In this article, we consider the attitude tracking control problem for rigid spacecraft with bounded external disturbances. We propose a predefined-time predefined-bounded attitude tracking control scheme based on a nonsingular predefined-time sliding-mode manifold. The proposed controller is continuous and it can achieve predefined-time predefined-bounded stability. That is, the attitude tracking errors are driven to a predefined-bounded region around the origin within a predefined time, which can be set as a tuning parameter during the controller design, independently of initial conditions. Finally, numerical simulations are carried out to evaluate the performance of the proposed control law.

While there is ample research on hardware design and reconfiguration control for modular self-reconfigurable satellites, relatively few reconfiguration planning algorithms, especially algorithms used in real-world reconfiguration have been developed. Decentralized path planning, which only uses partial observation for each module to make decision is an important problem for real-world task. This article presents partially observable self-reconfiguration path planning, addressing the reconfiguration path planning problem for a single module using partial observations while aiming to maximize the policy learning efficiency. An end-to-end algorithm is proposed by employing a recurrent Q-learning algorithm and a deep neural network, where a Long Short Term Memory network is used to remember useful features from historical observations. Moreover, a 3-D convolutional neural network is used to automatically extract high-level features from observation data and is shown to significantly increase the learning efficiency. Experiments performed on a test rig of electromagnetic self-reconfigurable satellite verified the potency of the proposed algorithm.

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.