Initial Results of the Precise Orbit Determination for the New-Generation BeiDou Satellites (BeiDou-3) Based on the iGMAS Network  
[PERSON]  
1 State Key Laboratory of Geodesy and Earth's Dynamics, Institute of Geodesy and Geophysics, Chinese Academy of Sciences, Wuhan 430077, China; [EMAIL_ADDRESS] (Y.N. ); [EMAIL_ADDRESS] (X.L.) 12 University of Chinese Academy of Sciences, No. 19A Yuquan Road, Beijing 100049, China 2  
[PERSON]  
1 State Key Laboratory of Geodesy and Earth's Dynamics, Institute of Geodesy and Geophysics, Chinese Academy of Sciences, Wuhan 430077, China; [EMAIL_ADDRESS] (Y.N. ); [EMAIL_ADDRESS] (X.L.) 1  
[PERSON]  
3 The Primary School of Vanke Golden City Attached to Central China Normal University, Wuhan 430065, China; [EMAIL_ADDRESS] 3  
[PERSON]  
1 State Key Laboratory of Geodesy and Earth's Dynamics, Institute of Geodesy and Geophysics, Chinese Academy of Sciences, Wuhan 430077, China; [EMAIL_ADDRESS] (Y.N. ); [EMAIL_ADDRESS] (X.L.) 12 University of Chinese Academy of Sciences, No. 19A Yuquan Road, Beijing 100049, China 2  
[PERSON]  
1 State Key Laboratory of Geodesy and Earth's Dynamics, Institute of Geodesy and Geophysics, Chinese Academy of Sciences, Wuhan 430077, China; [EMAIL_ADDRESS] (Y.N. ); [EMAIL_ADDRESS] (X.L.) 12 University of Chinese Academy of Sciences, No. 19A Yuquan Road, Beijing 100049, China 2  
Footnote 1: email: [EMAIL_ADDRESS] (B.T. ); [EMAIL_ADDRESS] (Y.Y. ); 124 SeiDou-24-9861, 24 Se  
successfully launched, which signaled the beginning of BDS's expansion from regional to worldwide coverage. By August 2016, five BeiDou-3 satellites, each of which has a new navigation signal system, inter-satellite links, and other test features, have been launched, which brings the satellite navigation system closer to completion. Four BeiDou-3 satellites are now in operation. The status of the BeiDou Navigation Satellite System (updated as of August 2016) is summarized in Table 1[2]. With the increasing quality requirements for civilian and scientific applications based on the emerging global BDS[3; 4; 5; 6; 7; 8; 9; 10; 11], achieving a precise orbit determination (POD) for the global BDS constellation has become one of the most challenging issues for the Global Navigation Satellite System (GNSS) community. Several studies have been performed on the POD of BeiDou-2 satellites. [PERSON] et al. [12] presented their results of BeiDou-2 satellites POD using three day arcs and nine solar radiation pressure (SRP) parameters of the Empirical CODE Orbit Model (ECOM) with a regional tracking network. The 3D orbit overlap comparison of GEO and IGSO is 3.3 m and 0.5 m in root mean square (RMS), respectively. [PERSON] et al. [13] reported the initial orbit and clock assessment of the regional BDS navigation satellite system, and the 3D orbit overlap comparison is 1-20 m in RMS. [PERSON] et al. [14] demonstrated several solutions of ECOM parameters for BeiDou non-GEO satellites, and only one ECOM SRP parameter in the direction of the Sun was estimated for BeiDou GEO satellites. The orbit consistency was on a 1-2 decimeter level for the IGSO satellites and on a several-decimeter level for the GEO satellites. [PERSON] et al. [15] introduced an additional constant acceleration in the along direction to compensate for the insufficiency of the ECOM model for GEO satellites, and the five-parameter ECOM SRP model was used. The 3D orbit overlap comparison accuracy was approximately 1.8 m for GEO and 0.3 m for IGSO and MEO satellites. The satellite laser ranging (SLR) residuals were approximately 0.7 m for GEO C01 and 0.1 m for IGSO C08. [PERSON] et al. [16] engaged the additional constant acceleration in the along direction for GEO satellites and five-parameter ECOM SRP model for non-GEO satellites in their study. The orbit overlap comparison