In-flight docking between unmanned aerial systems (UASs) is an essential capability for extending collaborative long-range missions. This work presents a planning strategy for a smaller multirotor UAS to autonomously dock with a non-stationary carrier/leader UAS in forward flight. Our method assumes the leader aircraft to be another multirotor, and first projects the hypotheses for its pose forward in time. Using a multi-objective cost function, we then solve an optimal control problem to obtain an interception trajectory to all these possible locations. We employ a cost formulation that allows us to generate piecewise smooth curves that favor different objectives during the course of the mission. Through a greedy strategy, the paths are iteratively refined online as the prediction is improved with new observations. We demonstrate and evaluate our method through a series of physics-based simulations with different operating conditions for both vehicles.