We address the problem of steering multiple unmanned air vehicles (UAVs) alonggiven paths (path-following) under strict temporal coordination constraints requiring, forexample, that the vehicles arrive at their final destinations at exactly the same time. Pathfollowingrelies on a nonlinear Lyapunov based control strategy derived at the kinematic levelwith the augmentation of existing autopilots with L1 adaptive output feedback control laws toobtain inner-outer loop control structures with guaranteed performance. Multiple vehicle timecriticalcoordination is achieved by enforcing temporal constraints on the speed profiles of thevehicles along their paths in response to information exchanged over a dynamic communicationnetwork. We consider that each vehicle transmits its coordination state to only a subset of theother vehicles, as determined by the communications topology adopted. We address explicitlythe case where the communication graph that captures the underlying communication networktopology may be disconnected during some interval of time (or may even fail to be connectedat any instant of time) and provide conditions under which the closed-loop system is stable.Flight test results obtained at Camp Roberts, CA in 2008 and hardware-in-the-loop (HITL)simulations demonstrate the benefits of the algorithms developed.
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