Sliding mode guidance law with impact angle constraint based on disturbance observer

To control the impact angle of missile attacking maneuver target, a sliding mode guidance law with impact angle constraint is proposed based on disturbance observer. The time-varying uncertainty of missile velocity and the unknown escaping maneuver of target are regarded as the disturbance of system of relative motion between missile and target. The disturbance observer is adopted to estimate the disturbance. Then a guidance law with the impact angle constraint is derived combining the disturbance observer and sliding-model control theory, and the asymptotical convergence is demonstrated based on Lyapunov stability theory. To ensure the guidance precision and eliminate the chattering caused by the guidance law, the guidance law is improved furthermore through adopting the boundary layer method. The relationship among guidance precision, boundary layer thickness and guidance law parameters is analyzed. Simulation results show that the proposed guidance law is of good guidance performance and robustness, and of less missile maximum normal acceleration and more gentle change of normal acceleration compared with the general sliding model guidance law, which is more helpful for realization in engineering.