Adaptive Optimal Control of Space Tether System for Payload Capture via Policy Iteration

The libration control problem of space tether system(STS)for post-capture of payload is studied.The process of payload capture will cause tether swing and deviation from the nominal position,resulting in the failure of capture mission.Due to unknown inertial parameters after capturing the payload,an adaptive optimal control based on policy iteration is developed to stabilize the uncertain dynamic system in the post-capture phase.By introducing integral reinforcement learning(IRL)scheme,the algebraic Riccati equation(ARE)can be online solved without known dynamics.To avoid computational burden from iteration equations,the online implementation of policy iteration algorithm is provided by the least-squares solution method.Finally,the effectiveness of the algorithm is validated by numerical simulations.

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.

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.

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.

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。

Controlled deployment of a long tether to operate as a partial space elevator

The deployment of a long tether to operate as a partial space elevator,starting from a nucleus in geostationary orbit,is studied.Uncontrolled deployment is an inherently unstable process because the center of orbit gradually decreases from the geostationary altitude when deployment progresses.It is also observed that the elasticity of the tether has an important effect on deployment stability.It is shown that the application of a transverse force on the main spacecraft,determined by using linear state feedback and appropriate gains,can stabilize the deployment.An LQR controller is developed.Simulations of the dynamics of the system are carried out using this controller for various parametric values of tether elasticity,deployment rates,etc.,to evaluate the efficacy of the controller.

Prediction and experimental verification of tether net entanglement for space debris capture

This study involved simulations and experiments aimed at assessing the efficacy of a tether net in encapsulating space debris.The tether net was modeled as a spring–mass–damper system considering the influence of aerodynamic and gravitational forces and the occurrence of debris collisions.To examine the influence of collision position and size disparity between the debris and the net on debris capture status,the entanglement nodes of the net were identified.Experiments were conducted to evaluate the wrapping capabilities of the tether net,focusing specifically on debris capture.Subsequently,the results were compared with those of the numerical simulation.In the experiments,radio frequency identification was used to identify the entanglement points of the tether net.Previous studies have indicated that the ideal collision point for capturing debris using a tether net with the debris intended to be captured is located at the center of the net.However,the experimental results of this study revealed that a collision position that is slightly shifted from the center of the tether net is more advantageous for capturing debris in terms of tether net entanglement.

Game theory based finite-time formation control using artificial potentials for tethered space net robot

The Tethered Space Net Robot(TSNR)is an innovative solution for active space debris capture and removal.Its large envelope and simple capture method make it an attractive option for this task.However,capturing maneuverable debris with the flexible and elastic underactuated net poses significant challenges.To address this,a novel formation control method for the TSNR is proposed through the integration of differential game theory and robust adaptive control in this paper.Specifically,the trajectory of the TSNR is obtained through the solution of a real-time feedback pursuit-evasion game with a dynamic target,where the primary condition is to ensure the stability of the TSNR.Furthermore,to minimize tracking errors and maintain a specific configuration,a robust adaptive formation control scheme with Artificial Potential Field(APF)based on a Finite-Time Convergent Extended State Observer(FTCESO)is investigated.The proposed control method has a key advantage in suppressing complex oscillations by a new adaptive law,thus precisely maintaining the configuration.Finally,numerical simulations are performed to demonstrate the effectiveness of the proposed scheme.

空间飞网系统动力学建模与仿真

空间飞网系统捕获带有自旋的空间碎片后,碎片会对捕获网与卫星间的连接绳施加扭矩,而目前绳索相关动力学模型无法完整描述其扭转行为。基于集中质量法,对绳索进行二次离散,建立了可以描述绳索扭转行为的动力学模型。通过与传统绳索动力学模型的对比及扭转实验,验证了该模型能够描述绳索在拉伸、弯曲及扭转载荷下的行为,发现绳索的扭转会产生额外的牵引力。针对飞网展开过程进行了仿真分析与实验,验证该动力学模型适用于飞网系统,并对飞网与空间碎片的组合体进行了仿真分析,发现因为绳索扭转产生的牵引力,会对主体卫星的稳定性产生一定的影响,忽略绳索的扭转行为会降低动力学仿真模型的准确性。

STS史学研究的时空交错线性方法——兼析《科技与社会大事总览》的体例结构

以大型学术文献《科技与社会大事总览》为案例,从STS研究的史学视角,从横向联系观察每个STS断面的要素与结构,从纵向时序串接诸多STS断面系列,以历史的惯性、刚性、必然性、规律性透视每片STS,在历史的横向剖切与纵向流动的立体交错与时空融合中进行判断及选择,在至高的历史耸立中俯瞰STS的广阔范阈和历史联系,并力图通过线性的、量化的、模式化的方法予以剖解。

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。

Strengthening Space Cooperation Looking Forward to 21st Century

Space Technology Development in China China began to develop space technology in the 1950s. After 40 years, China now has necessary facilities for the research, design, development, production and test of various satellites and series launch vehicles, many experts with rich experience and superb technology, three satellite launch bases in Jiuquan, Taiyuan and Xichang, and Xi’an TT&C Station, which have the ability to launch lowearth-orbit,

Flavour and Colour of Quarks in Spin Topological Space

An assumption that all the six flavour quarks are attributed to be the components of a same, a common isospin multiplets space named STS is proposed. Base on Pauli Exclusion Principle, every quark is assigned to different flavour marks in STS. Every flavour quark possesses its own colour spectral line array specially appointed. The collection of colour spectral line arrays of the six flavour quarks constructs together the CSDF, Colour Spectrum Diagram of Flavour, further baryons and mesons could be constructed from CSDF. STS, Spin Topological Space is a math frame with infinite dimensional matrix representation for spin angular momentum. Flavours is an isospin angular momentum coupling phenomena of the three-colour-quarks.

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.

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.

Dynamic analysis of tethered defunct satellites with solar panels

A precise dynamic model for towing and removing a defunct satellite with solar panels in orbit using a tethered net often has low computational efficiency owing to the complex contact and collision between the net and panels,which is not conducive to research.To solve this problem,a“single main tether–multiple subtether”bifurcation structure with beads was employed as the tethered net model.This study investigated the dynamics of tethered defunct satellites with solar panels,particularly the behavior of the attitude of the tethered satellite,oscillation of the main tether,and vibration of solar panels under different conditions.The results showed that different attachment configurations of the subtethers and the flexibility of the main tether have an evident impact on the dynamic characteristics of the system.