A Fixed-Time Convergence Adaptive Fast Sliding Mode Guidance Law with Angle Constraint

In this paper, a fixed-time convergence adaptive fast sliding mode guidance law with line-of-sight (LOS) angle constraint is designed for the terminal guidance problem of large maneuvering targets in the air. Firstly, the three-dimensional (3D) spatial missile-target relative equations of motion are constructed, and the terminal guidance model with LOS angle constraints is established. Secondly, a novel fixed-time nonsingular terminal sliding mode surface is designed, and by designing a fast convergence law, while avoiding system singularity and reducing end jitter, the LOS angle and angular rate of the missile are guaranteed to converge quickly to the desired value in a fixed time, and have the advantage that the upper bound of the convergence time can be artificially set. In addition, the interference observer is constructed using the good approximation property of RBF neural network for continuous functions, which provides an effective estimation of the unknown acceleration of the intercepted target, and increases the self-adaptive capability of the system. Finally, the effectiveness and superiority of the designed guidance law is verified by simulation.