Online entry trajectory planning with simultaneous constraints on terminal full-states, flight time and no-fly zones

The integration of terminal full-state constraints, flight time constraints, and no-fly zone constraints makes the reentry trajectory planning a highly underactuated planning problem, where profile-based methods are inefficient and analytical methods struggle to satisfy multi-constraints. To achieve both high adaptability to complex constraints and low computation cost, this paper proposes a novel trajectory planning approach. The approach begins by generating an optimal no-fly-zone-avoiding path using a directed graph-based strategy. Subsequently, a dual-layer longitudinal profile is constructed upon the path, comprising a velocity-altitude sub-profile and an altitude versus range-to-go sub-profile. This dual-profile structure facilitates the analytical satisfaction of terminal constraints on altitude, velocity, and flight path angle. Furthermore, the flight time integral is transformed into a fast algebraic expression via Chebyshev polynomial approximation, enabling explicit and low-cost time control. For lateral trajectory generation, a method based on bank reversal timing optimization is developed with the use of the longitudinal profile, where terminal constraints on latitude, longitude, and heading angle are satisfied by adjusting bank reversal timing. Numerical simulations validate the feasibility and robustness of the proposed method for trajectory planning of hypersonic glide vehicles (HGVs) operating in complex environments.