Finite-time sliding mode based terminal area guidance with multiple constraints

To fulfill multiple constraints of desired range, terminal altitude, velocity and flight-path angle for hypersonic vehicles in the reentry terminal area, a finite-time convergent sliding mode guidance method is developed in this paper. The vehicles mass-point motion equations are established with the downrange as independent variable. A sliding mode, which can converge to zero at finite downrange value, is designed according to the formation of the finite-time convergent sliding mode. Thus it is effectively to be avoided to estimate time-to-go when the finite-time convergent sliding mode is utilized in guidance. The designed finite-downrange convergent sliding mode is applied in longitudinal guidance to ensure that the desired terminal altitude, flight-path angle and velocity can be satisfied at the terminal downrange arrived. The guidance commands of drag force and lift force in longitudinal plane are determined. With a rather high lift-to-drag ratio of hypersonic vehicles, extra life force needs to be consumed in lateral motion. Thus the lateral bank-reverse logic is designed based upon a constant heading error corridor for lateral bank reversing. Desired energy state and flight path characteristics can be achieved. The simulation results, given in Fig.1-Fig.5, and their analysis show preliminarily that the proposed guidance method can effectively deliver the hypersonic vehicle to the auto-landing interface with multiple terminal constraints satisfied.