In view of the requirements of Tianwen-1 missions on precision orbit determination and scientific application, this paper proposes a high-precision open-loop velocity measurement method based on ground-based radio. At first, relying on space–ground TT&C resources of the Tianwen-1 probe, the paper designs an open-loop velocity measurement strategy based on China’s deep-space network. Then, it proposes a core algorithm of open-loop velocity measurement based on local cross-correlation reconstruction to obtain instantaneous Doppler frequency observables. This algorithm is characterized by a high ability to avoid phase lock loss, convenient and efficient implementation, and flexible parameter configuration and is suitable for high-precision velocity measurement in the case of high dynamics and low signal-to-noise ratios. On this basis, the similarity and difference of velocity observables between open-loop and baseband velocity measurements are analyzed comparatively. Finally, on the basis of the open-loop velocity measurement method, the paper carries out tests on high precision orbit determination with independent support of velocity measurement, as well as on Mars radio occultation. According to the research results, the accuracy of open-loop velocity measurement can reach 0.05 mm/s (in 1-s integration time), which is 2 to 3 times better than that of baseband velocity measurement. Open-loop velocity measurement can independently support orbit determination accuracy of 50 m of the Tianwen-1 probe and effectively support autonomous retrieval of Martian ionospheric electron density profiles. Thus, this method can be effectively applied to future missions of deep-space exploration and research of planetary radio science.

The Chang'E5 (CE-5)missionhas excellenttelemetry, tracking,and controlresources,providingconvenientconditionsfor verifyingnew ground-basedradiomeasurementmethods,engineeringapplications,and scientificresearch.This paperfocuseson the open-loopvelocitymeasurementand applicationof the CE-5probe.First,an open-loopDopplerfrequencyextractionalgorithmbasedon signalreconstructioncross-correlationwas proposed,and the completeimplementationstepsfrom signalinputand signalprocessingto observationoutputwere established.Second,the CE-5open-loopvelocitymeasurementexperimentwas performedbasedon the Chinadeepspacestation,and the CE-5downlinksignalswereprocessedand analyzed.The resultsshowthat the open-loopDopplermeasurementaccuracyofthe CE-5orbiterreachesthe levelof 2-3 MHz,whichis 3-4 timesbetterthan the basebandDopplermeasurementaccuracyof the deep spacestation.Third,the high-accuracyorbit determinationeffectivelyverifiesthe applicabilityofopen-loopvelocitymeasurement.The resultsshowthat the orbitdeterminationresidualof open-loopvelocitymeasurementis 0.12 mm/s,and the orbit determinationresidualof basebandvelocitymeasurementis 0.46 mm/s.Finally,the gravitationalredshiftverificationmethodfor the multibodyproblemwas proposed,and the potentialapplicationfeasibilityof gravitationalredshiftverificationbasedon open-loopvelocitymeasurementwas theoreticallyanalyzed.Theverificationexperimentschemewas preliminarilydesigned.Basedon the open-loopvelocitymeasurementresultsof theexistingCE-5orbiter, a specialexperimentfor gravitationalredshiftverificationcan be designed,and the gravitationalredshiftdetectionaccuracyis expected to achieve the level of 10-4to 10-5

China’s Tianwen-1 probe orbiting Mars provides necessary conditions for Mars-to-Earth Mars radio occultation observation, and can effectively support the exploration of Mars atmosphere and ionosphere retrieval. In this paper, the first domestic Mars radio occultation observation experiment based on Tianwen-1 was introduced. Firstly, Tianwen-1 was used to forecast the orbit and the occultation observation arc of the ground deep space station. Then, deep space stations were organized to observe the entire process of Tianwen-1 Mars occultation, and the original downlink signals of the probe were sampled and recorded. Finally, the self-developed deep space open-loop measurement software was used to process and analyze the downlink signals of Tianwen-1, to extract the radio occultation features of Mars. The results show that the amplitude diffraction speckles and frequency warping features in the signal were successfully extracted, which confirms that the Mars-to-Earth Mars radio occultation event has been effectively observed, and important technical experience and measurement data have been accumulated for subsequent scientific research on Mars atmospheric exploration based on Tianwen-1.

嫦娥五号（CE-5）任务具有天地联合的优势测控资源，为地基无线电测量新方法验证、工程应用与科学研究提供了优越条件。本文重点开展CE-5探测器开环测速精细提取及应用。首先，提出了基于信号重构互相关的开环测速多普勒频率提取算法，建立了从信号输入、信号处理到观测量输出的完整实现步骤；然后，基于中国深空网开展了CE-5轨道器开环测速试验，经信号处理分析结果表明：CE-5轨道器开环测速精度达到2~3mHz水平，优于深空站基带测速精度3~4倍；其次，通过CE-5轨道器精密定轨，有效验证开环测速观测量应用效果，结果表明：开环测速的定轨残差为0.12mm/s，基带测速的定轨残差为0.46mm/s；最后，提出了基于深空探测器的多体问题引力红移验证方法，从理论上分析了高精度开环测速在引力红移验证方面潜在应用可行性，初步设计了引力红移验证设想方案，评估了以现有CE-5轨道器开环测速结果为依据，建议可考虑开展引力红移验证专项试验，有望实现10-4~10-5水平的引力红移验证精度。

The radio occultation method, one of the methods used to provide planetary atmospheric profiles with high vertical resolution, was applied to China’s first Mars mission, Tianwen-1. We carried out observations based on the Chinese Deep Space Network, and one-way, two-way, and three-way modes were used for Doppler observations from the Tianwen-1 spacecraft. We successfully obtained effective observations from Tianwen-1 on 22 and 25 March 2022. An inversion system developed for Tianwen-1 radio occultation observations enabled the derivation of neutral atmospheric density, pressure, temperature, and electron density profiles of Mars. Utilizing one-way tracking data, Martian ionospheric electron density profiles were retrieved at latitudes between 68.7 and 70.7 degrees (N). However, the presence of strong random walk noise in one-way tracking data led to poor inversion results. Meanwhile, Martian ionospheric electron density and neutral atmosphere profiles were extracted from two-way and three-way tracking data at latitudes between 55.1 and 57.0 degrees (S) on 22 March and at latitudes between 62.8 and 63.4 degrees (S) on 25 March. Importantly, our inversion results from Tianwen-1 maintained consistency with results from the Mars Express and the Chapman theory (mainly in the M2 layer). Through two days’ observation experiments, we established and verified the occultation solution system and prepared for the follow-up occultation plans.

Delta-Differential One-Way Ranging (DeltaDOR) is widely used in deep spacecraft navigation, and cross support could enhance navigation accuracy with more interferometry baselines and longer baseline. In China Mars mission Tianwen-1, formal joint cross-support interferometry tracking between China Satellite Launch and TT&C General (CLTC) and European Space Operations Center (ESOC) under commercial contract was conducted around the critical stages of the mission, such as Mars orbit insertion. Cross-support interferometry is a new challenge to CLTC, as the correlator for routine DeltaDOR measurements do not fit for cross support, because of observable definition, blind station clock searching, and so on. This paper discusses the new method and algorithm adopted in joint cross support, especially for spacecraft tone signal processing and clock estimation when correlating with the data of two stations from different agencies. Results of the cross-support interferometry tracking activities are also analyzed. Observables from CLTC and ESOC are consistent with each other, and the difference in observables is in the order of tens of ps. All the baselines are induced to evaluate the accuracy of the spacecraft orbit determined and predicted by CLTC, and the DeltaDOR residuals have a root-mean-square (RMS) better than 0.5 ns (the goal is 1 ns), which could enhance the confidence of the orbit accuracy and the effectiveness of control parameters during critical orbit operation.

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.

The radio-occultation technique can provide vertical profiles of planetary ionospheric and atmospheric parameters, which merit the planetary-climate and space-weather scientific research so far. The Tianwen-1 one-way single-frequency radio-occultation technique was developed to retrieve Mars ionospheric and atmospheric parameters. The first radio-occultation event observation experiment was conducted on 5 August 2021. The retrieved excess Doppler frequency, bending angle, refractivity, electron density, neutral mass density, pressure and temperature profiles are presented. The Mars ionosphere M1 (M2) layer peak height is at 140 km (105 km) with a peak density of about 3.7 × 1010 el/m3 (5.3 × 1010 el/m3) in the retrieved electron-density profile. A planetary boundary layer (−2.35 km~5 km), a troposphere (temperature decreases with height) and a stratosphere (24 km–40 km) clearly appear in the retrieved temperature profile below 50 km. Results show that Tianwen-1 radio occultation data are scientifically reliable and useful for further Mars climate and space-weather studies.

The high accuracy radio Doppler frequency is critical for navigating a deep space probe and for planetary radio science experiments. In this paper, we propose a novel method based on the local correlation of segmented modeling to retrieve Doppler frequency by processing an open-loop radio link signal from one single ground station. Simulations are implemented, which prove the validity of this method. Mars Express (MEX) and Tianwen-1 observation experiments were carried out by Chinese Deep Space Stations (CDSS). X-band Doppler frequency observables were retrieved by the proposed method to participate in orbit determination. The results show that the accuracy of velocity residuals of orbit determination in open-loop mode is from 0.043 mm/s to 0.061 mm/s in 1 s integration; the average accuracy of Doppler frequency is about 3.3 mHz in 1 s integration and about 0.73 mHz in 60 s integration. The Doppler accuracy here is better than that of the digital baseband receiver at CDSS. The algorithm is efficient and flexible when the deep space probe is in a high dynamic mode and in low signal to noise ratio (SNR). This will benefit Chinese deep space exploration missions and planetary radio science experiments.

After more than fifty years lunar exploration, our understanding of the lunar space environment is still short. The information of lunar dusty exosphere was given by ARTEMIS mission and the lunar atmosphere and dust environment detector which were developed by NASA. Based on the radio experiments of several lunar missions, the existence of lunar ionosphere is proofed. The current status and observation of lunar exosphere and ionosphere are introduced in this paper. With the help of the low frequency radio astronomical payloads carried by chang'e-4 relay satellite and the lander, more information of lunar space environment will be detected.

In order to solve the problem that Independent component analysis (ICA) cannot achieve complete signal separation under underdetermined conditions, we propose an environmental sound source separation algorithm under underdetermined conditions based Improved Complete Ensemble Empirical Mode Decomposition with Adaptive Noise (ICEEMDAN) and Independent Component Analysis (ICA). This algorithm can effectively break through the limitations of ICA under underdetermined conditions, and solve the problems of insufficient number of observed signals and mode mixing existing in Empirical Mode Decomposition (EMD). Firstly, the algorithm uses ICEEMDAN to estimate the local mean of the signal to decompose the existing observed signals. Then, a filtering method based on kurtosis and correlation is used to filter the intrinsic mode functions (IMFs) generated in the decomposition process, and the appropriate IMFs are selected to construct the virtual channel. Finally, FastlCA is used to separate the reconstructed observation signals and obtain the estimated source signals. The experimental results show that compared with EMD-ICA and EEMD-ICA, the proposed algorithm has better separation ability for the observed signals constructed from both analog signals and dataset signals in terms of correlation coefficient, Mean Square Error (MSE) and Signal Distortion Ratio (SDR). The MSE increased by 61.3%, 34.2% and 35.2%, 69.7%, respectively. Taking glass breaking sound as an example, the correlation coefficient is increased by 10.8% and 4.3%, and the SDR is increased by 35.9% and 16.7%, respectively.

The APOD (Atmospheric density detection and Precise Orbit Determination) is the first LEO (Low Earth Orbit) satellite in orbit co-located with a dual-frequency GNSS (GPS/BD) receiver, an SLR reflector, and a VLBI X/S dual band beacon. From the overlap statistics between consecutive solution arcs and the independent validation by SLR measurements, the orbit position deviation was below 10 cm before the on-board GNSS receiver got partially operational. In this paper, the focus is on the VLBI observations to the LEO satellite from multiple geodetic VLBI radio telescopes, since this is the first implementation of a dedicated VLBI transmitter in low Earth orbit. The practical problems of tracking a fast moving spacecraft with current VLBI ground infrastructure were solved and strong interferometric fringes were obtained by cross-correlation of APOD carrier and DOR (Differential One-way Ranging) signals. The precision in X-band time delay derived from 0.1 s integration time of the correlator output is on the level of 0.1 ns. The APOD observations demonstrate encouraging prospects of co-location of multiple space geodetic techniques in space, as a first prototype. (C) 2017 Published by Elsevier Ltd on behalf of COSPAR.

Halo orbit nearby the Earth-Moon libration points is valuable to explore the lunar farside, which however must frequently be controlled to stay in the vicinity of libration points because of instability. With a consideration of the high fidelity force models, this paper focuses on maintenance of halo orbit nearby the Earth-Moon libration points. First, based on the dynamic characteristic of libration orbit in the circular restricted three-body problem (CRTBP), the mathematic model and control strategy of maintenance are studied. A control method named circling-continuation is put forward including the Halo-style and Lissajous-style ways. Then, with the solar radiation pressure and third-body perturbation considered, maintenance of halo orbit nearby the Earth-Moon L2 point is investigated on the control interval and velocity increment. Additionally, the maintenance costs and efficiencies of two control styles are compared. The results show that the Lissajous-style way is suitable for the halo orbit maintenance with a control interval about 7.4 days and a velocity increment less than 20m/s. The circling-continuation method has been successfully applied to the Chinese CHANG'E-2 and CHANG'E-5T1 extended mission nearby the Sun-Earth/Moon and Earth-Moon L2 libration points, which has been proved to be efficient and fuel-saving and suitable to the future lunar and deep space exploration.

This paper discussed the possibility of application of Interferometric tracking to track CE’3 during Soft Landing by China Deep Space Network.Algorithm of adaptive model reconstruction and interferometric phase unwrapping are discussed in details,which can avoid accuracy of predict orbit deteriorate caused by spacecraft maneuver and can keep interferometric phase continuous.Based on data analysis in project,the accuracy of the interferometric tracking is in the order of 0.3ns,which corresponds to 30nrad angular accuracy.

差分干涉测量技术是获取深空探测器高精度角位置信息的重要技术手段.本文以中国深空网在嫦娥3号(CE'3号)任务中首次应用为背景,论述深空网测控模式差分干涉测量技术的测量模型,相对于传统的短时交替观测模式,该方法能够全时段确保目标航天器的遥测、遥控通信,克服短时交替引起的航天器遥测信息中断以及应急遥控指令无法发送的问题.基于CE'3号环月轨道段的实测数据处理结果,通过与事后精密轨道的精度比对表明,测量数据时延精度在1 ns量级,相应于角位置精度97 nrad(地月距离上CE'3号位置精度37 m),与具有相似基线构型的采用短时交替模式的CVN网测量精度在同等量级.

Abstract: UT1-UTC is essential for interplanetary spacecraft navigation mission. Firstly, This paper introduces the method of UT1-UTC determination based on VLBI and UT1-UTC prediction in Beijing Aerospace Control Center(BACC). Then, The UT1-UTC determination and prediction results are compared with IERS, USNO and EOP_PCC. The compared results shows that BACC UT1-UTC products with high precision could effectively meet the requirement of interplanetary spacecraft navigation mission. Finally, UT1-UTC prediction products were successfully applied on China’s first reentry return flight test mission to support spacecraft’s orbit determination.

This paper presents the correlator software system in the interferometric center of China Deep Space Network and its first implementation performance in China CE-3 project. The correlator is designed to run in clusters combined with high performance computers. Based on time parallel strategy and multi-threads proc-essing, the parallel processing algorithm is analyzed. The performance of the correlator software in China CE-3 project is discussed. Compared with high accuracy orbit ephemeris, the observable error in △DOR measurement of the correlator software is on the scale of 1ns, which corresponds to an angular accuracy of about 90nrad or 37 m’s uncertainty on the probe position at 380 000 km. The interferometric tracking center has played an impor-tant role in CE-3 navigation.

This paper proposes a method of Earth polar motion parameters prediction by dual differential least-squares (LS) and autoregressive (AR) model. Firstly, polar motion parameters are processed by dual differential method, the stationarity of polar motion parameters is improved. Then, LS+AR method is utilized to analyze the dual differential polar motion parameters to obtain the preliminary prediction results. Finally, the preliminary prediction results are processed by inverse dual differential method to obtain high accuracy polar motion prediction results. The prediction results are compared with EOP prediction comparison campaign (EOP_PCC) results, it shows that the short-term polar motion parameters prediction error is at the same level of EOP_PCC. The one day prediction accuracy of PMX is at the level of 0.25 mas, PMY is 0.2 mas, they are better than EOP_PCC one day polar motion prediction accuracy.

This paper describes the first implementation of Delta-DOR (Delta-Differential One-Way Ranging) in CE'3 navigation within China DSN(Deep Space Network). Tracking data during CE'3 cruise to the moon is analyzed. Compared with high accurate orbit ephemeris, time delay error in the delta-DOR measurement is less than 1ns, which corresponds to an angular accuracy of about 90nrad or 37m uncertainty on the probe position at 380000km. Delta-DOR tracking has played an important role in CE'3 navigation.