# Advancing the Solar Radiation Pressure Model for BeiDou-3 IGSO Satellites  
[PERSON]  
1 GNSS Research Center, Wuhan University, 129 Luoyu Road, Wuhan 430079, China; [EMAIL_ADDRESS] (F.X. ); [EMAIL_ADDRESS] (D.C.)1  
[PERSON]  
1 GNSS Research Center, Wuhan University, 129 Luoyu Road, Wuhan 430079, China; [EMAIL_ADDRESS] (F.X. ); [EMAIL_ADDRESS] (D.C.)1  
[PERSON]  
1 GNSS Research Center, Wuhan University, 129 Luoyu Road, Wuhan 430079, China; [EMAIL_ADDRESS] (F.X. ); [EMAIL_ADDRESS] (D.C.)1  
[PERSON]  
3 School of Geomatics, Liaoning Technical University, Fuxin 12300, China; [EMAIL_ADDRESS] (F.N. )4  
[PERSON]  
5 College of Geology Engineering and Geomatics, Chang'an University, Xi'an 710054, China; [EMAIL_ADDRESS] (F.X. ); [EMAIL_ADDRESS] (F.X. ); chendz@wvhu. 10 compared with the RAFSs adopted onboard the BeiDou-2 satellites, and can be compared to the RAFSs employed onboard the GPS III satellites, as well as the PHMs used onboard the Galileo satellites [4]. The high-accuracy orbit and clock products are key requirements for the most demanding applications of the BeiDou satellites [5; 6]. Solar radiation pressure (SRP) is the largest non-gravitational perturbation for high-altitude satellites and constitutes a major challenge for navigation satellite systems that require cm-level orbit knowledge. The perturbing accelerations aroused by SRP for a satellite depends on its attitude, mass and dimensions as well as the optical properties of each surface facing the Sun [7]. Without precise surface information, the five-parameter Empirical CODE Orbit Model (ECOM) [8], developed at the Center for Orbit Determination in Europe (CODE), is widely applied for GNSS precise orbit determination (POD). However, for satellites of newly emerging systems, the model must be adapted and optimized as systematic once-per-revolution radial orbit errors were found. For example, the orbits of European Galileo and Japanese QZSS satellites with rectangular shapes based on the five-parameter ECOM model suffer from radial orbit errors with an orbital periodicity [9; 10]. [PERSON] et al. [9] identified that the stretched shape of navigation satellites introduces additional accelerations that cannot be considered by the ECOM model as the cause for these systematic radial orbit errors. Such errors in the Galileo and QZSS orbits have been proved to be reduced by using the extended ECOM model (ECOM2) [11; 12] or almost eliminated by adopting an a priori high-accuracy SRP model with the ECOM [9; 10]. A similar orbit error has been found while using the legacy five-parameter ECOM model for BeiDou-3 MEOs with a notably stretched body [13; 14; 15]. This can be confirmed by the BeiDou-3 MEO clock estimates and Satellite Laser Ranging (SLR) residuals. Based on the adjustable box-wing model (ABW) with clear physical interpretation for SRP [16], the a priori SRP models for BeiDou-3 MEOs have been established by [PERSON] et al. [14] and [PERSON] et al. [13], which could effectively reduce the systematic radial orbit errors. According to the BeiDou-3 metadata released by [17], BeiDou-3 IGSOs exhibit a notably rectangular shape. Hence, similar to BeiDou-3 MEOs, Galileo and QZSS, the BeiDou-3 IGSO orbits determined with the five-parameter ECOM model may also suffer from systematic radial orbit errors. More information from China Satellite Navigation Office (CSNO) demonstrates that BeiDou-3 IGSOs carry a regular hexagon and two circular communication payloads on the \(\pm X\) surfaces, as shown in Figure 1. There is a challenge to model BDS-3 IGSO SRP perturbations, as the contribution of communication payloads should be considered [18; 19]. Moreover, the GNSS orbits always show a lower performance during eclipse seasons than non-eclipse seasons. It is usually caused by the inaccurate attitude modeling [20] and unaccounted non-conservative forces, such as spacecraft's thermal effects during eclipse seasons [21; 22; 23]. At present, there is no systematic investigation on the POD performance of eclipsing BeiDou-3 IGSOs.