Adaptive Backstepping Impact Angle Guidance Law Accounting for Autopilot Lag

This paper presents a robust impact angle guidance law for maneuvering target interception with autopilot dynamics compensation based on a systematic backstepping control technique. Since the future course of action of the target, an independent entity, cannot be predicted beforehand, an adaptive-control approach is introduced in guidance law derivation. In order to address the problem of explosion of terms caused by analytic differentiation of the virtual control laws in the standard backstepping method, a tracking differentiator is adopted as an alternative way to obtain the derivatives of the virtual control laws. Stability analysis shows that both the line-of-sight angular rate and impact angle error can be stabilized in a small region around zero asymptotically. Simulation results explicitly show that accurate interception is achieved with a wide range of impact angles.