Flatness-based control in successive loops for the 6-DOF autonomous stratospheric airship

Autonomous stratospheric airships find use in meteorological and defense missions. Such airships exhibit a highly complex and nonlinear kinematic and dynamic model. In this article the control problem of 6-DOF autonomous stratospheric airships is considered. Their joint kinematic and dynamic model for flight-path tracking in an earth-fixed coordinates frame is formulated in state-space form and is shown to be differentially flat. The control problem for the 6-DOF stratospheric airship is solved with the use of a flatness-based control approach which is implemented in successive loops. To apply the multi-loop flatness-based control method, the state-space model of the 6-DOF stratospheric airship is separated into subsystems, which are connected in cascading loops. Each one of these subsystems can be viewed independently as a differentially flat system and control about it can be performed with inversion of its dynamics as in the case of input–output linearized systems. The whole control method is implemented in successive loops and its global stability properties are also proven through Lyapunov stability analysis. The proposed method achieves stabilization and precise flight-path following for the 6-DOF stratospheric airship without the need for diffeomorphisms and complicated state-space model transformations. The method is computationally efficient and ensures through clear and simple implementation stages the inversion of the kinematic-dynamic model of the stratospheric airship and the stabilization of this aerial vehicle, as well convergence of its state variables to the targeted setpoints and precise tracking of flight reference paths by the airship’s center of gravity.