Continuous second-order sliding mode based impact angle guidance law

In this paper, a new continuous robust impact angle constraint guidance law with finite-time convergence is proposed for intercepting maneuvering targets with unknown acceleration bounds. The presented guidance law is based on nonsingular terminal sliding mode (NTSM), smooth second-order sliding mode and finite-time convergence disturbance observer (FTDOB). In light of the introduced FTDOB, which is used to estimate and compensate the lumped uncertainty in missile guidance system, no prior knowledge of target maneuver is required. Thus, the proposed guidance law is capable of real implementation. Differently from the widely used boundary layer technique, chattering is eliminated effectively under the proposed guidance law without any performance sacrifice. Using finite-time bounded function approach and Lyapunov stability criteria, rigorous finite-time stability proof in both reaching and sliding phases is given. Theoretical analysis and numerical simulations show that the proposed guidance law can achieve more accurate interception with a wide range of intercept angles and superior overall performance than traditional NTSM algorithm.