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This paper is devoted to real-time optimal attitude reorientation control of rigid spacecraft control. Particularly, two typical practical problems - actuator misalignment and forbidden pointing constraints are considered. Within the framework of adaptive dynamic programming (ADP), a novel constrained optimal attitude control scheme is proposed. In this design, a special reward function is developed to characterize the environment feedback and deal with the pointing constraints. Notably, a novel argument term is introduced to the reward function for overcoming the inevitable difficulty in actuator misalignment. By virtue of the Lyapunov stability theory, the ultimate boundedness of state error and the optimality of the proposed method can be guaranteed. Finally, the effectiveness and performance of the developed ADP-based controller are evaluated by not only numerical simulations but also experimental tests with a hardware-in-loop platform.

This paper proposes a neural network-based fault diagnosis scheme to address the problem of fault isolation and estimation for the Single-Gimbal Control Moment Gyroscopes (SGCMGs) of spacecraft in a periodic orbit. To this end, a disturbance observer based on neural network is developed for active anti-disturbance, so as to improve the accuracy of fault diagnosis. The periodic disturbance on orbit can be decoupled with fault by resorting to the fitting and memory ability of neural network. Subsequently, the fault diagnosis scheme is established based on the idea of information fusion. The data of spacecraft attitude and gimbals position are combined to implement fault isolation and estimation based on adaptive estimator and neural network. Then, an adaptive sliding mode controller incorporating the disturbance and fault estimation results is designed to achieve active fault-tolerant control. In addition, the paper gives the proof of the stability of the proposed schemes, and the simulation results show that the proposed scheme achieves better diagnosis and control results than compared algorithm.

For high-resolution imaging implementations, the spacecraft attitude tracking control accuracy is crucial to determining the imaging quality. This investigation addresses the attitude tracking issue of imaging spacecraft subject to system uncertainties (unavailable inertia tensor, unexpected disturbances, and actuator faults). An adaptive sliding mode control (SMC) strategy is proposed to guarantee practical fixed-time closed-loop stability even in the presence of system uncertainties. Unlike existing methodologies, the sliding mode surface is developed to satisfy a novel sufficient condition of fixed-time stability. The sliding manifold design also circumvents the unwinding phenomenon arising in quaternion representations. Particularly, this controller is developed to generate a smooth control profile by using a new parameter update law. Rigorous Lyapunov analyses are further employed to ensure the fixed-time closed-loop stability irrespective of the system initial states. Finally, numerical examples are performed to demonstrate the feasibility and highlight the inherent features of the derived control law.

This article details the development and evaluation of a practical solution for path-constrained proximity maneuvers of spacecraft. Whereas no velocity measurement is utilized within the feedback structure, the controller rigorously enforces actuator magnitude constraints. Specifically, the control algorithm is constructed from a potential function method repelling the spacecraft from possible collisions. The proposed controller can guarantee potential functions to be navigated to the origin and thus overcome the stubborn local minima problem. Moreover, the control capability under any given control limit can be estimated and adjusted by changing the feedback gains. The specific performance with guaranteed safety can be also explicitly calculated by designers. The results are obtained through a Lyapunov-based stability analysis to prove uniformly ultimate boundedness. Numerical simulation results illustrate the performance and features of the developed control method.

This article addresses the formation tracking control problem for multiple spacecraft systems subject to limited communication resources and external disturbances. Considering that only a subset of the follower spacecraft can have access to the motion states of the dynamic leader, an event-based distributed observer is first developed to reconstruct the leader's information. Subsequently, to achieve the accompanying flight of the follower spacecraft around the leader with a desired formation configuration, for each follower spacecraft, a distributed event-triggered coordinated controller is proposed. In particular, by embedding simultaneously the position information and observer output into the triggering function, a novel unified event-triggered mechanism is designed to schedule information transmission in multiple spacecraft systems. The salient characters of the distributed coordinated control scheme are twofold: unnecessary occupancy of communication resources can be avoided significantly; and asymptotic stability of the whole closed-loop system is guaranteed without resorting to the separation principle. Finally, numerical simulations are carried out to illustrate the efficiency of the theoretical results.

In this article, a novel pose (i.e., concurrent position-attitude) tracking control framework is proposed for spacecraft proximity operations with a freely tumbling target, employing the prescribed performance control (PPC) methodology. Especially, the whole operations involved are divided into two synchronously occurring maneuvers: relative position tracking and boresight pointing adjustment. For the former, a new relative translational dynamics is established to facilitate its problem formulation and solving, while, for the latter, the desired attitude is extracted to align the boresight of the pursuer’s onboard vision sensor toward the target. Given this, a noncertainty-equivalence adaptive pose controller is designed based on the PPC design approach integrating a class of appointed-time performance functions. It is shown that the designed controller is able to achieve prescribed performance guarantees for the pose tracking errors and, meanwhile, guarantee asymptotic convergence of both the velocity and angular velocity errors, regardless of mass and inertia uncertainties. The salient feature of the proposed method is that, by judiciously imposing the performance specifications on the pose tracking errors, it can: 1) enable the pursuer to accomplish the proximity operations in a designer-appointed time and 2) ensure compliance with spatial motion constraints and avoid singularity of the attitude extraction algorithm. Finally, simulation results are presented to illustrate the effectiveness of the proposed method.

This paper addresses the relative position coordinated control problem for spacecraft formation flying under an undirected communication graph, whilst considering mass uncertainties, external disturbances, and limited communication resources. A new event-triggered information transmission mechanism is first presented, where each spacecraft only requires accessing to the states of neighbors intermittently. Subsequently, a novel event-based coordinated control scheme is proposed by combining a smooth adaptive projection rule that confines the parameter estimations to well-defined bounded convex hypercubes. Under the proposed control framework, the information exchange among spacecraft occurs only when the specified event is triggered, thereby significantly reducing the communication load and saving the onboard resources. Furthermore, a positive lower bound on interevent time intervals is guaranteed to exclude Zeno behavior. By virtue of Lyapunov stability analysis and graph theory, it is proved that the relative position tracking errors can converge to small invariant sets around the origin, and that all closed-loop signals are bounded, even in the presence of mass uncertainties and external disturbances. Finally, numerical simulations are given to evaluate the effectiveness and highlight the advantages of the developed control algorithm.

This paper addresses the attitude-maneuver control problem for a rigid-body spacecraft in the presence of attitude-constrained zones as well as input saturation. More specifically, attitude-constra...

This brief examines the problem of attitude tracking control with prescribed performance guarantees for a spacecraft subjected to actuator faults and input saturation. To pursue this, the open-loop tracking error dynamics with certain designer-specified performance constraints is first transformed into an equivalent “state-constrained” one, via an error transformation; furthermore, the resulting dynamics is augmented with a dynamic system, which is tactfully constructed to ensure that the control input satisfies the magnitude limits. Subsequently, a robust fault-tolerant controller is developed by using a low-pass filter and an auxiliary system in conjunction with adaptive backstepping design. It is shown that the control algorithm developed not only achieves the stable attitude tracking with prescribed behavioral metrics but also guarantees the boundedness of all the closed-loop signals. Finally, simulation results are given to evaluate the efficacy of the proposed scheme.

This paper is devoted to attitude tracking control of fractionated spacecraft with wireless communication. We consider the practical case that the spacecraft suffers from uncertain inertia parameters, external disturbances, and even unknown and time-varying actuator faults. Within the framework of the backstepping method, a novel event-triggered adaptive fault-tolerant control scheme is proposed. In our design, an event-triggering mechanism is introduced to determine the time instants for communication, which successfully avoids continuous communication and Zeno phenomenon. Then, with the aid of a bound estimation approach and a smooth function, the impacts of the actuator faults, as well as the network-induced error, are effectively compensated for. Moreover, by employing the prescribed performance control technique, it is shown that the attitude tracking errors can converge to predefined arbitrarily small residual sets with prescribed convergence rate and maximum overshoot, no matter if there exist unknown actuator faults. Compared with conventional adaptive attitude control schemes, the proposed scheme significantly reduces the communication burden, while providing high reliability and stable, rapid, and accurate response for attitude maneuvers. Simulation results are presented to illustrate the effectiveness of the proposed scheme. This work was supported in part by the National Natural Science Foundation of China under Grant 61673036, Grant 61661136007, and Grant 61603021, in part by the Beijing Natural Science Foundation under Grant 4182036, and in part by the Program for Changjiang Scholars and Innovative Research Team under Grant IRT_16R03.

This work mainly discusses the attitude tracking issue of spacecraft which ensures fixed-time convergence property. To achieve this, the attitude tracking dynamics model is first established. Then a novel sliding manifold is constructed based on the presented sufficient condition of fixed-time stability. Moreover, a sliding mode controller is developed to ensure fixed-time convergence. Also, the closed-loop fixed-time stability of the whole system is proven to be guaranteed based on Lyapunov stability theory. Finally, the simulation results are provided to verify the superior performance of the designed controller.

This paper investigates the relative position coordinated control problem for a group of formation flying spacecraft under a directed communication network and resource constraints. An event-based coordinated control scheme without resorting to neighbors’ velocity information is proposed to achieve the formation-keeping maneuvers. Considering expensive communication cost in spacecraft formation, a novel event-triggered mechanism is developed, where the information transmission among spacecraft is established only when the defined triggering threshold is exceeded; moreover, each spacecraft only needs to compute its own control command at triggering time instants, thus ameliorating the issue of computation limitation inherent in the space-qualified microprocessor. Apart from the above, an explicit positive lower bound on the inter-event time internals is rigorously guaranteed such that no Zeno behavior exhibits. By resorting to the input-to-state practical stability and Lyapunov theory, a sufficient criterion on parameters selection is derived to ensure that the overall closed-loop system is uniformly ultimately bounded stable. Finally, numerical simulations are carried out to demonstrate the effectiveness of the theoretical results.

This paper investigates the six-degrees-of-freedom (6-DOF) rendezvous and docking issue with an uncontrolled target for a servicing spacecraft under thruster misalignment and external disturbances. Initially, a 6-DOF relative motion dynamic model is established to depict the relative position–attitude between the servicing spacecraft and uncontrolled object (freely tumbling spacecraft). Then, an adaptive fixed-time control scheme with a novel sliding manifold is employed to accomplish the 6-DOF rendezvous (close-range) and docking mission for the servicing spacecraft. Unlike existing methods, the sliding-mode surface is designed by using the new sufficient condition to achieve the system's fixed-time convergence, and this condition reduces the conservativeness of the traditional ones with less dominated terms. Moreover, the settling time of relative translation-rotation tracking errors is guaranteed irrespective of initial motion conditions. Accordingly, the fixed-time stability of the closed-loop system is guaranteed by the rigorous Lyapunov theory analysis. Finally, numerical simulation results with various cases are implemented to verify the superiority of the presented sliding-mode control strategy.

This paper proposes a reinforcement learning (RL)-based six-degree-of-freedom (6-DOF) control scheme for the final phase proximity operations of spacecraft. The main novelty of the proposed method are from two aspects: 1) the closed-loop performance can be improved in real-time through the RL technique, achieving an online approximate optimal control subject to the full 6-DOF nonlinear dynamics of spacecraft; 2) Nontrivial motion constraints of proximity operations are considered and strictly obeyed during the whole control process. As a stepping stone, the dual-quaternion formalism is employed to characterize the 6-DOF dynamics model and motion constraints. Then, an RL-based control scheme is developed under the dual-quaternion algebraic framework to approximate the optimal control solution subject to a cost function and a Hamilton-Jacobi-Bellman equation. In addition, a specially designed barrier function is embedded in the reward function to avoid motion constraint violations. The Lyapunov-based stability analysis guarantees the ultimate boundedness of state errors and the weight of NN estimation errors. Besides, we also show that a PD-like controller under dual-quaternion formulation can be employed as the initial control policy to trigger the online learning process. The boundedness of it is proved by a special Lyapunov strictification method. Simulation results of prototypical spacecraft missions with proximity operations are provided to illustrate the effectiveness of the proposed method.

This article considers the connectivity preservation coordinated control problem for multiple spacecraft systems subject to limited communication resources and sensing capability. By constructing a novel bump function, a distance-dependent dynamic communication network model is first presented, which characterizes the interaction strength as a nonlinear smooth function varying with the relative distance of spacecraft continuously. Subsequently, based on an edge-tension potential function, a distributed event-driven coordinated control scheme is proposed to achieve formation consensus, while ensuring that adjacent spacecraft is always within the allowable connectivity range. Meanwhile, to avoid redundant data transmissions, a hybrid dynamic event-triggered mechanism with maximum triggering interval is developed to schedule the communication frequency among spacecraft. It is proven that the onboard communication resources occupation can be reduced significantly and the Zeno phenomenon is strictly excluded. Finally, the efficiency of the proposed method for, as an example, four-spacecraft formation system is substantiated.

A novel adaptive control solution for pose tracking problems of spacecraft proximity operations subject to not only motion constraints but also parameter uncertainties is proposed in this paper. Sp...

This work addresses the problem of observer-based closed-loop attitude stabilization in the presence of actuator faults, reaction wheel friction and external disturbances. As a stepping stone, an iterative learning disturbance observer (ILDO) is developed to estimate and compensate for the synthetic disturbances mentioned above. Specially, this ILDO does not need complex faults isolation operations or require knowledge related to these uncertainties. Furthermore, a typical proportional-derivative controller incorporating with the presented ILDO is employed to realize attitude stabilization for spacecraft subject to the actuator failures and uncertainties. The significant feature of the proposed strategy is that the uniformly ultimately bounded stability of the overall closed-loop system with observer-controller architecture could be guaranteed. The effectiveness and robustness of the developed scheme are investigated via a set of numerical simulations and analyses. Particularly, an experimental verification involving a hardware-in-loop platform is further provided to validate the engineering feasibility of the proposed strategy.

This paper addresses the approaching trajectory control problem for the final phase of non-cooperative spacecraft proximity operations in the presence of disturbances and even input saturation. As a stepping stone, a novel line-of-sight tracking model is developed to describe attitude maneuver towards the target in the proximity. Then, a two-stage artificial potential function is employed to enable the pursuer spacecraft to comply the safety trajectory during approaching the target. In each stage, gradients of potential function are analyzed and the local minimum problem associated with potential function can be addressed. Furthermore, a saturated control law is proposed to ensure a reliable real-time tracking measurement of the target, and the controller rigorously enforces safe path and actuator magnitude constraints. The associated stability proof is accomplished through Lyapunov method. Simulations are carried out to evaluate the effectiveness of the proposed method.

A new algorithm is proposed for rigid spacecraft attitude reorientation guidance under forbidden pointing constraints. Specifically, in view of the parameterized forbidden orientations using the un...

This paper considers the fixed-time translational operation control issue for the spacecraft rendezvous task with a free-tumbling target. The translation dynamics model of the rendezvous mission under actuator misalignments is first established in the line-of-sight coordinate frame. Then, a novel time-varying sliding mode surface is constructed and a control scheme with the sliding manifold is proposed to achieve the fixed-time convergence of relative parameters’ tracking errors. It is interesting that the preceding convergence time can be altered explicitly according to the specific rendezvous requirements. Meanwhile, a modified updating strategy is developed to ensure system's fixed-time convergence property in the presence of lumped uncertainties (external disturbance and actuator misalignments). The associated stability proof is constructive and accomplished by the development of a Lyapunov function candidate. Finally, numerical simulations on rendezvous missions are performed to demonstrate the effectiveness and the superiorities of the designed fixed-time control scheme.

This paper is devoted to adaptive attitude tracking control for rigid spacecraft in the presence of parametric uncertainties, actuator faults and external disturbance. Specifically, a dynamic model is established based on one-tank spacecraft, which explicitly takes into account changing Center of Mass (CM). Then, a control scheme is proposed to achieve attitude tracking. Benefiting from explicitly considering the changing CM during the controller design process, the proposed scheme possesses good robustness to parametric uncertainties with less fuel consumption. Moreover, a fault-tolerant control algorithm is proposed to accommodate actuator faults with no need of knowing the actuators’ fault information. Lyapunov-based analysis is provided and the closed-loop system stability is rigorously proved. Finally, numerical simulations are presented to illustrate the effectiveness of the proposed controllers. Keywords: Adaptive control, Attitude tracking, Changing center of mass, Fault-tolerant, Spacecraft

This brief investigates the problem of finite-time output feedback control for spacecraft attitude stabilization without angular velocity measurement. First, two new sufficient conditions for finite-time ultimate boundedness and local finite-time stability are derived, which reduce the conservativeness of the traditional conditions. Then, based on the two new sufficient conditions of the finite-time stability, a finite-time observer is proposed to estimate the unknown angular velocity by using the quadratic Lyapunov function method. Next, a finite-time attitude controller is designed based on the estimate of the angular velocity. The finite-time stability of the entire closed-loop system is analyzed through the Lyapunov approach. The rigorous proof shows that the observation errors and the spacecraft attitude will converge to a residual set of zero in finite time. Numerical simulation results illustrate the effectiveness of the proposed strategy.

Plug-and-play technology is an important direction for future development of spacecraft and how to design controllers with less communication burden and satisfactory performance is of great importance for plug-and-play spacecraft. Considering attitude tracking of such spacecraft with unknown inertial parameters and unknown disturbances, an event-triggered adaptive backstepping controller is designed in this paper. Particularly, a switching threshold strategy is employed to design the event-triggering mechanism. By introducing a new linear time-varying model, a smooth function, an integrable auxiliary signal and a bound estimation approach, the impacts of the network-induced error and the disturbances are effectively compensated for and Zeno phenomenon is successfully avoided. It is shown that all signals of the closed-loop system are globally uniformly bounded and both the attitude tracking error and the angular velocity tracking error converge to zero. Compared with conventional control schemes, the proposed scheme significantly reduces the communication burden while providing stable and accurate response for attitude maneuvers. Simulation results are presented to illustrate the effectiveness of the proposed scheme. Keywords: Adaptive control, Attitude tracking, Event-triggered control, Spacecraft, Uncertainties

This work investigates the challenging problem of fast robust fault tolerant attitude control for spacecraft to handle external disturbances, actuator failures and misalignments. More specially, a novel nonsingular terminal sliding mode based finite-time extended state observer is first designed to estimate and compensate for the lumped system faults or uncertainties. And the proposed extended state observer is analysed and proved to be stable in the sense of fast finite-time uniformly ultimately bounded stability. Then, utilizing the techniques of super-twisting and terminal sliding mode control synthetically, a novel continuous attitude control algorithm is developed. The finite-time stability of the closed-loop attitude control system is proved by using a continuously-differentiable, homogeneous and strict Lyapunov function. And also the proposed control scheme is continuous with the property of chattering restraining. Finally, some numerical simulation results are shown to verify the effectiveness and superior performances of the spacecraft attitude stabilization control system driven by the proposed fast robust fault tolerant attitude control scheme.

This work develops a novel disturbance observer and integral sliding mode technique based fault tolerant attitude control scheme for spacecraft, which is subject to external disturbance torques and actuator failures. More specifically, a simple and novel finite-time disturbance observer is first designed to reconstruct the synthetic uncertainty deriving from actuator failures and disturbances, by which the synthetic uncertainty is also compensated or restricted. Then, an integral sliding mode based finite-time fault tolerant attitude stabilisation controller incorporating with an adjusting law is investigated to ensure the closed-loop attitude control system converge to the stable region in finite time. And also the finite-time stability of the closed-loop attitude control system driven by the proposed attitude control scheme is analysed and proved utilising Lyapunov methodology. Finally, a simulation example for a rigid spacecraft model is carried out to verify the effectiveness and superiority of the proposed attitude control approach.

For the on-orbiting spacecraft, the accurate and reliable ACS is very important and necessary for the accomplishment of the aerospace missions, such as attitude stabilization, high-precision pointing, attitude tracking or maneuver.

This chapter gives a brief introduction to the attitude kinematics and dynamics of a rigid spacecraft, as well as some related basic knowledge.

In practical applications, the external disturbances and uncertainties are always exist for the spacecraft attitude control system.

Attitude control of a rigid spacecraft has attracted tremendous attention for the capability of achieving operational services, such as remote sensing, communication and variety of space-related research.

The six degrees of freedom (6DOF) control problem for spacecraft proximity operations is addressed in this work. During the docking process, the field-of-view constraint of the chaser is required to be satisfied, and both the position and attitude of chaser are required to track with the target simultaneously. More specifically, the integrated translational and rotational error dynamics are developed first, and a novel artificial potential function (APF) is designed involving the motion constraint information. Based on this, a feedback control law is proposed to ensure the chaser can reach the desired docking position and attitude with no violation of the constraint. The analysis for the proposed APF and the stability of the system are given based on Lyapunov theorem. Finally, numerical simulations are conducted to illustrate the effectiveness of the proposed control scheme.

In this paper, an attitude maneuver problem for an underactuated spacecraft is studied subject to one conical forbidden pointing constraint. The torqueless axis is assumed fixing in one direction of the spacecraft body. The constrained maneuver is achieved by planning two steps of principle Euler rotations. For prospects of less rotation path, two categories of planning solutions, i.e. internal and external tangency, are obtained respectively. Furthermore, a special control law is developed to track the planning trajectory. Finally, numerical simulations are conducted to validate the effectiveness of the planning scheme.

The pose estimation of non-cooperative space-borne object is of vital importance for on-orbit service and spacecraft approaching missions. Based on images taken by a monocular camera, an estimate algorithm is proposed to estimate the relative position and the relative attitude of non-cooperative spacecraft. The approach utilizes the off-the-shelf target detection network and key point regression network to predict 2D key points coordinates and combines the multiple view triangulation to reconstruct 3D model. Nonlinear least squares method is used to minimize 2D-3D corresponding coordinates to predict position and attitude. The proposed method effectively combines deep learning and geometric optimization algorithms, which is an innovative application of deep learning in the aerospace field. Finally, simulations are performed to prove the effectiveness of the theoretical results.

The attitude tracking control problem of a rigid spacecraft with actuator saturation is investigated in this paper. A finite-time attitude tracking control scheme is presented by incorporating sliding mode control (SMC) and adaptive technique. Specifically, a novel time-varying sliding mode manifold is first developed that aims at regulating the attitude tracking error to equilibrium point within a certain finite time. Moreover, it can be specified a priori by the designer according to the mission requirement. Subsequently, an adaptive controller is derived by using the SMC in conjunction with adaptive technique. The designed controller is capable of ensuring that the state trajectories reach to sliding regime within a finite time, and hence that attitude tracking error can converge to zero in a finite time with the aid of the developed sliding dynamics, despite the presence of exogenous disturbances, unknown inertia properties and saturation nonlinearities. Finally, the simulation experiments are carried out to demonstrate the effectiveness of the proposed control scheme.

This paper addresses the problem of designing an angular velocity observer and an output feedback attitude controller with finite-time convergence and disturbances for spacecraft. First, two new concepts of finite-time stability are proposed and defined as the local fast-finite-time stability and the fast-finite-time uniformly ultimately boundness, which can be seen as the extensions of the traditional fast-finite-time stability. Then, based on these two concepts of stability, a fast-finite-time observer is designed to estimate the unknown angular velocity. Next, based on the estimation of the angular velocity, a nonsingular and continuous attitude control algorithm is proposed to achieve the finite-time stability or finite-time boundness. With consideration of the observation errors and disturbances in the closed-loop system, a rigorous analysis of the proposed strategy is provided through Lyapunov approach. It shows that the observation errors and the spacecraft attitude will converge to a region of zero in finite time. Numerical simulation studies are presented to illustrate the effectiveness of the proposed observer-based attitude control scheme.

This paper addresses the integrated attitude and position control problem for the final phase proximity operations of spacecraft autonomous rendezvous and docking, in which important motion constra...

During the aerospace missions for the on-orbiting spacecraft, actuator faults are frequently encountered such that the control system performance may be degraded, even the unstable ACS may result in the completely collapse, immeasurable losses or catastrophic consequences. Thus, the spacecraft ACS should be capable of dealing with or tolerating possible actuator faults, while at the same time guaranteeing an acceptable performance in the presence of actuator faults. There exist some main approaches to improve the stability and reliability of the spacecraft ACS, such as high reliable control system design with redundant devices, FDD based FTC system design, CA based FTC system design and so on. Recently, CA techniques have drawn significant interests in the aircraft and spacecraft control [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13], especially in the FTC system design. Gui et al. [14] introduced an adaptive SMC law to dynamically compensate the perturbations due to actuator faults and other uncertainties, in which the real time CA algorithm delivers the control command to actuators. In [15], a novel dynamic near-optimal CA scheme with combination of a saturated baseline controller for spacecraft attitude control using single-gimbal control moment gyros. This dynamic control allocation is implemented with online update law, which has a modest computational complexity. All these methods can primarily generate commands to control effectors to achieve some demand moment or acceleration. Some of them take in account the position and rate limits, while some also allow for satisfying a secondary objective. Generally speaking, all the aforementioned CA can be implemented practically to address the concerned constraints and objectives. However, the authors in [16] illustrated that different CA algorithms can lead to different closed-loop maneuver performances owing to the CA errors between the designed signal and actual input. Usually, this CA error is treated as small and neglectable in the control design, which, in fact, may lead to a degraded performance or even potential closed-loop instability. In all the aforementioned references, it is assumed that the system state trajectories are governed by the baseline controller, and CA algorithms have no/little effect on the closed-loop performance.

This article investigates the velocity-free attitude coordinated tracking control scheme for a group of spacecraft with the assumption that the angular velocities of the formation members are not available in control feedback. Initially, an angular velocity observer is constructed based on each individual's attitude quarternion. Then, the distributed attitude coordinated control law is designed by using the observed states, in which adaptive control method is adopted to handle the external disturbances. Stability of the overall closed-loop system is analyzed theoretically, which shows the system trajectory converges to a small set around origin with fast convergence rate. Numerical simulations are performed to demonstrate fast convergence and improved tracking performance of the proposed control strategy.

The science objectives of a spacecraft mission place stringent performance requirements on the spacecraft attitude control system. However, it remains an open problem how to guarantee consistent control performance necessary to meet these requirements, especially in the event of actuator faults and input saturation. Motivated by this fact, in this paper, we address the problem of attitude tracking control with prescribed performance guarantees for a rigid spacecraft subject to unknown but constant inertia parameters, unexpected disturbances, actuator faults, and input saturation. First, certain performance functions specified a priori by the designer are adopted to impose desired performance metrics on the attitude tracking errors. Then, the original attitude tracking error dynamics with performance constraints is transformed into an equivalent “state-constrained” one whose robust stabilization is shown to be sufficient to solve the stated problem via a novel error transformation. Subsequently, based on the transformed system, an adaptive fault-tolerant controller is derived by incorporating backstepping control, the barrier Lyapunov function, and Nussbaum gains. It is proved that the designed controller is able to guarantee the satisfaction of the prespecified constraints on the transformed errors, as well as the boundedness of all other closed-loop signals, without resorting to a judicious selection of the control parameters. Finally, the effectiveness of the proposed control scheme is evaluated by means of simulation experiments carried out on a microsatellite.

The capture of a free-floating tumbling object using an autonomous vehicle is a key technology for many future orbital missions. Spacecraft proximity operations will play an important role in guaranteeing the success of such missions. In this paper, we technically propose a tracking control scheme for proximity operations between a target and a pursuer spacecraft that ensures accurate relative position tracking as well as attitude synchronization. Specifically, an integrated six degrees of freedom dynamics model is first established to describe the relative motion of the pursuer with respect to the target. Then, a robust fault-tolerant controller is derived by combining the sliding mode control and the adaptive technique. The designed controller is proved to be not only robust against unexpected disturbances and adaptive to unknown and uncertain mass/inertia properties of the pursuer, but also able to accommodate a large class of actuator faults. In particular, by incorporating a novel time-varying forcing function into the sliding dynamics, the proposed control algorithm is able to guarantee the finite-time convergence of the translational and rotational tracking errors, and the convergence time as an explicit parameter can be assigned a priori by the designers. Furthermore, a theoretical analysis is also presented to assess the fault tolerance ability of the designed controller. Finally, numerous examples are carried out to evaluate the effectiveness and demonstrate the benefits of the overall control approach.

This paper addresses the attitude stabilization problem with the optimization objective regarding system performance and energy consumption for rigid spacecraft. Novel state-dependent coefficient (SDC) parameterizations are developed to reduce the optimization problem to solving the state-dependent Riccati equation (SDRE). To be explicit, a proper SDC parameterization is selected for the stabilization mission among infinite feasible SDC representations by utilizing an improved guideline. Subsequently, a novel analytical SDC reconstruction is evoked alternatively at the mission breakdown region in which the derived SDC parameterization fails to operate. Behind the scenes, the anti-unwinding behavior is supported by the explicit sampling SDC forms derived for the scalar part of the unit quaternion. The novelty of two developed SDC parameterizations lies in that they not only render the maximal pointwise controllable space to facilitate the control mission, but also cover the whole maneuvering domain without any breakdowns. Moreover, the computational burdens for online SDRE solvability checking and numerical SDC reconstruction are alleviated significantly. Finally, comparative numerical simulations are implemented to highlight the superior performance of the presented scheme.

A smooth attitude-stabilizing controller is proposed for rigid spacecraft actuated by thrusters that achieves finite-time stability in the presence of external disturbance, input saturation, and in...

This paper investigates the attitude coordinated tracking control for a group of rigid spacecraft under directed communication topology, in which inertia uncertainties, external disturbances, input saturation and constant time-delays between the formation members are handled. Initially, the nominal system with communication delays is studied. A delay-dependent controller is proposed by using Lyapunov–Krasovskii function and sufficient condition for system stability is derived. Then, an integral sliding manifold is designed and adaptive control approach is employed to deal with the total perturbation. Meanwhile, the boundary layer method is introduced to alleviate the unexpected chattering as system trajectories cross the switching surface. Finally, numerical simulation results are presented to validate the effectiveness and robustness of the proposed control strategy.

The main problem addressed is the quaternion-based attitude stabilization control of rigid spacecraft without angular velocity measurements in the presence of external disturbances and reaction wheel friction as well. As a stepping stone, an angular velocity observer is proposed for the attitude control of a rigid body in the absence of angular velocity measurements. The observer design ensures finite-time convergence of angular velocity state estimation errors irrespective of the control torque or the initial attitude state of the spacecraft. Then, a novel finite-time control law is employed as the controller in which the estimate of the angular velocity is used directly. It is then shown that the observer and the controlled system form a cascaded structure, which allows the application of the finite-time stability theory of cascaded systems to prove the finite-time stability of the closed-loop system. A rigorous analysis of the proposed formulation is provided and numerical simulation studies are presented to help illustrate the effectiveness of the angular-velocity observer for rigid spacecraft attitude control.

A novel smooth attitude algorithm is presented for rigid spacecraft in the presence of assigned sensor and actuator saturations, as well as external disturbances. More specifically, an analog of variable structure control law is first developed by explicitly taking into account the velocity and control constraints simultaneously. In the proposed controller, behavior of the adaptive parameter is investigated to ensure the close-loop convergence and disturbance rejection. The straightforward relationship between the constraints given and parameters tuning is further analyzed. In addition, to avoid the unwinding phenomenon problem caused by quaternion attitude representation, a class of definition of attitude error vector is proposed to ensure that both two equilibria are locally asymptotically stable. Numerical simulations illustrate the performance of proposed attitude controller and the improvement of the anti-unwinding technic.

This paper addresses the translational control problem for the final phase of spacecraft rendezvous and docking. For safety concerns, during the approach process, the pursuer spacecraft is required...

In this paper, attitude coordinated tracking control algorithms for multiple spacecraft formation are investigated with consideration of parametric uncertainties, external disturbances, communication delays and actuator saturation. Initially, a sliding mode delay-dependent attitude coordinated controller is proposed under bounded external disturbances. However, neither inertia uncertainty nor actuator constraint has been taken into account. Then, a robust saturated delay-dependent attitude coordinated control law is further derived, where uncertainties and external disturbances are handled by Chebyshev neural networks (CNN). In addition, command filter technique is introduced to facilitate the backstepping design procedure, through which actuator saturation problem is solved. Thus the spacecraft in the formation are able to track the reference attitude trajectory even in the presence of time-varying communication delays. Rigorous analysis is presented by using Lyapunov-Krasovskii approach to demonstrate the stability of the closed-loop system under both control algorithms. Finally, the numerical examples are carried out to illustrate the efficiency of the theoretical results. Published version

This paper investigates a velocity-free finite-time attitude control scheme for a rigid spacecraft with actuator saturation and external disturbances. Initially, a finite-time observer is designed to compensate the unknown angular velocity information. With the estimated values, a finite-time controller is further developed under which the time-varying reference attitude trajectory can be tracked precisely. Moreover, input saturation problem is solved by adaptive method. Rigorous Lyapunov-based analysis shows that the states of the closed-loop system converge to a small neighborhood of the origin in finite time. Finally, the dynamic performance of attitude control system is presented by numerical simulation examples and the superiority of the finite-time control scheme is verified.