Multiple Spacecraft Formation Flying Control around Sun-Earth L2 Libration Point

Multiple spacecraft formation flying is an important concept for future deep-space exploration missions. It requires reliable techniques for the control of formation configuration. This paper addresses the control problem of spacecraft formation flying around the Sun-Earth L-2 libration point utilizing the framework of the circular restricted three-body problem (CR3BP). A leader/follower formation scheme consisting of one leader and three follower spacecraft is considered. The leader spacecraft is assumed to be in a fixed Halo orbit. The position of each follower spacecraft relative to the leader is controlled to be a constant using an active disturbance rejection control (ADRC) method. In this method, the unknown dynamics and external disturbances of the formation flying system are estimated by an extended state observer (ESO), and a nonlinear state error feedback control law is used to compensate for them in real time. Perturbative forces due to solar radiation pressure and the eccentric nature of the Earth's orbit are modeled as external disturbances. Numerical simulations and comparisons with an existing method show that desired formations are obtained with high accuracy using the proposed ADRC method.