Six-Degree-of-Freedom Vertical Landing Control for Launch Vehicles Based on Periodic Delayed Sliding Mode

Existing guidance and control methods for reusable launch vehicles (RLVs) during vertical landing often treat translational and rotational dynamics separately, which limits landing precision and robustness in the presence of strong coupling effects and external disturbances. To address this issue, this study proposes a systematic solution for precision vertical soft landing based on a comprehensive six-degree-of-freedom dynamic model of the vehicle. A novel high-accuracy position tracking control scheme is proposed, combining quartic polynomial guidance with sliding mode periodic delayed feedback control to ensure precise trajectory tracking within a prescribed time. Additionally, a trichannel attitude tracking controller is developed and integrated with the position control module, forming a closed-loop six-degree-of-freedom control system. Simulation results validate the effectiveness of the proposed method in suppressing disturbances and achieving pinpoint soft landings, highlighting its theoretical value and engineering applicability.