Fixed-time Attitude Tracking Research Articles

Velocity-free fixed-time attitude tracking fault-tolerant control for rigid spacecraft based on the homogeneity method

This paper examines the problem of fixed-time attitude tracking fault-tolerant for rigid spacecraft without angular velocity measurement, in the presence of uncertainties, external disturbances, and actuator faults. First, a fixed-time observer is established to obtain accurate estimates of the unmeasurable angular velocities, by applying a fixed-time observer, a fixed-time tracking control method is addressed to enable the tracking spacecraft to track the target spacecraft with time-varying attitude in a fixed time. A fixed-time output feedback attitude tracking controller is designed and the fixed time stability of the system is proved. In addition, the simulation results verify the effectiveness of the proposed control strategy.

Observer-based fault-tolerant fixed-time attitude tracking control for rigid spacecraft without angular velocity measurement

This paper investigates the problem of adaptive nonsingular fast terminal sliding mode fixed-time tracking control method for rigid spacecraft without angular velocity measurement. First, a novel fixed-time extended state observer is proposed to obtain accurate estimates of both unmeasurable angular velocities and integrated disturbance. Then, based on this sufficient qualification, an adaptive fast nonsingular terminal sliding mode controller is designed to make the state of the following spacecraft track a target spacecraft even when the tracking system has an actuator fault. Adaptive technology is introduced to compensate for the effect of observation error on the controller. Using the Lyapunov function and fixed-time property, it is proved that the control scheme can ensure that the attitude tracking error converges to the neighborhood of the origin in a fixed time and is independent of the initial conditions. Finally, numerical simulation examples are carried out to evaluate the effectiveness of the proposed fixed-time method.

Antisaturation fixed-time attitude tracking control based low-computation learning for uncertain quadrotor UAVs with external disturbances

External disturbances, uncertain parameters, asymmetric saturation input, and high computational burden can significantly damage the attitude tracking control performance of uncertain quadrotor unmanned aerial vehicles (UAVs). To accomplish the high-precision attitude tracking control, this study proposes an antisaturation fixed-time attitude tracking control based low-computation learning. Firstly, a fixed-time state observer is constructed to estimate the system states in fixed time. Secondly, by developing the fast fixed-time stable system with the time-varying gain function, a nonsingular fast fixed-time sliding mode surface is designed to improve the convergence speed and avoid the singularity problem. Thirdly, to solve the problem of asymmetric input saturation, an auxiliary compensation system is integrated to regulate the control inputs. Subsequently, an adaptive neural network (NN) technology is used to overcome the negative effects of external disturbances and uncertain parameters, where the designed adaptive mechanism is to adjust a virtual parameter online instead of the weight vector of the NN, which has the characteristics of low computational burden and simple structure. The Lyapunov-based stability analysis concludes that the closed-loop system is practical fixed-time stable and the tracking errors can converge to bounded regions around the origin in fixed time independently of the initial system states. Finally, comparative results are given to demonstrate that compared with the existing controllers, the controller developed in this study can achieve stronger robustness, faster convergence, and saturation elimination with lower error-index values.

Velocity-free fixed-time output feedback attitude tracking control of rigid spacecraft

This paper studies the problem of velocity-free fixed-time attitude tracking control for spacecraft. A new fixed-time sliding mode control method is proposed for the spacecraft attitude tracking control system. And, a novel fixed-time convergent sliding surface is designed based on the fixed-time control theory. In order to estimate the unmeasurable spacecraft information, the fixed-time observer was used to estimate the attitude information of the spacecraft. Combined with the above method, the fixed-time tracking controller is developed to guarantee the attitude tracking error of spacecraft converges to a small region within a fixed time. The fixed-time stability of the closed-loop system is proved based on the Lyapunov theory, and numerical simulations are presented to illustrate the effectiveness and superiority of the controllers.

Fixed‐time fault‐tolerance attitude tracking control for spacecraft without unwinding

In this paper, the attitude tracking control problem is investigated for rigid spacecraft subjected to external disturbance, inertia uncertainties, and actuator faults. The rotation matrix is used to model the spacecraft attitude control system which can get rid of the unwinding problem. A nonlinear observer is developed to achieve a high accuracy estimation for the lumped disturbance in fixedtime without the awareness of the boundary of disturbance. To restrain measurement noise, a tracking differentiator is used in the observer to construct signals instead of using the polluted measurement values. Based on the estimation provided by the disturbance observer, a fixed-time attitude tracking controller is proposed by backstepping technique to stabilize attitude tracking errors in fixed time regardless of initial values. The singularity problem in traditional fixed-time controllers based on signal function is eliminated with the help of the arctangent function in the proposed controller. The feature of the designed fixed-time attitude controller is that it can suppress actuator faults, measurement noises and has no unwinding problem. Theoretical analysis based on Lyapunov theory and numerical simulations are presented to illustrate the robustness and effectiveness of the proposed control strategy.

Coordinated Attitude Control of Spacecraft Formation Flying via Fixed-Time Estimators under a Directed Graph

This paper mainly studies the distributed fixed-time coordinated attitude tracking control problem of spacecraft formation with a dynamic leader spacecraft under directed communication topology. Follower spacecraft cannot communicate directly with the leader spacecraft; therefore, in order to enable them to obtain the target attitude information, a fixed-time state estimator that can be applied to directed graphs is designed. Based on the estimators, a distributed fixed-time attitude tracking control law is proposed. The settling time of the fixed-time algorithm is only related to the parameters of the control law and independent of the initial state; thus, the proposed control law can reduce the influence of the dynamic leader attitude on the spacecraft formation-coordinated attitude tracking control system. Moreover, external disturbances and spacecraft inertia uncertainty were also considered in the design of the control law. The stability of the system was verified by Lyapunov stability theory, and the effectiveness of the control law was verified by numerical simulation.

Neural-based fixed-time attitude tracking control for space vehicle subject to constrained outputs

This article aims to propose a novel neural adaptive control approach for the fixed-time attitude tracking of space vehicle subject to constrained outputs. The proposed controller is recursively synthesized by integrating with the barrier Lyapunov function (BLF) and neural approximation under the fixed-time backstepping control framework. The whole control design procedure involves two steps. In the first step, the virtual control signal is designed by adopting the BLF to guarantee the attitude tracking errors always within the predefined output constraints. In the second step, the actual control signal is designed by augmenting the neural network (NN) to approximate the uncertain term caused by unknown dynamics and disturbances. Theoretical analysis shows that the proposed controller can ensure all error signals in the closed-loop system stabilize to the small regions about the origin in fixed time even under unknown dynamics and disturbances. The effectiveness and excellent performance of the proposed control approach are validated by simulations and comparisons.

Adaptive Fixed-Time Attitude Tracking Control of Spacecraft With Uncertainty-Rejection Capability

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.

Nonsingular fixed-time attitude coordinated tracking control for multiple rigid spacecraft

This paper investigates the problem of fixed-time attitude coordinated control for multi-spacecraft systems with unknown external disturbance. Firstly, a distributed fixed-time observer is introduced to estimate the states of the virtual leader. The observer can track the leader completely in a fixed time without dependence on the initial conditions of the leader and observer. Then, we propose a novel nonsingular fixed-time sliding mode tracking controller to address the fixed-time attitude tracking problem. It is noteworthy that the requirement on initial conditions of spacecraft is removed in the proposed nonsingular sliding mode controller. Due to the robustness of sliding mode control, the influence of external disturbance can be eliminated, such that each spacecraft can track desired attitude trajectories precisely in a fixed time. Hence, the fixed-time attitude coordination for multiple spacecraft can be achieved. Finally, numerical simulation results and comparisons reveal the effectiveness of the proposed algorithms.

NN-Based Fixed-Time Attitude Tracking Control for Multiple Unmanned Aerial Vehicles with Nonlinear Faults

This paper focuses on the fixed-time fault-tolerant attitude tracking control problem for multiple unmanned aerial vehicles (MUAVs) with nonaffine nonlinear faults. First, the command filter and neural networks (NNs) are employed to characterize unknown nonlinearities in MUAVs, and the update law of NN is developed via convex optimization technique. Second, the algebraic loop problem caused by nonaffine nonlinear faults is adequately solved by introducing the Butterworth low-pass filter. Then, the curve-fitting method is utilized to construct a piecewise virtual control signal to avoid the singularity problem in fixed-time control. Furthermore, based on the Lyapunov stability theory, a general fixed-time stability criterion is adopted to prove that the designed fault-tolerant attitude controller can guarantee the stability of MUAVs in fixed time. Finally, the effectiveness of the proposed control design method is verified via illustrative examples.

Modeling and practical fixed-time attitude tracking control of a paraglider recovery system

The mathematical modeling and the control problem of the paraglider recovery system (PRS) are investigated in this paper. A 9-degree-of-freedom dynamic model describing the paraglider recovery control system is modeled including the inside relative rotation, the apparent mass, and the payload’s time-varying inertia. On the basis of the attitude tracking error system, a novel practical fixed-time attitude tracking control approach is then proposed. The attitude tracking error is governed to converge into the small regions of the origin with a fixed-time convergence rate. Moreover, this rate is independent of any initial states. Simulation results are finally presented to illustrate the PRS performance obtained from the proposed control scheme.

Fixed-time attitude tracking control for spacecraft based on a fixed-time extended state observer

Fixed-time attitude tracking control for spacecraft based on a fixed-time extended state observer

Fuzzy Adaptive Nonsingular Fixed-Time Attitude Tracking Control of Quadrotor UAVs

In this article, a fuzzy adaptive nonsingular fixed-time attitude tracking control scheme is proposed for the quadrotor unmanned aerial vehicles (UAVs) subject to inertia uncertainties, actuator saturation, and faults. A new nonsingular fixed-time sliding mode surface and an auxiliary function are constructed, such that the singularity problem can be avoided in the controller design without using any piecewise continuous functions. Then, a novel arccot function-based double power reaching law is developed to adjust the control gain and enhance the transient tracking performance. The fixed-time convergence of sliding variables and tracking errors are analyzed by rigorous theoretical proofs, and comparative experiments on a three-degree-of-freedom quadrotor platform are performed to illustrate the effectiveness of the presented scheme.

Neural-Network-Based Adaptive Singularity-Free Fixed-Time Attitude Tracking Control for Spacecrafts.

In this article, a neural-network-based adaptive fixed-time control scheme is proposed for the attitude tracking of uncertain rigid spacecrafts. A novel singularity-free fixed-time switching function is presented with the directly nonsingular property, and by introducing an auxiliary function to complete the switching function in the controller design process, the potential singularity problem caused by the inverse of the error-related matrix could be avoided. Then, an adaptive neural controller is developed to guarantee that the attitude tracking error and angular velocity error can both converge into the neighborhood of the equilibrium within a fixed time. With the proposed control scheme, no piecewise continuous functions are required any more in the controller design to avoid the singularity, and the fixed-time stability of the entire closed-loop system in the reaching phase and sliding phase is analyzed with a rigorous theoretical proof. Comparative simulations are given to show the effectiveness and superiority of the proposed scheme.

Distributed Fixed-Time Attitude Tracking Consensus for Rigid Spacecraft Systems Under Directed Graphs

Distributed fixed-time attitude tracking consensus is investigated in this letter for rigid spacecraft systems, with a directed communication graph containing a single leader which is the root of a directed spanning tree. The evolution of each follower is subject to unknown but bounded disturbances. First, a distributed fixed-time observer with heterogeneous coefficients is presented for each follower allowing cooperative estimation of the state of the leader at each follower. Then an observer-based fixed-time tracking protocol is designed to make the state of each spacecraft exactly track the state of the leader by the aid of backstepping technique. Finally, a simulation example is conducted to verify the analytical results.

Fixed‐time attitude tracking control for rigid spacecraft

This study addresses the fixed-time attitude tracking for rigid spacecraft with inertia uncertainties and external disturbances. Firstly, a new fixed-time sliding surface based on the bi-limit homogeneous theory is proposed. Secondly, a non-singular sliding mode control is designed to solve the robust fixed-time attitude tracking problem. It is proved that the proposed control can ensure that the sliding surface and attitude tracking errors converge to zero within fixed time. The appealing features of the proposed control are exact fixed-time tracking stability with fast convergence, high precision, strong robustness and easy implementation. Simulations verify the effectiveness and improved performance of the proposed approach.

Continuous Fixed-Time Sliding Mode Attitude Controller Design for Rigid-Body Spacecraft

Fast and high-precision attitude control for the rigid spacecraft is important for its broad applications in astronautics. In this paper, we address this problem via continuous nonsingular fixed-time sliding mode control approach. At first, by improving the adding power integral technique, a nonsingular nominal attitude controller is presented to achieve fixed-time convergence of the unperturbed attitude system, which underpins the basics for design of the sliding mode motion and surfaces for the subsequent proposed main results. Then, a fixed-time full-order sliding mode controller with an explicit bound of settling time is proposed to track the desire attitude even in the presence of external disturbances. However, this controller requires the angular acceleration signals which is usually unmeasurable. To this end, an integral sliding mode controller is further presented to achieve fixed-time attitude tracking without using any acceleration information. This proposed integral sliding mode controller can realize second-order sliding mode with rigorous proof of fixed-time convergence. Both the proposed fixed time full-order and integral sliding mode controller are inherent nonsingular and chattering-free. Numerical examples are illustrated to demonstrate the effectiveness of the results given herein in practical scenarios.

Fixed-time attitude tracking control for rigid spacecraft

The problem of fixed-time attitude tracking control for rigid spacecraft is addressed in this paper. Based on the backstepping technique and the idea of “adding a power integrator”, a novel fixed-time attitude control law is proposed. The control scheme derived here is continuous and nonsingular, and can guarantee the attitude tracking errors converging to the origin within fixed time if there are no uncertainties and measurement noises and to a small bounded region around zero if there are uncertainties and measurement noises. Finally, numerical simulations are presented to demonstrate the effectiveness of the proposed scheme.

Fixed-Time Fault-Tolerant Attitude Tracking Control for Rigid Spacecraft

Abstract This paper addresses the fixed-time attitude tracking problem of rigid spacecraft with inertial uncertainties, external disturbances, and partial loss of actuator effectiveness faults. A new fixed-time terminal sliding surface is proposed and a singularity-free fixed-time fault-tolerant sliding mode control (FTSMC) is designed. It is proved that the proposed FTSMC can ensure that the attitude tracking errors converge to an arbitrary small bound centered on the equilibrium point within fixed time and then go to the equilibrium point asymptotically. The appealing features of the proposed control are fixed-time tracking stability featuring fast convergence, high precision, and strong robustness. Simulations verify the effectiveness of the proposed approach.

Fixed-Time Attitude Tracking Control for Rigid Spacecraft Without Angular Velocity Measurements

This article considers the problem of velocity-free fixed-time attitude tracking control for rigid spacecraft. With the help of the homogeneity theorem, a semiglobal observer is introduced to estimate the unmeasured angular velocities within fixed time. Then, a velocity-free attitude tracking controller is designed to make the spacecraft attitude track a time-varying reference signal in finite time, which can be up bounded by a fixed number regardless of the initial conditions. Finally, numerical examples are provided to illustrate the efficiency of the present control scheme.