Spacecraft Formation Flying Control Around Sun-Earth Triangular Libration Points

Spacecraft formation flying in deep-space environment have a wide range of potential applications,and have been one of the research focuses in the field of aerospace engineering.The Sun-Earth triangular libration points,which is thermodynamically stable and an almost unobstructed view of celestial objects,are stable equilibrium regions in deep space.These points can be ideal platforms for complicated space missions.Due to the advantages of spacecraft formation flying and triangular libration points,this work studies the dynamics and control problem of formation flying around the Sun-Earth triangular libration points,which is of great significance.Firstly,the dynamic model of spacecraft formation flying around the Sun-Earth triangular libration points is established.Based on the model of circular restricted three-body problem,the stability of the libration points is analyzed,and mission orbits around these points are constructed.Sun-Earth triangular libration points are stable equilibriums,thus the leader/follower formation configuration is adopted and the nonlinear dynamic model of the follower spacecraft with respected to the leader is established.Secondly,using electric propulsion system as the follower spacecrafi's thrust system,two control systems of spacecraft formation flying around the Sun-Earth triangular libration points are designed.First,an integral sliding mode(ISM)control system is designed based on the nonlinear relative dynamic model.Second,an extended state observer(ESO)based ISM controller is proposed for the controller to overcome the dependence on system model and improve the robustness of the formation control system.Third,a set of numerical simulations are carried out to verify the effectiveness of the proposed controller for formation keeping and reconfiguration.The simulation results indicate that,for a formation baseline of 100-km level,the ESO based ISM controller is able to achieve millimeter-level formation precision and agile reconfiguration with only a small quantity of fuel consumption.Lastly,a spacecraft formation flying control system using solar sailing around the Sun-Earth triangular libration points is designed.Using solar radiation pressure as propulsion thrust,solar sails are able to overcome the restriction of propellant mass.First,the solar radiation pressure model and dynamic model of a solar sail around the Sun-Earth triangular libration points are established.Second,the ESO based ISM controller is used for solar sail formation control.Third,a set of numerical simulations are carried out to verify the feasibility of the proposed controller for solar sail formation keeping and reconfiguration.The simulation results indicate that,compared with electric propulsion,solar sails are also able to achieve millimeter-level formation precision and agile reconfiguration.