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.

Adaptive Fuzzy Attitude Control of Flexible Satellite

The adaptive fuzzy control is applied in the attitude stabilization of flexible satellite. The detailed design procedure of the adaptive fuzzy control system is presented. Two T-S models are used as both controller and identifier. The parameters of the controller could be modified according to the information of the identifier. Simulation results show that the method can effectively cope with the uncertainty of flexible satellite by on-line learning and thus posses the good robustness. With the proposed method, the precise attitude control is accomplished.

Flexible Satellite Attitude Control via Adaptive Fuzzy Linearization

The adaptive fuzzy control is combined with input-output linearization control to constitute the hybrid controller. The control method is then applied to the attitude maneuver control of the flexible satellite. The basic control structure is given. The rules of the controller parameter selection, which guarantee the attitude stabilization of the satellite with parameter uncertainties, have been analyzed. Simulation results show that the precise attitude control is accomplished in spite of the uncertainty in the system.

Attitude Control of a Flexible Satellite by Using Robust Control Design Methods

The increase of satellite’s dimensions has caused flexibility and formation of uncertainty in their model. This is because of space missions being more complex and using light moving structures in satellites. Satellites are also encountered with various circumferential disturbance torques. This uncertainty in model and disturbance torques will cause undesirable performance of satellites’ attitude control system. So, for attitude control of these satellites, those methods should be used which are robust to uncertainty of the plant’s model and can reject the effects of disturbances and the measurement noise. One of these methods is the robust control design method. But, because of pole’s place of these satellite’s dynamics equations, the designing procedure of robust control will face difficulties. In this paper, by using an internal feedback as a novel idea, the satellite’s dynamics equations are changed in such a way that the poles will be placed in proper locations. Then, for these new equations, by regarding the effects of flexibility as uncertainty and considering the uncertainty in inertia matrix of satellite, an H∞ controller has been designed and for better performance, a μ-controller has been improved. Afterwards, these two controllers are analyzed and compared for the original dynamic equations, not for the modified ones. Also, for comparison, a classic controller has been also designed for the original plant and eventually all these three controllers are compared with each other.

Control of a Rigid-Flexible Satellite Solar Panel with Non-collocated Sensor/Actuator

This paper presents a model and analysis for a flexible link with non-collocations of sensors and actuators. It shows the changes in the system dynamics and the appearance of zeroes in the right-plan complex, turning the system a non-minimum phase system. The performance of the PID （proportional-integral-derivative） and LQR （linear quadratic regulator） controller are discussed considering the zero dynamics of the system in three points of special interest： （I） the collocated case, when the sensor is in the base of the link; （2） the critical case, where the system starts to present zeroes in the right-plan complex and （3） the limit case, when the sensors are in the end point of the flexible link. Investigation for a simple rigid-flexible model with one mode, in the three cases, the PID and LQR controller performance are damage. To deal with this kind of problem, new control techniques should be developed.

New Method for Predicting the Motion Responses of A Flexible Joint Multi-Body Floating System to Irregular Waves

A new hybrid method of frequency domain and time domain is developed in this paper to predict the motion responses of a flexibly joint multi-body floating system to irregular waves. The main idea of the method is that the three-dimensional frequency method is used to obtain the hydrodynamic coefficients and the response equations are solved in time domain step by step. All the forces can be obtained at the same time. The motions and nonlinear mooring forces of a box type six-body floating system are predicted. A comparison of the theoretical method-based Solutions with experimental results has shown good agreement.

A flexible multi-body model of a surface miner for analyzing the interaction between rock-cutting forces and chassis vibrations

The discontinuous nature of rock cutting can easily cause unwanted vibrations in the structure of a surface miner.If these vibrations are not properly addressed,the related stress cycles can gradually damage the chassis resulting in fatigue failures.These events can seriously undermine the safety of operators and digging operations may be stopped for days,with an obvious economic impact.This work presents an analysis of the dynamics of a surface miner,focusing on the interaction between cutting machine dynamics and cutting forces,which is a new approach for this type of machine.For this purpose,the authors developed a numerical model of the cutting process made up of(1)a multi-body model of the cutting machine,which takes into account the chassis's flexibility;(2)a model of the rotating cutting head;and(3)a model of the interaction between the cutting head and rock,based on Shao's model.The model was compared with experimental results and then used to investigate the effects of cutting speed and cutting depth on the machine dynamics.

STUDY ON DYNAMICS, STABILITY AND CONTROL OF MULTI-BODY FLEXIBLE STRUCTURE SYSTEM IN FUNCTIONAL SPACE

The dynamics, stability and control problem of a kind of infinite dimensional system are studied in the functional space with the method of modern Mathematics. First, the dynamical control model of the distributed parameter system with multi-body flexible and multi-topological structure was established which has damping, gyroscopic parts and constrained damping. Secondly, the necessary and sufficient condition of controllability and observability, the stability theory and asymptotic property of the system were obtained. These results expand the theory of the field about the dynamics and control of the system with multi-body flexible structure, and have important engineering significance.

Articulated Lifting System Modeling Based on Dynamics of Flexible Multi-Body Systems

In lifting sub-system of deep-sea mining system, spherical joint is used to connect lifting pipes to replace fixed joint. Based on Dynamics of Flexible Multi-body systems, the mechanics model of articulated lifting system is established. Under the four-grade and six-grade oceanic condition, dynamic responses of lifting system are simulated and experiment verified. The simulation results are consistent with experimental ones. The maximum moment of flexion is 322 kN-m on the first pipe under six-grade sea condition. It is seen that the articulated connection can reduce the moment of flexion. The bending deformation of pipe center is researched, and the maximum is 0. 000479 m on the first pipe. Deformation has a little effect on the motion of system. It is feasible to analyze articulated lifting system by applying the theory of flexible multi-body dynamics. The articulated lifting system is obviously better than the fixed one.

Fluid-structure interaction simulation for multi-body flexible morphing structures

The multi-body flexible morphing airfoil can improve the aerodynamic characteristics based on different flight missions continuously.Recently researches have focused on the unsteady aerodynamic characteristics of flexible wings under passive actuation.However,the unsteady aerodynamic characteristics with the fluid-structure interaction effects in the multi-body active actuation process of morphing airfoil deserve further investigation.In this paper,a fluid-structure coupled simulation method for multi-body flexible morphing airfoil with active actuation subsystem was investigated,and the aerodynamic characteristics during deformation were compared with different skin flexibility,flow field environment,actuation mode and actuation time.The numerical results show that for the steady aerodynamic,the skin flexibility can improve the stability efficiency.In the unsteady process,the change trend of the transient lift coefficient and pitching moment are consistent with those of the active drive characteristics,while the instantaneous lift-drag ratio coefficient is greatly affected by the driving mode and can be improved by increasing the driving duration.

Design and simulation of fault diagnosis based on NUIO/LMI for satellite attitude control systems

This paper presents a scheme of fault diagnosis for flexible satellites during orbit maneuver. The main contribution of the paper is related to the design of the nonlinear input observer which can avoid false alarm arising from the disturbance from orbit control force. The effects of orbit control force on the fault diagnosis system for satellite attitude control systems, including the disturbing torque caused by the misalignments and the model uncertainty caused by the fuel consumed, are discussed, where standard Lu- enberger observer cannot work well. Then the nonlinear unknown input observer is proposed to decouple faults from disturbance, Besides, a linear matrix inequality approach is adopted to reduce the effect of nonlinear part and model uncertainties on the observer. The numerical and semi-physical simulation demonstrates the effectiveness of the proposed observer for the fault diagnosis system of the satellite during orbit maneuver.

Proposal of Functional Thermal Control Systems for High-Power Micro-Satellite and Its Demonstration under Thermal Vacuum Condition

In previous years, several high-power micro-satellites below ~100 kg have been developed for high-functional spacecraft. This paper proposes a functional and high-power thermal control system with no power supply and a simple configuration for micro-satellite: 100 W, 3 U. The proposed system consists of a heat storage panel (HSP) with pitch type CFRP (Carbon Fiber Reinforced Polymer), a micro loop heat pipe (m-LHP) and a flexible re-deployable radiator (FRDR) as an active thermal control system. The aim of this research is to try not only to verify the thermal control devices, but also to perform a water phase change experiment as a payload using an electric power generation of 100 W in space environment. In this paper, the basic design of the satellite, the analysis of the feasibility by the thermal mathematical model, and the fabrication of thermal test model including water phase chamber are reported. The main results of thermal analysis as feasibility verification showed that the paddles could absorb the thermal energy up to 97 W at the solar input of 180 W, and the operating temperature of bus equipment became within the allowable temperature range (0°C - 40°C). At thermal vacuum test, the difference between the analysis and the experiment for the temperature history of water due to the discordance for the value of thermal conductance was discussed.

高通量卫星资源管控系统现状与趋势研究

随着灵活载荷技术的发展,高通量卫星从大容量向兼顾灵活性发展,资源管控系统作为高通量卫星在轨应用的关键部分,对提升系统资源利用率和降低单位带宽使用成本至关重要。文章总结了国外高通量卫星资源管控系统及资源管控算法的最新研究进展,包括泰雷兹公司、GMV公司、欧洲卫星(SES)公司、卫讯(Viasat)公司等提出的高通量卫星资源管控系统。结合高通量卫星资源在轨灵活管控需求,提出后续高通量卫星资源管控系统的发展趋势,例如,基于人工智能的资源管控系统成为后续发展的重要方向,同时,随着星上处理能力与存储能力的提升,星载资源管控系统架构也成为有潜力的发展方向而受到运营商的关注。

面向卫星物联网的柔性多址接入技术

基于时隙ALOHA(S-ALOHA)的免授权上行随机接入能够显著降低卫星物联网(IoT)中的接入时延和复杂度。然而,随着物联网用户数量的增加,S-ALOHA碰撞概率会显著增加,从而影响系统性能。该文针对卫星物联网中存在海量设备上行接入的场景,专注于研究物联网终端的功率资源控制,以实现最大化系统和速率的目标。具体而言,该文提出基于S-ALOHA的柔性多址接入。当系统中存在碰撞时,采用非正交多址技术进行传输,从而避免了用户信息反复重传的问题,降低了传输时延。为了在终端功率受限的情况下实现系统和速率的最大化,该文将序列决策问题建模为马尔可夫决策过程,并采用优势演员-评论家算法(A2C)进行求解。仿真结果表明,所提出的柔性多址接入技术能够在海量物联网终端的场景下有效保证终端的接入成功率。同时,基于A2C的资源分配算法相较于传统的资源分配算法表现更为优越。

基于软件无线电的通信卫星柔性测试技术

针对通信卫星有效载荷地面测试系统专用化程度高、人员操作性差、软件兼容性低、迭代更新成本高的问题,文章提出一种基于软件无线电的卫星柔性测试技术,发挥软件无线电支持高级语言编程和灵活程度高的特点,将不同通信卫星有效载荷体制以软件自定义实现的方式统型到通用的硬件平台,设计可用于各型通信卫星有效载荷测试的通用化地面测试设备,实现卫星有效载荷测试技术经济一体化。经在卫星移动通信载荷和航空监视载荷中实际测试验证,结果表明:基于软件无线电的卫星柔性测试设备满足通信卫星有效载荷的测试需求,可为软件无线电技术在卫星测试领域的探索和应用提供参考。

从运营角度探讨GEO卫星演进关键技术

在卫星通信逐步转变为网络化运营的背景下,针对近年来低轨星座对同步静止轨道(Geostationary Orbit,GEO)卫星运营带来的挑战,提出了提高GEO卫星资源利用效率和降低通信成本的运营思路。在此基础上,结合卫星通信未来发展面对的时空变化的业务、高价值移动载体、天地协同泛在互联三类重要应用场景,根据各场景特点分析了GEO卫星提高服务性价比的关键技术,包括卫星灵活载荷技术和卫星与蜂窝网络融合技术,指出了这些技术的架构和功能要点,以及技术实施后对卫星资源利用的重要影响。

小卫星太阳翼铰链对挠性动力学方程耦合系数的影响

针对小卫星太阳翼机械系统产品选型时,展开机构的铰链类型、铰链刚度对卫星挠性太阳翼系统动力学方程中耦合系数影响规律不明确的情况,文章首先建立带挠性太阳翼的振动方程,给出使用动力学方程中的参量计算附件平动、转动耦合系数的公式;然后,基于小卫星常用的两种铰链类型以及铰链不同刚度,采用有限元法,对比相同卫星构型下铰链对太阳翼展开模态的影响;并获取相应的太阳翼振型、质量与质量元位置参数;最后,以某小卫星太阳翼为例,基于动力学方程中的耦合系数计算方法,采用输出参量与数据处理软件相结合方式,开展了不同铰链对耦合系数和铰链选型的影响分析。结果表明:文章分析的不同铰链、刚度的太阳翼结构参数以及耦合系数变化规律,对于铰链的设计和选型具有理论参考价值。

大跨度钢结构网壳屋架滑移施工监测技术研究与应用

以北京朝阳站交通枢纽工程柔性大跨度钢结构网壳屋架为研究背景,研究钢结构整体滑移施工中的应力应变以及温度变化对钢结构的影响,为施工提供理论指导。采用高精度北斗系统实现施工过程中三维位形的秒级数据采集与分析,代替传统的全站仪位形采集方式,提高发现问题的速度,从而保障提升过程施工安全。为了确保工程在施工期间和服役阶段内安全,建立北京朝阳站钢结构施工监测系统。通过监测系统施工阶段和服役期间的结构施工安全,详细记录施工过程数据,为类似工程提供参考。

面向卫星通导遥算融合的关键技术分析

空天技术深入发展后,用户对空天系统的要求将是融合通信、遥感、导航卫星的天基信息服务系统,以向用户提供高速数据传输、直达用户的实时遥感服务、精确到厘米以内的高精度定位导航、分布式协同计算资源等服务能力,从而应用于丰富的服务场景。现有的通信、导航、遥感卫星存在软件协议和物理设施上的屏障,不能融合应用,远远不能满足天基信息服务系统的建设要求,因此,有必要研究通信、导航、遥感、计算在卫星上的融合。融合关键点是硬件和软件资源的可调度、可共享,以及高效能、高稳定性的载荷器件。基于此,深入分析面向卫星通导遥算融合的关键技术,并分析通导遥算融合的典型应用服务方式,最后通过仿真实验可验证融合后的效能提升。

Attitude control without angular velocity measurement for flexible satellites

In this paper, by using quaternion models, the problem of attitude control is investigated for a class of flexible satellites. Two control laws are presented for the considered flexible satellite models to guarantee convergence of the closed-loop systems without using angular velocity measurement. One is in the form of a partial state feedback for the case where the modal variable is available, and the other is in the form of an observer-based partial state feedback for the case where the modal variable cannot be measured. Finally, an example is employed to illustrate the effectiveness of the proposed control laws.