In this paper, a new guidance law based on the variable structure system theory and an associated model-free target acceleration estimator are proposed. The composite guidance-estimation law is designed to intercept constant-velocity and maneuvering targets by missiles at a desired terminal impact angle. Specifically, the scenario of intercepting the targets with speed-disadvantaged missiles, which has not been studied in detail in the literature available, is considered in this paper. A multiple solution problem for the terminal impact angle and a final line-of-sight angle is clarified in this paper. To solve this problem, the generalized variable structure theory is used and an additional sliding mode surface is introduced in the proposed guidance law, by which missiles can reach a wider range of the final impact angle. In addition, the nonsingular terminal sliding mode control method is applied so that the states of the guidance dynamic system are finite time convergent. In order to intercept maneuvering targets, a Kriging-based model-free finite impulse response filter is employed. Based on this filter, this paper puts forward some improvements, including a data preprocessing method and a parameter offline tuning method by the simulated annealing algorithm. In this way, a model-free target acceleration estimator with strong practicality in engineering is proposed. The stability condition of the proposed composite guidance-estimation law is obtained via the Lyapunov theorem. Finally, simulation results in different initial intercepting scenarios are presented to validate the advantage of the proposed guidance law and target acceleration estimator.
['Zhiwei Hou', 'Lei Liu', 'Yongji Wang', 'Jian Huang', 'Huijin Fan']
Terminal Impact Angle Constraint Guidance With Dual Sliding Surfaces and Model-Free Target Acceleration Estimator