Design Of Earth-Moon Libration Point L2 Orbits For Solar Sail Spacecraft

Solar sail spacecraft has become an ideal spacecraft for deep space exploration missions because it doesn't need to consume refrigerants and has a long time continuous low-thrust;Labration point can provide an ideal platform for many special missions such as relay communication,sun and moon observation and deep space exploration because of its special space position.Both of them have attracted the attention of the space powers.In this paper,the design and control of Labration orbit for solar sail spacecraft are studied,taking L2 point orbits of Earth-Moon system as an example in simuiation analysis.Firstly,in the barycenter rotating coordinate system,the dynamic model of the Circular Restricted Three-Body Problem(CRTBP)of the Earth-Moon system with the normalized units was established.Then the basic dynamic characteristics were analyzed.Some important concepts such as Jacobi integral,zero velocity surface and Labration point were discussed,providing the preliminary knowledge for orbit design.Then,an dynamic model of solar sail spacecraft in earth-moon system was established in geocentric rotating coordinate system.In this model the direct and indirect influence of the sun and the eccentricity of the lunar orbit are considered on the basis of the CRBTP,and avoided frequent coordinate conversion between the inertial system and the round coordinate system.the real-time state information of the sun and moon is obtained by using JPL DE405 ephemeris.Then,the orbit of solar sail spacecraft at L2 point of Earth-Moon system was designed on the basis of the dynamic model.The orbit design methods used include differential correction method,second-order differential correction method and multiple shooting method.Using ephemeris of JPL DE405,the motion state of the L2 points which was calculated by the instantaneous motion of the moon was used to get the information of the splicing points in the Geocentric Rotating Coordinate System.Finally,the control for solar sail spacecraft in Halo orbit was designed by using LQR which is called linear quadratic controller.