Trajectory correction for lunar flyby transfers to libration point orbits using continuous thrust

Trajectory corrections for lunar flyby transfers to Sun-Earth/Moon libration point orbits (LPOs) with continuous thrusts are investigated using an ephemeris model. The lunar flyby transfer has special geometrical and dynamical structures; therefore, its trajectory correction strategy is considerably different from that of previous studies and should be specifically designed. In this paper, we first propose a control strategy based on the backstepping technique with a dead-band scheme using an ephemeris model. The initial error caused by the launch time error is considered. Since the perturbed transfers significantly diverge from the reference transfers after the spacecraft passes by the Moon, we adopt two sets of control parameters in two portions before and after the lunar flyby, respectively. Subsequently, practical constraints owing to the navigation and propellant systems are introduced in the dynamical model of the trajectory correction. Using a prograde type 2 orbit as an example, numerical simulations show that our control strategy can efficiently address trajectory corrections for lunar flyby transfers with different practical constraints. In addition, we analyze the effects of the navigation intervals and dead-band scheme on trajectory corrections. Finally, trajectory corrections for different lunar flyby transfers are depicted and compared.

Periodic Attitudes of Libration Point Spacecrafts in the Earth-Moon System

The attitude motion of a rigid spacecraft is studied in the Earth-Moon circular restricted three-body problem. Firstly, the equilibrium attitude and its stability as functions of the moments of inertia are discussed when the spacecraft is assumed at the libration points. Then, periodic attitudes of a spacecraft with mass distribution given in the stable regions are obtained. Regarding space mission applications, the Sun orientation is discussed, and the orbit-attitude resonances are constructed for spacecrafts working on the libration point orbits by means of a continuation procedure.