基于预设性能控制的超紧密航天器编队防避撞协同控制

研究了考虑具有外界干扰和防避撞约束的近地轨道超紧密航天器构型控制问题,将反步控制技术、预设性能控制相结合,提出了一种基于预设性能鲁棒控制的六自由度编队协同鲁棒控制方法。首先,给出了近地轨道完整的编队航天器相对位置和相对姿态非线性动力学方程,并根据状态约束条件转换了相对位置动力学模型。其次,设计了预设性能函数,通过误差转换,建立系统等效误差模型,基于反步法设计了预设性能鲁棒控制器,进一步应用Lyapunov稳定性定理证明了其闭环系统的一致最终有界性。最后在MATLAB/Simulink平台上进行了仿真验证,结果表明了方法的有效性。     

二阶多智能体系统自抗扰编队跟踪与避撞控制

在多智能体编队的目标跟踪任务中，智能体受环境中的障碍物的遮挡作用会丢失目标，而外部扰动会影响系统的时变编队跟踪的控制效果。为此，研究了这两种因素同时存在情况下的二阶多智能体系统时变编队跟踪和避撞控制。采用基于目标跟踪优先级的切换拓扑控制策略以实现在障碍物遮挡环境中对目标的持续跟踪，根据自抗扰理论设计包含扰动补偿项的编队跟踪控制器。首先，基于一致性方法提出切换拓扑下自抗扰时变编队跟踪控制协议，并给出一种基于跟踪微分器的编队指令生成方法；其次，设计了求解控制参数的算法并给出协议作用下系统的稳定性分析和证明；然后，基于人工势场法设计避撞控制协议；最后，提出障碍物遮挡环境下自抗扰时变编队跟踪控制协议。仿真实验结果表明:所设计的控制协议在上述两种因素存在时仍具有良好的控制效果。      

Robust model predictive control for satellite formation keeping with eccentricity/inclination vector separation

This study presents model predictive formation control based on an eccentricity/inclination vector separation strategy. Alternative collision avoidance can be accomplished by using eccentricity/inclination vectors and adding a simple goal function term for optimization process. Real-time control is also achievable with model predictive controller based on convex formulation. Constraint-tightening approach is address as well improve robustness of the controller, and simulation results are presented to verify performance enhancement for the proposed approach.     

Tube-based robust output feedback model predictive control for autonomous rendezvous and docking with a tumbling target

In this paper, a tube-based robust output feedback model predictive control method (TRMPC) is proposed for controlling chaser spacecraft docking with a tumbling target in near-circular orbit. The controller contains a simple, stable, Luenberger state estimator and a tube-based robust model predictive controller. Several practical challenges are also considered under dock-enabling conditions, such as the control saturation, velocity constraint, approach corridor constraint, and collision avoidance constraint. Meanwhile, uncertainties are carefully analyzed when designing the controller, including dynamics uncertainty, measurement error, and control deviation. The TRMPC ensures that all possible state trajectories with uncertainties lie in the minimum robust positively invariant set (mRPI, i.e., the so-called tube in this paper). The tube center is the solution of a nominal (without uncertainties) system. Another important contribution of this paper is to propose a technique where it is unnecessary to calculate the mRPI explicitly. Thereby, the ‘curse of dimensionality’ can be avoided for a six-dimensional system. To verify the feasibility of the proposed TRMPC strategy in the presence of uncertainties, two scenarios of autonomous rendezvous and docking (AR&D) are simulated. The simulation results show that the TRMPC method is more efficient in minimizing the uncertainties, fuel consumption, and computational cost, compared to the classic model predictive control (MPC) method.     

Optimal H∞ robust output feedback control for satellite formation in arbitrary elliptical reference orbits

A two degree-of-freedom signal-based optimal H_∞ robust output feedback controller is designed for satellite formation in an arbitrary elliptical reference orbit. Based on high-fidelity linearized dynamics of relative motion, uncertainties introduced by non-zero eccentricity and gravitational J2 perturbation are separated to construct a robust control model. Furthermore, a distributed robust control model is derived by modifying the perturbed robust control model of each satellite with the eigenvalues of the Laplacian matrix of the communication graph, which represent uncertainty in the communication topology. A signal-based optimal H_∞ robust controller is then designed primarily. Considering that the uncertainties involved in the distributed robust control model have a completely diagonal structure, the corresponding analyses are made through structured singular value theory to reduce the conservativeness. Based on simulation results, further designs including increasing the degrees of freedom of the controller, modifying the performance and control weighted functions, adding a post high-pass filter according to the dynamic characteristics, and reducing the control model are made to improve the control performance. Nonlinear simulations demonstrate that the resultant optimal H_∞ robust output feedback controller satisfies the robust performance requirements under uncertainties caused by non-zero eccentricity, J2 perturbation, and varying communication topology, and that 5 m accuracy in terms of stable desired formation configuration can be achieved by the presented optimal H_∞ robust controller. In addition to considering the widely discussed uncertainties caused by the orbit of each satellite in a formation, the optimal H_∞ robust output feedback control model presented in the current work considers the uncertainties caused by varying communication topology in the satellite formation that works in a cooperative way. Other new improvements include adopting a new method to more accurately describe and analyze the effects of the higher-order J2 perturbation, combining all the uncertainties into a diagonal structure, and utilizing a structured singular value to synthesize and analyze the controller.     

基于人工势场的星群松散编队控制

利用低成本的微纳卫星组成星群协同执行空间任务，近年来引起了航天界的广泛关注.针对星群松散编队控制任务，将人工势场法和基于相对运动动力学方程的速度反馈控制相结合，在各颗卫星和目标之间构造吸引势场，在各颗卫星之间建立基于位置信息的避碰势场，在空间障碍物附近建立避障势场，同时引入速度反馈控制律，综合实现星群松散编队控制，并通过仿真算例验证了控制方法的有效性.     

考虑能量最优的集群航天器避碰规划

针对传统集群聚集算法在航天器集群规划应用中存在燃料消耗大、不均衡以及耗时过长等问题,提出了向心聚集的能量最优聚类避碰算法。该算法首先基于集群相对运动方程与有限时间的能量最优模型,建立了自适应的向心聚集的能量最优模型;在此基础上,对于耗时较长且碰撞的问题,提出一种基于能量最优的聚类避碰算法,以模块间安全距离矢量作为避碰约束,将能量消耗作为聚类算法指标进行改进。仿真验证表明,该算法可以自适应选取集群聚类的中心,有效避免碰撞,减少集群聚集总能量的消耗以及模块间能量消耗的不均衡性,使得工质消耗达到全局最优,且耗时仅有常规遗传算法的万分之一。该算法为集群快速安全聚集提供了思路。     

多导弹协同攻击编队非线性最优控制器设计

针对多导弹协同攻击编队控制问题,采用仿射非线性系统最优控制理论设计了基于领弹-从弹法的多导弹编队控制器.首先采用基于微分几何理论的非线性系统精确线性化方法,将导弹非线性运动模型线性化;然后根据从弹、领弹间的相对运动关系,给出了包含领弹运动信息和队形信息的从弹期望轨迹,建立了基于从弹跟踪误差向量的系统状态方程;最后采用基于稳态解的黎卡提矩阵微分方程求解方法解决最优控制问题,设计了从弹的三维非线性编队控制器;仿真结果表明所设计的控制器能够在领弹机动地情况下快速、稳定地实现编队队形的形成和保持.      

Multi-agent Q-Learning control of spacecraft formation flying reconfiguration trajectories

This paper presents a novel approach based on multi-agent reinforcement learning for spacecraft formation flying reconfiguration tracking problems. In this scheme, spacecrafts learn the control strategy via transfer learning. For this matter, a new generalized discounted value function is introduced for the tracking problems. Due to the digital nature of spacecraft computer systems, local optimal controllers are developed for the spacecrafts in discrete-time. The stability of the controller is proven. Two Q-learning algorithms are proposed, in each of which the optimal control solution is learned on-line without knowledge about the system dynamics. In the first algorithm, each agent learns the optimal control independently. In the second one, each agent shares the learned information with other agents. Next, the collision avoidance capability is provided. The effectiveness of the presented schemes is verified through simulations and compared with each other.     

基于代理模型的卫星编队重构最短距离建模

针对编队卫星成员数量较多时,编队重构规划考虑碰撞规避会带来的巨大的计算开销。为降低计算开销和提升优化效率,基于CW方程和双脉冲轨道机动策略,建立了能够快速预测编队卫星重构过程最短距离的多种代理模型,并基于三种大小不同的训练集,从模型精度和效率两方面进行了对比。结果表明,克里金（KRG）模型在各种代理模型中精度最高,而且随着训练量的增加,克里金和人工神经网络（ANN）模型的性能得到了明显改善,模型精度有一定的保证。研究还发现,尽管KRG模型预测时间高于其他代理模型,但和真实模型相比,其耗时仍然很短,因此可用于提高考虑避碰约束时卫星编队重构轨迹优化的效率。     

一种抑制扰动的轴向磁轴承鲁棒控制新方法

从鲁棒稳定性和抑制扰动的动态性能角度,分析了干扰观测器应用到轴向磁轴承时其有效带宽较低的问题,指出磁轴承易受到低频干扰并提出了一种抑制扰动鲁棒控制方法.基于动态分析建立了轴向磁轴承的名义模型,并设计了内环控制的干扰观测器,采用标准H∞问题的方法设计抑制扰动鲁棒控制器作为外环控制.仿真分析与实验说明了该方法能够提高干扰观测器的带宽,同时,实验验证了对于系统参数不确定性具有较强的鲁棒性能,对比单一的控制方法具有良好的抑制扰动能力.     

Constant thrust collision avoidance maneuver under thruster failure

In this paper, the collision avoidance maneuver under the chaser’s thruster failure in radial direction is investigated. First, based on the vision measurement, the relative position parameters of the target spacecraft are obtained and the target maneuvre positions are calculated through the isochronous interpolation method. Then, by using coupling effects, the thrusters working time intervals can be computed by the time series analysis method. The perturbations and fuel consumptions are addressed during the computation of the thrusters working time intervals. Next, the switching control law under constant thrust is designed for active collision avoidance maneuvres along a specified trajectory.     

飞航导弹编队队形变换控制器设计

为满足飞航导弹编队协同作战中队形变换的需求,针对密集编队在队形变换时的碰撞冲突问题,考虑其低空突防背景与机动能力的限制条件,设计了基于局部模型预测控制的主动防碰撞队形保持控制器,并应用于编队队形的变换控制,提出了队形的状态转移变换方法,通过与直接变换方法的对比仿真,验证了其可行性和有效性.      

Robust optimal sliding mode control for the deployment of Coulomb spacecraft formation flying

Inter-spacecraft electrostatic force (Coulomb force) is desirable for close formation flying control because of its propellant-less and free contaminate characteristics attributed to the propellant exhaust emission. This paper presents robust optimal sliding mode control to deal with the problem of thruster saturation in tracking the formation trajectory for Coulomb spacecraft formation flying. The robust controller design is based on optimal control theory as a linear quadratic system, and it is augmented with an integral sliding mode control technique. The stability of the closed-loop system is guaranteed using the second Lyapunov method. The developed controller outperforms the existing ones, because it has a higher degree of fine-tuning to cope with the uncertainty. Numerical simulations are employed to confirm the efficiency of the developed controller.     

卫星规避方案量化分析方法研究

空间碎片数量日益增多,为保护在轨卫星的运行安全,需要针对碎片碰撞制定规避方案,用来规避碰撞风险.本文在调研国外卫星规避机动流程的基础上,分别研究了卫星规避相关的轨道机动方式、轨道预报模型以及交会风险计算模型,建立了卫星规避方案量化分析方法,为规避方案的选择提供参考.      

基于高斯伪谱法的碰撞规避策略研究

为保证在轨卫星运行安全，对于碰撞概率较高的空间交会情况需要进行规避机动，防止在轨卫星与空间碎片碰撞.选取连续推力策略进行规避机动，将空间碰撞规避过程转化为满足复杂约束的最优控制问题，采用高斯伪谱法对最优控制律进行求解，求解结果满足相应约束.研究结果为航天器有效规避空间碰撞威胁提供了有力支持.      

面向空中威胁的无人机动态碰撞区建模与分析

针对现有方法一般是基于时间或距离的定值来确定碰撞区域的问题,提出了一种基于入侵机和无人机(UAV)运动信息的无人机动态碰撞区建模方法.首先,根据无人机与入侵机的运动状态、两机之间的最小安全距离等信息,通过几何方法得出无人机不采取任何规避机动时两机将发生碰撞区域的解析表达式,即无机动碰撞区数学模型;其次,考虑无人机的机动能力约束,计算了无人机采取最大过载转弯机动(左转或右转)时两机恰好避免碰撞发生的边界,即最大机动碰撞区数学模型;在此基础上,提出了不可规避区的概念;进而定义了安全飞行包络,它是无人机能够规避入侵机威胁的分界线;最后通过理论和仿真结合分析了影响各区域的主要因素.仿真与分析结果表明所建碰撞区不仅可以帮助无人机选择规避机动方式,而且能够帮助无人机判定常规避撞机动是否失败,并使无人机及时采取最大过载转弯机动,对无人机安全避撞决策具有实际参考价值.      

基于视线测量的卫星编队机动控制方法

采用视线测量的方法,建立一种编队卫星队形保持与机动的协同控制策略。编队中每一个卫星跟踪自己轨道前方邻近卫星,产生一个视线测量矢量,编队的第一个卫星根据高级控制层指令追踪期望轨道,产生链式编队,将编队卫星之间的视线距离作为反馈控制量来实现队形控制。通过推导J2相对摄动力的表达式,控制模型考虑了模型不确定性和摄动影响,采用滑模控制器,实现了基于视线测量的编队卫星链式跟踪协同控制。仿真算例结果表明,该方法在实现编队卫星队形保持与整体机动控制上具有可行性。     

Energy-optimal reconfiguration of satellite formation flying in the presence of uncertainties

In this study, a two-step control methodology is developed for energy-optimal reconfiguration of satellites in formation in the presence of uncertainties or external disturbances. First, based on a linear deterministic system model, an optimal control law is analytically determined such that a satellite maneuvers from an initial state to a final state relative to another satellite. The structure of this optimal solution is predetermined and simply given by a linear combination of the fundamental matrix solutions associated with the original equations of relative motion. Only the coefficients are to be determined to satisfy given initial and final conditions. In the second step, an uncertain nonlinear formation system is considered and a robust adaptive controller is designed to compensate for the effects of uncertainties or disturbances that the formation system may encounter. Although the control strategy is inspired by sliding mode control, it produces smooth control signals, thereby avoiding chattering. Also, an adaptation law is added such that the uncertainty or disturbance effects are effectively and quickly eliminated without a priori information about them. The combination of these two controllers guarantees that the satellite accurately tracks the optimal path in the unknown environment. Numerical simulations demonstrate the effectiveness and accuracy of the proposed two-step control methodology, in which a satellite formation is optimally reconfigured under unknown environmental disturbances.     

Optimal guidance and collision avoidance for docking with the rotating target spacecraft

The guidance and control strategy for spacecraft rendezvous and docking are of vital importance, especially for a chaser spacecraft docking with a rotating target spacecraft. Approach guidance for docking maneuver in planar is studied in this paper. Approach maneuver includes two processes: optimal energy approach and the following flying-around approach. Flying-around approach method is presented to maintain a fixed relative distance and attitude for chaser spacecraft docking with target spacecraft. Due to the disadvantage of energy consumption and initial velocity condition, optimal energy guidance is presented and can be used for providing an initial state of flying-around approach process. The analytical expression of optimal energy guidance is obtained based on the Pontryagin minimum principle which can be used in real time. A couple of solar panels on the target spacecraft are considered as obstacles during proximity maneuvers, so secure docking region is discussed. A two-phase optimal guidance method is adopted for collision avoidance with solar panels. Simulation demonstrates that the closed-loop optimal energy guidance satisfies the ending docking constraints, avoids collision with time-varying rotating target, and provides the initial velocity conditions of flying-around approach maneuver. Flying-around approach maneuver can maintain fixed relative position and attitude for docking.