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This paper concentrates on robust attitude control issues for spacecraft formation in gravitational-wave detection missions. Notably, with the large-scale communication delays brought by the million kilometers-scale inter-satellite distance, the exponential convergence of the closed-loop delayed system is firstly achieved via a new delay-dependent nominal attitude coordinated control scheme. Then, a finite-time disturbance observer is deployed to reconstruct the unknown lumped disturbance from internal uncertainties and the external environment. Meanwhile, an integral sliding manifold is embedded in the delay-dependent attitude controller for superior systems' robustness. Finally, two simulation examples illustrate the feasibility and effectiveness of the proposed attitude control strategy for in-orbit gravitational-wave detection spacecraft systems. • Spacecraft formation attitude control in gravitational-wave detection is studied. • Large-scale communication delays (LCD) among formation members are firstly modeled. • An attitude coordinated controller is put forward to handle the LCD. • An integral sliding manifold with disturbance observer is embedded for superior robustness. [ABSTRACT FROM AUTHOR]

Abstract This paper investigates the fixed-time attitude tracking control problem for rigid spacecraft based on rotation matrix. Two anti-unwinding control schemes are developed such that the desired attitude can be tracked with bounded convergence time regardless of the initial conditions. The first controller is established on basis of a novel sliding mode surface without considering the external disturbance. In addition, the explicit description of the settling time can be provided under this controller. By revising the sliding mode surface and utilizing an adaptive law, the fixed-time stability can still be achieved under the second controller even in the presence of external disturbance. Theoretical analysis and numerical simulations are presented to demonstrate the validity of the proposed controllers. Highlights • Two attitude tracking controllers are designed for spacecraft. • Rotation matrix is used to construct the controllers. • Controllers in this paper are fixed-time stable. • Adaptive law is applied to deal with the external disturbances. [ABSTRACT FROM AUTHOR]

This paper studies a robust attitude coordinated control method for spacecraft formation flying system in the presence of external disturbances based on event-triggered control and sliding mode control. To decrease the communication frequency of the spacecraft formation flying system, a sliding mode coordinated controller without Zeno phenomenon is developed by using a novel triggering condition. For the first time, the proposed method addresses the problem that the existence of the closed-loop event-triggered control system solution in the classical sense may not be guaranteed due to the sliding mode surface with discrete variables fundamentally. The theoretical analysis and numerical simulation results demonstrate the effectiveness of the proposed control approach. • A novel method is developed for the theoretical analysis of the complex system based on ETC. • The existence of the closed-loop ETC system solution in the classical sense is guaranteed. • Both attitude consensus and angular velocity consensus are achieved without continuous communication among spacecraft. • A novel triggering condition is established based on exponential function and hyperbolic tangent function. [ABSTRACT FROM AUTHOR]

This paper presents a new image-based control scheme for spacecraft rendezvous and synchronization with an uncooperative tumbling target, which is capable of autonomously adjusting the camera focal length, in order to extend the working range of visual servoing and guarantee that the target remains within the camera field-of-view. Unlike conventional visual servoing, the new scheme is based on a system model that is invariant to changes in camera-intrinsic parameters. An active zooming strategy is proposed which ensures that the target remains in the image plane with a proper size during the visual servoing. By utilizing the image features as feedback information, a finite-time controller is designed, which is robust to the unknown target's motion as well as the external perturbations, with the ability to estimate and adapt to the upper bound of the uncertainties. The closed-loop system stability is proved using the Lyapunov theory. Simulation scenarios are studied for two different onboard cameras, namely, a fixed-focal-length camera and a zooming camera. In addition, a comparative study with a conventional sliding-mode controller is performed to evaluate the convergence and accuracy of the proposed control scheme. • Image-based spacecraft orbit–attitude control with zooming capability. • Far-range rendezvous and synchronization with uncooperative objects. • System model formulated in the invariant space. • Controller robust to unknown target motions and external perturbations. • Extensive simulation studies show superior performance. [ABSTRACT FROM AUTHOR]

This paper investigates the tracking and control problem of a spacecraft rendezvous with a non-cooperative and tumbling space target subject to parametric uncertainty and unknown external disturbances. The kinematics and dynamics of spacecraft position and attitude are described by dual quaternions. A novel adaptive sliding mode disturbance observer is proposed to track the pose of non-cooperative tumbling target without need for upper bounds of first and second derivatives of lumped disturbance. Based on the proposed observer, a finite time sliding mode control is developed in term of dual quaternion. Different from existing sliding mode control schemes, the conditions on the controller parameters bounds are relaxed. The stability and robustness of the overall closed-loop control is proved by the Lyapunov framework. The robustness and effectiveness of the proposed control scheme are validated by numerical simulations in comparison with existing approaches. • Track and control of spacecraft rendezvous with non-cooperative and tumbling targets. • Adaptive sliding mode disturbance observer. • Dual quaternion description of kinematics and dynamics of spacecraft. [ABSTRACT FROM AUTHOR]

Target capture is a fundamental and essential task of space robots for on-orbit servicing in the future. Accordingly, it is important to study the method for space robot stabilization after impact during target capture. In this paper, the stabilization control problem of a combined spacecraft after multiple impacts during target capture is studied. A dual-integral sliding mode (DISM) control method based on the reconfiguration of the reaction wheels is proposed. The stability control of the combined spacecraft is achieved by controlling the reaction wheels of the space robot to absorb the angular momentum arising from the impact. First, given the structure of the gripper, the contact detection algorithm and contact dynamics model are established, and then multiple impacts are simulated during the target capturing operation. Second, an improved sliding mode control method is proposed to overcome the influence of multiple impacts, and the stability of the controller is confirmed by the Lyapunov method. Third, through an optimization method, the configuration of the reaction wheels of the space robot is reconstructed to avoid control torque saturation. The validity and availability are eventually verified by simulations and experiments. The results show that the proposed method can achieve the stability of the combined spacecraft after the target capture, and the algorithm is robust and has engineering applicability. • The contact detection algorithm and contact dynamics model are established. • A dual-integral sliding mode control method is proposed to overcome the influence of multiple impacts. • The configuration of the reaction wheels of the space robot is reconstructed to avoid control torque saturation. [ABSTRACT FROM AUTHOR]

This paper addresses the problem of adaptive sliding mode attitude tracking control for a class of nonlinear flexible spacecraft systems with a redundant four reaction wheels' setting and unknown actuator dead-zone, where configuration misalignment and external disturbance are considered simultaneously. By using the Takagi-Sugeno (T-S) fuzzy modelling method, the overall nonlinear spacecraft attitude dynamics system is first reconstructed into several local linear systems. Then, an adaptive integral-type sliding mode control scheme is introduced based on a T-S fuzzy model to stabilize the considered attitude tracking control system of flexible spacecraft. In this design, the external disturbance with unknown bound is counteracted in real-time by the adaptive estimate technique. Additionally, the integral sliding surface we introduced is insured to be asymptotically stable under the condition of given matrix inequality. The proposed adaptive sliding mode controller guarantees the finite-time reachability of the specific sliding surface. A practical example with simulation results is given to verify the validity of the attitude tracking control strategy we put forward. • The flexible spacecraft attitude tracking control problem is investigated. • Configuration misalignment and input dead-zone are considered simultaneously. • A T-S fuzzy adaptive sliding mode control strategy is proposed. • The global asymptotical stability of attitude tracking errors is guaranteed. [ABSTRACT FROM AUTHOR]

This paper addresses the problem of suboptimal control for repointing maneuver of a staring-mode spacecraft where the optical axis is required to point to the target orientation. Different from the traditional reorientation maneuver, the angle of the spacecraft around the optical axis does not need to be controlled. First, a simple yet efficient representation for repointing error is introduced and kinematical descriptions are established correspondingly. Then, two different control algorithms are proposed for repointing control of a staring-mode spacecraft. The first one is the inverse optimal PD-like controller that drives the spacecraft to complete repointing maneuver and the optimality properties of the proposed control law are investigated by using dynamic programming theory. The other one is a control Lyapunov function (CLF) based suboptimal control scheme incorporated with the idea of equivalent control in sliding mode control theory. The switch mechanism between CLF control and sliding mode control is established where only one control switch is needed when the state reach the sliding surface. Compared with the classical CLF method, the sliding mode based CLF approach not only guarantees the optimality, but also enhances the system robustness against model uncertainties and disturbances. Finally, numerical investigations are conducted to demonstrate the utility and optimality of the proposed control algorithm. • The rotation of the spacecraft around the optical axis doesn't need to be controlled for repointing maneuver. • A new simple yet efficient attitude description for repointing maneuver is presented. • The PD like control law is optimal with respect to a meaningful performance index. • The sliding mode based CLF control approach improves the robustness and transient performance of the system. [ABSTRACT FROM AUTHOR]

This paper introduces an Optimal Fuzzy Sliding Mode (OFSM) controller for the control of fuel sloshing in a spacecraft during orbital maneuvers. In order to optimize controller's gains for minimizing control inputs, a Particle Swarm Optimization (PSO) algorithm is employed. A novel gain scheduling of the OFSM controller is developed for the coupled spacecraft-fuel system. Fuzzy gains are produced on-line based-on rules that utilize dynamic system variables and the sign of saturation function of sliding surfaces. The fuel slosh is modeled as a fixed spherical mass and two spherical pendulum masses moving in a spherical tank. Computer simulations illustrate the effectiveness of the proposed controller in maneuvering spacecraft while suppressing fuel sloshing. The performance of the OFSM controller is compared to that of the optimum State-Dependent Riccati Equation (SDRE) controller. • An Optimal Fuzzy Sliding Mode (OFSM) controller is designed for the control of fuel sloshing in 3D spacecraft maneuvers. • A Particle Swarm Optimization (PSO) algorithm is employed to optimize control gains. • The performance of the OFSM controller is compared to that of the optimum State-Dependent Riccati Equation (SDRE) controller. [ABSTRACT FROM AUTHOR]

Abstract This paper studies the relative position tracking and attitude synchronization problem of spacecraft rendezvous with the requirement of collision avoidance. To achieve the implementation of the rendezvous procedure, the docking port of the chaser is required to direct towards the counterpart of the target, while the relative distance between the two spacecraft should be larger than the radius of the danger zone during close proximity phase. In order to address the concerned problem, a novel sliding mode control strategy based on artificial potential function is developed, and more specifically, the sliding manifold of the close-loop system is chosen along the negative gradient of the artificial potential function. Within the Lyapunov framework, the proposed control laws are proved to guarantee the convergence of relative position and attitude errors while avoiding any accidental collision between the two spacecraft, even in the presence of external disturbance. Numerical simulations are carried out to demonstrate the effectiveness of the designed control laws. Highlights • Nonlinear relative pose control for spacecraft proximity operation with the requirement of collision avoidance is presented. • State feedback control laws are developed by employing artificial potential field and sliding mode technique. • A 6DOF simulation example is carried out to demonstrate the excellent performance of the proposed control laws. [ABSTRACT FROM AUTHOR]

High pointing accuracy and stabilization are significant for spacecrafts to carry out Earth observing, laser communication and space exploration missions. However, when a spacecraft undergoes large angle maneuver, the excited elastic oscillation of flexible appendages, for instance, solar wing and onboard antenna, would downgrade the performance of the spacecraft platform. This paper proposes a coupling control method, which synthesizes the adaptive sliding mode controller and the positive position feedback (PPF) controller, to control the attitude and suppress the elastic vibration simultaneously. Because of its prominent performance for attitude tracking and stabilization, the proposed method is capable of slewing the flexible spacecraft with a large angle. Also, the method is robust to parametric uncertainties of the spacecraft model. Numerical simulations are carried out with a hub-plate system which undergoes a single-axis attitude maneuver. An attitude control testbed for the flexible spacecraft is established and experiments are conducted to validate the coupling control method. Both numerical and experimental results demonstrate that the method discussed above can effectively decrease the stabilization time and improve the attitude accuracy of the flexible spacecraft. [ABSTRACT FROM AUTHOR]

Dual-arm space robots are more capable of implementing complex space tasks compared with single arm space robots. However, the dynamic coupling between the arms and the base will have a serious impact on the spacecraft attitude and the hand motion of each arm. Instead of considering one arm as the mission arm and the other as the balance arm, in this work two arms of the space robot perform as mission arms aimed at accomplishing secure capture of a floating target. The paper investigates coordinated control of the base's attitude and the arms' motion in the task space in the presence of system uncertainties. Two types of controllers, i.e. a Sliding Mode Controller (SMC) and a nonlinear Model Predictive Controller (MPC) are verified and compared with a conventional Computed-Torque Controller (CTC) through numerical simulations in terms of control accuracy and system robustness. Both controllers eliminate the need to linearly parameterize the dynamic equations. The MPC has been shown to achieve performance with higher accuracy than CTC and SMC in the absence of system uncertainties under the condition that they consume comparable energy. When the system uncertainties are included, SMC and CTC present advantageous robustness than MPC. Specifically, in a case where system inertia increases, SMC delivers higher accuracy than CTC and costs the least amount of energy. [ABSTRACT FROM AUTHOR]

Feasibility of achieving reliable control for spacecraft formation keeping and reconfiguration without the need for thrust in either the radial or along-track direction is explored in this paper. Analysis of the linearized dynamics without along-track input indicates the presence of an uncontrollable eigenvalue at the origin. A nonlinear controller is designed to indirectly stabilize the uncontrollable modes to a stable manifold around the equilibrium. Conditions for robustness against unmatched uncertainties and disturbances are derived to establish the regions of asymptotic stabilization. The benefits of the proposed control method are also validated via numerical simulations to show that precise formation maintenance can be achieved by dealing with the issues of system nonlinearities, variations in initial conditions, and external disturbances, concurrently. [ABSTRACT FROM AUTHOR]

Abstract: This paper addresses the synchronized control problem of relative position and attitude for spacecraft with input constraint. First, using dual quaternion, the kinematic and dynamic models of the six-degree-of-freedom relative motion of spacecraft are introduced. Second, a new adaptive sliding mode control scheme is proposed to guarantee the globally asymptotic convergence of relative motion despite the presence of control input constraint, parametric uncertainties and external disturbances. A detailed stability analysis of the resulting closed-loop system is included. Finally, simulation results are presented to illustrate the validity and effectiveness of the proposed controller, which has the following properties: (1) explicit accounting for the problem of input constraint, (2) fast convergent rate and accurate results can be obtained, (3) no chattering phenomenon is present in the control torque and control force, (4) self-adaptive regulation law is dynamically adjusted to ensure the tracking errors tend to zero asymptotically, (5) the upper bounds of unknown variables are estimated dynamically. [Copyright &y& Elsevier]

Abstract: This paper investigates the robust decentralized attitude control problem for spacecraft formations under uncertain communication topologies. Based on modified Rodrigues parameters representation and a Lagrange-like model, a class of decentralized attitude control schemes designed by the use of sliding mode control approach is proposed to steer the attitude of the spacecraft formation to a time-varying reference states with no assumption on the information exchange graph. By taking into account the model uncertainties and external disturbances simultaneously, the proposed robust control strategies are proven effective to overcome these unexpected phenomena. Finally, numerical examples are included to demonstrate the effectiveness and robustness of the developed control schemes. [Copyright &y& Elsevier]

Abstract: This paper addresses the tracking control problem of the leader–follower spacecraft formation, by which we mean that the relative motion between the leader and the follower is required to track a desired time-varying trajectory given in advance. Using dual number, the six-degree-of-freedom motion of the follower spacecraft relative to the leader spacecraft is modeled, where the coupling effect between the translational motion and the rotational one is accounted. A robust adaptive terminal sliding mode control law, including the adaptive algorithms, is proposed to ensure the finite time convergence of the relative motion tracking errors despite the presence of model uncertainties and external disturbances, based on which a modified controller is furthermore developed to solve the dual-equilibrium problem caused by dual quaternion representation. In addition, to alleviate the chattering, hyperbolic tangent function is adopted to substitute for the sign function. And by theoretical analysis, it is proved that the tracking error in such case will converge to a neighborhood of the origin in finite time. Finally, numerical simulations are performed to demonstrate the validity of the proposed approaches. [Copyright &y& Elsevier]

Abstract: This paper presents a general framework for synchronized multiple spacecraft rotations via consensus-based virtual structure. In this framework, attitude control systems for formation spacecrafts and virtual structure are designed separately. Both parametric uncertainty and external disturbance are taken into account. A time-varying sliding mode control (TVSMC) algorithm is designed to improve the robustness of the actual attitude control system. As for the virtual attitude control system, a behavioral consensus algorithm is presented to accomplish the attitude maneuver of the entire formation and guarantee a consistent attitude among the local virtual structure counterparts during the attitude maneuver. A multiple virtual sub-structures (MVSSs) system is introduced to enhance current virtual structure scheme when large amounts of spacecrafts are involved in the formation. The attitude of spacecraft is represented by modified Rodrigues parameter (MRP) for its non-redundancy. Finally, a numerical simulation with three synchronization situations is employed to illustrate the effectiveness of the proposed strategy. [Copyright &y& Elsevier]

Abstract: This paper presents a dual-stage control system design method for the rotational maneuver control and vibration stabilization of a flexible spacecraft. In this design approach, the sub-systems of attitude control and vibration suppression are designed separately using the low order model. Based on the sliding mode control (SMC) theory, a discontinuous attitude control law in the form of the input voltage of the reaction wheel is derived to control the orientation of the spacecraft, incorporating the L2-gain performance criterion constraint. The resulting closed-loop system is proven to be uniformly ultimately bounded stability and the effect of the external disturbance on both attitude quaternion and angular velocity can be attenuated to the prescribed level as well. In addition, an adaptive version of the control law is designed for adapting the unknown upper bounds of the lumped disturbance such that the limitation of knowing the bound of the disturbance in advance is released. For actively suppressing the induced vibration, strain rate feedback control method is also investigated by using piezoelectric materials as additional sensors and actuators bonded on the surface of the flexible appendages. Numerical simulations are performed to show that rotational maneuver and vibration suppression are accomplished in spite of the presence of disturbance and uncertainty. [Copyright &y& Elsevier]

Abstract: For the attitude stabilization of networked flexible spacecraft during large angle slew maneuver, a novel type of adaptive fuzzy sliding mode control (AFSMC) method for solving the dynamic model with network-induced delay, nonlinear and uncertain parameters is proposed in this paper. A novel and systematic sliding mode control (SMC) scheme, which integrates a time-advanced nonlinear predictor, is proposed to compensate for the network-induced delay and to overcome the negative effect of uncertainties. Then, an adaptive fuzzy system is used to approximate the strong coupling nonlinear dynamics between rigid hub and flexible appendages. Following that, the designed adaptive algorithms are developed in the sense of the Lyapunov stability theorem, so that system-tracking stability can be guaranteed. Finally, simulation results show that, with the application of the proposed method, not only high-precision attitude stabilization of flexible spacecraft is achieved, but also the elastic vibration of flexible spacecraft during maneuver is suppressed effectively, and the system is robust against system uncertainties, network-induced delays and any outer disturbances. [Copyright &y& Elsevier]

The purpose of this paper is to present a sliding mode control method that can be used to perform a spacecraft large angle maneuver with minimum time. An algorithm of minimum-time SMC is developed to provide the robust tracking control. The simulation results are compared with previous developed control schemes, eigenaxis quaternion regulator, to demonstrate the superiority of the proposed sliding mode control algorithm. [Copyright &y& Elsevier]