A hysteresis quantizer based artificial time delayed control strategy for re-entry phase of reusable launch vehicle

This work addresses the attitude tracking problem of reusable launch vehicle (RLV) in its re-entry phase under limited use of communication resources. The inherent nonlinear dynamics and challenging environmental conditions render the objective of navigating the RLV along a desired path to be a difficult task. In this regard, a time-delay based control (TDC) strategy with input hysteresis quantizer is proposed to achieve robustness against external disturbances and model uncertainties. The TDC approach utilizes input-output data of the immediate past instant for estimating the uncertainties effecting the space shuttle. While, the input quantizer discretizes the continuous TDC command to a finite set of predefined discrete levels. Thus, wireless transmission of control command to the actuator is carried out at a lower rate and obeys the communication constraint. Stability analysis using Lyapunov's method is carried out to demonstrate uniformly ultimately bounded (UUB) convergence of the system states on application of the proposed control scheme. Simulation studies have been included to highlight efficacy of the proposed control scheme in terms of robust tracking of the reference trajectory and control update reduction.