Nonlinear Autopilot Design for an Asymmetric Missile Using Robust Backstepping Control

This paper deals with the design of a robust nonlinear controller for a highly maneuverable missile. Stabilization and tracking are achieved, exploiting a detailed nonlinear model of the six-degree-of-freedom, nonminimum phase, uncertain, and time-varying dynamics of a non-axial-symmetric air-to-air tail-controlled missile. A robust backstepping approach is applied to the multi-input/multi-output model to achieve both bank-to-turn and skid-toturn maneuvers. Control objectives consist of following the reference signals in angle of attack, sideslip, and bank angle produced by the external guidance system, in order to pursue highly agile maneuvers. Uncertain terms, mostly due to aerodynamic coefficients and dynamic pressure, are suitably limited by bounding functions constructed using experience, a priori knowledge on system behavior, and a bit of conservatism. Robust sigmoidlike control functions are then used to dominate in size the uncertain terms. The whole control system is shown to be practically-robustly uniformly asymptotically stable and control objectives are met within a prescribed level of performance, in both bankto-turn and skid-to-turn maneuvers. Simulation results validate the quality of the proposed controller.