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The attitude tracking control problem of flexible spacecraft subjected to parameter uncertainties, time-dependent external disturbances, actuator input nonlinearity, and input actuator misalignment is investigated in this paper. Explicitly, the proposed strategy addresses the input actuator misalignment and dead-zone issues that increase the controller design difficulties. Initially, a new second-order sliding mode observer (SoSMO) using an extended state approach is developed by adding a correction function to improve observer performance to estimate unwanted system perturbations. Then, a distinct SoSMO-based integral-type sliding mode control (ISMC) structure is designed in a unified manner to guarantee the asymptotic stability of the closed-loop system. Comparative numerical simulations under input actuator misalignment, the dead-zone nonlinearity, external disturbance, and inertia uncertainty are performed to illustrate the effectiveness of the proposed controller. [ABSTRACT FROM AUTHOR]

Spacecraft attitude control employs quaternion representation to avoid singularity issues and obtain global maneuver stability. However, it has redundancy associated, resulting in dual equilibrium points. The attitude control may confront the unwinding phenomenon due to the presence of the equilibria. In this paper, an anti-unwinding controller for spacecraft stabilization in the presence of external disturbances and inertial uncertainties, angular velocity limit, actuator saturation and faults is presented. Specifically, a modified extended state observer (ESO) is designed to obtain total disturbance estimates of the rigid-body spacecraft. Auxiliary parameters are added in the design to avoid initial high estimates in the proposed ESO design resulting in faster convergence. The proposed disturbance observer is to release the assumption that requires the estimated disturbance to be constant or varying at slow rates. Using the ESO estimates, a particular back-stepping-SMC (ESO-BTSMC) controller is devised to formulate anti-unwinding control law for spacecraft stabilization. Lyapunov stability theory is employed to prove closed-loop stability of system and estimation error convergence. Comparative simulations are performed to demonstrate the performance of the proposed control scheme. It is found that the proposed control scheme gives smooth and precise control performance along with faster transient response. Additionally, it also alleviates the chattering phenomenon. [ABSTRACT FROM AUTHOR]

The paper discusses the effect of non-smooth dead-zone (NDZ), and input actuator misalignment (AMA) during spacecraft attitude tracking maneuver in presence of parametric uncertainties and external perturbations. Initially, the input AMA and NDZ models are formulated to transform spacecraft attitude model dynamics. Subsequently, a new second order disturbance observer (SODO) is devised to get the total disturbance. The observer is developed considering system perturbations as extended states, with an additional term Introduced to improve the observer performance. Finally, a distinctive integral sliding mode control (ISMC) law is developed and integrated with the proposed SODO to perform spacecraft attitude control operations. Comparative simulations are conducted on the spacecraft attitude control model with input AMA, NDZ, system parametric uncertainties and external disturbances to show the effectiveness of the proposed control structure. • A novel SODO-SMC control law is proposed in this work to attain precise attitude tracking of spacecraft subject to input AMA, NDZ, parameter uncertainty, and external disturbance. • The entire system perturbation is estimated via a new SODO. The proposed SODO improves performance with a corrective function. • An input AMA model for spacecraft attitude control is developed, considering the system fully-actuated. [ABSTRACT FROM AUTHOR]