Time-Varying Non-Singular Terminal Sliding Mode Attitude Control of Reusable Launch Vehicle

Abstract

This paper proposes a time-varying non-singular terminal sliding mode attitude control of reusable launch vehicle in re-entry phase. The dynamics of the reusable launch vehicle is converted to state space form using the Lagrangian formulation. The state-space representation is used to design a nonlinear sliding manifold which is then modified with a time-varying function to obtain the time-varying non-singular terminal sliding manifold. Expression of equivalent control is obtained from the designed sliding manifold using the principles of sliding mode control theory. The total control input is obtained by the linear sum of equivalent control input and sliding control input. The finite time stability of the system is proved and the expression of convergence time is also derived using the Lyapunov theorem. The designed control ensures finite-time convergence at any user-specified time and also guarantees global robustness in the presence of external disturbances. The parameters of the time-varying function are obtained from the pre-specified convergence time. Numerical simulations are used to elucidate the effectiveness of the proposed control algorithm.