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.
