Three-dimensional guidance law accounting for second-order dynamics of missile autopilot

A new three-dimensional (3D) guidance law is designed using the dynamic surface control method in this paper which is based on the target-missile dynamics in 3D coordinates and the second-order dynamics of the missile autopilot. Certain first-order low-pass filters are introduced into the designing process to avoid the occurrence of high-order derivatives of the line of sight angular rate in the expression of the guidance law, which makes it easy to implement in practical applications. The proposed guidance law is effective in compensating for the adverse influence of autopilot lag on guidance accuracy. In simulations of intercepting non maneuvering targets, targets with step acceleration, and targets with sinusoidal acceleration respectively, the guidance law is compared with the adaptive sliding mode guidance (ASMG) law, which is designed without accounting for the dynamics of the missile autopilot, and the 3D nonlinear guidance law, which is designed accounting for the first-order dynamics of missile autopilot. Simulation results show that the guidance law still ensures an accurate guidance result, even if the target escapes in a great and fast maneuver and the autopilot has a relatively large lag.