Transfer between libration orbits through the outer branches of manifolds for Phobos exploration

The transfer between libration orbits in the Mars–Phobos system is challenging under the strong gravitational perturbation of Mars and Phobos. In this paper, the outer branches of manifolds of libration orbits around Phobos are employed for impulse and continuous thrust transfer between orbits, respectively. The 1:1 resonant orbits are found to be appropriate intermediate orbits for impulse transfer, which can connect the manifolds of various kinds of libration orbits. For the continuous thrust transfer, the convex optimization method is adopted to design the low-thrust trajectory in the three-body problem. The Poincaré section is established to find the best matching points on the outer manifolds. The L₁/L₂ homoclinic and L₁−L₂ heteroclinic transfer trajectories are designed and discussed. The simulations show the feasibility of the transfer by outer manifolds with both impulse and continuous thrust. The proposed method can avoid the potential hazard caused by the complicated dynamics near Phobos and provide a reliable transfer method, which can be used in future Phobos exploration missions.