Semi-analytical optimal tracking control for emergency return trajectory of Earth-Moon flight transportation system

In recent years, Earth-Moon flight transportation has emerged as a research hotspot and a significant development goal for many countries due to its prominent advantages in shortening the haul-cycle time and achieving the high frequency round trip in the Earth-Moon system. To ensure the safety of space transportation, this study investigates methods for emergency return trajectory design and tracking control, focusing on situations where the Earth-Moon flight transportation system encounters unexpected circumstances during Earth-Moon transfer and needs to terminate the mission for an emergency return to Earth. Firstly, a relative dynamics model for periodic orbits in Earth-Moon space is established based on the circular restricted three-body problem. According to the practical requirements of emergency return missions, the Keplerian orbit and pseudo trajectory method are utilized to design two types of return trajectories: direct return and lunar-flyby return, respectively. Subsequently, based on the receding horizon control framework and the mode insertion gradients theory, a semi-analytic optimal tracking controller is designed through a combination of analytical derivation and low-complexity online numerical computations. Finally, numerical simulations are organized to validate the effectiveness of the designed emergency return trajectories and the semi-analytic optimal tracking control scheme.