Guidance law accounting for second-order dynamics of missile autopilot and impact angle constraints

In this paper, a planar guidance law accounting for second-order dynamics of missile autopilot and impact angle constraints is designed using backstepping method and nonsingular terminal sliding mode control (NTSM). Nonsingular terminal sliding mode was employed to drive the line of sight (LOS) angle to a desired impact angle in finite time without singularity. In backstepping design, some first-order low-pass filters are introduced to avoid the occurrence of high-order derivatives of LOS angular rate in the expression of guidance law. Using the Lyapunov stability theorem, it is proved that all signals in the closed loop system are ultimately bounded. Simulations of intercepting constant-acceleration maneuvering targets and targets with sinusoidal acceleration show that the guidance law still ensures the impact angle constraints and is able to compensate the autopilot lag.