Switching and performance variations of on-orbit BDS satellite clocks

The information of the satellite clock switching and performance variations on-orbit of Chinese BeiDou-2 Navigation System (BDS) is not available for the public. In order to detect the BDS satellite clock switching and performances variation, we analyzed the precise clock offset products with a total duration of 5?years every BDS satellite equipped four atomic clocks from four different manufactures from January 2013 to October 2017. Three important contributions are concluded as follows. (1) It is found that the average time of on-orbit operation for BDS satellite clocks is about 1–2?years. There have been 22 times of clock switching for BDS satellites, of which the C05 and C08 satellites have been switched to the fourth (last) atomic clock. (2) There are frequent phase adjustments for BDS on-orbit satellite clocks, and the frequency series is relatively stable. Furthermore, there are semi-annual sinusoid cycles in the frequency drift series of C06 and C09 satellites. (3) The performances of MEO satellite clocks perform better than the IGSO and GEO satellite clocks. The average ten-thousand frequency stability of BDS satellite clocks is about 1E-13, which is worse than that of GPS and Galileo but better than that of GLONASS.     

捕风一号卫星总体设计与技术特点

捕风一号卫星是中国首次实现基于星载导航卫星反射信号测量(global navigation satellite system-reflection,GNSS-R)技术的气象卫星,采用新型L波段海面风场信息探测技术,在风场测量、海面飓风风速反演等方面为国家气象、防灾减灾等行业提供服务.从系统设计角度介绍了捕风一号卫星的总...     

卫星在轨太阳辐射热流的简化计算方法

针对卫星在轨太阳辐射热流计算过程中计算参数多,计算过程复杂的问题,提出了一种简化的计算方法。该方法在分析卫星、地球和太阳三者之间空间几何关系的基础上,建立了新的计算坐标系,在计算坐标系中对卫星、地球和太阳的位置进行了重新规定,并在此坐标系中推导了卫星太阳辐射热流的计算公式。运用此方法对卫星太阳辐射热流进行分析求解时,轨道参数之间的空间角度关系更为简单,仅需对7个主要参数进行计算,与传统方法相比较计算量减少了约2/3。     

在轨地球同步卫星自主工程测控研究

地球同步卫星在轨工程测控任务通常由地面测控系统完成. 随着技术水平的发展, 如果在轨地球同步卫星能够实现自主工程测控, 将大大减轻地面测控系统负担, 提高卫星独自生存能力, 降低系统运行成本, 并将成为卫星测控技术新的发展方向. 本文提出卫星自主在轨测控方案, 研究了当前地球同步卫星在轨工程测控的主要项目及实现算法. 对其进行的可行性分析表明, 尽管受到轨道测量能力的制约, 在轨地球同步卫星仍可实现完全或地面有限参与情况下的自主工程测控. 在此基础上, 设计了一种地球同步在轨卫星完全自主工程测控的原理方案, 通过分析其技术难点及存在的风险, 提出应对措施. 研究结果表明, 基于目前卫星制造水平和成熟的在轨测控技术, 实现在轨地球同步卫星自主工程测控技术可行, 其是解决卫星数量急剧增加与地面测控能力有限这一突出矛盾的有效途径.      

Update on Fengyun Meteorological Satellite Program and Development

China began to develop its meteorological satellite program since 1969. With 50-years' growing, there are 17 Fengyun (FY) meteorological satellites launched successfully. At present, seven of them are in orbit to provide the operational service, including three polar orbiting meteorological satellites and four geostationary meteorological satellites. Since last COSPAR report, no new Fengyun satellite has been launched. The information of the on-orbit FY-2 series, FY-3 series, and FY-4 series has been updated. FY-3D and FY-2H satellites accomplished the commission test and transitioned into operation in 2018. FY-2E satellite completed its service to decommission in 2019. The web-based users and Direct Broadcasting (DB) users keep growing worldwide to require the Fengyun satellite data and products. A new Mobile Application Service has been launched to Fengyun users based on the cloud technology in 2018. In this report, the international and regional co-operations to facilitate the Fengyun user community have been addressed especially. To strengthen the data service in the Belt and Road countries, the Emergency Support Mechanism of Fengyun satellite (FY_ESM) has been established since 2018. Meanwhile, a Recalibrating 30-years' archived Fengyun satellite data project has been founded since 2018. This project targets to generate the Fundamental Climate Data Record (FCDR) as a space agency response to the Global Climate Observation System (GCOS). At last, the future Fengyun program up to 2025 has been introduced as well.      

基于恒星的电离层成像仪在轨几何定标

三轴稳定的地球静止轨道卫星在轨运行期间温度会有周期性变化.其上装载的远紫外电离层成像仪与卫星之间的热应力变化造成机械传递,导致仪器指向与装星时的初始位置发生偏差.恒星在惯性坐标系中的位置保持不变,可以将其作为电离层成像仪在轨几何定标的定标源.本文建立了基于恒星的电离层成像仪在轨几何定标模型,通过拍摄所筛选恒星图像,得出仪器在轨指向相对于初始值的偏离程度,从而提高电离层成像仪的成像几何精度.通过模拟试验,验证了运用此技术进行在轨几何定标的可行性.研究结果可为电离层成像仪常态化自动在轨几何定标奠定基础.      

天体对卫星红外地球敏感器干扰的研究

我国在轨运行的卫星多次因红外地平仪受天体的干扰而出现姿态异常的情况．本文介绍了各种红外地平仪工作原理，分析了它们受干扰的原因，给出了精确预报的方法，并在此基础上提出了相应的抗干扰措施，有些已成功运用到在轨运行的卫星上。     

中继卫星(TDRS)支持环月探测器的研究

给出了基于轨道根数的跟踪与数据中继卫星(TDRS)对月球探测器的可视算法,分析和比较了地面站和TDRS对月球探测器的测控跟踪能力.结果表明,与依靠地面站相比,使用TDRS后,在不考虑月球遮挡情况下,对环月探测器的测控覆盖率可由50%提高到99%.存在最大月球遮挡时也能达到60%,大大提高了对环月探测器的测控能力.最后讨论了TDRS跟踪环月探测器对TDRS卫星平台的要求,提出了地面站与TDRS相结合的测控方案.在当前TDRS天线运动范围受限情况下,仍能实现对月球探测器的大范围测控覆盖率.      

基于离散粒子群算法的多飞行器在轨服务任务分配

为解决多约束条件下飞行器在轨服务任务分配问题,以在轨卫星群为研究对象,提出了一种基于离散粒子群算法的多服务飞行器的目标分配方法,综合分析目标飞行器价值、服务飞行器消耗以及能量时间消耗等3项关键指标因素,建立了在轨服务任务分配问题的数学模型。通过构建粒子与实际问题间的对应关系,设计了新的离散粒子群位置和速度更新公式求解任务分配问题。仿真结果表明:离散粒子群算法具有收敛速度快,寻优能力强等优点,能够有效地解决多约束条件下的服务飞行器协同任务分配问题。     

空间遥感器用环路热管瞬态数值模拟与在轨验证

为满足空间遥感器环路热管（LHP）在轨应用需求，建立了高分九号卫星电荷耦合器件（CCD）用LHP瞬态数值模型。模型采用了节点-网络法和流动与传热关系式耦合的方法，考虑了蒸发器与储液器之间的传热传质过程。通过仿真与在轨数据的对比，发现LHP内部组件温度偏差为0.2~0.4℃，冷凝器测点温度偏差为0.5~2.0℃；预热器通过干度的变化调节了冷凝器外热流和热源工作模式的影响；热源的工作模式对蒸发器向储液器漏热、回路流阻及两相段长度均有影响。所提模型可用于不同轨道外热流及热源工作模式下，研究LHP内部各参数的变化规律，预测LHP系统的瞬态工作特性，并指导后续产品的设计与研发。      

中继卫星系统支持中/低轨航天器飞行测控任务技术研究

随着中继测控终端小型化和高增益、宽波束天线技术的发展, 特别是中国后续 中继卫星将具备S频段多址服务能力, 使得依靠中继卫星系统实现航天器飞行 测控和所有在轨卫星的日常管理成为可能. 通过分析中继测控支持中/低轨 道卫星在轨测控的能力、优势和基于中继测控实现卫星发射弹道优化策略, 提出了定向天线中继终端应急测控方法. 研究结果表明, 中继卫星系统能够为航天器飞行任务从发射、入轨到在轨管理提供测控服务, 特别是基于多址 服务能力的中继卫星系统从数量上完全满足中国在轨卫星的测控需求, 测控效率和应急能力将得到明显提升.      

卫星姿态控制系统在轨实时健康评估

面向航天器在轨智能自主管控的技术需求,提出一种基于多级模糊综合评价架构的卫星姿态控制系统的在轨实时健康评估方法.根据卫星姿态控制系统的性能特点,按实际功能将其划分为姿态测量、控制器和执行机构3个部分.在确定各部分单元部件健康信息的基础上,基于模糊综合评价算法对各部分的健康度分别进行评估.基于评估所得到的姿态测量、控制器和执行机构3部分健康信息,根据各部分对系统健康的影响情况结合变权综合原理确定健康影响权重,采用模糊综合评价算法实现对姿态控制系统整体健康性能的综合评估.仿真实验结果表明,所提出的方法能够有效实现卫星姿态控制系统的在轨实时健康评估.     

Estimation of QZSS differential code biases using QZSS/GPS combined observations from MGEX

As an important error source in Global Navigation Satellite System (GNSS) positioning and ionospheric modeling, the differential code biases (DCB) need to be estimated accurately, e.g., the regional Quasi-Zenith satellite system (QZSS). In this paper, the DCB of QZSS is estimated by adopting the global ionospheric modeling method based on QZSS/GPS combined observations from Multi-GNSS experiment (MGEX). The performance of QZSS satellite and receiver DCB is analyzed with observations from day of year (DOY) 275–364, 2018. Good agreement between our estimated QZSS satellite DCB and the products from DLR and CAS is obtained. The bias and root mean square (RMS) of DCB are mostly within ±0.3 ns. The day-to-day fluctuation of the DCB time series is less than 0.5 ns with about 96% of the cases for all satellites. However, the receiver DCB is a little less stable than satellite DCB, and their standard deviations (STDs) are within 1.9 ns. The result shows that the stability of the receiver DCBs is not significantly related to the types of receiver or antenna.     

Measurements of the earth radiation budget from satellites during the first garp global experiment

Two special measurements of the energy exchange between earth and space were made in connection with the FGGE. A global monitoring program using wide-field-of-view and scanner detectors from NASA's NIMBUS-7 satellite successfully returned measurements during the entire FGGE. This experiment system also used a black cavity detector to measure the total energy output of the sun to very high precision. A second set of high frequency time and space estimates of the radiation budget were determined from selected geostationary satellite data. Preliminary results from both radiation budget data sets and the solar “constant” measurements will be presented.     

Satellite measurements of atmospheric composition

Since 1978 a number of satellite borne sensors have been used to measure the composition of the earth's atmosphere. These include the LIMS and SAMS instruments on the Nimbus 7 satellite (launched in October 1978), the SAGE instrument on the AEM2 satellite (launched in february 1979) and various instruments on the SME spacecraft (launched October 1981). For many species, these have provided the first abundance measurements with high spatial and temporal resolution and with global coverage. In this paper the composition measurements that have become available from these programs will be reviewed. The paper will then describe some recent studies that have made use of the new data. As it is the exclusive subject of another invited paper, ozone will not be discussed in in any detail.     

利用GNSS反射信号载波测量湖面高度变化

给出一种利用导航卫星反射信号的载波相位测量光滑湖面高度变化的方法.首先建立载波相位观测方程,通过在直射与反射信号的观测量之间求单差,再在历元间求双差的方法,消除了大量误差并得到了直射与反射信号的几何路径差;然后根据各颗卫星的观测值和高度角等信息计算出湖面高度变化,并把各卫星得到的湖面高度度变化值进行加权平均以提高测量系统的精度和可靠性.仿真验证了方法在-15dB信噪比下达到了毫米级的测量精度.     

Evaluation of COMPASS ionospheric model in GNSS positioning

As important products of GNSS navigation message, ionospheric delay model parameters are broadcasted for single-frequency users to improve their positioning accuracy. GPS provides daily Klobuchar ionospheric model parameters based on geomagnetic reference frame, while the regional satellite navigation system of China’s COMPASS broadcasts an eight-parameter ionospheric model, COMPASS Ionospheric Model(CIM), which was generated by processing data from continuous monitoring stations, with updating the parameters every 2 h. To evaluate its performance, CIM predictions are compared to ionospheric delay measurements, along with GPS positioning accuracy comparisons. Real observed data analysis indicates that CIM provides higher correction precision in middle-latitude regions, but relatively lower correction precision for low-latitude regions where the ionosphere has much higher variability. CIM errors for some users show a common bias for in-coming COMPASS signals from different satellites, and hence ionospheric model errors are somehow translated into the receivers’ clock error estimation. In addition, the CIM from the China regional monitoring network are further evaluated for global ionospheric corrections. Results show that in the Northern Hemisphere areas including Asia, Europe and North America, the three-dimensional positioning accuracy using the CIM for ionospheric delay corrections is improved by 7.8%–35.3% when compared to GPS single-frequency positioning ionospheric delay corrections using the Klobuchar model. However, the positioning accuracy in the Southern Hemisphere is degraded due apparently to the lack of monitoring stations there.     

卫星导航用户机空时滤波抗干扰技术

卫星导航用户机在多个干扰源(包括宽带和窄带)或导航信号和干扰信号空间角谱接近的情 况下,系统定位精度降低甚至无法满足定位要求.为此提出具有方向约束条件的改进联合空 时处理算法,将干扰源来向检测和获取的导航卫星信息作为条件约束判据引入联合空时滤波 处理算法,在抑制干扰信号的同时使靠近干扰源来向的卫星信号正常接收.仿真表明,在有 限阵元规模情况下,保证干扰信号的高抑制度(大于40 dB),并提高干扰抑制自由度,最 重要的是当导航卫星信号与干扰信号的空间角谱接近时(10°左右),在部分区域内有效抑 制干扰的同时接收机仍然能够正常工作.该算法在一定程度上提高区域导航卫星系统在复杂 电子环境下的抗干扰能力.      

Current Status and Main Scientific Results of In-flight CSES Mission

The CSES (China Seismo-Electromagnetic Satellite) is the electromagnetism satellite of China's Zhangheng mission which is planned to launch a series of microsatellites within next 10 years in order to monitor the electromagnetic environment, gravitational field. The CSES 01 probe (also called ZH-1) was launched successfully on 2 February 2018, from the Jiuquan Satellite Launch Centre (China) and is expected to operate for 5 years in orbit. The second probe CSES 02 is going to be launched in 2022. The scientific objectives of CSES are to detect the electromagnetic field and waves, plasma and particles, for studying the seismic-associated disturbances. To meet the requirements of scientific objective, the satellite is designed to be in a sun-synchronous orbit with a high inclination of 97.4° at an altitude around 507 km. CSES carries nine scientific payloads including Search-coil magnetometer, Electric Field Detector, High precision Magnetometer, GNSS occultation Receiver, Plasma Analyzer, Langmuir Probe, two Energetic Particle Detectors (including an Italian one), and Tri-Band Transmitter. Up to now, CSES has been operating in orbit for 2 years with stable and reliable performance. By using all kinds of data acquired by CSES, we have undertaken a series of scientific researches in the field of global geomagnetic field re-building, the ionospheric variation environment, waves, and particle precipitations under disturbed space weather and earthquake activities, the Lithosphere-Atmosphere-Ionosphere coupling mechanism research and so on.      

精密热控技术在太极一号卫星上的应用

为探测空间引力波,中国科学院提出了太极计划,其第一步是通过近地轨道卫星太极一号对核心载荷的关键技术进行验证.由于温度稳定性直接影响干涉仪测距和加速度的测量精度,太极一号卫星提出了(T±0.1)K的高精度、高稳定度温控指标.针对该指标要求设计热控方案,从热组件的选取到单机设备的应用均依照高指标进行控制.为了保证方案实施的...