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.