Trans-Lunar Cruise Trajectory Design of GRAIL (Gravity Recovery and Interior Laboratory) Mission

The Gravity Recovery and Interior Laboratory (GRAIL) mission is a part of NASA’s discovery program that will map the lunar gravity field in order to better understand the internal structure of the Moon by sending two orbiters in a low-energy trans-lunar cruise (TLC) trajectory, whose flight time is 90-115 days. This paper focuses on the low-energy TLC trajectory design of the GRAIL mission. The trajectory enters into the Sun-Earth three body region to lower the instantaneous lunar orbit insertion (LOI) V. Since the two spacecraft are launched from a common launch vehicle, two deterministic mid-course maneuvers are required for each trajectory. LOI targets are determined according to the requirements and needs of the GRAIL orbital phases. Once LOI targets are determined, the dual spacecraft low-energy TLC trajectories can be generated optimally depending on the desired constraints and cost functions. The launch targets are one of the products of the trajectory optimization. Some interesting results pertaining to the low-energy TLC trajectories are presented in the form of data and plots.