The remarkably long distances covered by deep space probes result in extremely weak downlink signals, which poses great challenges for ground measurement systems. In the current climate, improving the comprehensive utilization of downlink signal power to increase the detection distance or enhance the measurement accuracy is of great significance in deep space exploration. Facing this problem, we analyze the delta Differential One-way Range (ΔDOR) error budget of the X-band of the China Deep Space Network (CDSN). Then, we propose a novel interferometry method that detunes one group of DOR beacons and reuses the clock components of regenerative pseudo-code ranging signals for interferometry delay estimation. The primary advantage of this method is its ability to enhance the power utilization efficiency of downlink signals, thereby facilitating more efficient tracking and measurement without necessitating additional design requirements for deep space transponders. Finally, we analyze and verify the correctness and effectiveness of our proposed method using measured data from CDSN. Our results indicate that the proposed method can save approximately 13% of the downlink signal power and increase the detection distance by about 6.25% using typical modulation parameters. Furthermore, if the relative power of other signal components remains unchanged, the power of the DOR tone can be directly increased by more than 100%, improving the deep space exploration ability more significantly.

针对嫦娥五号探测器(CE-5)开展基于深空网测量数据的定轨能力分析.首先从测量原理分析了深空网VLBI数据的误差源,然后利用CE-5的精密轨道评估了 VLBI数据的误差,最后基于实测数据与协方差分析理论,分析UXB与VLBI数据的定轨能力.结果表明:转移阶段,单独利用深空网测量数据可以获取优于1 km的转移轨道精度,标校VLBI系统偏差后可以实现优于500 m的轨道精度;环月阶段,轨道解算精度优于200 m,VLBI数据对轨道改进有限,系统偏差甚至会降低轨道精度;基于协方差分析表明,VLBI数据可以降低转移阶段的形式误差近1个量级,但对于环月阶段改进量小于10％.

The algorithm, processing strategy and performances of the Global Ionospheric Map (GIM), generated based on the global GNSS tracking network observations by international GNSS Monitoring and Assessment System BAC Analysis Center (BAC), is analyzed in this paper. First, during the “Tianwen-1” Mars Exploring Mission Mars-docking-orbit phase, the comparison among the GIM products of BAC, Center for Orbit Determination in Europe (CODE) and Jet Propulsion Laboratory (JPL) shows that the BAC GIM product performances similar to JPL GIM product and slightly worse than their CODE peer; however, in the middle latitude area where China’s Deep Space Network (DSN) is located, BAC GIM product is the best in model bias. Second, the BAC GIM products are also compared with the ionospheric delay data observed by GNSS receivers mounted at two DSN stations (Kashi and Namibia). It is found that the two data sets show an obvious similarity and the correlation coefficients are within (0.943 – 0.977). Last, the BAC GIM products’ application in the “Tianwen-1” Mars Exploring Mission is also performed. The ionospheric delays in range and rate measurements collected at Jiamusi, Kashi and Argentina DSN stations are corrected; the orbit determination residuals corresponding to the range measurements decrease up to 20

Deep space exploration navigation requires high accuracy of the Doppler measurement, which is equivalent to a frequency estimation problem. Because of the fence effect and spectrum leakage, the frequency estimation performances, which is based on the FFT spectrum methods, are significantly affected by the signal frequency. In this paper, we propose a novel method that utilizes the mathematical relation of the three Chirp-Z Transform (CZT) coefficients around the peak spectral line. The realization, unbiased performance, and algorithm parameter setting rule of the proposed method are described and analyzed in detail. The Monte Carlo simulation results show that the proposed method has a better anti-noise and unbiased performance compared with some traditional estimator methods. Furthermore, the proposed method is utilized to process the raw data of MEX and Tianwen-1 satellites received by Chinese Deep Space Stations (CDSS). The results show that the Doppler estimation accuracy of MEX and Tianwen-1 are both about 3 millihertz (mHz) in 1-s integration, which is consistent with that of ESA/EVN/CDSN and a little better than that of the Chinese VLBI network (CVN). Generally, this proposed method can be effectively utilized to support Chinese future deep space navigation missions and radio science experiments.

In deep space exploration, signal of very far-away spacecraft is usually highly dynamic and weak. During the operation of spacecraft maneuver, usually omnidirectional antenna with low power is adopted, which makes it difficult to achieve reliable telemetry reception and decoding. In this paper, we present a new method of monitoring the status of spacecraft maneuver with radiometric doppler tracking, the method only depends on the carrier without decoding telemetry signal. The basic theorem and algorithm are discussed in detail, and experiment demonstration could testify the effectiveness of the method presented in the paper.

According to the interferometric observation data of Jiamusi deep space station and Kashi deep space station of China deep space network during the mission of Chang'E-4 prober, the orbit determination accuracy of real-time data and post-correction data respectively combined with the USB data is analyzed. The difference between the Earth Moon transfer section and the precise orbit is 100 meters, and the difference between the ring moon section and the precise ephemeris is 10 meters. At the same time, the influences of VLBI data weight setting on the orbit accuracy is analyzed. In view of theChina deep space network in subsequent deep space missions such as Chang’E 5, a time-sharing acquisition mode is proposed to reduce the amount of VLBI data. The influence of this mode on orbit accuracy is analyzed by using the measured VLBI data of Chang’E 4 prober. The results show that the real-time data accuracy of China’s deep space network VLBI data has reached the accuracy of post-correction data, which can support the follow-up deep space exploration tasks in China. At the same time, for 2 to 3 hours per day of common viewing time of two stations, in the time-sharing acquisition mode, the total 20 minutes per day data and 1 minute acquisition step can ensure that the orbit accuracy does not decrease.

China’s deep space interferometry system has participated in orbit measurement for the Chang’E-5 mission officially, which has provided high-precision angular position information. The tropospheric delay hybrid model was proposed to ensure the accuracy of real-time interferometry. Using the non-continuous tracking technology, fast intercontinental interferometry was carried out for the first time, which provided high-precision angular position with the advantage of baseline length. The performance was evaluated based on the orbit measurement results of Chang’E-5 probe. These results show that the deep-space interferometry system has played an important role in the fast orbit determination.

Synchronization is a long-standing challenge in modern large-scale distributed systems, and newly deployed systems such as 5G and modern netted radars require more extensive synchronization.As the number of distributed stations increasing, new synchronization solution with much effort on extensibility is highly expected.In this paper we first analyze the requirements on extensibility of fiber-based sync systems, and then propose a phase-stabilized side-branch radio-over-fiber (RoF) link, which fully satisfies the extensibility requirements.The extensible sidebranch link can be constructed at any intermediate point along the main link, without any reconfiguration at the central station, which is especially feasible when adding extra stations in system capacity expansion.The main link phase shift is first stabilized by tuning the optical carrier wavelength, while another phase-locked-loop constructed at the starting point of the branch link stabilizes the phase shift from the central station to the end of branch link, by phase locking two phase-varying signals.Moreover, the phase-stable side branch is inherently extensible to multiple frequency signals, which can be used in receivers requiring multiple local oscillators (LOs).Two frequency signals are simultaneously disseminated to the end of branch link in the experiment, with frequency stability optimization of two orders of magnitude on both LOs achieved.The proposed stable side-branch RoF link shows the potential of constructing a highly-extensible frequency dissemination network for the synchronization in modern distributed systems.

低轨非合作空间目标的测定轨对于地面重要目标或区域的空间态势感知、安全防卫具有十分重要的作用.地基无线电测量方式是对低轨非合作目标最有效的监测手段之一,但其面临难快速跟踪、难精确测量、难精密定轨等问题,开展实际低轨非合作目标的实测验证试验,将对关键技术验证与性能评估具有重要意义.首先,介绍了基于连线干涉测量(CEI)系统对低轨非合作目标的跟踪试验情况;然后,采集与记录目标外测信号;接着,通过事后信号处理方式,获取了非合作卫星的干涉测量时延观测量、单向开环测速观测量.在有效信号带宽300kHz条件下,干涉测量时延精度为30ns,多普勒频率测量精度为50mHz;最后,通过单基线时延参与定轨验证,成功实现了对于低轨非合作目标从跟踪、测量到定轨的全链条、全系统验证.

针对航天器未搭载干涉测量信标机的情况,提出了一种基于通用下行信号相关处理的干涉测量方法.首先分析了通用下行信号相关处理中载波重建、整周模糊解算和系统时延偏差估计等技术;然后,结合试验,针对某地球同步卫星下行信号特点,提出了一种递进解模糊的载波提取方法;最后,对同步卫星实测数据进行了处理,得到了1.03 ps量级的时延估计精度,验证了所提方法的有效性.

A radio interferometry method is proposed to resolve the problems of the process of weak spacecraft signal received in deep space exploration. Firstly，based on the analysis of the original wavelet correlation filter，an improved one is proposed which contains shift correlation，the processing order from higher scale to lower one and the threshold filtering of the highest scale coefficients. Secondly，the wide band signal model in deep space exploration is analyzed and constructed，and the radio interferometry scheme based on wavelet correlation filter is provided. Finally，results of Monte Carlo simulation and data processing for some GEO satellite measured signal prove a better performance of the interferometry measurement，and the group delay accuracy of the GEO satellite is improved by 10%.

The lunar spacecraft Chang'E-5 includes the orbiter, the returner, the lander and the riser. During the round-moon flight phase, the real-time monitoring of separation between two combinations, the orbiter/returner assembly and the lander/riser assembly, is the key detection section of flight control. It is proposed that a nearly real-time separation monitoring by using very long baseline interferometry (VLBI) technology. Particularly, during the separation process, the state-of-art measuring technique of same-beam interferometry (SBI) can be obtained from the downlink signals transmitted from the different antennas of the two assemblies, and the resulting relative phase delay can improve the relative distance resolution. The Chang'E-3 static test shows that the relative distance between the two antennas of its lander is solved with the accuracy of <0.3 m with the SBI measurements on a single baseline and the average error is about 0.15 m. The simulated Chang'E-5 separation shows that the separation response time based on SBI measurements is determined with double thresholds with a delay of no more than 30 s.

To obtain high precision position of spacecraft,a 3-D relative position measurement model is established,and an algorithm to calculate the 3-D position based on a single-baseline same-beam interferometry (SBI) is proposed by using Least squares. SBI measurements between TT&C antenna and directional antenna of Chang'E-3 lander are conducted to verify the proposed model and its calculation algorithm. Results show that the random error of SBI delay is about 0.225 ps (0.07 mm),the distance error between TT&C antenna and directional antenna is about 0.216 m, and the direction error between them is about 30.4°, which will be used for high precision relative measurement between sub-spacecraft of Chang'E-5 and other deep-space exploration missions.

Aiming at the demand of more accurate interferometry in the following deep space exploration ,a novel interferometry scheme based on signal combination is proposed and analyzed. By studying the mainstream signal combination algorithms ,an improved Sumple algorithm based on phase comprehension is put forward.This algorithm is more efficient than the original Sumple algorithm ,and moreover its combined signal has the same phase performance as that of the reference signal ,which is the premise of antenna array technique used for interferometry.Finally , tests are conducted by using phased array data and simulated DOR signal data.The processing results show that the signal combination improves the delay estimation accuracy of interferometry ,and is of special meaning in deep space exploration.

In view of the commonly used downlink signal of deep space explorer and the characteristics of radio interferometry,a novel interferometry method is proposed to process DOR signal and data-transmission signal simultaneously for frequency synchronization. Firstly, the difference phase of the two kinds of signal is obtained by correlation. While, the time delay is estimated by utilizing DOR signal's difference phase and is modeled during the processing. Then the phase difference between DOR and data-transmission signal at data signal carrier is acquired by using the constructed time delay model, compensating the difference phase of data-transmission signal. Finally,the difference phase of DOR signal and the compensated difference phase are processed for frequency synchronization and time delay estimation. The processing results of measured data in China deep space TT&C network show that the time delay accuracy is improved significantly by fusion process, while the improvement is decreased lightly with the influence of medium delay error. The proposed method improves the accuracy of time delay estimation just by fusion process, which not only promotes the signal use efficiency, but also enhances the robust of the TT&C system,having special significance in emergency situation.

针对深空差分干涉测量(DOR)信号受数传副瓣信号干扰问题,首次研究了数传副瓣信号(泄露频谱)的干涉测量,建立了数传副瓣信号干涉测量优化模型,并利用嫦娥三号着陆器实测数据验证比对了数传干涉时延与DOR干涉时延.实验结果表明,干涉带宽相仿条件下,数传信号干涉时延随机误差约0.02 ns(STD),优于DOR干涉时延0.17 ns(STD)的随机误差;利用射电源差分观测后,DOR干涉时延与数传干涉时延基本吻合;以干涉相时延为基准,数传干涉时延的波动误差约为0.14 ns(STD),稳定性优于波动误差约为0.46 ns(STD)的DOR干涉时延.该结论对嫦娥五号、载人登月等任务中下行数传信号阶段提高干涉测量精度、火星探测任务中DOR信号与数传信号分时工作模式下增加干涉测量覆盖弧段具有直接的工程价值.

The very long baseline interferometry (VLBI) in China Deep Space Net (CDSN) mainly uses the classical model for tropospheric delay modification in real-time processing, while the measuring accuracy is constrained by the model performance. In view of this problem, an accurate regional tropospheric delay model is constructed. Firstly, the correction factor of Saastamoinen zenith tropospheric delay is determined by comparison of measured and estimated value, which leads to the zenith delay estimation bias reducing to about 0.9 ps from 1.24 ns. Secondly, in order to overcome the restriction of meteorological data, the UNB3m model with height correction is introduced to construct reginal atmospheric parameter estimation model, and results show that the estimation bias of atmospheric pressure, temperature and vapor pressure is about 3.9 mbar, 6.7 K, 0.63 mbar, respectively, moreover, the difference of zenith delay is about 14 ps when the measured and modeled meteorological data are as input, which enhances the real-time performance of zenith delay estimation. Finally, the characteristics of Niell mapping function are analyzed and the factor a in dry function is confirmed as the key parameter, whose optimal value is obtained by least-square processing. The measured data processing results show that the tropospheric delay estimation bias is about 0.3 ns when the elevation angle is 10°, which decreases nearly an order compared with the original model. Furthermore, the orbit determination error of Chang’E-4 detector is basically identical when using measured and the proposed tropospheric delay model, both results are significantly better than that of the original model. The regional model proposed here is of meteorological data independence and of high accuracy, which improves the support ability of VLBI system in CDSN for real-time orbit determination.

在嫦娥四号中继星任务期间某次干涉测量标校射电源观测无效、微卫星轨控后预报星历无法提供精确时延模型的背景下,提出了一种为微卫星轨控后轨道确定提供辅助约束测量信息的方法.该方法通过迭代相关处理修正时延模型,解决了轨控后微卫星预报星历不准的难题;利用中继星观测估计系统时延并修正微卫星干涉测量观测量,得到了实时条件下微卫星干涉测量观测信息,与事后相关处理结果的偏差约为4.2ns(约1.2m).进一步分析了相对干涉测量中的误差因素,结果表明相对干涉测量的随机误差约2ns,与事后相关处理精度相当.最后,给出了应用于辅助探测器轨道确定的相对干涉测量数据处理方案,为后续相关背景下的干涉测量提供参考.

A same-beam interferometry based mathematical model of spacecraft attitude was established, and a solution method was proposed. The solvability of the model and the precision factor were analyzed. Numerical simulations of spacecraft attitude determination based on same-beam interferometry were carried out, where an on-orbit spacecraft was simulated, and the relationship between calculation error and observation pitch angle were analyzed and verified. The results show that the effective spacecraft attitude can be obtained by using three ground stations to carry out the same-beam interferometry for three downlink antenna signals with a constraint of precision factor,and the highest accuracy achieved is 0.001 degrees. The method proposed can be used as an attitude measurement backup for on-orbit spacecraft.

中国深空探测网(CDSN)干涉测量系统目前由佳木斯深空站(JM01)、喀什深空站(KS01)、纳米比亚深空天线(NB01)和南美深空站(NM01)及北京相关处理中心组成,系统最长基线达到12000km.首先以嫦娥三号着陆器、嫦娥四号中继星和火星为目标,分析CDSN干涉测量系统的覆盖性.结果表明在统计时段内,NB01和NM01的建成将系统单站观测弧段及干涉测量观测弧段均提高一倍以上,显著增强了系统的定轨支持能力.然后利用嫦娥三号着陆器开展干涉测量观测试验.数据处理结果表明,干涉测量时延随机误差达到0.2ns,其中KS01-NM01基线的时延随机精度接近0.1ns,相应测角精度约为1.2nrad;KS01-NB01-NM01的闭合时延平均值约为0.1ns,显示了CDSN干涉测量系统具备较好的系统误差性能.最后分析CDSN干涉测量系统的限制因素及后续工作方向.