Flatness-based control in successive loops of the attitude of reentry space vehicles

In this article, the control problem for the multivariable and nonlinear 6-DOF dynamics of the attitude of autonomous reentry space vehicles is solved with the use of a flatness-based control approach which is implemented in successive loops. To apply this control scheme, the state-space model of the 6-DOF attitude dynamics of the autonomous reentry space vehicles is separated into two subsystems, which are connected between them through 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 flat systems. The state variables of the second subsystem become virtual control inputs for the first subsystem. In turn, exogenous control inputs are applied to the second subsystem. The global stability properties of the control method are also proven through Lyapunov stability analysis. The proposed method achieves stabilization of the attitude dynamics of the space vehicle without the need of diffeomorphisms and complicated state-space model transformations.