Finite-Time Disturbance Observer Based Fractional Order Nonsingular Terminal Sliding Mode Attitude Control of Satellites

This study presents a method for implementing rigid satellite output feedback control that considers dynamic uncertainties and external disturbances, all while avoiding the need for velocity state measurement. The dynamics of a rigid satellite are first represented using the modified Rodrigues parameter (MRP), and then transformed into Euler-Lagrangian form to provide the state-space representation of the dynamics. The availability of angular velocity data for practical applications is often limited by cost or technical limitations. Consequently, angular velocity is considered to be immeasurable. In order to minimize the need for extra mathematical calculations and the creation of separate observers to estimate uncertainties and system states, a finite time disturbance observer (third order sliding mode (TOSM) observer) was used to simultaneously estimate both uncertainties and system states. The main component of the suggested controller incorporates the fractional order nonsingular terminal sliding mode technique, which guarantees stability within a finite time and avoids chattering. The simulation results of the proposed methodology have been presented and compared with the results of techniques available in the literature, showcasing the efficacy of the method described in this study and the enhancement of the findings of previous relevant research.