Objectives   Unmanned aerial vehicles (UAVs) can perform target identification and provide ships with detailed images of the target area. In order to realize the rapid data acquisition and unloading of UAVs as a means of high-altitude communication at sea, this paper proposes a 3D trajectory optimization method for UAVs based on the hp-adaptive pseudospectral method under multiple constraints with the goal of minimizing the communication task time.

  Methods  The method first models the dynamics of a fixed-wing UAV in 3D space and describes the trajectory optimization problem of its communication as a state-constrained optimal control problem. Based on the ship motion model, a channel model is established in combination with the positioning error of the moving target; considering the energy limitations of the UAV, the communication constraints and energy constraints are added on the basis of the original problem, and a trajectory optimization method based on the hp-adaptive Radau pseudospectral method is proposed, which transforms the original problem into a finite-dimensional nonlinear programming problem and solves it. The simulation analysis is carried out under five constraint scenarios, then compared with the results of the p-pseudospectral method.

  Results  Given positioning error, the UAV and ship can still communicate rapidly under various constraints.

  Conclusions  The results of this study provide an effective solution for maritime communication systems and provide references for the trajectory optimization problem in communication between UAVs and ships.