Precise Orbit Determination for the FY-3C Satellite Using Onboard BDS and GPS Observations from 2013, 2015, and 2017

Using the FengYun-3C (FY-3C) onboard BeiDou Navigation Satellite System (BDS) and Global Positioning System (GPS) data from 2013 to 2017, this study investigates the performance and contribution of BDS to precise orbit determination (POD) for a low-Earth orbit (LEO). The overlap comparison result indicates that code bias correction of BDS can improve the POD accuracy by 12.4%. The multi-year averaged one-dimensional (1D) root mean square (RMS) of the overlapping orbit differences (OODs) for the GPS-only solution is 2.0, 1.7, and 1.5 cm, respectively, during the 2013, 2015, and 2017 periods. The 1D RMS for the BDS-only solution is 150.9, 115.0, and 47.4 cm, respectively, during the 2013, 2015, and 2017 periods, which is much worse than the GPS-only solution due to the regional system of BDS and the few BDS channels of the FY-3C receiver. For the BDS and GPS combined solution (also known as the GC combined solution), the averaged 1D RMS is 2.5, 2.3, and 1.6 cm, respectively, in 2013, 2015, and 2017, while the GC combined POD presents a significant accuracy improvement after the exclusion of geostationary Earth orbit (GEO) satellites. The main reason for the improvement seen after this exclusion is the unfavorable satellite tracking geometry and poor orbit accuracy of GEO satellites. The accuracy of BDS-only and GC combined solutions have gradually improved from 2013 to 2017, thanks to improvements in the accuracy of International GNSS Service (IGS) orbit and clock products in recent years, especially the availability of a high-frequency satellite clock product (30 s sampling interval) since 2015. Moreover, the GC POD (without GEO) was able to achieve slightly better accuracy than the GPS-only POD in 2017, indicating that the fusion of BDS and GPS observations can improve the accuracy of LEO POD. GC combined POD can significantly improve the reliability of LEO POD, simply due to system redundancy. An increased contribution of BDS to LEO POD can be expected with the launch of more BDS satellites and with further improvements in the accuracy of BDS satellite products in the near future.     

Spacecraft electrical power subsystem: Failure behavior, reliability, and multi-state failure analyses

This article investigates the degradation and failure behavior of spacecraft electrical power subsystem (EPS) on orbit. First, this work provides updated statistical reliability and multi-state failure analyses of spacecraft EPS and its different constituents, namely the batteries, the power distribution, and the solar arrays. The EPS is shown to suffer from infant mortality and to be a major driver of spacecraft unreliability. Over 25% of all spacecraft failures are the result of EPS failures. As a result, satellite manufacturers may wish to pursue targeted improvement to this subsystem, either through better testing or burn-in procedures, better design or parts selection, or additional redundancy.Second, this work investigates potential differences in the EPS degradation and failure behavior for spacecraft in low earth orbits (LEO) and geosynchronous orbits (GEO). This analysis was motivated by the recognition that the power/load cycles and the space environment are significantly different in LEO and GEO, and as such, they may result in different failure behavior for the EPS in these two types of orbits. The results indicate, and quantify the extent to which, the EPS fails differently in LEO and GEO, both in terms of frequency and severity of failure events. A casual summary of the findings can be stated as follows: the EPS fails less frequently but harder (with fatal consequences to the spacecraft) in LEO than in GEO.     

Ground resource optimization for navigation constellation based on satellite link scheduling

The Global Navigation Satellite System (GNSS) provides autonomous geospatial positioning and time synchronization services for civilian and military purposes. GNSS satellite links are used to transmit signals for constellation management and other applications. To minimize the number of stations required in participant ground-based management and reduce management costs in the GNSS network, this study solves the satellite link scheduling problem over the dynamic satellite network, including the hybrid and fast-varying inter-satellite link (ISL) working system. Firstly, the management problem is divided into two phases. Secondly, a two-level solving scheme is designed according to the characteristics of the scheduling problem. Finally, a performance analysis of different scenarios is conducted. The experimental results show that the hybrid ISL working system provides more effectively utilized data transmitting bandwidth of satellite links, thereby reducing the use of ground-based management resources. This study provides a technical reference for the management of future large-scale satellite networks.     

Comparison of a ground and a satellite clock by three-way microwavetime transfer

A three-way time transfer system for comparing a satellite clock and a ground clock is described. It eliminates not only distance variations like a two-way system but also ionospheric signal delay by the third way. The accuracy of such a system is limited of course by signal-to-noise ratio but essentially by controlling the equipment delay times     

GPS在轨卫星原子钟性能评估

卫星钟在轨性能评估对于卫星钟差预报与系统完好性监测具有重要作用。利用国际GNSS服务组织发布的事后GPS精密卫星钟差数据,基于频率准确度、漂移率、万秒稳定度及天稳定度对GPS Block IIR、IIR-M、IIF与IIIA 4类卫星的星载钟性能进行评估。结果表明:1) GPS卫星钟的频率准确度与天漂移率分别在10^-13～10^-12量级与10^-15～10^-14量级;2) 星载铷钟的万秒稳定度与天稳定度分别可达10^-14与10^-15量级,比星载铯钟的同类指标高近一个数量级;3) 新型Block IIIA卫星的星载钟的天稳定度比另外3种类型卫星的星载钟的天稳定度更高,达到(3～5)×10^-15的水平;4) 无论对于不同系列卫星还是同一系列卫星,各星载钟之间均存在一定的性能差异,这种差异与卫星钟在轨运行时间长短无显著关系。     

北斗在国际海事组织开展标准化工作初探

本文依据北斗卫星导航系统在航海领域应用的规划和考虑,介绍了国际海事组织（IMO）卫星导航标准现状以及对GNSS的政策与发展规划,阐释了航海领域制定GNSS相关标准现状及发展趋势,分析了北斗卫星导航系统开展IMO国际标准化工作的机遇与挑战,并给出了北斗卫星导航开展在IMO国际标准化工作的初步考虑与建议。     

Attitude and orbit control for satellite broadcasting missions

This paper gives a broad introduction to the problems of attitude and orbit control of geostationary communications satellites. It specifically discusses the relationships between the satellite user’s requirements for a broadcasting mission and the design of the attitude and orbit control system. To put the subject in perspective, a brief review of past and present satellites is presented first. Then orbit control is described in terms of the forces that act on a satellite in geostationary orbit and the necessary station-keeping strategies. The design of attitude control systems for three-axis stabilised satellites is presented by considering the disturbance torques, attitude sensors and actuators and by identifying the various system problems and their solutions. Sources of error in pointing the satellite towards the earth are discussed together with the formulation of error budgets. Finally, the design approach for missions that require extremely accurate pointing is considered, and some remarks are given regarding the achievable accuracy for this class of satellite missions.     

INS/GNSS组合导航系统校准方法

惯性导航系统(INS)和全球导航卫星系统(GNSS)组合的导航系统应用越来越广泛,它的校准问题亟待解决。本文简要介绍了目前广泛使用的各种导航系统,论述了INS/GNSS组合导航系统的工作原理及组合算法;详细分析了INS/GNSS组合导航系统各种测试及校准方法,比较了各种校准方法的优缺点;提出了INS/GNSS组合导航系统校准装置应具备的条件:可产生标准的空间位置和速度、可产生标准的姿态角度变化、可有效地接收GNSS卫星信号、统一的时间基准与同步信号。     

Comparison of remote time scales by satellite communications channels. Method,apparatus, and error

We consider the design of a unified software-hardware system for synchronizing remote time scales by a satellite communications channel with nanosecond accuracy. The main principles are described for the construction of a system for the transmission of time scales and a system for delay calibration of the transceiver equipment of satellite communications station, the comparison errors due to ionospheric effects are analyzed, a procedure is given for calculating the relativistic errors, and the main requirements are formulated for software for comparison of remote time scales.Translated from Izmeritel'naya Tekhnika, No. 1, pp. 18–21, January, 1994.     

A study of the thermal behaviour of carbon fibre-reinforced thermoplastic structures in geosynchronous equatorial orbit

A detailed examination has been undertaken of the thermal response of a carbon fibre composite tubular truss member during passage through the earth's umbral region in geosynchronous earth orbit (GEO), using finite difference (FD) and finite element (FE) techniques. Results from this analysis have then been used in a second FD and FE analysis of the thermal behaviour in GEO of a carbon fibre composite space structure, comprising a tetrahedral truss of 21 tubular members connected at nine cluster node joints. From these analyses it has been possible to determine the temperature distributions in the structures in orbit and it is found that the most severe thermal loading conditions are established on exit from the earth's shadow in each orbit. Parametric studies indicate that a material tailored for use in an orbital environment should possess large heat capacity and thermal conductivity, coupled with low surface absorptivity and large surface emissivity, and have near-zero coefficient of thermal expansion across the operating temperature range of the spacecraft.     

Consistency of MGEX Orbit and Clock Products

The analysis centers of the Multi-GNSS Pilot Project of the International GNSS Service provide orbit and clock products for the global navigation satellite systems (GNSSs) Global Positioning System (GPS), GLONASS, Galileo, and BeiDou, as well as for the Japanese regional Quasi-Zenith Satellite System (QZSS). Due to improved solar radiation pressure modeling and other more sophisticated models, the consistency of these products has improved in recent years. The current orbit consistency between different analysis centers is on the level of a few centimeters for GPS, around one decimeter for GLONASS and Galileo, a few decimeters for BeiDou-2, and several decimeters for QZSS. The clock consistency is about 2 cm for GPS, 5 cm for GLONASS and Galileo, and 10 cm for BeiDou-2. In terms of carrier phase modeling error for precise point positioning, the various products exhibit consistencies of 2–3 cm for GPS, 6–14 cm for GLONASS, 3–10 cm for Galileo, and 10–17 cm for BeiDou-2.     

中巴地球资源卫星

介绍了中巴地球资源卫星概况及与国外同类卫星的比较。描述了五谱段CCD相机和四谱段红外扫描仪等有效载荷。扼要介绍了卫星的公用服务平台各分系统和在轨测试性能。在首发星的基础上充分汲取用户意见,把后继星的工作做好。     

静止轨道高分辨率光学遥感探索

为了实现地球静止轨道高分辨率光学遥感,研究了在运载的动力学环境上与低轨的差异。分析了主动飞行段时间长、力学环境差、在成像方法上采用面阵成像、轨道高等原因使相机体积增大的问题。对静止轨道21.5m分辨率模拟相机进行了研究,开展了动力学模拟试验,得到了相机关键部位的测试参数,证明了地球静止轨道高分辨率光学遥感的核心环节即有效载荷研制的可行性。     

HY-2卫星激光观测精密定轨技术

2011年8月16日发射的海洋二号(HY-2)卫星是中国第一颗海洋动力环境卫星,配备的卫星激光测距跟踪系统即作为HY-2卫星定轨基准系统,同时又是HY-2卫星定轨系统之一。本文较为详细地介绍了HY-2卫星激光观测、轨道预报和激光跟踪系统(SLR)定轨技术,并对SLR定轨结果进行了初步检验。     

地球同步轨道卫星对地点波束天线在轨热分析

卫星在轨运行期间,卫星天线部件的温度会随着不断变化的外热流和辐射交换而变化。对温度变化敏感的部件如天线反射器在这种情况下易发生热致振动现象,从而影响其正常功能。对在轨运行的卫星天线所进行的热分析为卫星天线的热控设计和热致振动的预测提供了温度数据。首先建立某型号卫星天线系统的物理模型,然后利用UG-TMG软件对其进行在轨运行空间瞬态热分析,最后分析天线反射器的温度结果,为以后的热致振动研究提供参考和数据支持。     

某高轨星载数传天线的振动分析

为了确保天线系统在发射阶段和入轨工作阶段的安全，对研制的某月球轨道小型星载数传天线进行了振动分析。通过有限元建模仿真方法对该高轨星载天线在发射阶段和入轨工作阶段的振动性能进行了分析和计算，并以此为根据对天线系统结构进行优化设计。进而，通过振动试验对天线系统进行了真实振动环境条件下的测试，结果表明天线系统结构安全。振动试验后对天线电气性能进行了复测，测试结果表明其电气性能稳定，由此验证了天线系统的可靠性和有限元分析的可信性。目前，该数传天线已随星发射并入轨运行，其各项性能指标稳定，工作状态良好。研究结果对提高相关星载天线的振动安全性具有一定的参考作用。     

中国的极轨气象卫星

气象卫星是具有巨大经济和社会效益的应用卫星，中国的极轨气象卫星经历了从试验阶段到业务应用阶段的发展历程。文章简要介绍了“风云一号”（FY-1）极轨气象卫星的发展概况和技术性能，星载十通道扫描辐射计和长寿命、高可靠极轨卫星平台取得的成功；重点介绍了中国新一代的极轨气象卫星“风云三号”（FY-3）的总体概况，归纳了卫星的技术特点。     

地球低轨道卫星天线在轨热致振动分析

由于地球的频繁遮挡,当地球卫星在低轨道运行时,卫星的可展开天线会处在高低温交替的环境中,从而形成剧烈变化的温度场。剧烈的温度梯度变化会导致柔性较大的可展开天线发生热致振动,降低卫星全极化探测头部等关键部件的寿命。首先建立某型号卫星的物理模型,然后利用有限元法对其进行在轨时的空间瞬态热分析,得到可展开天线的温度场,将温度作为约束映射到结构仿真中,再在结构有限元模型上分析卫星的热变形,实现卫星天线热致振动的预测并为天线结构优化设计提供数据支持。对卫星模型进行热分析可以监测各时期的温度场以及预测有可能发生的热致振动,从而在不断优化设计的基础上避免这种不利的扰动。     

基于GNSS/INS联合仿真的组合导航终端测试方法研究

为解决GNSS/INS组合导航终端动态定位性能的实验室测试问题,本文在转台惯性仿真测试和卫星导航仿真测试技术的基础上,提出了GNSS/INS联合仿真两步法,即先通过惯性传感器实物测试获得其特征误差模型,再使用测试场景中载体初始条件和轨迹数据驱动该误差模型产生惯性传感器的模拟输出数据流,最后同步GNSS信号仿真的方法实现GNSS/INS联合仿真的过程。仿真测试结果与外场实测对比后,证明该方法获得的测试数据准确度满足预期指标、结果可靠,而且比其他传统测试方法的成本低、效率高。     

北斗标准化发展战略思考

鉴于全球卫星导航系统（GNSS）在军事和民用领域的巨大促进作用,世界主要国家已将卫星导航产业上升为国家战略。标准化作为抢占技术前沿、引领科技创新、开拓国际市场、谋求经济利益的有效手段,在推动卫星导航技术飞速发展和提高国际竞争力等方面的地位和作用日趋突出,促使北斗对其标准化战略的需求日益迫切。本文介绍了国内外标准化战略现状及卫星导航标准化工作情况,深入分析了北斗对标准化发展战略的需求,系统阐述了北斗标准化发展战略的重点方向和主要任务,进而提出相应的战略举措建议,为北斗标准化发展战略的研究提供借鉴。