Standoff Target Tracking Guidance using Line-of-Sight Distance Bifurcation

Abstract

Unmanned aerial vehicle (UAV) applications that continue to receive significant attention are target acquisition and tracking. There exist many paths to track a stationary target from a prescribed altitude. The most widely used ones are straight lines and circular orbits. Circling a target at a constant radial distance is known as standoff tracking or circumnavigation. In this regard, an evolved requirement by the UAV is to reach a specified radial distance from the target within the stipulated time and continue circumnavigating the target with that radial distance. In doing so, it is desired that the UAV uses an easily computable guidance command with deterministic performance characteristics.

The thesis addresses the standoff target tracking problem by considering a modified two-parameter transcritical bifurcation in UAV-target line-of-sight distance dynamics. Appropriate choice of the bifurcation parameters results in the existence of a stable equilibrium point of the proposed line-of-sight distance dynamics which corresponds to the desired standoff radius. Further analysis relates the control parameters to the desired settling time, that is, the time taken by the UAV to settle on the desired standoff circle. A closed-form analytical expression is derived for the set of achievable settling times as a function of the two bifurcation parameters, the UAV speed, and initial separation. Simulation studies are carried out by considering a second-order heading-hold autopilot, a first-order speed control, and a limited turn rate for the UAV. Additional simulation studies are performed for realistic scenarios considering the presence of wind, noisy sensor measurements, and variable initial conditions. Simulation results demonstrate the robustness of the proposed guidance algorithm in achieving standoff target tracking with a constraint on the settling time. Overall, the proposed method offers a simple and easy-to-implement guidance solution.