In this paper, three-dimensional terminal guidance problem of a missile intercepting a maneuvering target is studied by using a composite control scheme based on finite-time control and nonlinear disturbance observer technique. The threedimensional model is characterized by nonlinear interception geometry, which the azimuth angle and elevation angle are coupled with each other. Many existing results are studied for planar model which ignores the coupled terms of threedimensional model. In this paper, the coupled terms of guidance system can well be solved by selecting a special Lyapunov function, and guidance laws with finite-time convergence characteristic are derived, which have the ability to track target maneuver. Based on sliding mode control method, discontinuous switching functions are involved as augmented terms to suppress the target accelerations which are regarded as unknown bounded external disturbance of guidance systems. To improve the disturbance rejection performance of guidance system, the gains of switching functions are selected to be larger than the bounds of accelerations. However, the guidance system could generate the chattering phenomenon caused by discontinuous switching functions. To handle the chattering problem, nonlinear disturbance observers are constructed to estimate the target accelerations. The estimated target accelerations are introduced into the finite-time guidance laws and used as the feedforward compensation terms to reject the actual target accelerations. This is an efficient approach to suppress the chattering phenomenon. Then, novel composite guidance laws are presented based on finite-time feedback control and disturbance feedforward compensation. Finally, simulation results on three-dimensional missile-target interception examples are provided to demonstrate the effectiveness of the proposed approaches.

In this paper, a nonlinear suboptimal guidance system is presented for the missile targeting an unknown arbitrary target. An integrated quadratic performance index is minimized in this guidance law, and the whole design is based on the exact 3D nonlinear missile-target dynamics without any linearization. Considering that the Hamilton–Jacobi–Bellman equation of a nonlinear system is quite difficult to be solved, the [Formula: see text] method is used to obtain the approximate solution without complicated online computations. Moreover, the target accelerations are regarded as the unknown disturbances, and the robustness against the target maneuvering and the external disturbances is enhanced by introducing the feedforward compensation based on the nonlinear disturbance observer. In addition, no priori knowledge like the time-to-go is needed in this suboptimal guidance law. Simulation studies show that the proposed composite guidance system can guarantee that the missile intercepts the arbitrary maneuvering target with satisfied performance.

A composite three-dimensional (3D) missile guidance law is proposed for manoeuvering targets with the consideration of the first-order autopilot dynamics without any linearization. This guidance law consists of a backstepping controller and a feedforward compensation based on disturbance observers. In this control scheme, the unknown target acceleration is regarded as part of the lumped disturbance, estimated by a disturbance observer, and then feedforward compensated. The backstepping controller is introduced to deal with unmatched disturbances. Moreover, both the nonlinear disturbance observer (NDOB) and the generalized proportional integral observer (GPIO) are employed in the derivation. Simulation studies demonstrate the effectiveness of the proposed guidance law, and compare the guidance performance of the two composite guidance laws with different disturbance observers.

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