Continuous time-varying sliding mode based attitude control for reentry vehicle

The attitude control for reentry vehicle is responsible for the robust operation to avoid the major deterioration from parametric uncertainties and external disturbances. Targeting these practical issues, both the cases with and without a priori knowledge of upper bound on the lumped uncertainty (i.e. the joint effect caused by external disturbance and inertia matrix uncertainty) are addressed, and correspondingly two continuous time-varying sliding mode based attitude controller design strategies are proposed to achieve the robust tracking of the attitude commands while alleviating the control chattering. Firstly, to deal with the case where the upper bound on the second derivative of the lumped uncertainty is known in advance, a nonlinear disturbance observer based continuous time-varying sliding mode control algorithm is developed so that the asymptotic stability of the closed system is guaranteed. Furthermore, in order to address the more practical case that the upper bound on the lumped uncertainty is unavailable, a continuous adaptive time-varying sliding mode control algorithm is derived with the related switching gains adjusted on-line, by which the trajectories of the closed-loop system are guaranteed to be uniformly ultimately bounded. Finally, the proposed strategies are applied to the attitude control of X-33 RLV in the reentry phase to illustrate the effectiveness of the theoretical results.