A Predefined-Time Extended-State Observer-Based Approach for Velocity-Free Attitude Control of Spacecraft

This article addresses the velocity-free attitude control problem for rigid spacecraft with bounded external disturbances. To obtain an accurate estimate of the spacecraft's velocities and external disturbances, a semiglobal practical predefined-time extended-state observer is presented in terms of a time-dependent scaling function. Next, a continuous and nonsingular sliding mode surface is designed, and a predefined-time observer is introduced to estimate the derivative of a term in the sliding mode surface. Then, a practical predefined-time velocity-free attitude control scheme is proposed for rigid spacecraft. The developed controller can ensure that the upper limit of the resulting settling time is predefined without dependence on initial conditions or any other parameters. One further salient feature of the present control approach is that a reduced magnitude of the applied control torques is required to achieve satisfactory attitude control performance. Finally, numerical simulation examples are conducted to show the effectiveness of the derived control scheme.