Design of minimum-time low-thrust transfer between quasi-periodic orbits

This paper develops a novel methodology for constructing time-optimal low-thrust transfers between quasi-periodic orbits (QPOs) in the vicinity of the libration points L₁ and L₂. Initial guesses for the optimization are derived from their heteroclinic connections found in a previous study. These heteroclinic connections are fuel-free transfer trajectories connecting the QPOs, and low-thrust control helps shorten their long time of flight by consuming more fuel. The minimum-time optimization problem is formulated as a successive convex optimization problem aided by time regularization. Time regularization replaces real time with fictitious time, allowing the real-time variable to be treated as one of the state variables. Thus, this technique enables the time of flight to be set as the objective function in the convex optimization scheme. Numerical results demonstrate the way to select a time regularization method appropriate for the optimization problem. Moreover, the time-optimal transfers with different thrust levels are investigated to understand the structure of optimal solutions.