Three-dimensional terminal angle constrained robust guidance law with autopilot lag consideration

Based on sliding mode control theory and back stepping design technique, this paper proposes a robust guidance law considering autopilot dynamics for maneuvering target interception in three-dimensional environment and terminal angle constraints. The proposed guidance law is summarized as an “observer–controller” system. More specifically, to estimate the knowledge of target maneuvers, an adaptive second-order sliding mode observer is presented whose design parameters can be adjusted autonomously according to the estimation error, and a nonsingular switchable sliding manifold based finite time convergent controller is proposed to drive the line-of-sight angle error and angular rate to a small region around zero, further, enable the missile accurately intercept the target in finite time. Finally, by formulating the autopilot lag as a first-order or second-order dynamics, the higher-order comprehensive model is built and complex guidance laws are presented. The simulation results demonstrated the proposed properties.