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Objectives: On July 31, 2020, China's BeiDou-3 satellite navigation system (BDS-3), which operates independently, has been fully completed and officially opened for service. The signal system of BDS-3 has been redesigned to provide public service signals of five frequencies: B1I, B3I, B1C, B2a and B2b. Methods: Based on the observations of international global navigation system monitoring and assessment service and multi-GNSS experiment (MGEX) tracking stations, this paper analyzes the characteristics of pseudoranges multipath error, signal to noise ratio, geometry-free ionosphere-free phase(GFIFP) combined observations of the new signal system, as well as the precise orbit determination (POD) performance evaluation of BDS-3 satellites. Results and Conclusions: The results show that the multipath noise level of BDS-3 satellites signal is better than that of BeiDou-2 navigation satellite system satellites, and there is no systematic deviation related to altitude angle, B1C is more significantly affected by multipath and noise. The GFIFP sequences of different signal combinations of BDS-3 satellites show periodic systematic error related to satellite, and the peak value is about 2 cm. For BDS-3 satellites, the one-step POD method is used. The two frequencies ionospheric free combination of B1I & B3I and B1C & B2a is adopted respectively. The orbit boundary discontinuity and satellite laser ranging carried out an orbit accuracy check, and the results show that when the number of available observations is less than B1I & B3I, the orbit accuracy of B1C & B2a is equivalent to that of B1I & B3I, and the radial internal coincidence accuracy is 6.1 cm and 6.6 cm respectively. [ABSTRACT FROM AUTHOR]

Copyright of Geomatics & Information Science of Wuhan University is the property of Geomatics & Information Science of Wuhan University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Geomatics & Information Science of Wuhan University is the property of Geomatics & Information Science of Wuhan University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The global constellation network of BeiDou-3 navigation satellite system (BDS-3) has been completed, which means that BDS-3 has entered a new era of providing high-quality positioning, navigation and timing service for global users.Methods: To comprehensively compare the performance of BDS-3 uncombined precise point positioning (PPP) with other global navigation satellite systems (GNSS), this paper focuses on three aspects, including the consistency of BDS-3 precise orbit and clock products among different analysis centers, the satellite availability of BDS-3/GNSS, the positioning performance of BDS-3/GNSS single-system and multi-system PPP.Results: Based on the precise orbit and clock products from five analysis centers, the three-dimensional root mean square error of BDS-3 static PPP is between 2.31 cm and 4.00 cm, and its convergence time is significantly slower than that of other GNSS. The intro‐ duction of GPS observations can achieve the most obvious improvement among BDS-3/GNSS dual-system joint PPP. Besides, the quad-constellation observations can effectively shorten the convergence time of PPP and improve the positioning accuracy on kinematic mode. Conclusions: With the development of BDS-3 and the improvement of its orbit and clock products, BDS-3 has a great potential to provide highquality positioning services as other GNSS. [ABSTRACT FROM AUTHOR]

Objectives: With the development of deep-space technology of China, the Jupiter exploration program has been added into the schedule. The precise orbit determination (POD) and gravity field recovery play an important role in Jupiter exploration. Methods: This paper focuses on the precise orbit determination of Juno and low degree gravity field recovery of Jupiter. Firstly, the coordinate system and dynamics model of the Jupiter probe are given, and the Juno precision ephemeris of jet propulsion laboratory (JPL) is used for verification. Then, the deep-space Doppler measurement model is presented and the trajectory of Juno is calculated by using the tracking data. Results: The dynamical fitting position difference is on the order of 10 m, and the velocity difference is less than 6 mm/s. The difference with the reference orbit given by JPL is better than 1 kilometer. Conclusions: The simulation data is used to verify the reliability of gravity field solution, and the measured data near 4 perijove points of the Juno is used to calculate the gravity field coefficients of Jupiter, obtaining the gravity field zonal coefficients up to 8 degrees [ABSTRACT FROM AUTHOR]

Objectives: Tianwen-1 is the first independent interplanetary mission of China, and it was launched on 23 July 2020 and delivered directly into the Earth-Mars transfer orbit, which arrived at Mars in February 2021. It will complete orbiting, landing, and roving tasks in one operation. Exploiting tracking da‐ ta from gathered during this science exploration and extended mission, this paper explores possible ways to improve the Mars gravity field model by simulation. Methods: We designed two types of orbits, including the polar orbits with near zero eccentricity and the near equatorial orbit with large eccentricity. Based on these two types of orbits, we recovered six gravity solutions considering various error sources, such as measurement noise, solar pressure error, rotation model error, and tracking time length. We used the power spectrum method to analyze and evaluate these recovered gravity models. Results: We find that a month of tracking data from the polar orbit or the combined polar and near equatorial orbit could be used to properly reconstruct the Mars gravity field model with orders and degrees of 42 under the 0.1 mm/s measurement noise. When 10% solar pressure error is added, the gravity model solution only suffers a slight influence showing in the power spectrum analysis. Furthermore, when Mars rotation model error is added, the degree variances of gravity models are affected only after the 35-order and degree. Conclusions: The results show that considering the influence of comprehensive error, the accuracy of gravity field solutions of the two types of orbits is similar. Nevertheless, the orbit with large eccentricity near the equator has a slightly stronger constraint on more than 35-order and degree coefficients. Besides, when the track tracking data collected from the near equatorial orbit phase are added in the recovering of Mars gravity model, the pro‐ posed model can improve the precise orbit determination accuracy of a spacecraft with near-equatorial orbit. [ABSTRACT FROM AUTHOR]

Copyright of Geomatics & Information Science of Wuhan University is the property of Geomatics & Information Science of Wuhan University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

BDS precise orbit and precise clock products provided by IGS analysis centers may differ due to the use of different antenna phase center models, which has a great impact on the comparison between precise products and the use of precise products to evaluate the accuracy of the BDS signal-inspace user range error. In this paper, the influence of different antenna phase center correction models on the precise orbit and clock products is analyzed in depth by using the measured observation data. Based on this, the BDS signal-in-space user range error evaluation method is proposed considering different antenna phase center correction models. With the precise orbit and clock products provided by the Center for Orbit Determination in Europe (CODE) , Deutsches GeoForschungs Zentrum(GFZ) and Wuhan University (WHU),we evaluate the broadcast orbit,broadcast clock and signal-in-space user range error. The results show that after considering the difference of the satellite antenna phase center correction model? the accuracy of the signal-in-space user range error evaluated by the BDS precise orbit and precise clock products provided by different analysis centers is basically the same. Geostationary orbit is better than 1. 68 m, inclined geosynchronous orbit is better than 0. 78 m, medium earth orbit is better than 0. 66 m, which verifies the correctness of the evaluation method proposed in this paper [ABSTRACT FROM AUTHOR]

Objectives: Slow convergence has always been an important factor of limiting the development of precise point positioning (PPP). Studies have shown that the convergence speed of PPP can be significantly improved with high ‑precision ionospheric delay correction, and then to achieve PPP ‑ real time kinematic (PPP ‑RTK). At present, the ionosphere in the regional PPP ‑RTK mainly adopts the satellite ‑based ionospheric model with polynomial function (SIM_POLY) and the satellite‑based ionospheric model with in‑ verse distance weight function (SIM_IDW) for construction. Methods: In order to verify the modeling accuracy of the above two models at different latitudes, this paper first used the observation data of Guangdong, Hubei and Hebei provinces to establish ionospheric delay models, and then applied the above models to float and fixed solutions PPP under single GPS and GPS+BDS systems. Finally the results were compared with IFPPP (ionosphere‑free PPP) and CODE GIM (Centre for Orbit Determination in Europe Global Ionospheric Map, CODG) correction. Results: Experimental results showed that in the low‑latitude provinces, SIM_IDW model slightly outperformed SIM_POLY model, but there was no significant difference in the middle and high latitude provinces. Compared with IFPPP and CODG correction, PPP under SIM_IDW and SIM_POLY correction has a better performance. Besides, Hebei province achieved the fastest convergence speed compared with Guangdong and Hubei provinces, and compared with IFPPP, the positioning accuracy in single GPS solution under SIM_IDW and SIM_POLY model correction is improved by 43.7% and 43.0%, respectively. In the fixed PPP, the success rate of first epoch to fix the ambiguity of PPP‑RTK under the correction of SIM_IDW and SIM_POLY models in GPS+BDS solution could reach 86.09% and 89.13% in Hebei province. Besides, positioning accuracy could converge to 5 cm in the first epoch in horizontal direction, and converge to 10 m within 1.5 minutes in vertical direction. The positioning accuracy after convergence of GPS+BDS PPP ‑RTK had a significant improvement compared with single GPS, which was 1.3 cm in horizontal direction and 3.5 cm in three‑dimensional direction under the correction of SIM_IDW and SIM_POLY models. Conclusions: Establishing a regional ionospheric model through SIM_IDW and SIM_POLY models to realize PPP‑RTK can significantly shorten the PPP convergence time and improve positioning accuracy. [ABSTRACT FROM AUTHOR]

The satellite Fengyun 3C(FY3C) launched in 2013 and carried a global navigation satellite system (GNSS) occultation sounder, which is the first BDS/GPS compatible radio occultation sounder in the world and records both GPS and BDS measurements. It provides an opportunity for investigating the precision realtime orbit determination based on space‐borne GPS/BDS measurements. In order to realize the real‐time orbit determination based on space‐borne GPS/BDS measurements with decimeter‐level accuracy, this paper carries out in‐depth research in the following aspects. Firstly, the real‐time orbit determination mathematical model based on the space‐borne GPS/BDS carrier phase observations is introduced. Then the properties of the errors in the signal’s propagation path that originates from GPS/BDS broadcast ephemeris are analyzed, and the signal‐in ‐propagation path error(SIPPE) statistics of different kinds of GPS/BDS satellites are also presented. Based on the analysis, a pseudo‐ambiguity is modeled as a stochastic process and estimated in the real‐time orbit determmination(RTOD) filter to absorb the SIPPE error, and then the decimeter‐ level accuracy can be realized. The space‐borne GPS/BDS data from China’ s FY3C satellite are em ‐ ployed for the simulative RTOD test using the SATODS software. Results have demonstrated that the position and velocity accuracy of 30 cm and 0.3 mm/s, respectively, are achieved when using GPS/BDS carrierphase data and broadcast ephemeris. Although the accuracy of BDS broadcast ephemeris is obviously worse than that of GPS, orbit results of the GPS/BDS fusion solution with reasonable stochastic models for pseudo‐ambiguities will be slightly superior to that using single GPS data. For example, when the FY3C satellite flew over Asia/Pacific region where more BDS satellites can be tracked, the orbit accuracy can be improved by 10% with the GPS/BDS fusion solution. [ABSTRACT FROM AUTHOR]

The BeiDou navigation satellite system have three attitude control modes-yaw-steering(YS) mode, orbit-normal(ON) mode and continuous yaw-steering(CYS) mode. The orbit accuracy and best orbit determination projects for different satellites were a hot topic at present in different time and different attitude control mode, which are researched and whose the dynamical mechanisms is analyzed in this paper. The results are as follows. For BeiDou-2 satellites, multi-satellite precise orbit determination by fixing satellite/station clock offset and extended CODE model (ECOM) 5 SRP should be the best project, user equivalent range errors (UERE) root mean square (RMS) in ON mode is 2.08 m,global satellite laser ranging (SLR) data fitting RMS is ablout 1 m. For BeiDou-3 satellites, multi-satellite precise orbit determination and ECOM 5 SRP should be the best project, UERE RMS in CYS mode is 1.22 m,SLR data fitting RMS is 0.23 m, which is comparable to that in YS mode. For GEO satellites near spring or autumn equinox, multi-satellite precise orbit determination by fixing satellite/station clock offset and ECOM 9 SRP should be the best project, UERE RMS is 0.72 m. [ABSTRACT FROM AUTHOR]

Very long baseline interferometry plays a critical role on the orbit determination of the lunar and deep space probes, as well as the radio science research. Based on a first-order approximation model of the probe's topocentric range-rate, this paper proposes a new narrow band tracking method for the weak signal received by an antenna with relatively small aperture. As long as the Doppler dynamics has been estimated from the signal received by a large antenna with high G/T value, the weak signal, received by the small antenna during the same time duration, could be Doppler compensated. The raw data acquired by Chinese Jiamusi station and European Space Agency's New Norcia station have been processed, and the results demonstrate the effectiveness of this method. Digital phase locked loop with 5 Hz noise bandwidth could be used to track the differential one-way ranging(DOR) tone received by New Norcia, after Doppler compensation by estimation results from Jiamusi carrier tracking, and the root mean square of the tracking phase errors for DOR tone is around 3.4 degree. This method could be used in the radio metric navigation for the future lunar and deep space missions, as well as the inter-agency cross-supports. [ABSTRACT FROM AUTHOR]