Sliding mode based integrated pitch-yaw acceleration autopilot design for varying-velocity missile

A design of integrated pitch-yaw acceleration autopilot based on sliding mode control (SMC) with a nonlinear observer (NLO) is proposed for skid to turn (STT) velocity-varying missile. Missile autopilot design faces a great challenge owing to nonlinear aerodynamics, missile parameters' variation, coupling effect between channels, and unavailability of measuring all states. Moreover, the autopilot should be designed for the entire flight envelope, including boosting, sustaining, and gliding phases where fast variation of velocity and parameters exists. Thus the robustness against the quick variation of velocity and parameters is exceedingly required. The suggested missile model considers the velocity variation, the gravity effect, the missile parameters' variation. The proposed autopilot controls the normal acceleration of pitch-yaw channels simultaneously using multiple sliding surfaces and reaching laws. NLO is proposed to estimate the immeasurable states and its inputs are the measurable missile angular rates and its accelerations, and control signals. The closed loop system stability including the NLO stability is discussed. Finally, Numerical simulation is established to evaluate performance of the proposed acceleration autopilot.