A novel missile autopilot with remarkable robustness

A missile lateral autopilot is described and demonstrated that exhibits a high degree-of-robustness to model uncertainty and external disturbances. The novel aspect of the autopilot is a new feedback-loop topology that is a combination of feed-forward and feedback loops. This topology, called the Integral Command Augmentation for Robustness (ICAR) loop, is designed to be added as an additional layer to an existing, fully functional closed-loop autopilot. It does not alter the existing system dynamics except to add a high degree-of-robustness to model uncertainty in the original closed-loop autopilot. The mathematical basis for the ICAR loop is derived and its operation is demonstrated using a simple plant. The ICAR loop is then extended to the missile lateral autopilot application by means of a unique decomposition of the autopilot into moment-control and moment-resolver functions. Results of a series of simulation experiments are presented demonstrating exceptional robustness and disturbance rejection capability that substantiate performance claims made with the mathematical derivation and simple plant. Incidental to the paper is derivation of a simple-to-design three-loop PID autopilot. The paper concludes with observations that the ICAR loop can be applied to a much broader domain of control systems beyond the missile autopilot.