Abstract:A re-entry trajectory planning method based on the rapidly-exploring random tree* (RRT*) algorithm is proposed for the Reusable Launch Vehicle (RLV) under multiple constraints. During the longitudinal profile planning, a multi-constraint flight corridor is constructed in the altitude-velocity space according to dynamic pressure, load, heat rate and equilibrium glide condition constraints. In order to obtain a smooth, controllable altitude-velocity reference trajectory, three types of cost have been proposed, i.e., cost of control, smooth trajectory and range, which improves the RRT*. By doing so, a feasible reversal point can be guaranteed which will be used to design the lateral trajectory to the heading alignment circle (HAC) and the 3DOF trajectory design is realized. Further, the RRT* algorithm is employed to solve the derived optimal problem quickly. The proposed algorithm transforms the re-entry trajectory planning problem under multiple constraints into a path cost setting problem in the RRT* algorithm that greatly improves the speed and reliability of trajectory planning. The simulation results show that the designed reference trajectory is smooth, and the logic is simple and easy to implement in engineering.