Modeling of Solar Radiation Pressure for BDS-3 MEO Satellites with Inter-Satellite Link Measurements  
Yifei Lv  
1 School of Remote Sensing and Geomatics Engineering, Nanjing University of Information Science and Technology, No. 219 Ning.Liu Road, Nanjing 210044, China; [EMAIL_ADDRESS] (Y.L. ); [EMAIL_ADDRESS] (Z.L. )1 School of Remote Sensing and Geomatics Engineering, Nanjing University of Information Science and Technology, No. 219 Ning.Liu Road, Nanjing 210044, China; [EMAIL_ADDRESS] (Y.L. ); [EMAIL_ADDRESS] (Z.L. )1 School of Remote Sensing and Geomatics Engineering, Nanjing University of Information Science and Technology, No. 219 Ning.Liu Road, Nanjing 210044, China; [EMAIL_ADDRESS] (Y.L. ); [EMAIL_ADDRESS] (Z.L. )1 School of Remote Sensing and Geomatics Engineering, Nanjing University of Information Science and Technology, No. 219 Ning. the BDS-3 from regional to global relies on the Ka-band inter-satellite link (ISL) payloads carried. Different from the BeiDou regional navigation satellite system (BDS-2), BDS-3 has the ability to inter-satellite range and real-time update the navigation message via its ISLs [4; 5], so that it can provide global standard point positioning (SPP) service with an accuracy of 10 m [1]. For high-precision positioning users, however, ISL observations are not available, and thus it is not practically used for the enhancement of post precise orbit and clock offset estimation. Currently, a total of five analysis centers (ACs) routinely provide the precise orbit and clock products for the BDS-3 satellite [6; 7], but none of them are estimated with ISL observations in the product generation. The orbit accuracy of the MEO satellites as evaluated by SLR residuals is on the level of 4-9 cm [6]. The analysis of SLR residuals and the stability of clock offsets demonstrated that the main error that comes from precise orbit determination (POD) with respect to the \(\beta\) angle is derived from the imperfect SRP modeling. The deficiencies in the SPR model led to a degraded orbit and thus reduced the clock quality. Therefore, refinement of the SRP model is a prerequisite for further improvement of the orbiting accuracy and clock difference accuracy. SRP is a kind of non-conservative force that occurs when satellites are exposed to sunlight as they fly in space. The SRP acceleration of the BDS-3 MEO satellite is in the range of about 60-150 \(\mathrm{nm}/\mathrm{s}^{2}\)[8], which affects the daily orbit determination by several hundred meters. However, the geometric structure and optical parameters of the satellite surface cannot be accurately obtained, and the operating attitude is generally difficult to accurately describe. Satellites may enter the shadowed areas of Earth. As a result, it is difficult to model such effects on satellites. SRP modeling of GNSS satellites usually employs either an analytical model or a semi-analytical model. The analytical model can calculate the SRP acceleration according to the surface dimensions and optical properties, such as specular and diffuse reflection coefficients, providing a clear physical interpretation. Typical models are the ROCK series models and box wing models [9; 10; 11; 12; 13]. However, these models' accuracy is limited by incomplete disclosure of satellite properties and the omission of material aging effects. In other words, the analytical model is unable to utilize real observation to adjust the optical properties. In contrast, the advantage of the semi-analytical model lies in its ability to utilize the measurement to adjust a priori optical parameters of the satellites. This allows it to overcome the limitation of inaccurate known optical parameters. The adjustable box-wing (ABW) model is one of the widely used semi-analytical models [14]. However, this model contains 9 parameters to be estimated and the correlation between them is high.