Attitude Control Of Flexible Spacecraft Research Articles

Exact-time neural attitude control for flexible spacecraft with conditional disturbance negation

Exact-time neural attitude control for flexible spacecraft with conditional disturbance negation

Neural network-based control for the on-orbit assembly of heterogeneous spacecraft cluster based on Vicsek fractal

On-orbit assembly is a highly effective technique for building large space structures. This paper presents the dynamics and control of an on-orbit assembly of a large space structure based on a heterogenous spacecraft cluster comprising both rigid and flexible spacecraft. The topology of the large space structure is inspired by the Vicsek fractal. A distributed assembly strategy is proposed for the spacecraft team. Radial Basis Function neural networks (RBFNNs) are utilized to approximate the bounded uncertain terms in translational and attitude dynamics. To avoid collisions during the pre-assembly phase, a neural network (NN)-based controller with collision avoidance force is designed for relative position motion. During the assembly phase, only proportional-derivative (PD) law is employed for relative position control. In addition, an NN-based controller is designed for relative attitude control for both rigid and flexible spacecraft. To estimate the unmeasured flexible vibrations, modal coordinate observers are introduced for the flexible spacecraft. The stability of the closed-loop system is proved via Lyapunov functions. Moreover, numerical results are presented to validate the effectiveness of the proposed controllers and assembly strategy.

Designing a fixed-time observer-based adaptive non-singular sliding mode controller for flexible spacecraft

This paper investigates the stabilization problem with a fixed-time approach for a flexible spacecraft subject to vibrations of flexible modes, unknown bounded disturbance, and inherent uncertainty. To estimate the modal variables of a flexible spacecraft which are often unmeasurable in practice, an observer with guaranteed fixed-time convergence is designed. Using the estimated modal variables, a fixed-time non-singular sliding mode controller is designed so that the desired attitude can be reached before a pre-specified time threshold regardless of the spacecraft's initial attitude. By incorporating the estimated modal variables in the control design, significant reduction in the steady-state error of the system response is achieved. The proposed control system is further enhanced with an adaptive law to increase robustness against unknown external disturbances and uncertainties. Stability analysis based on Lyapunov theory guarantees the convergence of observer estimation error and spacecraft attitude error to a pre-determined set before a fixed threshold. Simulation results validate the promising performance of the proposed control system, highlighting its effectiveness in achieving accurate and robust attitude control for flexible spacecraft.

Design of anti-unwinding attitude coupling controller for flexible spacecraft using positive position feedback control

Flexible vibration has a great impact on flexible spacecraft attitude control, which will reduce the pointing accuracy of the spacecraft platform and bring severe challenges to the design of a high-precision attitude control system for flexible spacecraft. Aiming at the problem of attitude and vibration coupling control of flexible spacecraft, an anti-unwinding attitude coupling controller using the positive position feedback (PPF) control is proposed in this paper. The model compensation control term is constructed based on the prior information to improve the tracking performance. The proposed attitude coupling control method can effectively suppress the flexible vibration while achieving more accurate attitude control. The obtained closed-loop system under the proposed control scheme is asymptotically stable, which is proved by the Lyapunov stability theory. The numerical simulation illustrates that the proposed method can effectively improve the attitude control accuracy of the flexible spacecraft and is capable of large-angle attitude maneuver control because of its prominent performance in attitude tracking and its unwinding-free performance.

Fixed-time fault-tolerant attitude control for flexible spacecraft without angular velocity sensor

This paper deals with the appealing problem of fixed-time fault-tolerant attitude control, using attitude-information-only, for a flexible spacecraft under the influence of inertial parametric variations, external disturbances, and multiple actuator faults while suppressing the flexible appendages’ vibrations without using additional sensors or smart vibration suppression actuators. First, an adaptive fixed-time model-free observer (AFTMFO) is designed, using the attitude information, for rapid estimation of unavailable angular velocity. A novel adaptive continuous control is then synthesized based on an anti-unwinding fast fixed-time nonsingular sliding surface (AFFTNSS), utilizing variable gains in both the control law and sliding surface; that simultaneously alleviates the chattering but also improves the convergence speed when compared to existing fixed-time approaches. The proposed scheme offers superior performance characteristics such as velocity sensor-free fixed-time attitude maneuvering with high pointing accuracy, fault tolerance, vibration suppression, nonsingular and chattering-free control. The spacecraft can carry out the coveted control objective in a predeterminable time independent of the knowledge of initial states while overcoming the unwinding effect to reduce the control effort and time. The fixed-time closed-loop stability of the proposed scheme is corroborated via Lyapunov techniques. Finally, a comparative simulation analysis with the existing results elucidated the proposed scheme’s efficacy.

Adaptive dynamic programming-based fault-tolerant attitude control for flexible spacecraft with limited wireless resources

Adaptive dynamic programming-based fault-tolerant attitude control for flexible spacecraft with limited wireless resources

Output feedback attitude control of flexible spacecraft under actuator misalignment and input nonlinearities

The attitude tracking control problem of flexible spacecraft subjected to parameter uncertainties, time-dependent external disturbances, actuator input nonlinearity, and input actuator misalignment is investigated in this paper. Explicitly, the proposed strategy addresses the input actuator misalignment and dead-zone issues that increase the controller design difficulties. Initially, a new second-order sliding mode observer (SoSMO) using an extended state approach is developed by adding a correction function to improve observer performance to estimate unwanted system perturbations. Then, a distinct SoSMO-based integral-type sliding mode control (ISMC) structure is designed in a unified manner to guarantee the asymptotic stability of the closed-loop system. Comparative numerical simulations under input actuator misalignment, the dead-zone nonlinearity, external disturbance, and inertia uncertainty are performed to illustrate the effectiveness of the proposed controller.

Nonlinear finite time attitude control of flexible spacecraft based on a novel output redefinition method

A finite time attitude controller is designed for a flexible spacecraft based on a novel output redefinition method, in this paper. To make the flexible appendages vibration suppression effective, the appendage tip-point is selected as the output. First, a novel output redefinition method is proposed to overcome the non-minimum phase property of the dynamic model. The proposed method not only makes the system model minimum phase but also improves the attitude control system performance. Consequently, the precise attitude pointing and stabilization are achieved. Then, a nonlinear finite time H∞ controller is designed based on the backstepping approach. For the situation where the modal variables measurements are not available, a modal observer is also designed. The simulation results show the effectiveness of the proposed method in the presence of the model uncertainties and environmental disturbances.

PDE-based prescribed performance adaptive attitude and vibration control of flexible spacecraft

This article presents a prescribed performance adaptive control scheme for the attitude tracking and vibration reduction of flexible spacecraft modeled by partial differential equations (PDEs). First, the original constrained problem is converted to an equivalent unconstrained one by adopting a prescribed error transformation. Then, a boundary control torque law and a boundary control force law are developed to track the desired attitude and reduce the vibration, respectively. Moreover, the parametric adaptation technique is integrated with the boundary control laws to estimate the disturbances. The closed-loop system is evaluated to be asymptotically stable through the Lyapunov stability theorem and LaSalle's invariance principle. The developed controller has two distinctive features as follows. One is the controller can guarantee the attitude tracking error and tip deformation always satisfy the prescribed performance constraints. Another is the controller can acquire the strong robustness owing to the feedforward disturbance compensation. Lastly, the derived results are demonstrated by simulated studies.

Prescribed performance fault‐tolerant attitude control for flexible spacecraft under limited communication network

AbstractThis paper investigates the prescribed performance fault‐tolerant attitude tracking control for flexible spacecraft under limited communication network, where the controller and the actuator are connected via wireless network. The hysteresis quantizer is employed to quantize the control signal, which can reduce the communication burden of the network onboard. First, a novel iterative learning observer is developed by combining with neural‐network approximation method to reconstruct the actuator faults and estimate the unmeasurable nonlinear rigid‐flexible dynamics simultaneously. Then, the signal quantization technique is introduced for control command quantization, and the concerned parametric quantization error is given. Based on the learning observer output, prescribed performance design procedure, and a quantization error compensation method, an active fault‐tolerant control strategy is developed for flexible spacecraft attitude tracking to deal with actuator faults, unmeasurable system nonlinearity, quantization errors, and external disturbances. The stability analysis of the closed‐loop system proves that the quantization errors, modal vibrations, disturbances can be effectively rejected, moreover, the convergence of the transformed performance states and angular velocity states can be guaranteed, which achieves the tracking problem with predetermined transient‐state and steady‐state performance requirements. Finally, a numerical simulation is conducted to illustrate the validness of the proposed control strategy.

Finite element dynamic modeling and attitude control for a slender flexible spacecraft

This paper aims to study the dynamic modeling and attitude control of a kind of slender flexible spacecraft. The basic structure of this kind of spacecraft is different from the traditional structure of a center rigid body with flexible appendages, but rigid bodies at both ends, which are connected by a flexible truss structure. Firstly, the finite element modeling method is adopted to establish the dynamic model of this kind of spacecraft, and the vibration frequency and damping of the flexible structure are obtained. The unconstrained modes of the flexible spacecraft are obtained through mathematical analysis, finite element analysis and frequency domain analysis. In addition, a nonlinear sliding surface with angular velocity constraint is designed. On this basis, an adaptive sliding mode (ASM) controller is proposed, stability of the close-loop system under the controller is proved, and the dynamic model is verified through mathematical simulation.

Constrained Attitude Control for Flexible Spacecraft: Attitude Pointing Accuracy and Pointing Stability Improvement

This work deals with the complicated problem of constrained fixed-time attitude control for flexible spacecraft in view of actuator saturations and fault. The proposed controller is composed of two parts. The first part provides fast fixed-time convergence of system trajectories using a novel nonsingular terminal sliding mode control. The second part offers the desired performance specification, such as the rate of convergence, overshoot, and steady-state bounds for attitude/rotation velocity to improve attitude-pointing accuracy and pointing stability. The constrained control method ensures the desired performance in the transient/steady-state phases. It obtains a much simpler structure in comparison with other constrained controls. The simulations on a flexible spacecraft validate the efficacy of the planned scheme.

Fault-tolerant attitude control for liquid-filled flexible spacecraft without angular velocity measurements based on disturbance observer

The problem of robust, angular velocity-free control and fault-tolerant control for liquid-filled flexible spacecraft attitude maneuver subject to unknown external disturbances is investigated. Moreover, state variables measurement uncertainty and actuator failures are explored. The liquid sloshing effect of spacecraft fuel is equivalent to a two-order spring-mass model, and the flexible attachments are equivalent to the Euler–Bernoulli beams. The external disturbance, multiple failures of the output actuator, and the coupled interference caused by liquid sloshing and vibrations of flexible attachments are distinguished as continuous and percussive disturbances. First, a fault-tolerant control method against the percussive disturbances is proposed, and the robustness performance and characteristics of this method are analyzed. Then, both continuous and percussive disturbances are considered to propose a new fault-tolerant control method based on a nonlinear disturbance observer, which is used to estimate the integrated disturbance. The Lyapunov stability theory proves that the proposed control strategy can make the state variables converge to a small neighborhood of the origin in finite time. Finally, the numerical simulation is used to verify the effectiveness and robustness of the proposed control strategy.

Attitude Synchronization of Heterogenous Flexible Spacecrafts by Measurement-Based Feedback With Disturbance Suppression

In this paper, we investigate multiple flexible spacecrafts attitude synchronization with parametric uncertainties and external disturbances. A large number of results on this problem rely on accurate measurements, ignoring measurement noises in attitude and angular velocity feedback. However, the existence of inherent noises and accumulated measurement errors are invertible, such that the performance of synchronization may be damaged. By developing a decentralized measurement-based attitude controller, we achieve attitude synchronization having input-to-state stability (ISS) with respect to measurement noises as external input. Moreover, thanks to the ISS-based robust design procedure, each of flexible spacecraft attitude control subsystem gains modeled external disturbance rejection, as well as unmodeled actuator disturbances attenuation and robustness with regarding to uncertain parameters.

Hybrid nonfragile intermediate observer-based T-S fuzzy attitude control for flexible spacecraft with input saturation

This paper investigates a hybrid nonfragile intermediate observer-based T-S fuzzy attitude control strategy subject to multi-source complex disturbances to achieve integrated attitude stabilization and vibration suppression for the flexible spacecraft. A refined T-S fuzzy model for flexible spacecraft is introduced to represent the nonlinear characteristics in large-angle attitude maneuver. Then a hybrid nonfragile observer with coexisting additive and multiplicative perturbations is designed to estimate state information and disturbance simultaneously. Consequently, based on the closed-loop system, the quadratic stability and robust H∞ performance are proved via the Lyapunov stability analysis with corresponding conditions in terms of linear matrix inequalities (LMIs). It is worth mentioning that different from the limiter directly used in much literature, input saturation is disposed as a disturbance during the proof to satisfy the stability requirements. Finally, numerical simulations of a flexible spacecraft attitude control system are performed which demonstrate the effectiveness and superiority of the proposed control strategy.

Active fractional-order sliding mode control of flexible spacecraft under actuators saturation

In this article, a novel multi-objective modified fractional-order nonsingular terminal sliding mode (MFONTSM) controller is designed for the flexible spacecraft attitude control and passive vibration suppression, assuming the control torque saturation in the system dynamics. Then, by considering the effects of flexible components on the appendages modal equation as an external disturbance, an active FONTSM controller is designed separately to suppress any residual vibrations using piezoelectric actuators. The practical fixed-time stability of the closed-loop system is analyzed and proved using the Lyapunov theorem. Finally, the proposed controllers’ performance has been tested in the presence of uncertainties, external disturbances, and the absence of the damping matrix to study the proposed method’s effectiveness. It was observed that the proposed passive and active control strategies were able to achieve fast attitude stabilization while providing substantial vibration suppression under uncertainty and disturbance even in the absence of any damping terms in the system.

Observer-Based Fuzzy Sliding Mode Attitude Control for Flexible Spacecraft

In this paper, the attitude stabilization of flexible spacecraft with unmeasurable states and disturbances is addressed by an observer-based fuzzy integral sliding mode control scheme. First, a Takagi–Sugeno fuzzy model of flexible spacecraft is established and an observer is proposed based on this model. The convergence conditions of the estimation errors are given by Lyapunov function and the gains of the observer are thus determined. According to the obtained estimates, a novel fuzzy sliding mode control strategy is designed to compensate the influence of disturbance. Finally, an example of flexible spacecraft is employed to verify the effectiveness of the proposed observer and control law.

Finite-time active fault-tolerant attitude control for flexible spacecraft with vibration suppression and anti-unwinding

In this paper, a finite-time active fault-tolerant control scheme is designed for a flexible spacecraft’s attitude control experiencing inertial parametric variations, external disturbances, multiple actuator faults, and estimation errors while suppressing the flexible appendages’ vibrations without using smart vibration suppression actuators. First, relative attitude dynamics of a flexible spacecraft with multiple actuator faults are outlined, and a sliding mode observer is designed to estimate flexible appendages-related vibrations. The proposed fault detection and identification (FDI) strategy can efficiently detect actuator faults, avoiding the false alarms caused by uncertainties and disturbances, and accurately estimate the cumulative fault effects on the spacecraft via Chebyshev neural network (CNN) based estimator. Based on a novel fast nonsingular terminal sliding mode surface, a finite-time, unwinding-free, and adaptive fault-tolerant attitude controller is designed to acclimatize the detected faults and uncertainties effectively, also heeding the errors in the estimation of flexible modes and faults. The spacecraft can carry out the coveted control objective in a definable time, and the stability of the proposed controller is corroborated via Lyapunov techniques. Finally, a comparative simulation analysis with the existing results elucidated the proposed scheme’s efficacy.

Robust adaptive attitude control of flexible spacecraft using a sliding mode disturbance observer

A composite control scheme based on a disturbance observer is presented in this paper to deal with the attitude control problem of flexible spacecraft. Specifically, a sliding mode disturbance observer (SMDO) is developed to attenuate the unmodeled system dynamics, parameter uncertainties, and multiple external disturbances. The key feature of this approach is to relax the assumption imposed on disturbance to be constant or changing at a slow rate, which is a typical assumption in this class of problems involving a disturbance observer. Then, an exclusive adaptive integral sliding mode controller is combined with the SMDO to get the improved closed-loop control performance of the system. The underlying benefit of the proposed control scheme is improved robustness against time-dependent external disturbances and system model uncertainties. The stability analysis of the closed-loop system is provided using Lyapunov’s stability theory. Simulation results are provided to show the effectiveness of the proposed control scheme, especially in comparison with existing results.

Flexible spacecraft's active fault-tolerant and anti-unwinding attitude control with vibration suppression

Reliable spacecraft's attitude control is one of the core research areas of the space industry due to the need for sustainable space exploration and advancements in space technology. In this paper, an active fault-tolerant control scheme is designed for a flexible spacecraft's attitude control experiencing multiple actuator faults, inertial uncertainties, external disturbances, and fault estimation errors while suppressing the flexible appendages' vibrations. First, a nonlinear flexible spacecraft's relative attitude model with multiple actuator faults is outlined. A sliding mode-based flexible vibration observer is proposed to estimate the flexible appendage-related vibrations. The designed active fault-tolerant control scheme comprises an adaptive time-varying fault-detection strategy for quickly detecting actuator faults and avoiding false alarm rates caused by uncertainties and disturbances. An extended state observer then estimates the lumped faults effects, including the multiple actuator faults and uncertainties. The driving control is switched from nominal to fault-tolerant once the faults are successfully identified with acceptable accuracy. Besides, based on the information from the fault identification and flexible vibration observer, a novel, unwinding-free, and adaptive fault-tolerant attitude controller is designed to effectively acclimatize the detected faults, despite errors in lumped faults and flexible modes' estimations. With multiple actuator faults and uncertainties, the remunerative and precise attitude tracking control with vibration suppression is realized without using smart vibration-suppression materials. Finally, the efficacy of the propounded scheme is illustrated via comparative simulation outcomes with the existing results.