Optimal Rendezvous Scheduling for Charging Coordination Between Aerial-Ground Vehicles

In this article, we address a charger-assisted unmanned aerial vehicle (UAV) application in which the UAV must follow a long predefined route composed of an ordered sequence of points of interest. To support the UAV's limited flight range, an unmanned ground vehicle (UGV) serves as a mobile charger and can travel to designated charging locations to recharge the UAV's battery. Our objective is to generate a rendezvous schedule-that is, to determine where (locations) and when (times) the UAV and UGV should meet for recharging. The schedule is subject to the constraint that recharging may only occur at predefined charging sites, and that the UAV's flight time between consecutive charges must not exceed its maximum range. We formulate the scheduling problem as a minimum-time optimal control problem and demonstrate how its specific properties can be exploited to enable efficient solution via dynamic programming. The resulting algorithms are shown to be suitable for real-time applications across a wide variety of mission scenarios, accounting for factors such as landing type (docked or dockless), muling (enabled or disabled), charging time variability (fixed or varying), and final location constraints. Our approach scales effectively to large missions while ensuring mission time optimality.