NDOB-based three-dimensional guidance law with fast and finite-time convergence

In this paper, a three-dimensional finite-time guidance law is proposed for both nonmaneuvering and maneuvering targets. Unlike the usual approach of decoupling the engagement dynamics into two mutually orthogonal two-dimensional planes, a fast and finite-time guidance law for the coupled engagement dynamics is derived by selecting a special Lyapunov function. The proposed guidance law is constructed through a combination of finite-time stability theory and nonlinear disturbance observer (NDOB) technique. More specifically, augmented functions are involved to improve the convergence of the guidance system, while the NDOBs are used to compensate the unknown target accelerations and handle the chattering problem. Finally, simulation results on three-dimensional missile-target interception examples are included to verify the effectiveness of the proposed approach.