Abstract: First-stage return trajectory optimization and onboard generation of the horizontal launch Two-Stage To Orbit (TSTO) reusable vehicles are studied. The optimization strategy of the first stage return trajectory is firstly proposed: the lateral profile is given prior to solution of the three-dimensional trajectory by piecewise optimization. A lateral bank angle profile is designed to meet the large steering requirements during the first stage reentry process. In view of the remarkable characteristics of aerodynamic variations in the wide velocity domain of the first stage, the multi-segment optimization strategy is designed to avoid repeated trajectory jumps, and Gauss Pseudospectral Method (GPM) is used to design the three-dimensional trajectory. To solve the initial state deviation caused by separation disturbance of the TSTO vehicle, the parameter space of the Adaptive Multivariate Pseudospectral Interpolation (AMPI) method is extended to generate the onboard trajectory for the first stage. The simulation results show that the proposed lateral bank angle profile can ensure the alignment of the flight course with the landing field without the need for repeated reversals of the bank angle, and the multi-segment optimal strategy can ensure a stable trajectory, and the AMPI method can generate onboard trajectory quickly and accurately under the condition of large initial deviations.

Key words: Two-Stage To Orbit (TSTO) vehicles, Reusable Launch Vehicle (RLV), return trajectory, trajectory optimization, onboard trajectory generation, Adaptive Multivariate Pseudospectral Interpolation (AMPI)