Entry guidance with terminal approach angle constraint

Achieving a desired terminal approach angle is required by an advanced entry vehicle in missions of landing or defense penetration. An entry guidance method is developed to satisfy the terminal approach angle constraint as well as the conventional constraints. The guidance method consists of a lateral guidance logic based on multiple aiming points and a two-phase trajectory tracking law. The aiming points are selected from a reference ground track and used to determine bank reversals for the lateral guidance logic. With the aid of aiming points, the vehicle can reach the entry terminal in a desired direction. The two-phase trajectory tracking law, corresponding to a two-dimensional and a three-dimensional trajectory, are designed to cooperate with the lateral guidance logic. Numerical results show that the guidance method is capable of flying the vehicle to the terminal zone with various desired approach angles, and meanwhile, robust to typical entry dispersions. The advantage of the guidance strategy is also verified by comparisons.