Adaptive improved super-twisting integral sliding mode guidance law against maneuvering target with terminal angle constraint

This paper investigates the maneuvering target interception problem considering terminal angle constraint, the input saturation and the second-order autopilot lag with the unavailable missile's acceleration. The considering problem is formulated as an output feedback control problem of a four-order nonlinear uncertain weakly observable system, which is challenging to address by general composite methods directly. Hence, the liner normal equivalent control model of the original guidance system is firstly derived to facilitate the extended state observer (ESO) based method design. Then, a nonlinear ESO is introduced to estimate the unmeasured system states and modeled disturbances as well as compensate for control saturation. Thereafter, the ESO-based guidance scheme is developed by integrating a novel four-order integral sliding mode manifold and an adaptive improved super-twisting algorithm. The main novelty is that a novel integral sliding mode manifold is proposed to replace the linear sliding mode manifold of super-twisting sliding mode to further reduce the convergent time of closed-loop system states. Besides, the conventional super-twisting algorithm is improved by modifying the reaching law and designing the adaptive gains to guarantee the continuity of guidance command and suppress the large constant gains and parameter uncertainties. Notably, only the output relative information is utilized in its design process. Numerical simulations validate the previous analyses and show the superiorities in reducing the energy consumption in high maneuvering target interception and achieving robustness to a certain margin under various uncertainties.