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The widespread use of unmanned aerial vehicles (UAVs) by the military,commercial companies, and academia continues to push research for autonomousvehicle navigation, particularly in varying environmental conditions andbeyond-line-of-sight (BLOS) applications. This article addresses trajectorygeneration for UAVs operating in extreme environments where the winddisturbances may exceed the vehicle's closed-loop stability bounds. To do this,a controller is developed that has two modes of operation: (1) normal mode, and(2) drift mode. In the normal mode the vehicle's thrust and sensor limitationsare not exceeded by environmental conditions, whereas in the drift mode theyare. In the drift mode, a drift frame that moves with the prevailing wind isestablished in which the vehicle maintains control authority to generate andtrack trajectories. The vehicle maintains control authority by relaxing theinertial frame trajectory tracking requirement and re-planning the trajectoryin the drift frame. Guarantees are established to ensure tracking of thetrajectory, collision avoidance, and respecting the vehicle thrust and sensorlimitations. Simulation results demonstrate the algorithm properties throughtwo scenarios. First, the performance of two quadrotors is compared where oneutilizes the drift mode and the other does not. Second, multiple vehiclesnavigate through two narrow openings between protected and windy environmentsto demonstrate on-board updates to navigation parameters based on environmentalconditions.

Trajectory Generation for UAVs in Unknown Environments with Extreme Wind Disturbances