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Summary: This article investigates the issue of orbit coordination control for a class of multi‐spacecraft formation systems in presence of limited communication and external disturbance. To solve the limitation of communication sources, a dynamic event trigger (DET) mechanism is developed to reduce the communication frequency between the follower spacecrafts. Subsequently, we explore a robust DET mechanism‐based distributed self‐learning sliding mode control design, in which a variable learning intensity‐based iterative learning algorithm is designed to approximate and compensate space perturbation. This approach can guarantee an event triggering sequence without Zeno phenomenon and accurate coordination control for formation configuration simultaneously. Compared with the traditional event‐triggered control and other state‐of‐the‐art approaches, the distributed DET control scheme achieves higher control accuracy of formation configuration meanwhile requires less communication resource. Finally, a series of numerical simulations demonstrate the feasibility and superiority of the event triggered control method. [ABSTRACT FROM AUTHOR]

This paper studies the issue of learning radial basis function neural network (RBFNN)-based robust reconfigurable fault-tolerant configuration control for spacecraft formation flying (SFF) systems subject to thruster faults and space perturbations. To robustly reconstruct thruster faults, a novel learning RBFNN estimator is innovatively explored, in which the P-type iterative learning algorithm is utilized to online update the weight matrix of the RBFNN model and the H∞ control technique is adopted to attenuate the effect of space perturbations. Further, a learning RBFNN output-feedback fault-tolerant control (FTC) method is developed for spacecraft formation configuration maintenance with high accuracy, and the learning RBFNN algorithm is used to update and compensate the synthesized perturbation. Finally, a numerical example is simulated to verify the presented learning RBFNN-based spacecraft formation FTC approach is feasible and superior. [ABSTRACT FROM AUTHOR]

This paper investigates a performance‐adjustable prescribed performance control (PPC) policy under event‐triggered sampling for spacecraft attitude‐orbit coupled tracking with consideration of limited communications and performance constraints. Firstly, a logarithmic barrier Lyapunov function is introduced to derive the attitude‐orbit coupled tracking controller with guaranteed transient and steady‐state behaviors by applying the PPC algorithm. Then, to reduce the burden of the signal transmission under limited communications, the event‐triggered mechanism is applied to determine when the above attitude‐orbit coupled tracking controller updates. Furthermore, an indirect adaptive method with less computation that does not involve complex regression matrices or neural networks is designed to resist external disturbances. Compared with the traditional spacecraft control policies, the proposed strategy fully considers the state convergence performance, sampling performance, and calculation performance. The proposed one here can arbitrarily adjust the sampling performance and state convergence performance in an excellent trade‐off. Finally, a group of illustrative examples is organized to demonstrate the effectiveness of the proposed control policy. [ABSTRACT FROM AUTHOR]

This paper focuses on the triaxial augmentation ability of the active disturbance rejection control (ADRC) technique on the tailless layout with a fully moving wing tip to achieve high control performance for the supersonic tailless aircraft. Firstly, the stability characteristics and controllability of the flying wing layout are analyzed to determine the coupling characteristics of this kind of aircraft. Secondly, an attitude controller is designed based on ADRC theory, and the linear ADRC frequency domain analysis method is introduced to analyze the influence of the bandwidth of linear extended stator on the control system. In addition, the tuning process of the attitude control law is given. Carrier dropping simulations of flight missions under nominal condition, model parameter perturbation, and wind disturbance are conducted. The results show that the designed controller can achieve full-speed domain triaxial augmentation of supersonic flying wing. This work has the potential to significantly boost the engineering acceptability and robustness of supersonic aircraft control design in real-world scenarios. The presented cascaded ADRC approach can significantly improve the performance and robustness of supersonic vehicles. [ABSTRACT FROM AUTHOR]

In order to meet the constraints of velocity and acceleration of displacement and attitude motion of an unmanned helicopter during an automatic carrier landing mission, an asymmetric tracking differentiator, which could set the speed and acceleration limits in two directions of tracked signal motion respectively, was derived based on the tracking differentiator in the active disturbance rejection control method. Based on the proposed asymmetric tracking differentiator, a fal-extended state observer based on the fal function was added to construct the attitude and angular velocity controller which is programmable during the transition process of unmanned helicopters. The mathematical simulation and result analysis show that the newly proposed attitude estimation algorithm effectively compensates for the deficiencies of the existing methods, improves the anti-jamming capability and the accuracy of attitude estimation in the maneuvering process, achieving the expected design purposes. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to study the attitude control problem with mutating orbital rate and actuator fading. Design/methodology/approach: To avoid malicious physical attacks and hide itself, the spacecraft may irregularly switch its orbit altitude within a specific range, which will bring about variations in orbital rate, thereby causing mutations in the attitude dynamics model. The actuator faults will also cause changes in system dynamics. Both factors affect the control performance. First, this paper determines the potential switching orbits. Then under different conditions, design controllers that can accommodate actuator faults according to the statistical law of actuator fading. Findings: This paper, to the best of the authors' knowledge, for the first time, introduces the Markovian jump framework to model the possible unexpected mutating of orbital rate and actuator fading of spacecraft and then designs a novel control policy to solve the attitude control problem. Practical implications: This paper also provides the algorithm design processes in detail. A comparative numerical simulation is given to verify the effectiveness of the proposed algorithm. Originality/value: This is an early solution for spacecraft attitude control with dynamics model mutations. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to address the spacecraft attitude regulation problem in the presence of extrinsic disturbances and actuator faults. Design/methodology/approach: Based on adaptive backstepping design technique, a new concise adaptive dual-mode control scheme is proposed, which can either use the fault information detected by fault diagnosis mechanisms or switch to the fault-unknown mode when the fault diagnosis information is non-existent for control signal generation. These two modes share an adaptive mechanism that reduces the complexity of the algorithm. Findings: The new fault-tolerant attitude control algorithm can accommodate both modes with and without fault diagnosis mechanisms. Originality/value: The proposed algorithm in this paper can be applied to both cases when the attitude control system is equipped with or without fault diagnosis capability. This also enhances the robustness of attitude control algorithm. This study performs numerical simulations and verifies that the algorithm could effectively adapt to both modes. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to investigate the attitude regulation for spacecraft in the presence of time-varying inertia uncertainty and exogenous disturbances. Design/methodology/approach: The high gain approaches are typically used in existing researches for theoretical advantages, bringing better performance but sensitive to parameter selection, making the controller conservative. A reset-control policy is presented to achieve the spacecraft attitude control with easy control parameter tuning. Findings: The reset-control policy guarantees satisfying control performance despite using performance tuning function and saturation function besides reducing the conservativeness of the controller, thus reducing the effort in tuning control parameters. Originality/value: Notably, the adaptive function owns a reset mechanism, which is reset to a preset condition when the controlled variable crosses zero. The mathematical analysis also shows the system trajectory can converge to a set centered at the origin. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to study the general actuator modeling in spacecraft attitude control systems. Design/methodology/approach: The proposed module in this paper provides various non-ideal factors such as the second-order dynamic time response, time-delay, bias torques, dead-zones and saturation. The actuator module can make the simulation as close to the practical situation as possible. Findings: This paper presents a practical integrated module for the simulation of attitude control algorithms. Based on theoretical modeling, we give simulation modules and numerical examples. The proposed model can be directly used in spacecraft control simulation. Instead of considering only a few of them, it makes the simulation more convincing. Though it may not be perfect, it is better than totally ignoring the actuator dynamics. Originality/value: The authors provide an integrated actuator model for spacecraft attitude control simulation, considering as many nonlinear factors as possible once time. [ABSTRACT FROM AUTHOR]

Purpose: Recent spacecraft attitude control systems tend to use wireless communication for cost-saving and distributed mission purposes while encountering limited communication resources and data exposure issues. This paper aims to study the attitude control problem with low communication frequency under the sampled-data. Design/methodology/approach: The authors propose constructive control system structures based on quantization and event-triggered methods for intra-spacecraft and multi-spacecraft systems, and they also provide potential solutions to shield the control system's data security. The proposed control architectures can effectively save communication resources for both intra-spacecraft and multi-spacecraft systems. Findings: The proposed control architectures no longer require sensors with trigger-ing mechanism and can achieve distributed control schemes. This paper also provides proposals of employing the public key encryption to secure the data in control-loop, which is transmitted by the event-triggered control mechanism. Practical implications: Spacecraft attempts to use wireless communication, yet the attitude control system does not follow up promptly to accommodate these variations. Compared with existing approaches, the proposed control structures can save communication resources of control-loop in multi-sections effectively, and systematically, by rationally configuring the location of quantization and event-triggered mechanisms. Originality/value: This paper presents several new control schemes and a necessary condition for the employment of encryption algorithms for control systems based on event-based communication. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to investigate the attitude cooperation control of multi-spacecraft with in-continuous communication. Design/methodology/approach: A decentralized state-irrelevant event-triggered control policy is proposed to reduce control updating frequency and further achieve in-continuous communication by introducing a self-triggered mechanism. Findings: Each spacecraft transmits data independently, without the requirement for the whole system to communicate simultaneously. The local predictions and self-triggered mechanism avoid continuous monitoring of the triggering condition. Research limitations/implications: This investigation is suitable for small Euler angle conditions. Practical implications: The control policy based on event-triggered communication can provide potential solutions for saving communication resources. Originality/value: This investigation uses event- and self-triggered policy to achieve in-communication for the multi-spacecraft system. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to investigate the feasibility of using the combination of Lorentz force and aerodynamic force as a propellantless control method for spacecraft formation. Design/methodology/approach: It is assumed that each spacecraft is equipped with several large flat plates, which can rotate to produce aerodynamic force. Lorentz force can be achieved by modulating spacecraft's electrostatic charge. An adaptive output feedback controller is designed based on a sliding mode observer to account for unknown uncertainties and the absence of relative velocity measurements. Aiming at distributing the control input, an optimal control allocation method is proposed to calculate the electrostatic charge of the Lorentz spacecraft and control commands for the atmospheric-based actuators. Findings: Numerical examples are provided to demonstrate the effectiveness of the proposed control strategy in the presence of J2 perturbations. Simulation results show that relative motion in a formation can be precisely controlled by the proposed propellantless control method under uncertainties and unavailability of velocity measurements. Research limitations/implications: The controllability of the system is not theoretically investigated in the current work. Practical implications: The proposed control method introduced in this paper can be applied for small satellites formation in low Earth orbit. Originality/value: The main contribution of the paper is the proposal of the propellantless control approach for satellite formation using the combination of Lorentz force and aerodynamic force, which can eliminate the requirement of the propulsion system. [ABSTRACT FROM AUTHOR]

This paper presents the finite‐time attitude synchronization and tracking control method of undirected multi‐spacecraft formation with external disturbances. First, a modified adaptive nonsingular fast terminal sliding mode surface (ANFTSMS) is designed by introducing a user‐defined function, both of which avoid the singularity problem and continuous sliding surface, and, therefore, can freely adjust relative weighting between angular velocity error and attitude error adaptively, such that the controller can provide sufficient maneuvers and precision. This provides designers with a new technique to adjust and improve formation control performance. Second, by applying the ANFTSMS associated with adaptation, two proposed decentralized ANFTSM‐controllers provide finite‐time convergence, robustness to disturbance, and chattering free for continuous design. Finally, simulation results validate the proposed algorithms. [ABSTRACT FROM AUTHOR]

This paper investigates the attitude fault-tolerant stabilization problem for a spacecraft subjected to its actuator effectiveness loss, inertia uncertainties and space disturbances. A novel Iterative Learning Sliding Mode Observer (ILSMO) is proposed to reconstruct the actuator effectiveness factors robustly and accurately by combining the P-type iterative learning algorithm with the sliding mode approach. Based on the reconstructed fault signals, an Iterative Learning Sliding Mode Controller (ILSMC) is designed to guarantee the closed-loop spacecraft attitude fault-tolerant stabilization by compensating for its lumped disturbance. The ILSMO and ILSMC stabilities are guaranteed using the Lyapunov direct approach, respectively. Finally, the numerical simulation results show that the proposed ILSMO-ILSMC-based spacecraft attitude fault-tolerant stabilization method is effective and superior. [ABSTRACT FROM AUTHOR]

This brief investigates the problem of attitude tracking control using a variable learning intensity (VLI) online-learning control (OLC) scheme. The unique specialty of the proposed VLI-OLC scheme is that it achieves control performance enhancement via learning the previous control information online. The implementation is performed by a simple algebraic equation, which achieves decent control robustness while avoiding a complex control design and saving computational resources. The OLC's saturation response caused by the extensive system error during execution is noticeably weakened by introducing a VLI approach. Compatibility with previous algorithms can be guaranteed. The application example shows that control performance and saturation reduction are guaranteed concurrently. [ABSTRACT FROM AUTHOR]

This paper proposes a neural network and event-based fault-tolerant control scheme for spacecraft attitude stabilization in the presence of lumped disturbances, which consists of space disturbances, inertia uncertainties, and actuator faults. A neuro-adaptive estimator is employed to approximate the lumped disturbances, with the help of its powerful adaptive estimation capability of approximating any unknown smooth nonlinear function with arbitrary accuracy. The estimation is then utilized to formulate an integrated event-based dual-channel control scheme that can both guarantee the system's convergence and ensure the event triggering sequence possessing no-Zeno behavior simultaneously. The proposed control scheme provides a new and straightforward way for spacecraft attitude control to deal with lumped disturbances while requiring a low actuator updating frequency, thus saves on-board communication resources. Numerical simulations show the effectiveness of the algorithms. [ABSTRACT FROM AUTHOR]

This paper studies the spacecraft attitude stabilization problem with external disturbances. A new control scheme entitled online-learning control is proposed to achieve a robust, accurate, and simple-structure control algorithm. Compared with the conventional control design, an obvious distinction of the online-learning control algorithm is that it together utilizes the previous control input information and the system's current state information, as if learning experience from previous control input. In contrast, the conventional control scheme does not fully use the existing information and chooses to discard the previous control input information when generating control instructions. Due to the learning strategy, the utility of adaptive- or observer-based tools can be avoided when designing a robust control law, making a simple, effective algorithm, moreover saving system resources. The proposed control law can stabilize the attitude system by achieving the uniformly ultimately bounded convergence. [ABSTRACT FROM AUTHOR]

This paper addresses the robust attitude synchronization issue in a multi-spacecraft formation system subjected to limited communication, space disturbances, modeling uncertainties, and actuator faults. To accommodate limited inter-spacecraft communication, a dynamic event-triggered mechanism is designed to reduce the communication trigger frequency by dynamically adjusting the trigger threshold. Moreover, an event-based distributed self-learning neural-network control (SLN2C) law is developed to guarantee robust attitude synchronization during multi-spacecraft formation. In the SLN2C scheme, a learning radial basis function neural network (RBFNN) model is proposed to online approximate and compensate for lumped disturbances, in which an iterative learning algorithm with a variable learning intensity is adopted to update the weight matrix of the RBFNN model. Compared with the traditional fixed learning intensity, a variable one can reduce initial oscillation and weaken the saturation response. Numerical simulations and comparisons are performed to illustrate the effectiveness and superiority of the proposed event-based spacecraft attitude synchronization control method. [ABSTRACT FROM AUTHOR]

In this paper, a prescribed performance control (PPC) scheme for spacecraft attitude tracking with anti-disturbance and performance-adjustable properties is proposed. The proposed controller is based on the barrier Lyapunov function (BLF) approach, which can arbitrarily adjust the state convergence performance and possess high steady-state performance. Compared with previous works, this strategy is more robust to external disturbances and thus has higher steady-state performance with low computing resource occupancy. What's more, it has the property of freely adjusting performance to meet the control objectives and performance requirements in different scenarios. Simulation results in this paper verify the effectiveness and superiority of the proposed method. [ABSTRACT FROM AUTHOR]

This paper is devoted to solving the multi-spacecraft attitude synchronization problem via performance adjustable event-triggered control in the presence of external disturbances and model uncertainties. In the proposed control policy, the inter-spacecraft information interaction is determined by an event-triggered sampling mechanism, and the influences of external disturbances and model uncertainties are counteracted by an adaptive estimation. This sampling method does not only reduce communication resource consumption but also provides a trade-off between resource savings and synchronization accuracy. Moreover, the corresponding performance-adjustable triggering function can achieve Zeno-free triggering. According to the comparison of some numerical simulation results, this paper shows that the provided control policy is effective and superior. [ABSTRACT FROM AUTHOR]

This article presents a finite-time prescribed performance (FTPP) control approach based on a learning Chebyshev neural network (LCNN) for spacecraft attitude tracking with modeling uncertainties, actuator faults, and external disturbances. An FTPP function is designed to specify the desired accuracy boundary and finite-time convergence. Further, an FTPP-based learning sliding mode controller (LSMC) is constructed, where the lumped disturbance is approximated and compensated via a novel LCNN model. Unlike conventional adaptive CNN models, the LCNN model employs an iterative learning mechanism for adjusting the weights of the CNN model, reducing computing costs. The FTPP-based LSMC approach is presented with a detailed stability analysis. The proposed method offers a broad range of applications with the FTPP criteria satisfied. A series of simulations are performed to verify the validity and applicability of the proposed approach. [ABSTRACT FROM AUTHOR]

In this study, the issue of the performance guaranteed fault-tolerant control for formation reconfiguration with collision avoidance in the multi-spacecraft system subjects to space perturbations and thruster faults is investigated. A new nonlinear iterative learning disturbance observer is constructed to accurately reconstruct the synthesized disturbance no matter it is time-varying or not. Then, an exponential artificial potential function with a simple structure and low computation requirement is designed to avoid collision between spacecrafts. A nonsingular terminal sliding mode fault-tolerant control method is explored to accomplish fault-tolerant formation reconfiguration with collision avoidance ability and prescribed robust performance. Finally, numerical simulations and comparisons are performed to validate the effectiveness and superiority of the proposed approaches. [ABSTRACT FROM AUTHOR]

This paper investigates an adaptive leader-following formation tracking control approach for multiple spacecraft under a directed communication topology with consideration of external disturbances, formation safety and limited sensing ranges. Through developing a novel logarithmic potential function-based approach, the neighboring spacecraft can always move within the region of maintaining connectivity and avoiding collision. Additionally, by establishing a new state-independent performance function, the specified-time stability of the SFF system can be guaranteed, wherein, the convergence time can be arbitrarily appointed in advance. Compared with the existing results, the major advantage of the proposed scheme is that the specified-time stability, connectivity preservation and collision avoidance can be considered simultaneously with superior capacity of rejecting disturbance. Meanwhile, the formation tracking performance of the SFF system can be ensured a priori. By virtue of the Lyapunov theory, the detailed theoretical analysis for the proposed protocol has been derived. Finally, extensive simulations are carried out to validate the effectiveness of the proposed control protocol. [ABSTRACT FROM AUTHOR]