A Positioning System based on Communication Satellites and the Chinese Area Positioning System(CAPS)

The Chinese Area Positioning System （CAPS） is a positioning system based on satellite communication that is fundamentally different from the 3＂G＂ （GPS, GLONASS and GALILEO） systems. The latter use special-purpose navigation satellites to broadcast navigation information generated on-board to users, while the CAPS transfers ground-generated navigation information to users via the communication satellite. In order to achieve accurate Positioning, Velocity and Time （PVT）, the CAPS employs the following strategies to over- come the three main obstacles caused by using the communication satellite： （a） by real-time following-up frequency stabilization to achieve stable frequency; （b） by using a single carrier in the transponder with 36 MHz band-width to gain sufficient power; （c） by incorporating Decommissioned Geostationary Orbit communication satellite （DGEO）, barometric pressure and Inclined Geostationary Orbit communication satellite （IGSO） to achieve the 3-D posi- tioning. Furthermore, the abundant transponders available on DGEO can be used to realize the large capacity of communication as well as the integrated navigation and communication. With the communication functions incorporated, five new functions appear in the CAPS： （1） combination of navigation and communication; （2） combination of navigation and high accu- racy orbit measurement; （3） combination of navigation message and wide/local area differen- tial processing; （4） combination of the switching of satellites, frequencies and codes; and （5） combination of the navigation message and the barometric altimetry. The CAPS is thereby labelled a PVT5C system of high accuracy. In order to validate the working principle and the performance of the CAPS, a trial system was established in the course of two years at a cost of about 20 million dollars. The trial constellation consists of two GEO satellites located at E87.5° and E110.5°, two DGEOs located at E130° and E142°, as well as barometric altimetry as a virtual satellite. Static and dynamic performance tests were completed for the Eastern, the Western, the Northern, the Southern and the Middle regions of China. The evaluation results are as follows： （1） land static test, plane accuracy range： C/A code, 15-25 m; P code, 5-10 meters; altitude accuracy range, 1- m; （2） land dynamic test, plane accuracy range, C/A code, 15-25 m; P code, 8-10m; （3） velocity accuracy, C/A code, 0.13-0.3 m s-1, P code, 0.15-0.17 m s- 1; （4） timing accuracy, C/A code, 160 ns, P code, 13 ns; （5） timing compared accuracy of Two Way Satellite Time and Frequency Transfer （TWSTFT）, average accuracy, 0.068 ns; （6） random error of the satellite ranging, 10.7 mm; （7） orbit determination accuracy, better than 2 m. The above stated random error is 1σ error. At present, this system is used as a preliminary operational system and a complete system with 3 GEO, 3 DGEO and 3 IGSO is being established.

利用恒星与低轨卫星同时成像实现地面定位的算法

天文定位技术抗干扰性强,隐蔽性好,误差不随时间积累,在陆基、海基、空天基平台上应用广泛。近些年,低轨巨星座技术迅猛发展,为导航技术的发展提供了契机。本文提出了一种基于低轨卫星光学观测的定位算法,以星间角距作为基本观测量,详细推导了定位模型,分析了影响定位精度的主要误差源,给出了误差传播公式。基于星链星座的仿真试验表明,本文算法平均定位精度可达30.5 m,其中北向、东向、天向平均定位精度分别为4.3、6.3、29.5 m。本文算法不仅保留了传统天文定位技术的优点,而且无须水平基准,为小型化、快速化和自动化天文导航装备的研制提供了一种思路,具有潜在的应用价值。

基于Daisy的天文卫星数据处理软件系统设计与实现

天文卫星数据处理是开展空间天文学领域科学研究的重要内容,也是当前研究的热点。然而,在大数据背景下,由于需要进行大规模数据处理,传统的数据处理方式已经无法满足当前应用的需求。针对这一问题,本文提出了一种数据处理软件系统,该系统基于Daisy(Data Analysis Integrated Software System)研发,实现天文卫星数据处理流程的自动化和规范化。首先,通过分析卫星数据产品间的依赖关系,采用数据分块处理技术,实现系统内存管理;其次,通过对数据处理算法和工具进行标准化,实现底层代码的统一管理;最后,研发工作流调度平台,实现数据处理流程的自定义配置和实时监控。实验验证了该系统具有有效性和实用性,能够克服传统数据处理方法的不足,实现数据处理流程的自动化和规范化,为相关软件系统的设计提供指导。

基于科学工作流的通用卫星数据处理调度系统

天文卫星产生的海量观测数据下传至地面后,需要经过一系列的处理流程生成可供科学研究人员的数据产品。传统数据处理方式需要耗费大量的时间和人力成本,同时存在缺乏灵活性、任务管理困难及执行效率低下等缺陷。基于上述问题,为实现卫星数据产品生成的自动化和规范化,该文研究并设计了一种基于科学工作流的通用卫星数据处理调度系统。通过封装卫星数据处理算法,结合科学工作流、可视化编辑等相关技术,实现卫星数据处理的自动化和可配置,用户更新需求时无需修改代码,只需重新配置参数;利用可拔插组件设计机制实现系统的通用性,满足不断扩增的卫星的不同数据处理需求。根据已有卫星的数据处理需求进行应用测试,应用实例表明,该系统能够实现卫星数据的自动化处理,并且能够极大地提高处理流程的灵活性、可维护性和执行效率,有利于科学研究人员根据自己的需求获取卫星数据产品。

Status of the Hard X-ray Modulation Telescope Project

The Hard X-ray Modulation Telescope(HXMT) is China's first astronomical satellite.It will perform a broad band(1–250 keV) scan survey and do pointed observations of X-ray sources to study their spectra and multi-wavelength temporal properties. The pre-flight models of the satellites have been finished, and the flight models are in production. The expected launch date of HXMT is in late 2015.

Hard X-Ray Modulation Telescope(HXMT) Mission

The HXMT mission concept consists of a slat-collimated hard X-ray detector assembly sensitive in 20～250 keV with a collection area of about 5000 cm2. Based on the reconstruction technique by direct demodulation developed in recent years, HXMT is mainly devoted to performing a hard X-ray all-sky imaging survey with both high sensitivity and high spatial resolution. It can also be used to make pointed observations of X-ray sources to study their spectroscopic and temporal properties in details. The main detector of HXMT consists of 18 individual cylindrical NaI(T1)/CsI(Na) phoswich modules, each with anarea of 283.5 cm2 and a field of view of 5.7°× 1.1° (FWHM). Its spatial resolution and position accuracy are 5′ and 1′ by using the direct demodulation in 1994, and in 2000 its feasibility and technical demonstration study was selected as a project under the Major State Basic Research Program of China. In October 2005, this project entered the full design phase and was listed as a candidate for the first dedicated astronomy satellite around 2010. We are now also considering secondary low energy instruments for this satellite.

IMAGING IN HIGH ENERGY ASTRONOMY

Space research is usually costly, and this restricts participation of developing countries. With traditional techniques one must construct high resolution instrument,more and more complicated and expensive, to obtain high resolution results from space observations. It is a difficult task to make observations with both high sensitivity and high resolution. Applying advanced inversion technique, one can subtract more information from old data in public domain,and, furthermore, conduct high sensitive and high-resolution experiments with low-cost low-resolution instruments. So developing and applying data analysis technique is of great importance for developing countries to do basic space science.In this paper we summarize efforts of Chinese scientists in recent years along this direction on imaging in space high energy astronomy.

The Response of the Earth's Lower Ionosphere to Gamma-Ray Solar Flares and their Associated X-ray

The present work aims to explore the impact of solar gamma-ray fiares(GRFs),detected by the Fermi-Large Area Telescope(LAT),and their associated X-ray fiares(XRFs)on the Earth’s lower ionosphere.The data of ionospheric parameter fmin were collected from the Yamagawa mid-latitude ionosonde station in Japan.Because most of the GRFs used in this study are associated with soft X-ray(SXR)emissions,detected by the Geostationary Operational Environmental Satellite(GOES),we classified them into three types:simultaneous(S),delayed(D)and not associated(N),refiecting the phase occurrence of the solar fiares.Generally,the ionospheric D layer responds strongly to XRFs more than GRFs.The temporal profiles of the ionospheric parameter fmin show distinct behaviors as a response to the various GRF types.In the case of the S-type,a single strong peak,with an average value of 5.2 MHz,emanates in the fmin profile within an average interval of time of less than half an hour.In the case of the D-type,two successive peaks appear in the fmin profile,with an average value of 6.0 MHz for the second peak through a time interval of one hour after the onset of gamma-ray(GR)emissions.The response of the fmin parameter to the N-type fiares appears as a single peak with an average value of 4.8 MHz within about an hour.We notice that the difference between the fmin peak values and the corresponding reference ones(dfmin)is more convenient and representative than the fmin values,where the median GR fiux of the S-,D-and N-types tends to increase as the average dfmin increases.

In-Orbit Calibration and Data Analysis of China＇s First Grazing Incidence Focusing X-Ray Pulsar Telescope

The grazing incidence focusing X-ray pulsar telescope(iFXPT), as the main payload of the X-ray Pulsar Navigation Test Satellite(XPNAV-1), will have great significance on China's space scientific exploration and X-ray pulsar navigation. With PSR B0531+21(Crab Pulsar) as the observation target, the pulsar profile has been recovered based on the data obtained by iFXPT, realizing the main objective of "observing" PSR B0531+21 for the first time in China. This payload mainly consists of the Wolter-I X-ray optics, silicon drift detector, magnetic deflector, electronics, high-energy particle shield and high-stability structures. Currently, the iFXPT, with its good in-orbit performance, has obtained a considerable observation data. The effective area, sensitivity and energy response have been calibrated both on ground and in-orbit, demonstrating a high degree of consistency. Meanwhile, the in-orbit observation data and information for pulsar navigation has also been analyzed simultaneously. As a result, the feasibility of the exploration scheme and the performance of the telescope have been fully validated.

Global Mg/Si and Al/Si Distributions on the Lunar Surface Derived from Chang'E-2 X-ray Spectrometer

The technique of X-ray fluorescence remote sensing plays a significant role in research related to the chemical compositions of the Moon. Here we describe the data analysis method for China＇s Chang＇E-2 X-ray spectrometer in detail and present the preliminary results about the first global Mg/Si and Al/Si maps of the lunar surface. Our results show that the distributions of Mg/Si and Al/Si correlate well with terrains on the Moon. The higher Mg/Si ratio corresponds to the mare regions while the lower value corresponds to the highland terrains. The map of the Al/Si ratio shows a reversed distribution compared with the map of the Mg/Si ratio.

主要定向技术比较与GNSS快速定位定向仪研制进展

首先介绍了定向的定义、基准和应用背景,总结并比较了目前几种主要定向技术的特点。在此基础上分析了卫星定向技术的优势和改进需求;重点介绍了GNSS快速定位定向仪(臂长1.1 m)研制的基本情况、基本组成和特点。该仪器采用单接收机旋转方式定位定向。经过大量实验鉴定,通过3 min的连续测量可实现优于0.5个密位(108″)的定向精度和优于5 m的定位精度。

低轨星载光学测量确定静止卫星轨道的方法

为了研究低地球轨道(LEO)卫星对地球静止轨道(GEO)卫星的跟踪定轨能力,文章提出利用LEO星载光学测量技术对GEO卫星进行轨道确定。文章充分考虑光学可视条件与星载相机的观测区域,对LEO卫星跟踪GEO卫星的空间环境以及测量模式进行模拟。利用模拟得到的测角数据采用数值方法对GEO卫星进行定轨并与参考轨道进行重叠对比。通过仿真算例对单圈及多圈跟踪情况下GEO目标定轨精度进行分析,结果表明,在平台轨道误差3m、测量精度5"情况下,随着观测圈数的叠加,GEO卫星的轨道确定精度可由500m量级提升至百米量级。若提升平台精度和测量精度,则轨道确定性可进一步提高。

天文卫星下传数据处理系统的规划

天文卫星获取的数据需要经过卫星下传数据处理系统的一系列加工,生成可以分析的数据产品,这些产品及相应软件要发布给国内外用户,同时数据处理系统还要监测载荷状态、数据质量及天体源爆发等。这样,下传数据处理系统的建设直接关系到物理成果的获取,规划该系统就变得非常有意义。从数据产品定义、子系统规划、数据流程等方面介绍卫星下传数据处理系统的规划,并提出以模块化开发方式从整体上协调各个子系统的开发,使各个系统及其软件相互配合,共同促进科学产出。

基于改进遗传算法的天文卫星任务规划研究

空间天文卫星任务规划是一个复杂的多目标优化问题,是为了确定空间天文卫星需要执行的观测活动,有效研究确定在轨方案。通过抽象空间天文卫星任务规划问题相关要素,建立了空间天文卫星的任务规划数学模型,并在原有多目标遗传算法的基础上,设计了基于观测窗口序列的多目标遗传算法,改进了遗传算法的编码能力,能够得到每个观测任务的观测窗口序列,提高了规划结果的灵活性和适用性。从规划仿真结果看,使用改进后的多目标遗传算法能够满足空间天文卫星任务规划的具体需求,是有效的方法。

天文探测卫星定点观测模式外热流变化规律分析

针对天文探测卫星定点观测模式下的特定姿态,结合相关科学观测约束、整星能源和热控设计约束及轨道特点,进行了多约束条件下的外热流变化规律分析,对比了有、无遮阳挡板情况下,卫星外热流的差异,并通过虚拟热沉温度,分析了卫星各个舱板的散热能力。基于有、无遮阳挡板的外热流分析结果,从热控角度建议在定点观测模式下,对卫星的观测姿态进行约束,对有低温需求的天文探测器建议加设遮阳挡板,可为天文探测卫星的热控设计提供参考。

天文卫星巡天扫描智能规划模型及仿真

巡天扫描是天文卫星进行天体观测的基础,但是使用传统方法很难实现全天球覆盖,并且会遇到能源输出瓶颈。因此,针对天文卫星巡天扫描所遇到的问题,提出了使用多目标遗传算法对卫星飞行任务进行智能规划的模型。该模型通过调整飞行任务很好解决了能源输出的问题,与仅依靠被动的分段式扫描方法相比,还大大缩短了巡天扫描的时间。从仿真结果来看,该模型是十分有效的。

白天用CCD摄象机对天体目标的探测及实验

文中介绍了用ＣＣＤ摄象机及相应的光学系统对天体目标的探测能力计算及白天用ＣＣＤ摄象机对天体目标的探测实验。给出了计算被测天体目标星等的计算表达式，指出白天在天空背景亮度在１２００ｃｄ／ｍ~２至２７００ｃｄ／ｍ~２时用普通低照度ＣＣＤ摄象机与大口径天文望远镜配合可探测到４至４．

双波长卫星激光测距

双波长卫星激光测距不必借助大气改正模型,利用双波长往返时间差就可以进行大气折射改正。采用皮秒级事件计时器等技术测量往返时间差,修正精度可以达到毫米量级。介绍了这一领域的研究进展、双波长大气改正的基本原理,分析了双波长激光测距的精度,最后对双波长卫星激光测距前景进行了展望。

上海天文台VLBI,SLR和GPS站的归心结果与分析

本文重新处理了最近几年来利用GPS技术测定上海天文台GPS站坐标的资料，给出了GPS站相对于VLBI，SLR站的基线矢量，并与利用常规方法归心的最新结果进行了比较和分析，得到了IGS’92联测中上海天文台GPS技术解算的SH01站坐标，与VLBI技术解算的结果比较，两者相差小于26cm，同时得到GPS技术归心的外符精度好于1cm。

不同太阳、月亮坐标算法对GNSS部分系统误差的影响研究

研究天文年历、JPL星历计算的太阳、月亮坐标的差异及对GNSS导航定位的影响。结果表明,不同星历计算的太阳坐标差异最大为5×108m,月亮坐标差异最大为3×106m。天文年历与DE421计算的星固系X方向之间的夹角最大达30′(Y方向与X方向类似)。太阳坐标差异引起的相位绕转改正之间的差异最大达0.3mm,卫星天线相位中心偏差改正之间的差异最大达3mm。太阳、月亮坐标差异导致固体潮改正之间的差异最大达3mm。经实测GPS数据验证,不同星历计算的太阳、月亮坐标差异对PPP的影响可以忽略,建议在PPP中采用计算效率高的天文年历。