Three-dimensional Guidance Law with Impact Angle Constraints Considering Autopilot Dynamics

For maneuvering threats, a unique guiding law with considerations for impact angle constraint, autopilot dynamic features, and fixed-time convergence is devised. First, a backstepping approach is used to build the guiding law based on non-singular terminal sliding mode control. To address the issue of 'differential expansion' in traditional backstepping control, a first-order nonlinear filter is introduced to filter the virtual quantity. To tackle the lag problem in the autopilot, a second-order dynamic model of the autopilot is incorporated to reduce the delay. Then, the fixed-time convergence of the guidance law is demonstrated using the Lyapunov stability theory. Lastly, the superiority and efficacy of the suggested guidance law are illustrated by simulations.