常推力作用下飞行器固定时间最优交会

研究了在常推力作用下,两个空间飞行器的固定时间最省燃料交会问题。通过对飞行器交会过程中最优推力弧段的研究,给出了关于飞行器的最优推力弧段的几个性质。这些结果为空间飞行器交会对接的工程设计提供了理论依据。     

苍穹飞吻——空间交会与对接

中国首次空间交会对接任务已进入发射实施阶段,在先后发射天宫一号目标飞行器和神舟八号飞船后,中国还将发射神舟九号、神舟十号飞船,继续实施空间交会对接飞行任务,并将在2020年建造长期载人空间站。本刊特编撰"空间交会与对接"专题,以飨读者。     

众人拾柴火焰高与天宫-1有关的四大系统改进

2011年9月29日,天宫-1目标飞行器由长征-2FT1运载火箭成功发射入轨,为我国实现首次空间交会对接任务开了个好头。我国载人航天工程由八大系统组成,为了完成天宫-1目标飞行器与神舟-8飞船进行的首次空间交会对接任务,除空间实验室系统外的其他几大系统都进行了多项改进,尤其是航天员系统、空间应用系统、运载火箭系统和测控通信系统改进较大,其中天宫-1上的乘员分系统和有效载荷分系统分别属于航天员系统和空间应用系统。     

交会对接光学成像敏感器中合作目标的分析与设计

交会对接技术是实现太空梭、太空平台和空间运输系统的装配、回收、补给、维修、太空人交换及营救等在轨服务的先决条件，交会对接光学成像敏感器是两航天器交会对接近距离平移靠拢段唯一能够提供六自由度相对导航信息的敏感器，由安装于追踪飞行器上的相机和安装于目标飞行器上的合作目标组成，采用角反射器作为合作目标标志，完成两飞行器间的相对位姿的解算.对其需求分析、设计方案、回光能量测试等进行了讨论，该方案已在神舟十一号载人飞船、天舟一号货运飞船与天宫二号的交会对接任务中成功验证，后续针对空间站及光学舱任务进行适应性修改.     

低成本多小天体并行交会技术

小天体资源开发方兴未艾,为降低开发风险和成本,需要发射无人探测器交会观测多个待选目标小天体。传统多目标探测方案存在无法多次交会、成本高,周期长等不足。提出的低成本多小天体并行交会技术,能够对多小天体探测任务进行解耦,实现基于微纳飞行器的低成本多目标并行交会勘查,从而降低探测成本,缩短探测周期。该技术结合行星借力与不变流形机制构建了低能量星际转移方案。然后引入扰动流形思想,使微纳飞行器能够实现与目标小天体的快速交会。进一步,提出了一种多目标小天体探测全局搜索方法,该方法基于在日地halo轨道上停泊的微纳飞行器集群,逐次确定小天体探测目标,并利用上述方法完成了多微纳飞行器与多小天体的交会。数值仿真结果表明,该方案能够大幅度降低转移过程的燃料消耗,并缩短转移时间。     

目标飞行器交会对接轨道的设计和控制

根据目标飞行器轨道高度和追踪飞行器入轨轨道高度,给出了目标飞行器交会对接轨道初始相位的设计方法。针对目标飞行器交会对接轨道控制要求,建立了共面相位计算模型以及轨道相位、高度和圆化度的多目标参数求解模型。基于定轨误差、轨道控制误差和轨道预报误差的调相时间分析,制定了目标飞行器调相控制策略。仿真计算表明,实现的目标飞行器交会对接轨道满足要求,验证了调相控制量优化原则的正确性,并对标称共面与虚拟共面的共面时刻和共面相位进行了比较。所提出的计算模型、控制策略和分析方法适用于目标飞行器交会对接轨道设计和控制实施。     

神舟八号飞船交会对接制导、导航与控制系统及其飞行结果评价

介绍神舟八号飞船交会对接制导、导航与控制系统的组成和工作原理,交会对接任务阶段划分,系统实现需关注的问题,以及神舟八号飞船与天宫一号目标飞行器首次交会对接飞行试验的结果和评价.     

交会对接步骤详解

神舟八号载人飞船与天宫一号目标飞行器整个交会对接过程分为交会对接准备段、交会段、对接段、组合体飞行段和撤离段。交会对接准备段:载人飞船发射前,天宫一号目标飞行器降低轨道并调整朝向,完成交会对接准备。交会段:飞船发射入轨后,首先     

神舟八号飞船航天测控纪念

2011年11月1日,中国用改进型长征二号F运载火箭,在酒泉卫星发射中心成功发射了神舟八号飞船,并与开宫一号目标飞行器进行了空间交会对接试验。在此次任务中,西安卫星测控中心和所属的国内、国外以及国际联网测控站圆满完成了神舟八号飞船发射测控、空间交会对接测控和神舟八号飞船返回舱搜索回收等任务。     

立方体星交会对接和空间飞行演示

正空间交会对接技术问世至今已有50年历史,在这半个世纪期间交会对接已经从探索、研究、实验阶段逐步走向成熟和应用阶段。现在交会对接已经变成一件日常例行的空间操作。但是过去和现在交会对接技术复杂,重量和功耗巨大,只能在大、中型航天器实现。例如:上世纪70~80年代,苏联"和平"号空间站和"联盟"号飞船仅交会对接机构和有关交会对接设备的重量都在2吨~3吨以上。如     

高动态环境下GPS信号捕获研究

高动态环境信号的捕获是GPS接收机的关键技术,接收机处于高速运动的状态使GPS信号产生相位延迟和多普勒频移,增加了信号的捕获难度。分析了滑动相关捕获和基于FFT捕获两种算法,给出了基于FFT捕获算法的FPGA实现架构,并采用GPS信号仿真器对该设计的可行性进行了捕获验证。结果表明：在导航星相对载体的速度为1 000m/s,加速度为5g的情况下,基于FFT捕获算法可以实现信号的可靠捕获。     

一种惯性信息辅助下的GPS快捕方法

全球定位系统(GPS,Global Positioning System)信号的捕获时间直接影响高动态环境下GPS接收机的使用性能.在分析传统的外部信息辅助GPS捕获方法的基础上,提出了一种在惯性信息辅助下进行快速捕获的方法,该方法由粗捕获和精捕获构成.详细分析了该方法的实现方法和性能,进行了MATLAB/Simulink系统级仿真及蒙特卡罗仿真试验.仿真结果表明:在保证码相位捕获精度和提高频率分辨率的前提下,运用该方法可以显著缩短GPS接收机搜索捕获的时间,提高接收机的动态性能,相对无外部信息辅助的情况总捕获时间缩短至2%~3%.     

基于FPGA与TDC的GPS-铷钟时间同步系统

描述了一种高精度的GPS-铷钟时间频率同步系统,系统输出标准10MHz频率,同时输出高精度的1PPS同步时间信号,在GPS信号驯服下系统同步精度可达到7.2ns,输出频率准确度优于1E-12。论文阐述了系统的原理,给出了测试数据,结果表明,系统指标满足工程应用要求。     

Orbit determination performances using single- and double-differenced methods: SAC-C and KOMPSAT-2

In this paper, Global Positioning System-based (GPS) Orbit Determination (OD) for the KOrea-Multi-Purpose-SATellite (KOMPSAT)-2 using single- and double-differenced methods is studied. The requirement of KOMPSAT-2 orbit accuracy is to allow 1 m positioning error to generate 1-m panchromatic images. KOMPSAT-2 OD is computed using real on-board GPS data. However, the local time of the KOMPSAT-2 GPS receiver is not synchronized with the zero fractional seconds of the GPS time internally, and it continuously drifts according to the pseudorange epochs. In order to resolve this problem, an OD based on single-differenced GPS data from the KOMPSAT-2 uses the tagged time of the GPS receiver, and the accuracy of the OD result is assessed using the overlapping orbit solution between two adjacent days. The clock error of the GPS satellites in the KOMPSAT-2 single-differenced method is corrected using International GNSS Service (IGS) clock information at 5-min intervals. KOMPSAT-2 OD using both double- and single-differenced methods satisfies the requirement of 1-m accuracy in overlapping three dimensional orbit solutions. The results of the SAC-C OD compared with JPL’s POE (Precise Orbit Ephemeris) are also illustrated to demonstrate the implementation of the single- and double-differenced methods using a satellite that has independent orbit information available for validation.     

高动态GPS信号C/A码捕获方案及实现

为检测高动态GPS(Global Positioning System)信号,需要设计码环及载波环捕获与跟踪数字系统.尽量缩短盲捕时间,快速捕获到信号,是研制高动态GPS接收机技术的关键,而GPS信号C/A码的快速捕获是码跟踪和载波捕获与跟踪的基础.主要讨论了在高动态GPS信号C/A码捕获中,并行搜索法和串行搜索法的原理与实现,并结合GEC公司的十二通道相关器GP2021,给出基于DSP(数字信号处理器)技术用串行搜索法捕获高动态GPS信号C/A码的算法实现.     

一种用于GPS时差比对数据处理的卡尔曼滤波器设计

介绍了一种用于GPS时差比对数据处理的自适应卡尔曼滤波器,在Matlab环境下编写了离散时间形式的卡尔曼滤波算法程序,利用该算法对GPS信号与铯原子频标的时差比对数据进行了分析处理,最后介绍了该算法的数字芯片FPGA实现。     

Retrieval of the change of precipitable water vapor with zenith tropospheric delay in the Chinese mainland

As a preliminary step for assessing the impact of global positioning system (GPS) refractive delay data in numerical weather prediction (NWP) models, the GPS zenith tropospheric delays (ZTD) are analyzed from 28 permanent GPS sites in the Chinese mainland. The objectives are to estimate the GPS ZTD and their variability in this area. The differences between radiosonde precipitable water vapor (PWV) and GPS PWV have a standard deviation of 4 mm in delay, a bias of 0.24 mm in delay, and a correlation coefficient of 0.94. The correlation between GPS ZTD and radiosonde PWV amounts to 0.89, indicating that the variety of tropospheric zenith delay can reflect the change of precipitable water vapor. The good agreement also guarantees that the information provided by GPS will benefit the NWP models. The time series of GPS ZTD, which were derived continuously from 2002 to 2004, are used to analyze the change of precipitable water vapor in Chinese mainland. It shows that the general trend of GPS ZTD is diminishing from the south-east coastland to the north-west inland, which is in accordance with the distribution of Chinese annual amount of rainfall. The temporal distribution of GPS ZTD in the Chinese mainland is that the GPS ZTD reaches maximum in summer, and it reaches minimum in winter. The long term differences between the observational data sources require further study before GPS derived data become useful for climate studies.     

基于GPS/北斗组合系统的高轨卫星定位技术研究

针对目前高轨GPS信号可用性差及定位精度低的特点, 对GPS/北斗组合系统的 高轨卫星定位技术进行研究, 对比分析了单GPS系统与GPS/北斗组合系统的卫 星可见性和几何精度因子. 结果表明, GPS/北斗组合系统比单GPS系统的卫星可 见性好, 且定位精度高. 同时通过提出在星载接收机上采用高精度原子钟, 可实现三星定位, 降低对接收机的技术要求.      

Effects of physical correlations on long-distance GPS positioning and zenith tropospheric delay estimates

The global positioning system (GPS) has become an essential tool for the high precision navigation and positioning. The quality of GPS positioning results mainly depends on the model’s formulations regarding GPS observations, including both a functional model, which describes the mathematical relationships between the GPS measurements and unknown parameters, and a stochastic model, which reflects the physical properties of the measurements. Over the past two decades, the functional models for GPS measurements have been investigated in considerable detail. However, the stochastic models of GPS observation data are simplified, assuming that all the GPS measurements have the same variance and are statistically independent. Such assumptions are unrealistic. Although a few studies of GPS stochastic models were performed, they are restricted to short baselines and short time session lengths. In this paper, the stochastic modeling for GPS long-baseline and zenith tropospheric delay (ZTD) estimates with a 24-h session is investigated using the residual-based and standard stochastic models. Results show that using the different stochastic modelling methods, the total differences can reach as much as 3–6 mm in the baseline component, especially in the height component, and 10 mm in the ZTD estimation. Any misspecification in the stochastic models will result in unreliable GPS baseline and ZTD estimations. Using the residual-based stochastic model, not only the precision of GPS baseline and ZTD estimation is obviously improved, but also the baseline and ZTD estimations are closer to the reference value.     

Uncertainties and effects on geocenter motion estimates from global GPS observations

Global positioning system (GPS) observations can be used to estimate the geocenter motion, but are subjected to large uncertainties and effects due to uneven distribution of GPS stations and high-degree aliasing errors. In this paper, uncertainties and effects on geocenter motion estimates from global GPS observations are investigated and assessed with different truncated degrees and selected GPS network distributions based on different plate motion models, including NUVEL-1A, MORVEL56 and ITRF08. Results show that the selected GPS stations have no big effects on geocenter motion estimates based on different plate motion models, while large uncertainties are found at annual and semi-annual components when using different truncated degrees. Correlations of geocenter motion estimates from selected GPS networks with GRACE and SLR are better with truncated degree 3, and higher truncated degrees will degrade geocenter estimates. Smaller RMS also shows better results with the truncated degree 3 and the NUVEL1A has the worse results because more GPS sites are eliminated. For annual signal with truncated degree 3, four GPS strategies can reduce annual amplitudes by about 29.2% in X, 5.6% in Y, and 27.9% in Z with respect to truncated degree 1. Annual phases of all GPS solutions from MORVEL56 and ITRF08 are almost close to the GRACE solution with truncated degrees from 3 to 10, while the semi-annual signals are relatively weaker for all cases.