infty{rcub}{dollar} control with {dollar}{lcub}cal D{rcub}{dollar}-implementation gain-scheduling and nonlinear dynamic inversion using the assumption of a two-time-scale separation, for the autopilot design of a BTT air-to-air missile.; The first portion of the work presents an analysis of the stability of the closed-loop missile system with a dynamic inversion controller to verify the validity of the time-scale separation assumption. It is proven under certain reasonable assumptions that the closed-loop system can be made exponentially stable about commanded constant state values by choosing a sufficiently large inner-loop frequency. The method used in the proof allows the calculation of a sufficiently large inner loop frequency to guarantee stability with a substantial domain of attraction which is used to show command following. This result is applied to the complete longitudinal/lateral missile dynamics.; The proof is derived using two Lyapunov functions that take advantage of the two-time-scale structure the dynamic inversion controller imposes on the system dynamics. The dissertation also contains a generalization of the stability theorem to a general nonlinear system of a certain form, stating that the dynamic inversion controller using the two-time-scale separation can exponentially stabilize the closed-loop system about the commanded values.; The second portion of the work examines the design of {dollar}{lcub}cal H{rcub}sb{lcub}infty{rcub}{dollar} and dynamic inversion controllers for the complete missile system. The performance of the two controllers is compared for nominal performance, robustness to aerodynamic uncertainty, and sensitivity to measurement noise. The performance comparison is carried out on a six degree-of-freedom simulation using the complete aerodynamic data for the missile. Although the two systems have comparable nominal performance, the {dollar}{lcub}cal H{rcub}sb{lcub}infty{rcub}{dollar} controller is more robust to aerodynamic uncertainties.