Impact angle constraint guidance law using fully-actuated system approach

Aiming at the terminal impact-angle constraint in the interception of large maneuvering targets, this paper proposes a three-dimensional (3D) interception guidance law combined with the high-order fully-actuated system approach and the cascaded linear extended state observer (LESO). First, a complete second-order nonlinear model with full actuated characteristics is developed for the missile-target relative dynamics without small-angle assumption. Subsequently, the nonlinear system is transformed into a quasi-feedback system, and then, a high-order fully-actuated model is developed. A cascaded LESO able to estimate the system state and target maneuver information is introduced, and the controller is designed to convert the closed-loop system into a linear time-invariant closed-loop system with the desired characteristic structure, which makes the closed-loop system have the desired closed-loop poles. Finally, the controller parameter matrix is solved using the desired closed-loop poles, and the convergence is validated by the Lyapunov stability theory. Consequently, the linearization of the 3D nonlinear system is realized, and the channel coupling is eliminated. The effectiveness of the proposed method is verified by simulation and analysis.