Ascent trajectory optimization for stratospheric airships with thermal effects

Ascent trajectory optimization with thermal effects is addressed for a stratospheric airship. Basic thermal characteristics of the stratospheric airship and the energy equations about the ship film and the internal gas are introduced. Besides, the equations of motion for the airship include the factors about aerodynamic force, added mass and wind profiles which are developed based on horizontal-wind model. For minimum flight time, the trajectory optimization problem with the path and terminal constraints is constructed and then converted into a parameter optimization problem by a direct collocation method. In different scenarios, the optimal trajectories are developed by a numerical nonlinear solver, SNOPT. It is shown that the solutions are greatly affected by the thermal behaviors. For the minimum flight time trajectory, the thermal effects are discussed, and moreover, the numerical solutions show that different take-off time conducts the different control and state performances. Solar irradiation is the most important factor and, in addition, the natural wind also affects the thermal performance during ascent.