Nonlinear robust autopilot for rolling and lateral motions of an aerodynamic missile

The paper deals with robust stabilization of lateral and rolling motions of a skid-to- turn missile taking into account inertial, kinematic and aerodynamic couplings. The main diffculties that rise in control design are related to the highly uncertain, time-varying and nonlinear aerodynamic forces that affect the system. To handle them, the design of the autopilot is based on "backstepping", a nonlinear control design approach which rouses the aerospace community's interest. Robustness is achieved using a C1 sigmoid-like function, which compensates the uncertainties' effects by dominating them in size. The recursive and flexible composition of the control law makes easy the compensation of three different kinds of uncertainties: matched, equivalently matched and unmatched, whose criticality in robust control design is well known. The peculiarity of the control scheme proposed lies in the fusion of a revisited version of the classical Lyapunov redesign controller into the standard backstepping design procedure, thus simplifying the handling of matched uncertainties. The whole design makes massive use of Lyapunov direct criterion in the context of robust uniform global asymptotic stability theory. The autopilot is designed to regulate bank angle, roll-rate and sideslip angle according to the tight requirements imposed by the external guidance loop and by navigation needs. Simulation results show the effectiveness of the proposed nonlinear controller in presence of extra perturbations and disturbances. © 2012 by Giovanni Mattei.