Coordinated Standoff Tracking of Moving Targets: Control Laws and Information Architectures

In this paper, we present work on the control of autonomous vehicle formations in the context of the coordinated standoff tracking problem. The objective is to use a team of unmanned aircraft to fly a circular orbit around a moving target with prescribed intervehicle angular spacing using only local information. We use the recently introduced Lyapunov guidance vector field approach to achieve the desired circular trajectory. The contributions of this paper involve both single-vehicle path planning and multiple-vehicle coordination. For single-vehicle path planning, we complete a proof of heading convergence using feedback, which has thus far not been fully addressed in the literature. We also offer a novel approach for heading convergence that does not require continuous feedback in the ideal case (no wind, stationary target), taking advantage of an analytical solution for the guidance field. Further, we use a variable airspeed controller to maintain the circular trajectory despite unknown wind and unknown constant velocity target motion. Adaptive estimates of the unknown wind and target motion are introduced to ensure stability of the circular trajectory. A novel feature of our results is rigorous satisfaction of vehicle-specific kinematic constraints on heading rates and airspeed variations. For multiple-vehicle coordination, we again use a variable airspeed controller to achieve the prescribed angular spacing. We make a connection with some recent work that addresses information architecture in vehicle formations using rigid graph theory. Specifically, we discuss two types of information architectures, symmetric and asymmetric, and implement decentralized control laws that are based on these architectures. The information architectures are scalable in that the number of required communication/sensing links increases linearly with the number of vehicles. The control laws are decentralized in that they use only local information. [PUBLISHER ABSTRACT]