Wave control of a flexible space tether based on elastic metamaterials

This study proposes a spider‐web elastic metamaterial to suppress vibrations in space slender structures,such as flexible space tethers.The metamaterial consists of unit cells that are periodically distributed on the space tether to obtain band gaps.The finite element model of the unit cell is established by employing the absolute nodal coordinate formulation(ANCF)due to the large deformation of the structure.The eigenfrequencies and corresponding vibration modes of the unit cell are obtained by ANCF.Moreover,the band gap of the unit cell is calculated based on the phonon crystal theory.The relationship between the vibration modes and the band gaps is analyzed.Finally,an experiment is conducted to verify the vibration transmission characteristics of finite period cells.The results show the effectiveness of the spider‐web elastic metamaterial for vibration suppression of a flexible tether.This study provides insights into the use of elastic metamaterials for vibration isolation in space tether systems.

Nonlinear dynamics of flexible tethered satellite system subject to space environment

The paper studies the nonlinear dynamics of a flexible tethered satellite system subject to space environments, such as the J2 perturbation, the air drag force, the solar pressure, the heating effect, and the orbital eccentricity. The flexible tether is modeled as a series of lumped masses and viscoelastic dampers so that a finite multi- degree-of-freedom nonlinear system is obtained. The stability of equilibrium positions of the nonlinear system is then analyzed via a simplified two-degree-freedom model in an orbital reference frame. In-plane motions of the tethered satellite system are studied numerically, taking the space environments into account. A large number of numerical simulations show that the flexible tethered satellite system displays nonlinear dynamic characteristics, such as bifurcations, quasi-periodic oscillations, and chaotic motions.

Dynamic analysis of tethered space system deployment process

Discusses in detail the deploying strategies and feature of the motion of the Tethered Space System and the effects of some parameters, such as the property and initial length of the tether, the perturbation of the atmosphere, the ellipse of the orbit and the mass distribution of the system and points out the deploying strategy is based on the controlling of tension and the length of tether. And concludes from the computer simulation results of a tethered atmosphere probing satellite deployment that the deploying strategy presented does work well.

Nonlinear dynamics and coupling effect of libration and vibration of tethered space robot in deorbiting process

In order to control the growth of space debris,a novel tethered space robot(TSR) was put forward.After capture,the platform,tether,and target constituted a tethered combination system.General nonlinear dynamics of the tethered combination system in the post-capture phase was established with the consideration of the attitudes of two spacecrafts and the quadratic nonlinear elasticity of the tether.The motion law of the tethered combination in the deorbiting process with different disturbances was simulated and discussed on the premise that the platform was only controlled by a constant thrust force.It is known that the four motion freedoms of the tethered combination are coupled with each other in the deorbiting process from the simulation results.A noticeable phenomenon is that the tether longitudinal vibration does not decay to vanish even under the large tether damping with initial attitude disturbances due to the coupling effect.The approximate analytical solutions of the dynamics for a simplified model are obtained through the perturbation method.The condition of the inter resonance phenomenon is the frequency ratio λ_1=2.The case study shows good accordance between the analytical solutions and numerical results,indicating the effectiveness and correctness of approximate analytical solutions.

Advances in dynamics and control of tethered satellite systems

The concept of tethered satellite system （TSS） promises to revolutionize many aspects of space exploration and exploitation. It provides not only numerous possible and valuable applications, but also challenging and interesting problems related to their dynamics, control, and physical implementation. Over the past decades, this exciting topic has attracted significant attention from many researchers and gained a vast number of analytical, numerical and experimental achievements with a focus on the two essential aspects of both dynamics and control. This review article presents the historic background and recent hot topics for the space tethers, and introduces the dynamics and control of TSSs in a progressive manner, from basic operating principles to the state-of-the-art achievements.

摩擦力对空间非导电绳系释放动力学的影响

当前空间非导电绳系释放过程因摩擦力数据缺乏,导致释放动力学仿真结果不能有效反映真实情况。为此,基于绳系地面释放平台,开展非导电绳系释放摩擦力测量实验,研究了系绳材料、直径、缠绕方向和释放速度对系绳释放所受摩擦力的影响,阐明非导电绳系释放过程影响球形效应不稳定现象的主要因素,确定非导电绳系释放摩擦力与释放条件之间的定量关系。进一步建立考虑摩擦力的绳系释放动力学模型。仿真结果表明,非导电绳系释放摩擦力对释放过程影响较大,对于500 m长的系绳,初始释放速度为2 m/s,在未考虑释放摩擦力时,绳系释放完成时间与考虑摩擦力的实际情况相差约20%。

空间长方形绳网展开动力学及多参数特性分析

空间绳网系统是一种针对空间碎片的柔性捕获系统,针对带有太阳翼的空间目标,提出一种用于捕获目标主体的长方形绳网。为分析其展开效果,建立有限元模型,通过对比地面试验结果来验证有限元模型的可靠性。建立长方形绳网的评价指标,并通过各项评价指标对比不同牵拉模式、牵引绳分布圆直径及牵引体发射角度下的绳网展开特性。结果表明:仿真结果与试验结果吻合,有限元模型可靠;在八点牵拉、十点牵拉和十二点牵拉3种模式下,十点牵拉所能达到的展开效果最好;牵引绳分布圆直径增大,所能达到的最大展开面积和保形距离减小,展开距离增大;牵引体的发射角度增大,长方形绳网的最大展开面积和保形距离增大,展开距离减小。

Retrieval strategy for failed satellite on tether’s optimal balance swing angle

A retrieval control strategy for failed satellite,which is connected to a servicing spacecraft by a tether,is studied.The Lagrange analytical mechanics based dynamics modeling for the system composed of a servicing spacecraft,a tether and a failed satellite,is presented under the earth center inertia coordinate system,then model simplification is conducted under the assumption that the failed satellite’s mass is far smaller than the servicing spacecraft’s,meanwhile the tether’s length is far smaller than the size of the servicing spacecraft’s orbit.Analysis shows that the retrieval process is intrinsically unstable as the Coriolis force functions is a negative damping.A retrieval strategy based on only the tether’s tension is designed,resulting in the fastest retrieval speed.In the proposed strategy,firstly,the tether’s swing angle amplitude is adjusted to 45?by deploying/retrieving the tether;then the tether swings freely with fixed length until it reaches negative maximum angle–45?;finally,the tether is retrieved by the pre-assigned exponential law.For simplicity,only the coplanar situation,that the tether swings in the plane of the servicing spacecraft’s orbit,is studied.Numerical simulation verifies the effectiveness of the strategy proposed.

空间多体绳系编队动力学与控制研究综述

针对空间多体绳系编队的构型进行了分类,分析了国内外对绳系编队动力学模型的研究现状,并总结了常用于绳系系统动力学模型建立的三种系绳模型。此外,对绳系编队全流程控制,包括绳系编队构型形成、构型稳定保持以及刚体姿态机动控制进行了梳理和分析,同时对现有的地面试验装置及方法进行了概括。最后针对目前绳系编队的动力学建模与控制、地面试验装置研究中存在的不足进行了总结,对未来的发展方向提出了建议。

Strict finite-time sliding mode control for a tethered space net robot

Tethered Space Net Robot(TSNR)is considered to be a promising approach for space debris removal,and accordingly it is also an interesting control problem due to its time-varying disturbances caused by an elastic and flexible net and a main connected tether.In this situation,the control scheme should be robust enough,low-frequency,and finite-time convergent in presence of external disturbances.In this paper,a robust controller with an advanced adaptive scheme is proposed.To improve robustness,the disturbance is skillfully involved in the adaptive scheme.It is strictly proven that the closed-loop system can converge to the desired trajectory in finite time in both reaching and sliding processes.Based on the theoretical proof,adaptive gains and corresponding dynamic stability characteristics are further discussed.Finally,the efficiency of the proposed control scheme is numerically proven via a TSNR.The proposed control scheme utilizes small and continuous control forces to compensate for the disturbance efficiently and track the desired trajectory quickly.

太空天梯网的稳定性分析与应用构想

太空天梯技术是实现低成本、高效、安全航天运输的一种重要途径.传统的地球天梯和月球天梯对材料强度的要求远超现有技术水平,工程实现难度很大.而土星卫星普遍质量较小,建设土星卫星太空天梯可以有效克服现有材料技术瓶颈并极大促进土星系探索和开发利用.首先,以土卫二为例,建立了“刚性杆-珠点”天梯模型,推导出拉格朗日动力学方程.在此基础上,完成了系统的稳定性分析,利用线性稳定性理论以及拉格朗日定理分析了不同建模精度以及空间站质量下系统的稳定条件,并将计算结果推广至土星系其他卫星.之后,提出了土星系太空天梯网构想,并初步设计了能够实现在任意两颗卫星之间无工质转移的天梯网构型.最后分析了天梯网的效能和建设可行性.计算结果表明,设计的天梯网中所有天梯均能够在平衡位置保持稳定,且部分天梯能够采用现有复合材料完成建造.相比传统轨道机动方法可节省数千米每秒的速度增量,具有巨大的潜在应用价值.提出的方法和得到的结论可以为天梯网的进一步设计提供支撑.

Evaluation of E-sail parameters on central spacecraft attitude stability using a high-fidelity rigid–flexible coupling model

This study examines the impact of electric solar wind sail(E-sail)parameters on the attitude stability of E-sail’s central spacecraft by using a comprehensive rigid–flexible coupling dynamic model.In this model,the nodal position finite element method is used to model the elastic deformation of the tethers through interconnected two-node tensile elements.The attitude dynamics of the central spacecraft is described using a natural coordinate formulation.The rigid–flexible coupling between the central spacecraft and its flexible tethers is established using Lagrange multipliers.Our research reveals the significant influences of parameters such as tether numbers,tether’s electric potential,and solar wind velocity on attitude stability.Specifically,solar wind fluctuations and the distribution of electric potential on the main tethers considerably affect the attitude stability of the spacecraft.For consistent management,the angular velocities of the spacecraft must remain at target values.Moreover,the attitude stability of a spacecraft has a pronounced dependence on the geometrical configuration of the E-sail,with axisymmetric E-sails proving to be more stable.

在轨服务中空间系绳的应用及发展

针对空间系绳在空间在轨服务中的应用与发展问题,在简述空间系绳传统应用及试验情况的基础上,综述了空间绳系机器人、空间绳网机器人两类新在轨应用方式的研究和发展,主要包括动力学建模、结构设计、相对状态测量、逼近/抓捕控制、拖曳变轨等。最后进一步讨论了空间系绳未来的研究方向。

柔性绳网动力学建模与天地差异性分析

采用有限元模型研究了柔性绳网系统的动力学特性。针对空间绳网直接弹射展开方式,首先将绳网离散为若干单元,各单元处理为非线性"半阻尼弹簧"模型,然后分别计算各单元所受气动力和重力,最终建立绳网系统多柔体动力学模型。基于所建立的动力学模型分别对柔性绳网在地面和太空展开的动力学过程进行了仿真分析,研究了绳网在展开面积、空间位形和飞行距离等方面的天地差异性及其动力学机理,为未来空间绳网系统的分析设计提供理论参考。

空间绳系机器人姿态容错控制方法研究

在精确姿态控制阶段,由于反作用轮的故障,空间绳系机器人会出现姿态控制失稳的问题,为此,提出了一种空间绳系机器人姿态容错控制的新方法。该容错控制方法利用时间延迟控制算法,将前一个周期的控制量引入到当前控制律中,估计并补偿由于反作用轮故障引起的当前控制量变化。在推导该容错控制方法的基础上证明了它的稳定性,从反作用轮无故障和有故障两个方面,对利用时间延迟控制算法与利用PD控制算法的控制律进行了仿真比较。仿真结果表明,利用时间延迟控制方法跟踪目标姿态精度高、鲁棒性强;将时间延迟控制方法用于调整反作用轮故障状态下空间绳系机器人姿态具有较强的稳定性。

空间绳系组合体拖曳动力学分析及振动控制

空间绳系捕获系统捕获目标物后的组合体在拖曳离轨过程中常产生振动,为此,建立了切向连续推力作用下的空间拖曳绳系组合体面内动力学模型,并对模型进行了横向摆动与纵向振动耦合分析。针对组合体的纵向振动问题提出了一种以张力控制为内环、速度控制为外环的双闭环振动控制策略。进行了振动控制仿真分析,并根据动力学的相似性,建立地面模拟实验系统,仿真与实验结果表明该控制策略可迅速抑制组合体纵向振动、减小系绳冲击并可避免出现系绳松弛现象。

空间绳系系统自由展开建模与仿真

运用Hamilton原理建立了空间绳系展开动力学模型,研究绳系展开过程中绕线盘出线、系绳振动以及末端质量的运动规律,并利用中心差分法、四阶Runge-Kutta和预估校正法等数值方法对绳系的自由展开过程进行仿真,仿真结果显示该模型可以较精确描述绳系系统在展开过程中的复杂非线性动力学行为,绳系自由展开不能满足稳定展开的要求,仿真数据可以为后续的绳系展开控制提供参考依据。

空间绳网多收口质量块收口过程动力学分析

针对空间绳网捕获应用,进行了多收口质量块收口过程的动力学分析。以一种自适应双卷筒卷取机构为研究对象,考虑包含有三个质量块的收口系统,通过建立收口质量块质点运动微分方程、收口绳长约束方程并利用非正交变换方法,给出了各收口质量块质心运动与缆绳卷取运动耦合的动力学模型,仿真分析了质量块平动发射和系统自旋发射等典型收口过程的运动特点,给出了一些收口过程的驱动控制策略,同时也说明此类自适应收口质量块具有较强的自适应性和容错性,适用于空间绳网捕获系统。另外,以上分析也适用于采用缆绳控制的绳系卫星编队系统。

空间绳系机器人目标逼近姿态协调控制

针对空间绳系机器人对目标逼近过程中的姿态协调控制问题,设计了一种基于可移动系绳点的姿态协调控制机构,利用系绳实现姿态的协调控制。针对该类型空间绳系机器人,进行动力学建模,并对其动力学特性进行了分析。为了克服利用系绳拉力进行姿态协调控制过程中,拉力波动对姿态控制的影响,采用具有较强鲁棒性的滑模变结构方法设计了姿态协调控制器。可移动系绳点的姿态协调控制机构提供空间绳系机器人两个方向的姿态控制力矩,另一个方向的控制力矩通过空间绳系机器人自身提供,从而实现逼近过程中姿态协调控制。仿真结果表明,通过可移动系绳点的姿态协调控制机构,利用系绳拉力可实现空间绳系机器人目标逼近过程中的姿态控制,并且达到节省姿态控制燃料消耗的目的。

空间绳系机器人抓捕非合作目标的质量特性参数辨识

针对空间绳系机器人抓捕非合作目标/空间垃圾后需要对其进行回收/拖曳的精确控制问题,提出了一种利用抓捕后保持阶段的振动特性辨识目标参数的方法。首先,根据质量特性参数辨识的需要,推导了系统的动力学模型。不同于以往将本体卫星和被抓捕目标简化为质点的动力学模型,本文针对任意的目标抓捕位置,在考虑重力梯度影响的基础上,利用拉格朗日法获得系统各广义坐标的动力学公式。然后,分析非合作目标和系绳在后抓捕保持阶段的姿态运动。最后,在非合作目标与本体卫星没有任何信息交互的情况下,利用后抓捕阶段目标卫星和系绳特有的振动,并使用具有鲁棒性可遗忘因子的递推最小二乘法,提出了包括转动惯量和质心到任意抓捕点距离在内的质量特性参数辨识算法。