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An autonomous fault detection and fault-tolerant control solution combining Model Predictive Control (MPC) and Label Distributed Learning (LDL) is developed for the position tracking and attitude synchronization problems in autonomous satellite rendezvous and docking. The proposed algorithm can deal with center of mass (CM) variations and time-varying mass characteristics due to satellite fuel consumption, actuator saturation and fault, and external disturbances. Firstly, a six-degree-of-freedom (6-DOF) satellite translation-rotation coupling model was established to express the relative motion between the satellite and the target, taking the above factors into account. Subsequently, an on-board autonomous closed-loop fault-tolerant control algorithm using MPC is proposed, in which an LDL-based fault detection mechanism is embedded. The scheme specifies that propulsion faults are estimated by calculating the difference between the MPC's prediction of the satellite's future state and the measured change in the actual state. And the mapping matrix between the commanded force/torque and the actual force of the propulsion system is updated in real time to achieve autonomous fault detection and compensation on board the satellite. Among them, the LDL-based fault detection scheme is trained offline. It requires only simple matrix operations for on-orbit use, which is low-cost and suitable for resource-limited space environments. The additional creation of a time-varying disturbance observer allows the estimation and compensation of unmodelled errors and external disturbances. The stability of the proposed fault-tolerant control algorithm is rigorously demonstrated using Lyapunov analysis. Finally, numerical simulations show that the proposed method can successfully achieve autonomous satellite docking under different combinations of thruster faults. [ABSTRACT FROM AUTHOR]

This paper proposes a Multiplexed MPC algorithm for the dual-rate piecewise affine (PWA) model to control the attitude of a low-Earth-orbit (LEO) moving mass satellite. Although still facing an inherent inertial disturbance problem, the moving mass technology is a promising way to counter the strong aerodynamic torques in LEO. To make the satellite attitude fully actuated, a magnetorquer is used to cooperate with the moving mass system, resulting in a two-input control system. Through a strategy that updates inputs asynchronously, the proposed algorithm effectively balances the inertial disturbances caused by mass motions, the system's dynamic performance, and the controller's computational complexity. Error attitude kinematic and dynamic equations are derived, to convert the tracking problem into an equivalent regulation problem. The PWA approximation is used to transform the nonlinear attitude control equations described by error modified Rodrigues parameter to a linear state-space model for MPC design. Then, a new form of Multiplexed MPC, namely dual-rate PWA-MMPC, is developed for this dual-rate PWA model, which updates two control inputs at different rates. Despite only finding sub-optimal solutions to the original problem by stability analysis, this algorithm outperforms other control strategies through its ability to coordinate multiple inputs, deal with constraints, and reduce computational complexity. Hardware-in-the-loop simulations are conducted to demonstrate the effectiveness of the proposed methodology for the attitude control. [ABSTRACT FROM AUTHOR]

The rapid attitude manoeuvre is a control challenge for a CubeSat in low magnetic environments, which include lunar orbits, geosynchronous (GEO) orbits or other higher Earth orbits. Therefore, a rapid attitude manoeuvre control method based on the segmented sliding mode was proposed for CubeSat in a low magnetic environment. The segmented sliding mode control algorithm was applied to the CubeSat attitude manoeuvre control, where the segmented sliding mode surface was designed to guarantee fast convergence to the origin point of the whole attitude manoeuvre process, and the hyperbolic tangent function was used in the reaching law of the controller to alleviate reaction saturation of the wheels. In addition, innovative control strategies were proposed for the hybrid actuators of the reaction wheels and microthrusters, and a guide rail of the microthruster was innovatively designed to move the microthruster to offset the change in moment of inertia caused by propellant consumption. Finally, hardware-in-loop simulation results reveal that our method has a stronger anti-saturation ability and faster manoeuvre speed than the traditional control method, and the operational life cycle of the thrusters can be accordingly increased. [ABSTRACT FROM AUTHOR]

The orbital manoeuvre of a CubeSat is an essential ability in the process of constellation deployment and other missions. Therefore, an attitude control method based on piece-wise affine (PWA) MPC was proposed for CubeSats during orbital manoeuvres. Then, a solid thruster with high thrust that was previously applied only to large and traditional satellites was innovatively applied to CubeSats for orbital manoeuvres. However, the solid thruster with high thrust has a large eccentric torque from the thrust deviation, so it will cause rapid attitude rolling and result in orbital manoeuvre mission failure. Hence, PWA-MPC strategy with the disturbance observer was designed, which can solve the eccentric torque problem and achieve high accuracy attitude control by a hybrid actuator composed of momentum wheels and a cold gas thruster. In addition, during the orbital manoeuvre process, propellant consumption results in a continuous change in the moment of inertia of a CubeSat. In order to offset this change, the guide rail of the cold gas thruster was innovatively designed to move the cold gas thruster in the working process of the solid thruster. Finally, real-time hardware-in-loop simulation results show that the PWA-MPC strategy has higher attitude stability than those of other MPC strategies in the orbital manoeuvre process of a CubeSat and deserves to be applied. [ABSTRACT FROM AUTHOR]