Precision orbit determination of Tianwen-1 using one-way Doppler is a first trial in deep space exploration of China. In this paper, a method of orbit determination with one-way Doppler is proposed. Firstly, the observation model of one-way Doppler is established and the theoretical error is analyzed. Secondly, the orbit determination of Tianwen-1 is carried out using one-way Doppler during the relay orbit phase. The orbital accuracy is evaluated in two ways, the first one is orbital comparison with precision orbit determined using UXB and VLBI, the second one is overlap comparison. The results show that the instability of ultra-stable oscillator and phase scintillation error are the main error sources that affect the accuracy of one-way Doppler measurement. The orbital accuracy can be better than 1 km using only one-way Doppler during the relay phase, and can provide important support for China ’s future deep space exploration missions.

针对全球导航卫星系统(GNSS)如何支持月球探测器导航的问题,根据信号功率电平计算模型,辅助航天器姿态模型信息,全面考虑发射/接收天线增益方向特性、飞行轨道特征、飞行姿态和天线安装位置及指向等因素,改进GNSS信号可见性分析方法,并利用嫦娥-5 T1探测器的实测数据验证了改进方法的正确性.以嫦娥五号探测器为例,利用该方法分析了GNSS信号可见性,结果表明:相比单GPS系统,采用GPS+"北斗"双模工作模式,可以显著增加可见卫星数,最大增幅可达100％.对于地月转移轨道段,接收机载噪比门限达到21 dBHz即可满足月球探测器GNSS导航定位的可见卫星数需求.

The complete expression of pointing calibration model (PCM) for the axis related errors (ARE) of the radio telescope is derived directly. The definition of the common axis related parameters in both pointing correction model of ARE and Lösler's indirect model (IM) is unified, then the relationship between PCM and IM of the radio telescope is established. Thus, the deflection of the vertical (DOV) determination of VLBI stations is realized by using radio telescope azimuth axis information. As a direct surveying approach, this method does not rely on special DOV surveying equipment. It could only depend on pointing calibration surveying data for telescope aperiodic maintenance and the local surveying data including leveling. Verified by a variety of DOV surveying methods, the DOV obtained by our method shows a good agreement with real surveyed DOV in west-east component. Owing to the non-uniform distribution of the radio sources sky coverage of the station during its pointing calibration, the north-south component of DOV has the same direction as the surveyed DOV, but has a difference in value. In the future, further providing an optimized telescope pointing calibration, the high precision surveying of DOV will be obtained by using VLBI telescope azimuth axis.

推导了传统全球卫星导航定位系统(GNSS)测定垂线偏差(Deflection of theVertical,DOV)形式误差的表达式;提出一种可用以解算并置站DOV的小网参数转换法.利用乌鲁木齐南山多技术并置站控制网观测信息,开展了算法验证,并对该站内多个地点DOV开展了实测.结果表明,高精度的小网DOV仅由点位观测精度最高、覆盖面积最广的3个站点决定.个别精度较差的点会为DOV的测定值带来较大的不确定性;采用小网转换法所解算的DOV与实测值间的一致性分别为?2.3′′±4.3′′(子午分量)和0.2′′±4.6′′(卯酉分量);小网转换求取DOV的方法在精度上与经典的GNSS水准方法相当,但步骤更加简便.鉴于多技术并置站会不定期地开展本地测量,可利用该方法实现多技术并置站DOV的零成本长期监测.

目前,对流层大气湍流造成的随机变化的相位误差已严重影响了高频段深空测控通信系统的工作性能.为了量化湍流强度,基于超短基线干涉仪系统接收的地球同步卫星信号,统计信号干涉相位的标准偏差,结合经典的Kolmogorov Obukhov“2/3”扰动理论和随机场理论建立了大气湍流参数计算模型,实时获取表征湍流强度的物理量:大气折射率结构常数C2n.分别在郑州、杭州进行了连续多天的晴天、雨天相位观测试验,利用试验数据计算C2n,并利用气象探空数据经验模型进行了验证.试验数据计算结果显示:C2n在郑州晴天的正午前后要明显高于早晨和傍晚,而在杭州雨天则没有明显的规律性.C2n在10-15～10-13的数量级范围变化,与经验模型计算的结果相吻合,验证了算法的合理性和准确性.

为在本地测量中更精确地测定VLBI(very long baseline interferometry)天线参考点(reference point,RP)点位,分析了水平钢轨残余形变对四轮座架式天线的影响,首次提出并推导了用以改正归心解算靶标点(target point,TP)坐标的水平钢轨残余形变模型,结合实测靶标坐标与钢轨水准数据,解释了TP坐标残差中的系统性效应,精化了TP理论坐标,显著提高了参考点测定精度.结果 表明,采用水平钢轨残余形变改正模型与估算模型可分别使靶标坐标归心拟后残差中误差提高50％和65％,归心精度均可提高约30％.此外,本钢轨残余形变估算模型还可有效用于该类天线钢轨形变的监测.

精密轨道确定在深空探测中至关重要,而定轨数据中的白噪声会影响定轨性能.基于零相位分析,比较了FRR(forward-filter reverse-filter reverse-output)、RRF(reverse-filter reverse-filter forward-output)和Matlab中的filtfilt这3种滤波器的优劣,设计了一种零相位Kaiser窗低通滤波器.利用火星快车号(Mars Express,MEX)的仿真数据和实测数据验证了零相位Kaiser窗低通滤波器的性能,结果发现滤除白噪声后MEX数据的定轨精度有了显著改善.双程测速数据残差均方根(root mean square,RMS)减小为原来的1/3左右,达到了0.031 mm/s;轨道位置和速度与欧空局(European Space Agency,ESA)精密轨道的差异明显变小.该滤波算法作为定轨前的数据预处理可以提高定轨精度,从而为中国火星探测器的轨道数据处理提供一定的参考.

In light of the entry descent and landing flight in Chinese Mars exploration mission，this paper has analyzed the difficulties of this mission phase based on the characteristics of Mars atmosphere and terrain. All the past soft landing missions on Mars have been reviewed and the potential reasons for mission failure have been summarized. The communication architecture in Mars Science Laboratory has been introduced to illustrate all the potential communication methods. The key technologies include communication strategies for blackout，selection of signal modulation and high dynamic signal detection at low SNR. Finally，suggestions have been proposed for the implementation of EDL flight in Chinese Mars Exploration missions.

With the implement of China’s Lunar Exploration Program in three stages，which consist of orbiting，landing，and returning， China’s deep space TT&C（Tracking，Telemetry and Command）system has been built up. The future Mars Exploration Program will further enhance the full capability of the system. In this paper, the development of China’s deep space TT&C system is reviewed，including the details of key technology research，top design，and system construction. The future trend of this system is discussed based on the latest development of deep space TT&C technologies.

我国探月工程三期“嫦娥五号”月球探测器(CE-5)将实现月球采样返回探测,月球交会对接是CE-5工程中的关键技术,CE-5任务中将采用地基无线电测距测速技术联合同波束VLBI测量技术实现对轨道器和上升器的联合测定轨,以支持月球交会对接过程特别是远程导引阶段的多探测器测控.本文分析了同波束VLBI测量数据在多探测器定轨中的应用,利用仿真数据分析了月球交会对接远程导引段的轨道器和上升器定轨精度,特别是两器间的相对定轨精度.选取的长弧和短弧定轨典型算例分析表明,利用10 ps精度的同波束VLBI数据,联合测距数据对轨道器和上升器定轨,可以达到1m的相对定轨精度.

针对月球着陆巡视探测活动中的月面着陆器与巡视器的相对定位问题,建立了月面双目标相对运动方程和状态方程,给出了同波束差分时延测量量关于双目标相对位置的测量方程,进而实现了基于统计估计方法解算双目标相对位置的算法.结合嫦娥三号探测器跟踪测量条件,利用该算法开展仿真分析.结果表明:在测量弧段达到5 min以上、同波束干涉测量(SBI)时延仅有1 ns随机误差的情况下,相对定位精度可达20 m;测量数据存在3 ns系统误差时,相对定位精度为200m,此时如果增加甚长基线干涉测量(VLBI)时延数据,可将相对定位精度提高到150m.利用嫦娥三号实测数据处理结果验证了此算法的正确性和仿真分析的有效性,可为合理制定月面双目标相对定位策略提供参考.

X-band is the primary frequency band used by deep space TTC(Tracking,Telemetry and Command) systems.X-band range-rate measurement is more accurate than those of S-band as validated in X-band deep space TTC system experiments of Chang'E-2 spacecraft.The precision of range-rate measurement is about 1 mm/s.For X-band range-rate,theoretical error caused by Doppler effect approximate calculation formula is analyzed.This error could become 1 cm/s during translunar and lunar-orbiting phases.Furthermore,measurement residual error is analyzed based on the precision ephemerides of post orbit determination for X-band deep space TTC system experiment of Chang'E-2 spacecraft.The results show that the range-rate residual error induced by the approximation increases by 1 mm/s compared to what is calculated by equations.It is close to the actual measurement precision.Therefore,the Doppler effect approximate calculation formula is no longer applicable and the exact formula should be used in the lunar and deep space exploration projects in the future.

结合CCSDS(空间数据系统咨询委员会)给出的相关技术标准,介绍了我国目前正在建设的深空测控网甚长基线干涉测量系统,包括系统定义与性能需求,系统的设计与实现等方面.阐述了相关的设计原则和设计思路:对射电源信号,通过将2个测站接收到的同一射电源信号进行互相关的方式求取信号延迟; 对航天器信号,利用对正弦信号的统计处理方法,对正弦相位进行估计再差分求取时延.最后简要分析了与欧空局开展机构间交互支持的性能指标.

The engineering background and significance of three-way measurement(including three-way ranging and three-way Doppler) are introduced.The mathematical model and application scenarios for real-time trajectory determination using three-way measurements are given and the theoretical error of data is analyzed.The result of residual error analyses of Chang'E-1 three-way measurement shows that without time synchronization,three-way ranging error is approximately 200m and three-way Doppler error is approximately 2 cm/s in 100 km×100 km lunar orbit.Therefore,three-way measurement data can be used independently for orbit determination and it is feasible to use three-way measurement in future deep space missions.

Based on measurement models of the tracking data including ranging,range rate,interferometric delay and delay rate,the information array of lunar probe's state vector is presented.Error equations and covariance matrixes for RTN components of orbit-determination error are derived.The numerical relation between RTN components of error and the measurement accuracy are calculated for lunar orbit.According to measurement error and station/baseline distribution in the China lunar exploration program,the influence and level of error factors are analyzed and calculated for RTN components of errors in the position and velocity for various lunar orbits.The orbit-determination results using measurement data of Chang'e-1 and Chang'e-2 probes validate this analysis method,which will be as an important reference for RTN components of errors in the lunar decent initial orbit in the second phase of China lunar exploration program.

我国区域卫星导航定位系统的星座设计包括了5颗或更多地球同步卫星,GEO卫星相对于地面测站的运动较小,且由于需要维持轨位而必须较频繁地机动轨道,这两个特点对GEO导航卫星的精密定轨都提出了新的挑战.目前已有采用C波段转发式测距和L波段直发式伪距测量实现GEO卫星精密定轨的成功实践.本文将在探月工程“嫦娥一号”和“嫦娥二号”测定轨中发挥重要作用的VLBI技术应用于GEO卫星测定轨,介绍了VLBI的测定轨原理和系统差校正方法,VLBI测量主要约束了GEO卫星的南北和东西位置分量.中国VLBI网(CVN)对某GEO导航卫星进行了24 h观测试验,本文综合利用VLBI测轨数据和C波段转发式测距数据进行定轨分析,VLBI时延测量精度约3.6 ns,时延率约0.4 ps/s.分析表明,VLBI数据提供了对测距数据系统差的标定,而综合两种类型数据联合定轨可以显著提高卫星机动后轨道快速恢复定轨预报精度.

China’s COMPASS satellite navigation system consists of five or more geostationary (GEO) satellites. The roles of GEO satellites are to improve the regional user’s positioning accuracy and provide the continuous Radio Determination Satellite Service. The motion of GEO satellites relative to a ground tracking station is almost fixed, and regular orbit maneuvers are necessary to maintain the satellites’ allocated positions above the equator. These features present difficulties in precise orbit determination (POD). C-band ranging via onboard transponders and the L-band pseudo-ranging technique have been used in the COMPASS system. This paper introduces VLBI tracking, which has been successfully employed in the Chinese lunar exploration programs Chang’E-1 and Chang’E-2, to the POD of GEO satellites. In contrast to ranging, which measures distances between a GEO satellite and an observer, VLBI is an angular measurement technique that constrains the satellite’s position errors perpendicular to the satellite-to-observer direction. As a demonstration, the Chinese VLBI Network organized a tracking and orbit-determination experiment for a GEO navigation satellite lasting 24 h. This paper uses the VLBI delay and delay-rate data, in combination with C-band ranging data, to determine the GEO satellite’s orbit. The accuracies of the VLBI delay and delay rate data are about 3.6 ns and 0.4 ps/s, respectively. Data analysis shows that the VLBI data are able to calibrate systematic errors of the C-band ranging data, and the combination of the two observations improves orbit prediction accuracy with short-arc data, which is important for orbital recovery after maneuvers of GEO satellites. With the implementation of VLBI2010, it is possible for VLBI to be applied in the COMPASS satellite navigation system.

DORIS system is based on accurate measurements of Doppler shifts,which are usually processed as range-rate data and the accuracy is better than 0.5mm/sec.To investigate the orbit determination accuracy through processing of DORIS data,this paper uses a set of simulation experiments to analyze various error sources,such as distribution of the ground-based beacons,observation error and atmospheric density model error,which may affect the accuracy.The results indicate that wider distribution of ground-based beacons brings better orbital accuracy.At the same time,atmospheric density model significantly reduces orbital accuracy.Furthermore,a comparison is made between simulation tests and actual data processing.From the comparison,we come to the conclusion that the accuracy of the position can be better than 30 cm(1σ) under the distribution of eight ground-based beacons using twenty-four hours Doppler range-rate data to determine a sun synchronous polar orbit at an altitude of 800km,and the result can be better than 20 cm(1σ) for global distribution of thirty ground-based beacons.

The paper discusses selection of the latitude for deep space stations.Technical analysis is given on the constraints,e.g.tracking range and performance of large-aperture antenna systems,for selection of the optimized latitude for a deep space station site.Finally,a proposal is put forward for selection of the latitudes for China's deep space stations.

Chinese lunar exploration satellite CE-I will make use of Unified S-Band (USB) and Very Long Baseline Interferometry (VLBI) to determine the orbit.Because the orbit of SMART-1 satellite is similar to CE-I mission orbit, the test on USB-VLBI’s joint tracking of SMART-1 was carried out in May, 2006.We investigated the quality of the data, analyzed the precision in orbit determination with different arcs and data combination types using GEODYN II orbit determination software and and came up with some useful conclusions.