Adaptive fixed-time observer-based impact angle control guidance law for intercepting maneuvering target

The guidance law for impact angle control against maneuvering targets while considering autopilot lag is addressed in this paper. First, an adaptive super-twisting disturbance observer incorporating fixed-time stable theory is introduced to address the unknown target acceleration. Furthermore, an improved fixed-time guidance law integrating the integral sliding mode method is proposed, which ensures that the impact angle converges to the desired value despite the initial condition. In addition, a backstepping guidance law based on the fixed-time converged integral sliding mode is further proposed to eliminate the effect of autopilot lag. In particular, a tracking differentiator is implemented to simplify the complex derivative calculation. The fixed-time stability of the closed-loop system is rigorously proved via the Lyapunov method. Finally, numerous numerical simulations are conducted to demonstrate the performance of the proposed guidance law.