Bézier Curve Path Planning for Parafoil Terminal Guidance

Autonomous parafoil terminal guidance plays a critical role in landing accuracy but is inherently difficult due to underactuation and path disturbances caused by winds. Terminal path planners must generate flight paths that deliver the parafoil as close as possible to the destinationwhile landing into thewind.This paper presents a novel pathplanning scheme capable of highly general trajectory shapes that enable successful path planning from a wide set of initial conditions in constrained three-dimensional environments. The path-planning approach parameterizes the two-point boundary value guidance solution in the formof one ormoreBézier curves that connect the current parafoil location with a final approach point downwind of the target. Online nonlinear optimization of curve parameters allows for path regeneration given changing winds. Furthermore, generality of the trajectory shape provides a wide set of initial conditions at which terminal guidance may be initiated in obstacle-constrained scenarios, reducing coupling between landing accuracy and terrain constraints in the target area. Additional advantages include yawangle smoothness guarantees and ease of path-length optimization. Following a description of the path generator, sexdegree-of-freedom simulation results show example cases in which the path planner computes terminal guidance solutions in realistic terrain with changing winds. Monte Carlo simulations verify robustness of the proposed trajectory generation technique.