LOW ENERGY TRAJECTORY OPTMIZATION FOR CE-2'S EXTENDED MISSION AFTER 2012

摘要

CE-2, the second lunar satellite of China, has been the first satellite in the world to transfer from lunar polar orbitto the Sun-Earth L2 libration point. CE-2 will remain in the L2 Lissajous trajectory until the end of 2012, when about120 m/s delta-v will be left. This paper studies trajectory optimization for CE-2's extended mission after 2012. Theprimary goal of this work is to design a suitable trajectory that maximizes science data return in different regions ofthe Sun-Earth-Moon system. The mission design should encompass as many regions as possible. Both the invariantmanifolds of libration point and lunar gravity assist are used to design the low energy trajectories. A multiple regionsexploration scenario including four main phases is proposed. First, the satellite follows the unstable manifolds toleave the Sun-Earth L2 Lissajous trajectory. After the first lunar flyby, the satellite enters into an Earth high ellipticorbit, from which geomagnetic tail and space environment could be studied. With another one or two lunar flyby,the spacecraft follows the stable manifolds to the Sun-Earth L1 Halo orbit, from which solar physics could be studied.Finally, the spacecraft follows the unstable manifolds to leave the Sun-Earth L1 Halo orbit, and fly towards the Sun-Earth L4 libration point. The spacecraft encounters an asteroid on the way to the L4 point. This paper also discussesthe trajectory optimization for Chang'e 2's practical flight to the Toutatis asteroid, about 22 m/s delta-V is savedcompared to the baseline trajectory. Hence the saved delta-V could be used for trajectory correction maneuvers toinsure the probability of the successful asteroid flyby. This work demonstrates practical applications of advancedastrodynamic concepts in the Sun-Earth-Moon system, including chaotic three-body orbits, periodic three-bodyorbits, gravity assist, and the conic patched method. The result is a practical mission design of a grand tour for theSun-Earth-Moon system using limited fuel resources.