Nonlinear attitude tracking control for spacecraft formation with multiple delays

This paper addresses the attitude tracking control for spacecraft formation with delay free and communication delays. With help of the idea of sliding control, an adaptive attitude synchronization control architecture is established. Furthermore, by introducing a nonsmooth feedback function, a new class of nonlinear controllers for the attitude tracking of spacecraft is developed. Both parameter uncertainties and unknown external disturbances are dealt with via the kind of controllers. Finally, some simulation results are given to demonstrate the effectiveness and advantages of the proposed results.     

Finite-time relative orbit-attitude tracking control for multi-spacecraft with collision avoidance and changing network topologies

This paper addresses the relative position tracking and attitude synchronization control problem for spacecraft formation flying (SFF). Based on the derived relative coupled six-degree-of-freedom dynamics, a robust adaptive finite-time fast terminal sliding mode controller is proposed to achieve the desired formation in the presence of model uncertainties and external disturbances. It is shown that the designed controller is effective for changing information exchange topology making it robust to node failure. Then, the artificial potential function method is employed to generate collision avoidance schemes to modify the controller such that inter-agent collision avoidance can be ensured during the formation maneuver, which is critical for practical missions. The stability of the overall closed-loop system is proved by using Lyapunov theory. Finally, numerical examples for a given SFF scenario are presented to illustrate the performance of the controller.     

可重复使用运载器递归积分滑模姿态控制方法

针对存在模型不确定和外部干扰的可重复使用运载器再入段姿态控制问题,提出了一种基于自适应滑模干扰观测器的递归积分滑模控制方法。首先,基于可重复使用运载器再入段姿态运动模型,建立了面向控制的模型;其次,设计了自适应滑模干扰观测器,以精准估计和补偿由模型不确定和外部干扰构成的复合干扰;然后,基于递归思想设计了一种新型递归积分滑模控制器,利用Lyapunov稳定性理论证明了闭环系统的有限时间稳定性;最后,数值仿真结果验证了该方法具有较强的鲁棒性和较快的收敛速度。     

航天器编队飞行多目标姿态跟踪终端滑模控制

研究航天器编队飞行多目标姿态跟踪控制问题.为避免姿态大范围跟踪可能出现的奇点,采用欧拉参数描述航天器姿态.基于终端滑模技术,设计多目标姿态跟踪终端滑模控制器,并应用Lyapunov稳定性理论和扩展的Lyapunov有限时间稳定性理论证明控制系统稳定性和有限时间收敛性.该控制器参数方便调整,易于实现.由于没有对复杂多体航天器动力学进行线性化处理,从而保证了姿态跟踪控制精度.仿真结果表明,存在惯量参数摄动和外部干扰力矩的情况下,所设计的多目标姿态跟踪控制器具有良好鲁棒性和优越的跟踪性能.     

一类不确定分数阶混沌系统的滑模自适应同步

基于滑模自适应控制理论、Lyapunov稳定性理论和分数阶线性系统稳定性理论,在考虑系统存在模型不确定和外部扰动的情况下,选用一种具有较强鲁棒性的分数阶滑模曲面,设计了合适的自适应滑模控制器。所设计的控制器能够将系统状态控制到滑模面上,实现两个不确定分数阶混沌系统的同步,且不需事先知道不确定项上界。该控制器结构简单,控制代价小,具有较好的通用性,对未知扰动具有较强的鲁棒性。数值仿真验证了该方法的正确性和有效性。     

基于模糊神经网络干扰观测器的组合体航天器姿态控制

针对非合作目标存在对抗性力矩输出情况下的组合体航天器姿态控制系统,提出了一种基于模糊神经网络干扰观测器（Fuzzy Neural Network Disturbance Observer,FNNDO）的非奇异终端滑模（Nonsingular Terminal Sliding Mode,NTSM）有限时间控制策略。首先以服务航天器为基准,建立组合体航天器姿态数学模型,然后针对包含惯量不确定性、目标对抗性力矩等的等效干扰力矩,设计了一种具有自适应能力的FNNDO,可以实现对等效干扰的有效跟踪。在FNNDO的基础上,设计NTSM控制器,利用Lyapunov理论证明闭环系统的有限时间稳定性。最后,仿真实验结果表明了控制策略的有效性和观测器在观测性能上的优越性。     

基于ESO的可重复使用飞行器积分滑模控制器设计

考虑参数不确定和外界干扰对姿态控制的影响,开展基于扩张状态观测器(ESO,extended states observer)的可重复使用飞行器姿态控制研究.首先,对飞行器运动模型进行描述,在合理假设条件下,得到面向控制器设计的纵向和横侧向姿态模型;其次,分别针对纵向和横侧向姿态模型设计积分滑模控制器(ISMC,integral sliding mode control);然后,引入ESO对耦合作用、参数不确定及外界干扰进行估计,并在控制器中进行补偿;最后,六自由度仿真结果表明,本研究给出的控制策略能够实现对给定制导指令的稳定跟踪,确保安全再入飞行.     

Neural network-based sliding mode control for atmospheric-actuated spacecraft formation using switching strategy

This paper presents an adaptive neural networks-based control method for spacecraft formation with coupled translational and rotational dynamics using only aerodynamic forces. It is assumed that each spacecraft is equipped with several large flat plates. A coupled orbit-attitude dynamic model is considered based on the specific configuration of atmospheric-based actuators. For this model, a neural network-based adaptive sliding mode controller is implemented, accounting for system uncertainties and external perturbations. To avoid invalidation of the neural networks destroying stability of the system, a switching control strategy is proposed which combines an adaptive neural networks controller dominating in its active region and an adaptive sliding mode controller outside the neural active region. An optimal process is developed to determine the control commands for the plates system. The stability of the closed-loop system is proved by a Lyapunov-based method. Comparative results through numerical simulations illustrate the effectiveness of executing attitude control while maintaining the relative motion, and higher control accuracy can be achieved by using the proposed neural-based switching control scheme than using only adaptive sliding mode controller.     

航天器非奇异自适应终端滑模姿轨联合控制

为了实现航天器姿态与轨道的同步控制，提出了一种航天器姿态与轨道联合控制的非奇异自适应终端滑模控制律。首先，建立了航天器姿轨耦合运动的对偶四元数模型；其次，提出了一种姿轨联合跟踪控制的非奇异终端滑模控制律，并设计了自适应控制律以改善质量特性不确定性的影响，利用李雅普诺夫函数证明了所提控制律的稳定性；最后，绕飞小行星的跟踪控制仿真算例表明了控制律的有效性。结果表明:所提控制律具有较高的控制精度，能够在有限时间内收敛，仿真过程中不存在奇异点，抑制了质量特性的不确定性对控制的影响，且对滑模的抖振特性有抑制效果。      

CMGs驱动空间机械臂的自适应终端滑模控制

摘要： 针对V构型控制力矩陀螺（CMGs）驱动的空间机械臂的轨迹跟踪控制问题,研究一种自适应非奇异终端滑模（ANTSM）控制方法.利用基于Kane方程的递推组集算法建立了系统的动力学模型.以跟踪误差为变量,构造非奇异滑动面,以保证跟踪误差在滑动面上有限时间收敛.针对系统质量特性参数与关节处干扰力矩的不确定性,设计自适应控制器用以调节控制增益.该控制方法无需不确定性的上界,且闭环系统具有最终一致有界性.仿真结果表明,该控制器可使系统准确跟踪期望轨迹,并对质量特性参数不确定性和关节干扰力矩具有良好的鲁棒性.     

Adaptive fuzzy neural network control for a space manipulator in the presence of output constraints and input nonlinearities

Space manipulator is considered as one of the most promising technologies for future space activities owing to its important role in various on-orbit serving missions. In this paper, a novel adaptive fuzzy neural network (FNN) control scheme is proposed for the trajectory tracking control of an attitude-controlled free-flying space manipulator in the presence of output constraints and input nonlinearities. The parametric uncertainties and external disturbances are also taken into the consideration. First, a model-based controller is designed by using the barrier Lyapunov function (BLF) to prevent the position tracking errors from violating the predefined output constraints. Then, an adaptive FNN controller is designed by using two FNNs to compensate for the lumped uncertainties and input nonlinearities, respectively. Rigorous theoretical analysis for the semiglobal uniform ultimate boundedness of the whole closed-loop system is provided. The proposed adaptive FNN controller can guarantee the position and velocity tracking errors converge to the small neighborhoods about zero, while ensuring the position tracking errors within the output constraints even in the presence of input nonlinearities. To the best of the authors’ knowledge, there are relatively few existing controllers can achieve such excellent control performance in the same conditions. Numerical simulations illustrate the effectiveness and superiority of the proposed control scheme.     

基于扰动观测器的指数时变滑模再入姿态控制

针对再入飞行器姿态控制问题,设计了一种全局鲁棒的基于扰动观测器的指数时变滑模姿态控制器,使得在存在匹配模型参数不确定性和外部扰动情况下仍能够实现精确的姿态控制。首先对飞行器模型进行反馈线性化解耦,将俯仰、滚转、偏航通道分解为3个独立的二阶系统。然后以俯仰通道为例,设计指数时变滑模控制器,使得系统具有全局鲁棒性。进一步,为了减小采用饱和函数消除滑模控制抖振而带来的系统跟踪误差,引入扰动观测器,设计了一种基于扰动观测器的指数时变滑模控制系统。最后,以某飞行器为例建立六自由度仿真模型,在考虑大气密度、转动惯量偏差以及外部高频扰动的情况下,验证了加入扰动观测器后对系统性能的提高。     

Adaptive sliding mode control of spacecraft attitude-orbit dynamics on SE(3)

In this paper, to solve the problem of parameters uncertainty in spacecraft tracking control, an adaptive controller based on sliding mode is proposed for the relative spacecraft attitude-orbit dynamics on the Lie group SE(3). The dynamic equations of relative attitude orbit error for two spacecraft are established in the framework of Lie group SE(3). Considering the uncertainty of spacecraft parameters, a formal decomposition of known and unknown parameters, the state variables and control variables is firstly made in the original system. An online estimator is designed to evaluate the unknown parameters. A sliding mode controller is developed to actuate the spacecraft to track the target spacecraft. Then a Lyapunov function of tracking error and parameters estimated error is designed to prove the stability of the closed-loop system. Finally, the simulation results and analysis are presented to verify the effectiveness and feasibility of the proposed method.     

Fault tolerant small satellite attitude control using adaptive non-singular terminal sliding mode

The Attitude Control System (ACS) plays a pivotal role in the whole performance of the spacecraft on the orbit; therefore, it is vitally important to design the control system with the performance of rapid response, high control precision and insensitive to external perturbations. In the first place, this paper proposes two adaptive nonlinear control algorithms based on the sliding mode control (SMC), which are designed for small satellite attitude control system. The nonlinear dynamics describing the attitude of small satellite is considered in a circle reference orbit, and the stability of the closed-loop system in the presence of external perturbations is investigated. Then, in order to account for accidental or degradation fault in satellite actuators, the fault-tolerant control schemes are presented. Hence, two adaptive fault-tolerant control laws (continuous sliding mode control and non-singular terminal sliding mode control) are developed by adopting the nonlinear analytical model to describe the system, which can guarantee global asymptotic convergence of the attitude control error with the existence of unknown external perturbations. The nonlinear hyperplane based Terminal sliding mode is introduced into the control law design; therefore, the system convergence performance improves and the control error is convergent in “finite time”. As a result, the study on the non-singular terminal sliding mode control is the emphasis and the continuous sliding mode control is used to compare with the non-singular terminal sliding mode control. Meanwhile, an adaptive fuzzy algorithm has been proposed to suppress the chattering phenomenon. Moreover, several numerical examples are presented to demonstrate the efficacy of the proposed controllers by correcting for the external perturbations. Simulation results confirm that the suggested methodologies yield high control precision in control. In addition, actuator degradation, actuator stuck and actuator failure for a period of time are simulated to demonstrate the fault recovery capability of the fault tolerant controllers. The numerical results clearly demonstrate the good performance of the adaptive non-singular terminal control in the event of actuator fault compare with the continuous sliding mode control.     

Robust fault-tolerant saturated control for spacecraft proximity operations with actuator saturation and faults

In this paper, the motion control problem of autonomous spacecraft rendezvous and docking with a tumbling target in the presence of unknown model parameters, external disturbances, actuator saturation and faults is investigated. Firstly, a nonlinear six degree-of-freedom dynamics model is established to describe the relative motion of the chaser spacecraft with respect to the tumbling target. Subsequently, a robust fault-tolerant saturated control strategy with no precise knowledge of model parameters and external disturbances is proposed by combining the sliding mode control technique with an adaptive methodology. Then, within the Lyapunov framework, it is proved that the designed robust fault-tolerant controller can guarantee the relative position and attitude errors converge into small regions containing the origin. Finally, numerical simulations are performed to demonstrate the effectiveness and robustness of the proposed control strategy.     

刚体航天器大角度姿态机动控制算法

针对刚体航天器在参数不确定及环境扰动情况下的大角度姿态机动问题,提出一种自适应离散变结构姿态控制算法.建立包含航天器姿态运动学及动力学的仿射模型,并精确反馈线性化解耦;对得到的各线性动态方程离散化处理,由离散指数趋近律推导了参数化的离散变结构姿态控制律.最后基于Lyapunov稳定性理论设计了控制参数的自适应更新律,有效克服了模型中的各时变项及干扰项影响.仿真结果表明,该算法可有效减小干扰引起的姿态指令角跟踪偏差,确保了大角度姿态机动控制的精确性与鲁棒性,并且消除了常规变结构控制的抖振现象.     

Formation flying for magnetic sails around artificial equilibrium points

This paper investigates the problem of magnetic sail-based spacecraft formation control around the artificial equilibrium points (AEPs), which can eliminate the requirement of the propellant. The thrusts are achieved by utilizing the interaction between the solar wind and the artificial magnetosphere generated by superconducting current coil onboard. The circular restricted three-body problem (CRTBP) of magnetic sail is discussed including the allowed regions and linear stability of AEPs, the locations of collinear AEPs and the possibility of existence of periodic orbits around the collinear AEPs. Next, the dynamical models of magnetic sail formation around the collinear AEPs are established. A novel fast fixed-time nonsingular terminal sliding mode controller (FFNTSM) based on fixed-time disturbance observer (FTDO) is developed to account for external disturbances. Several numerical simulations are conducted to substantiate that spacecraft formation can be precisely controlled by the proposed propellantless propulsion method in the presence of external disturbances.     

高超声速飞行器全局有限时间姿态控制方法

以高超声速飞行器6自由度模型为研究对象,设计了一种基于终端滑模的全局有限时间姿态控制方法。在控制器设计中,通过动态逆实现对俯仰、偏航和滚转通道的解耦处理。在考虑模型不确定性和外部干扰的情况下,终端滑模变结构控制方法用于保证系统的鲁棒性。同时,通过改进指数趋近律,实现闭环系统在滑模面趋近阶段和沿滑模面滑动阶段均是有限时间收敛的。基于李雅普诺夫稳定性理论,控制器的全局有限时间收敛特性得到证明。仿真实验结果验证了高超声速飞行器全局有限时间姿态控制方法的有效性。      

基于神经网络的电液转台非线性积分滑模控制

针对高精度电液飞行仿真转台具有高度非线性、参数不确定和不确定非线性等特点,提出了一种基于RBF（Radial Basis Function）神经网络的非线性积分滑模鲁棒控制方法.采用自适应RBF神经网络对该系统存在的参数不确定性和不确定非线性进行补偿,从而降低滑模控制器对切换项的增益的需求,进而减小系统抖振幅值.积分滑模面的设计能消除外部干扰对系统带来的稳态误差.根据积分滑模变结构控制器的特点,将控制律分为等效控制律和到达控制律.等效控制律使系统运动于滑模面附近,到达控制律可使处于状态空间内任意初始位置的系统趋近于滑模面,并进一步通过Lyapunov方法证明了系统的渐近稳定性.实验结果表明,所提出的非线性控制器不仅能满足电液转台的高精度跟踪性能的要求,且对参数不确定性和不确定非线性具有一定的鲁棒性.     

Adaptive sliding mode fault-tolerant control for satellite attitude tracking system

In this paper, an adaptive modified sliding mode control approach is developed for attitude tracking of a nano-satellite with three magnetorquers and one reaction wheel. A sliding variable is chosen based on finite-time convergence of the nano-satellite attitude tracking error and avoiding the singularity of the control signal. The control gain of the proposed method is developed adaptively to reduce the tracking error and improve the closed-loop control performance. The sliding variable and adaptive parameter are also employed in the reaching phase of the control law to decrease the chattering phenomenon. In addition, the finite-time convergence of attitude variables in the presence of actuator faults, inertia uncertainty, and external disturbances is proved using the extended Lyapunov theorem. The simulations are conducted to evaluate the performance of the proposed method according to different evaluation criteria. Monte Carlo simulations are also used to survey the reliability of the system in the presence of the mentioned condition.