Design Strategies for Low Thrust Transfers in the Earth-Moon System

The increased interest in deep space missions is creating an increased interest in cislunar space. The need for fast and efficient methods of traversing the lunar vicinity in creases as more spacecraft enter the region. This investigation discusses methods of low thrust transfer design in order to create low cost and low time of flight transfers. Indirect optimization is employed to compute minimum energy and minimum fuel transfers in the circular restricted three body problem. Sigmoid smoothing techniques are leveraged to ap proximate the optimal bang-coast-bang solution with continuous functions. The minimum fuel solution is employed as an initial guess to target an inertially fixed thrust direction transfer. This process is applied to a variety of cislunar orbital transfer problems. Transfers are constructed between orbits in the L1 halo, L2 halo, distant retrograde, and L4 short period orbit families. The resulting trajectories are compared to impulsive and free transfers from the literature based on the required propellant mass and time of flight.