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 semi-global 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.

Fault-tolerant attitude tracking control for rigid-flexible coupled spacecraft is studied in this article. Taking actuator faults, measurement errors of attitude and angular velocity, unmeasured modal displacements, model uncertainties, and external disturbances into consideration, an adaptive fault-tolerant attitude tracking control is designed. Then, based on the sequential Lyapunov method, the stability of the closed-loop system is analyzed showing that if the attitude and angular velocity measurement errors are bounded, then successively less conservative bounds on the attitude tracking error and the angular velocity error can be obtained.

This paper designs a novel 6-Degree-of-Freedom (6-DOF) relative motion control scheme for spacecraft proximity operations with quantitative precision (QP), which simultaneously focuses on strict convergence time and accuracy constraints. First, a modified dual quaternions based 6-DOF relative motion model for spacecraft proximity operations is proposed, which better keeps validity and clarifies the inheritance relationship with unit quaternions. Then, an original quantitative precision second-order temporal transformation (QPST-Trans) is proposed, ensuring the continuity and non-singularity of system signals and effectively avoiding the chattering and weakening of control inputs. Benefiting from QPST-Trans, a QP controller is designed with an innovative QPST-Trans function and a new robust term, which alleviates the input saturation phenomenon. With numerical simulations, it can be verified that the QP controller can drive spacecraft 6-DOF relative motion error to converge within the given accuracy before the designated convergence time even under input saturation faults.

In this paper, we consider the attitude tracking control problem for rigid spacecraft with external disturbances and model uncertainties. An attitude controller with prescribed time and prescribed error bound is proposed based on scaling transformation and back-stepping. The controller can drive the attitude tracking error of spacecraft converge into a prescribed-bounded region around the origin before the prescribed time with non-singular and continuous torque. Numerical simulations are carried out to evaluate the performance of the proposed controller.

This article investigates the coupled attitude and orbit tracking maneuver control problem of a spacecraft system in close space missions with model uncertainty, unknown disturbance, and input saturation. An adaptive compact control scheme with featuring of disturbance rejection and antiwindup is reported. First, the exponential coordinates on Lie group SE(3) are employed to describe the relative pose, which includes the relative position and attitude, and the tracking error system is established by introducing an instrumental error variable, which contains exponential coordinates and velocity tracking error. Then, a dynamic disturbance compensator is constructed based on the idea of internal model design to finely compensate for a class of unknown harmonic disturbances. Furthermore, a nonsingular auxiliary system is proposed to overcome input saturation, in which a time-varying parameter is introduced to improve the performance of the antiwindup auxiliary system. This parameter makes the closed-loop system possess two properties: the timeliness of saturation compensation and the asymptotic convergence of tracking errors. With the developed control law, the stability of the obtained feedback system is strictly proved by means of Lyapunov stability theory. Finally, the numerical simulation is carried out for an on-orbit servicing mission, which validates the effectiveness of the proposed integrated controller in solving the pose tracking control problem.

This article investigates the finite-time attitude tracking control problem of spacecraft with angular velocity sensor failures and actuator saturation. A model-free angular velocity observer is proposed first to reconstruct the unmeasurable angular velocity in finite time. Invoking the reconstructed information, a saturated finite-time attitude tracking controller is then designed via the fast terminal sliding mode control technique, while the Legendre polynomial-based neural network is incorporated to approximate the unknown nonlinear dynamics. The finite-time stability of the closed-loop attitude tracking system from the proposed observer and the controller is proved despite the external disturbances. The main feature of the proposed controller is that it can accomplish the attitude tracking maneuver without model and angular velocity information. Numerical and experimental results are presented to verify the effectiveness of the proposed scheme.