Enhancement of Precise Orbit Determination for GPS III Satellites by Constructing the a Priori Solar Radiation Pressure Model

Precise and reliable satellite orbit and clock products are crucial for the Global Positioning System (GPS) to provide high-precision positioning, navigation, and timing services. However, for the new-generation GPS III satellites, their stretched satellite body poses challenges in the accurate modeling of solar radiation pressure (SRP), thereby limiting the accuracy of precise orbit determination (POD) and clock estimation. This contribution constructs the a priori box-wing (PBW) SRP model for GPS III satellites based on the surface optical coefficients estimated with true GPS III measurements. The proposed model, known as PBW, is then validated in comparison with the five-parameter empirical CODE orbit model (ECOM) and the nine-parameter extended ECOM (ECOM2). The superiority of PBW is demonstrated through the decreased 3-D orbit day boundary discontinuities (DBDs) by 9.9 mm (18.4%) and 24-h overlapping clock errors by 1.4 mm (4.8%) compared to the ECOM model during noneclipse periods. In contrast to ECOM2, the PBW model shows more stable error characteristics in both indicators, while noticeable improvements can also be observed in 24-h overlapping clock errors. To overcome the degradation of POD performance during eclipse seasons, the proposed PBW model is further enhanced by introducing an additional first-order sine term in the Sun-satellite direction (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${D} _{s}$ </tex-math></inline-formula>) within the shadows. In comparison to ECOM2, PBW, and ECOM <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$+ {D}_{s}$ </tex-math></inline-formula>, the PBW model with <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${D} _{s}$ </tex-math></inline-formula> achieves a 12.7%, 35.6%, and 21.0% decrease in terms of 3-D DBDs as well as 20.5%, 40.5%, and 15.5% decrease in terms of 24-h overlapping clock errors, respectively.