Multiple time scale sliding mode control of reusable launch vehicles in ascent and descent modes

A reusable launch vehicle control problem during ascent and descent is addressed via multiple-time scaled continuous sliding mode control. The proposed sliding mode controller utilizes a two-loop structure and provides robust decoupled tracking of both orientation angle command profiles and angular rate command profiles in the presence of bounded external disturbances and plant uncertainties, including aerodynamic surfaces and engine failures. Sliding mode control causes the angular rate and orientation angle tracking error dynamics to be constrained to linear, decoupled, homogeneous, and vector valued differential equations with desired eigenvalues. The dual-time scale sliding mode controller was designed for the X-33 technology demonstration sub-orbital launch vehicle in the ascent and descent modes. Simulation results show that the designed controller provides robust, accurate, decoupled tracking of the orientation angle command profiles in ascent and descent in presence of external disturbances and vehicle inertia uncertainties. The designed robust controller is to significantly reduce the time and cost associated with flying to new orbits, with new payloads, and with modified vehicles.