CHANG'E-5T1 extended mission: The first lunar libration point flight via a lunar swing-by

This paper introduces the extended mission of the Chinese circumlunar return and reentry test (i.e., the CHANG'E-5T1 mission), the first Chinese flight in the Earth-Moon libration orbit and the first spacecraft to reach the Earth-Moon libration orbit via a lunar swing-by. The extended mission utilized the remaining propellant from the CHANG'E-5T1 mission. Based on the normal trajectory and satellite state at the end of the CHANG'E-5T1 mission, a lunar return and a flight in the lunar libration orbit were determined to be the flight goals of the extended mission. Two schemes were then proposed for the CHANG'E-5T1 extended mission, including a possible Earth-Moon libration orbit. The methodology for the trajectory design and maneuvering included the direct libration-point orbit transfer and injection method, which is characterized by a reduced calculation burden compared with the prevalent invariant manifold method. The scenarios were compared in terms of flight time, control energy and number of maneuvers, flight distance, and achieved flight goals. The comparison indicated that the scheme, including the Earth-Moon L2 point and return to the Moon, was preferred for the CHANG'E-5T1 extended mission. Furthermore, the actual flight parameters of the CHANG'E-5T1 extended mission are also presented to validate the selected scheme.