# Transfer To The Collinear Libration Point L3 In The Sun--Earth+Moon System

- Paper number
IAC-07-C1.4.08

- Author
Dr. Hou Xiyun, China

- Coauthor
Dr. Tang Jingshi, Nanjing University, China

- Coauthor
Prof. Lin Liu, Nanjing University, China

- Year
2007

- Abstract
The collinear libration points L3 is on the other side of the sun, opposite to the earth. The thermal condition there is constant and ideal for astronomy observation. However the distance between this point and the earth is very large. The large distance makes the transfer of and communication with the spacecraft difficult. Different from the collinear libration points L1 and L2, the instability of the motion around L3 is very weak. The stable or unstable invariant manifolds may spend thousands of years to leave the proximity of L3 and can not closely approach the earth. So it is not proper to transfer the spacecraft to the invariant manifolds of L3, just as we can do with the spacecraft transferred to the points L1 and L2. However, the stable and unstable invariant manifolds of the point L2 can approach the proximity of the point L3. If the unstable invariant manifold of L2 and the nominal orbit of the spacecraft around L3 intersect at point

**Q**, we can first transfer the spacecraft from the earth though the unstable invariant manifold to point**Q**, and then change the speed of the spacecraft to insert it to the nominal orbit. With proper maneuvers, the spacecraft can depart from its nominal orbit and go back to the earth through the stable manifold of the point L2. During the lifetime of the spacecraft, the communication between it and the earth may be shielded by the sun. A method to solve this problem is to put a relay station around the equilateral equilibrium point L4 or L5 (we pick L5). Since the equilateral points are stable, considering perturbations from other celestial bodies, the orbit control of the relay station is not energy-consuming. Fortunately, the unstable manifolds of L2 go through the proximity of points L5, so we can transfer the relay station along with the spacecraft. When the carrier passes the point L5, the relay station is ejected and the remaining part goes on to the nominal orbit. Based on this scenario, we did some theoretical works under the model of Circular Restricted Three-Body Problem (CRTBP).- Abstract document