Optimal trajectories of hypersonic vehicle for global reach

Both maximum glide trajectory and fuel-optimal cruise trajectory are investigated in this paper. Direct shooting method is introduced to convert the trajectory optimization problem into nonlinear programming problem. The optimization technique which combines the non-gradient-based optimization algorithm and gradient-based optimization algorithm is used for maximum range glide trajectory problem. The range of the optimal glide trajectory can be increased by 1.83% over the range of maximum lift-to-drag trajectory. The optimal periodic cruise problem is solved with the same aircraft model and the direct method. The initial guesses of the control variables for the optimal periodic cruise trajectory are given. The decrease of vehicle mass is considered. The optimal periodic cruise trajectory achieves a fuel savings of 4.75% over the global optimal steady-state cruise trajectory and the heat load for the optimal periodic cruise is 10.4% lower than that of global optimal steady-state cruise over one period. The result for long range periodic flight determined by this optimization procedure is consistent with the single period result. The performance of optimal periodic cruise is much better than that of maximum glide trajectory.