Dynamically feasible trajectory and open-loop control design for unmanned airships

This paper describes a method for planning six DOF trajectories for an underactuated unmanned airship and for computing the open-loop controls. Beginning with a smooth inertial 3D trajectory to be tracked by the center of mass of the vehicle, the proposed algorithm, based on the dynamics of the system, provides the 3D corresponding body-fixed linear and angular velocities and the vehicle orientation, yielding a feasible 6 DOF trajectory. The derived trajectory is further used to compute the three available open-loop controls. Since the variables of the trajectory are consistent with the vehicle´s dynamics, a closed-loop tracking controller can significantly improve its performance incorporating these variables. Furthermore, examining the resulting open-loop controls, the designer can judge about the capability of the actuators to meet the requirements of tracking the specific trajectory.