中继卫星系统组网运行问题研究

随着我国中继卫星系统的不断建设与发展,如何完善系统的组网运行管理,构建一个高可靠性和高可用度的系统是摆在我们面前的重要课题。在对美国TDRSS(跟踪与数据中继卫星系统)的卫星在轨备份、轨道漂移、卫星共位、地面终端站配置以及系统总体性能等方面进行分析的基础上,总结出其组网运行的4个特点:空间段具有备份节点、备份星;地面段配置备份中心、备份站;系统具备2颗卫星共位能力;系统具备轨道漂移能力。结合我国中继卫星系统建设与发展实际,得出了以下几点启示:加快备份星和备份站的部署与建设;适时形成单节点多星的星群配置;增加支持卫星轨道漂移和共位的能力;增加大椭圆轨道卫星的部署。     

一种偏置动量轮在轨维护的变带宽控制方法

针对长寿命运行卫星在轨维护中出现的备份偏置动量轮离散性差异较大,导致俯仰角收敛缓慢的问题,在姿态现象分析的基础上,根据卫星姿态动力学原理,建立偏置动量轮工作模式下的俯仰姿态的PID(Proportion Integration Differentiation,比例积分微分)控制模型,并进行系统开环与闭环传递函数公式推导。然后在伯德图(Bode Diagram)基础上,重点分析相位裕量的敏感参数,给出俯仰姿态控制回路的带宽调整方法,实现变带宽控制。卫星偏置动量轮在轨切换维护的结果表明,通过及时调整PID参数,减小回路带宽,可以有效改善相位裕量,保持卫星控制性能,实现俯仰姿态快速收敛,且俯仰角控制精度优于0.03°,取得较好的应用效果。     

航天器专家故障知识模型的建立和应用

随着我国航天事业的不断进步和国际业务的拓展,在轨航天器的数量逐年增加,航天器长期有效的管理对保障航天器长寿命运行具有十分重要的意义。传统的地面监测人员对航天器的监视已经不能满足要求。本文介绍了一种多航天器专家故障知识模型的建立方法,简要说明了基于这种模型的应用可以增加航天器在轨管理的智能化,提高工作效率。     

模块化可重构卫星在轨自重构的分层规划

模块化可重构卫星具有组织灵活、操作方便、适应性强等特点，可以有效降低卫星研制和发射成本、提高卫星对紧急任务的响应速度、延长卫星寿命。重构规划问题对模块的具体移动方式进行求解，是实现自重构需要解决的核心问题之一。针对同构式旋转立方结构，给出其离散运动模型，推导出运动空间求解算法。为降低重构规划问题的不确定性和复杂程度，采用分层规划策略，将规划任务分解为设计中间构型的上层规划和求解实现中间构型移动方式的下层规划，每层规划内部独立进行求解。设计了利用Kuhn-Munkres算法实现上层规划的重构规划算法，使中间构型具有较小的结构跨度，特别适合在轨自重构的重构规划问题求解。仿真结果表明了所提规划策略和所设计规划算法的可行性和有效性。     

航天器在轨可更换模块机构与结构设计

航天器常在其任务中出现功能失效,造成巨大的损失,而在轨模块更换技术则是利用空间机械臂自主对可接受在轨服务航天器进行故障模块更换、升级、补充消耗品等。通过对在轨可更换模块在轨服务的任务、在轨可更换模块的组件构成,从而得出在轨可更换模块的机构设计方案,进而又对在轨可更换模块进行结构设计,利用 SolidWorks 软件建立该结构的三维模型,实物模型验证了其可行性。     

面向航天器在轨装配的数字孪生技术

构建航天器在轨维修维护能力是确保空间系统长期稳定工作的有效途径,而对于空间环境中的在轨装配过程的模拟、监控、诊断和预测,目前的研究尚处于探索阶段,研究成果相对较少且缺乏整体解决方案。提出采用构建航天器数字孪生体的方式,来抽象表达航天器完成在轨装配的过程、状态和行为。首先分析了在轨装配航天器的结构组成及功能需求,然后系统阐述了航天器数字孪生体的数据组成、实现方式和作用,最后给出了航天器数字孪生体在设计、制造和在轨服务阶段的实施途径,并对航天器数字孪生体的作用进行了总结和展望。     

支持无人机设计的全寿命周期成本建模技术研究

在无人机设计阶段对相关成本进行分析评估，引入按费用设计理念，对于控制无人机装备指标参数与复杂程度、鉴别高费用设计、修正设计进程、提高标准化程度，进而降低全寿命周期费用，实现技术与经济的最佳匹配，达到最优效费比，将起到极其重要的作用。本文分析了一种无人机全寿命周期成本估算框架，研究了无人机全寿命周期成本体系架构，提出了无人机飞机平台全寿命周期成本估算模型，将该模型在某型无人机上进行验证，可以用于无人机研制过程中的设计方案权衡分析和基于成本的设计优化。     

美军空间系统在轨试验问题综合研究

首先,按照空间系统的采办类型将美空间系统分为试验型系统和操作型系统,并介绍了美军两种类型的空间系统试验鉴定管理机制;其次,从试验技术、试验模式、试验手段、试验资源和试验能力多个角度,综合分析了美军空间系统在轨试验的主要做法与特点;最后,对我国空间系统在轨试验的发展提出启示建议。     

空间多功能在轨维护机器人系统及其末端执行器设计

空间机器人是空间在轨服务的一种重要工具。以合作目标与非合作目标的在轨维护为目的,通过对现有空间机器人研究现状的调研和分析,提出了基于末端工具可快换的多功能在轨维护机器人系统,并提出多种末端执行器设计方案。其中三指-三瓣式末端执行器作为末端工具快换装置,不仅具有机械接口捕获对接的功能,还具有电力/信号传输功能,以及机械臂动力传输功能;钢丝绳缠绕式末端执行器具有优越的容差和软捕获性能,适合用于实现对安装有捕获接口的合作目标以及非合作目标卫星发动机喷管的捕获;而欠驱动三指末端执行器具有良好的待捕获目标物体形状自适应功能以及软捕获功能,因此可用于对空间形状不规则的太空垃圾等目标进行非合作目标捕获。通过对多功能在轨维护机器人系统及其末端工具快换过程以及末端执行器对目标捕获操作的研究,所提出的基于末端工具快换的多功能在轨维护机器人系统有较好的应用前景。     

航天器在轨服务技术体系解析

针对国内学术界和工程界对在轨服务的定位不统一、技术研究较零散的问题,在吸收现有多种不同概念合理内核基础上,对在轨服务概念的内涵和外延进行了界定,明确了在轨服务是以在轨航天器为对象,围绕运行保护、状态维护和功能维持进行的,以外援式、自主式或二者融合方式实现的航天工程活动;基于上述的概念界定,构建了在轨服务"三叶草"结构模型和四元素映射关系模型,描述了在轨服务涉及的补充给养、清除障碍、监视行为、诊断病态、处置故障、延长寿命六个方面内容与"去得了、跟得上、测得准、抓得住、修得好、放得开、躲得掉"七项目标,归纳了服务技术的基本架构,提出了我国在轨服务技术优先发展的四项建议。上述结果可为在轨服务技术研究奠定一个相对系统的框架体系。     

An atmosphere-breathing propulsion system using inductively coupled plasma source

CubeSats have attracted more research interest recently due to their lower cost and shorter production time. A promising technology for CubeSat application is atmosphere-breathing electric propulsion, which can capture the atmospheric particles as propulsion propellant to maintain long-term mission at very low Earth orbit. This paper designs an atmosphere-breathing electric propulsion system for a 3 U CubeSat, which consists of an intake device and an electric thruster based on the inductively coupled plasma. The capture performance of intake device is optimized considering both particles capture efficiency and compression ratio. The plasma source is also analyzed by experiment and simulation. Then, the thrust performance is also estimated when taking into account the intake performance. The results show that it is feasible to use atmosphere-breathing electric propulsion technology for CubeSats to compensate for aerodynamic drag at lower Earth orbit.     

Information space of sensor networks: Lagrangian,energy-momentum tensor,and applications

It is a challenge to investigate the interrelationship between the geometric structure and performance of sensor networks due to the increasingly complex and diverse architecture of them. This paper presents two new formulations for the information space of sensor networks, including Lagrangian and energy–momentum tensor, which are expected to integrate sensor networks target tracking and performance evaluation from a unified perspective. The proposed method presents two geometric objects to represent the dynamic state and manifold structure of the information space of sensor networks. Based on that, the authors conduct the property analysis and target tracking of sensor networks. To the best of our knowledge, it is the first time to investigate and analyze the information energy–momentum tensor of sensor networks and evaluate the performance of sensor networks in the context of target tracking. Simulations and examples confirm the competitive performance of the proposed method.     

Wireless sensor networks: scheduling for measurement and data reporting

An optimal load allocation approach is presented for measurement and data reporting in wireless sensor networks with a single level tree network topology. The measurement problem investigated involves a measurement space, part of which can be sampled by each sensor. We seek to optimally assign sensors part of the measurement space to minimize reporting time and energy usage. Three representative measurement and reporting strategies are studied. This work is novel as it considers, for the first time, the measurement capacity of processors and assumes negligible computation time which is radically different from the traditional divisible load scheduling research to date. Aerospace applications include satellite remote sensing and monitoring and sensor networks deployed and monitored from the air.     

Design,Development, Implementation,and On-orbit Performance of the Dynamic Ionosphere CubeSat Experiment Mission

Funded by the NSF CubeSat and NASA ELaNa programs, the Dynamic Ionosphere CubeSat Experiment (DICE) mission consists of two 1.5U CubeSats which were launched into an eccentric low Earth orbit on October 28, 2011. Each identical spacecraft carries two Langmuir probes to measure ionospheric in-situ plasma densities, electric field probes to measure in-situ DC and AC electric fields, and a science grade magnetometer to measure in-situ DC and AC magnetic fields. Given the tight integration of these multiple sensors with the CubeSat platforms, each of the DICE spacecraft is effectively a “sensor-sat” capable of comprehensive ionospheric diagnostics. The use of two identical sensor-sats at slightly different orbiting velocities in nearly identical orbits permits the de-convolution of spatial and temporal ambiguities in the observations of the ionosphere from a moving platform. In addition to demonstrating nanosat-based constellation science, the DICE mission is advancing a number of groundbreaking CubeSat technologies including miniaturized mechanisms and high-speed downlink communications.     

复杂退化系统的组合维修策略优化

由于现有视情维修研究中没有考虑定期维护的影响,无法准确反映定期维护下的系统性能退化规律,因而不利于合理制定定期维护与视情维修组合的维修策略。针对该问题,重点开展了该组合维修策略下的性能退化建模与维修决策研究。通过结合组合维修策略下的性能退化特点,从失效机理出发,利用复合Poisson过程建立了性能退化模型,并通过退化强度函数描述了仅恢复累积性能退化量而不改变性能退化规律的维修效果。同时,分析了该条件下的可靠度函数,说明了其具有阶梯型变化和突变性的特性。基于性能退化模型,建立了长期运行条件下以费用率最低为目标、失效风险为约束的组合维修决策优化模型,并求解确定了最优维护周期和预防性维修阈值。通过数值分析,描述了费用率随维修策略值变化的规律,说明了优化解的存在性。同时,通过与系统自身寿命规律比较,说明采用该优化模型,可以有效地延长系统的使用时间,实时控制失效概率,确保其具有较高的安全等级,进而有效地降低维修费用。     

ENGINE SENSOR FAULT DIAGNOSIS USING MAIN AND DECENTRALIZED NEURAL NET WORKS

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基于最小跳数的无线传感器网络跨层设计

传统的严格分层参考模型无法实现对无线传感器网络资源的有效管理和运用,跨层设计是提高网络整体性能的一种有效方法。针对无线传感器网络能量、计算资源、存储资源和带宽资源有限的特点,提出一种基于最小跳数的路由层和MAC层的跨层协议设计方案。MAC层和路由层通过共享sensor节点到sink节点的最小跳数信息,在MAC层建立时间梯度,解决多个节点共享无线信道的问题;并在路由层建立路由表,解决路由选择问题。仿真结果表明,该方案在降低网络能耗的同时,在降低传输延迟,提高数据投递率方面也取得了良好的性能。     

Performance deterioration modeling and optimal preventive maintenance strategy under scheduled servicing subject to mission time

Servicing is applied periodically in practice with the aim of restoring the system state and prolonging the lifetime. It is generally seen as an imperfect maintenance action which has a chief influence on the maintenance strategy. In order to model the maintenance effect of servicing, this study analyzes the deterioration characteristics of system under scheduled servicing. And then the deterioration model is established from the failure mechanism by compound Poisson process. On the basis of the system damage value and failure mechanism, the failure rate refresh factor is proposed to describe the maintenance effect of servicing. A maintenance strategy is developed which combines the benefits of scheduled servicing and preventive maintenance. Then the optimization model is given to determine the optimal servicing period and preventive maintenance time, with an objective to minimize the system expected life-cycle cost per unit time and a constraint on system survival probability for the duration of mission time. Subject to mission time, it can control the ability of accomplishing the mission at any time so as to ensure the high dependability. An example of water pump rotor relating to scheduled servicing is introduced to illustrate the failure rate refresh factor and the proposed maintenance strategy. Compared with traditional methods, the numerical results show that the failure rate refresh factor can describe the maintenance effect of servicing more intuitively and objectively. It also demonstrates that this maintenance strategy can prolong the lifetime, reduce the total lifetime maintenance cost and guarantee the dependability of system.     

An accelerated life test model for harmonic drives under a segmental stress history and its parameter optimization

Harmonic drives have various distinctive advantages and are widely used in space drive mechanisms. Accelerated life test(ALT) is commonly conducted to shorten test time and reduce associated costs. An appropriate ALT model is needed to predict the lifetime of harmonic drives with ALT data. However, harmonic drives which are used in space usually work under a segmental stress history, and traditional ALT models can hardly be used in this situation. This paper proposes a dedicated ALT model for harmonic drives applied in space systems. A comprehensive ALT model is established and genetic algorithm(GA) is adopted to obtain optimal parameters in the model using the Manson fatigue damage rule to describe the fatigue failure process and a cumulative damage method to calculate and accumulate the damage caused by each segment in the stress history.An ALT of harmonic drives was carried out and experimental results show that this model is acceptable and effective.     

无线传感器网络的异构性研究

随着无线通信技术和微电子技术的快速发展,低成本、高度集成和自组织的无线传感器网络将会逐渐普及.首先总结归纳了无线传感器网络异构性的几种表现形式,如计算能力异构性、节点能量异构性、链路异构性及网络协议异构性,然后介绍了异构无线传感器网络层次网络体系结构和两种适用于无线传感器网络的标准.最后对无线传感器网络的安全问题进行简单探讨.