The terminal guidance problem for an unpowered lifting reentry vehicle against a stationary target is considered. In addition to attacking the target with high accuracy,the vehicle is also expected to achieve a desired impact angle. In this paper,a sliding mode control(SMC)-based guidance law is developed to satisfy the terminal angle constraint. Firstly,a specific sliding mode function is designed,and the terminal requirements can be achieved by enforcing both the sliding mode function and its derivative to zero at the end of the flight. Then,a backstepping approach is used to ensure the finite-time reaching phase of the sliding mode and the analytic expression of the control effort can be obtained. The trajectories generated by this method only depend on the initial and terminal conditions of the terminal phase and the instantaneous states of the vehicle.In order to test the performance of the proposed guidance law in practical application,numerical simulations are carried out by taking all the aerodynamic parameters into consideration. The effectiveness of the proposed guidance law is verified by the simulation results in various scenarios.
This paper proposes a finite-time robust flight controller, targeting for a reentry vehicle with blended aerodynamic surfaces and a reaction control system(RCS). Firstly, a novel finite-time attitude controller is pointed out with the introduction of a nonsingular finite-time sliding mode manifold. The attitude tracking errors are mathematically proved to converge to zero within finite time which can be estimated. In order to improve the performance, a second-order finite-time sliding mode controller is further developed to effectively alleviate chattering without any deterioration of robustness and accuracy. Moreover, an optimization control allocation algorithm, using linear programming and a pulse-width pulse-frequency(PWPF) modulator, is designed to allocate torque commands for all the aerodynamic surface deflections and on–off switching-states of RCS thrusters.Simulations are provided for the reentry vehicle considering uncertain parameters and external disturbances for practical purposes, and the results demonstrate the effectiveness and robustness of the attitude control system.
