Online Trajectory Planning of RLV Terminal Area Energy Management Phase

The terminal area energy management (TAEM) phase of the reusable launch vehicle (RLV) determines whether it can reach the landing window safely and accurately. Compared with offline trajectory planning, online trajectory planning is more robust to the uncertainties of actual flight. This paper investigates the online trajectory planning algorithm of TAEM phase. Firstly, the trajectory profile design method based on fixed range-to-go is proposed, and the non-linear least squares optimization algorithm is used to automatically design a trajectory profile that satisfies the fixed range-to-go. Secondly, in order to adapt to high-speed and high-sinking flight, according to the approximate linear characteristics of the dynamic pressure transition point with the fixed range-to-go, a dual optimization algorithm is used to quickly find the dynamic pressure transition point with the shortest time and satisfying the range-to-go. By establishing the trim data table, the planning time is less than 1s, which fully meets the real-time requirements of the online planning. The simulation results show that the online planning algorithm is simple, efficient and robust.