A real-time path planning algorithm is developed to generate time-optimal trajectory for helicopter shipboard landing. The trajectory optimization problem is translated to the lower dimensional Hal output space by exploiting the differential flatness property of the simplified helicopter model. Then, the flat outputs are parameterized using piece-wise spline functions with adjustable coefficients, which are used to shape the trajectory and approximate the optimal solution. Further, by allowing the flexible selection of each spline segment's time-duration and enforcing additional path constraints, the time-optimality of the planned trajectory is largely preserved without violation of state and input bounds. Compared to pure temporal discretization methods, the proposed algorithm employs considerably less decision variables and significantly reduces the computational time by 75%, which only leads to a 0.5% growth in the optimal flight time as the trade-off. The improvement in computational efficiency enables the real-time recalculation of the time-optimal trajectories on-the-fly if there are unforeseen deviations from the planned flight path.
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