Coordinated Standoff Tracking Using Path Shaping for Multiple UAVs

A coordinated standoff target tracking strategy using path shaping for multiple unmanned aerial vehicles (UAVs) is presented. In performing a tracking mission of a ground target of interest, UAVs are to approach a target and to keep a standoff distance from it with a prescribed inter-vehicle angular separation around the target in order to track it while acquiring accurate target information. Since fixed-wing UAVs without hovering capability fly efficiently at a nominal airspeed, it is desirable that they can keep angular separation between vehicles while holding a constant velocity in a mission duration point of view. The work presented here introduces a new path shaping technique using two constant curvature segments satisfying the turn radius constraint and having more flexibility and fewer discontinuous points on a curvature command compared with the Dubins path at the expense of the path length. Moreover, a simultaneous arrival concept is introduced as a coordinated tracking strategy for multiple UAVs, which initialises UAVs on a standoff orbit with a desired angular separation. In order to address arrival time delay or failure of the UAV, a two-orbit approach is proposed in which UAVs first arrive at the outer orbit and subsequently shrink to the desired inner orbit at different times, while adjusting the angular separation between constant-speed UAVs. The feasibility and benefits of the proposed approach are evaluated via numerical simulations for a ground target using two cooperative UAVs.