Improved box-wing modelling for the low Earth orbiting Sentinel satellites

The Sentinel-1,-2, and -3 mission are part of the European Copernicus Programme. The low Earth orbiting satellites are designed for specific Earth observation applications, e.g., InSAR, optical imaging, and radar altimetry. The satellites are all equipped with geodetic-grade GPS receivers allowing for precise orbit determination on the few cm level. Such high accuracies are strongly required in particular for Sentinel-1 (C-band SAR) and Sentinel-3 (radar altimetry).Precise orbit products for all three missions are generated from the Copernicus POD (Precise Orbit Determination) Service as part of the Copernicus Processing Data Ground Segment (PDGS). A GMV-led consortium is operating the Copernicus POD Service and it is delivering the orbital and auxiliary products.The precise orbit determination procedure relies on sophisticated models for the gravitational and non-gravitational forces acting on the satellites. Box-wing models for the satellites are commonly used to apply the non-gravitational forces based on the direction and area of the individual surfaces and if applicable of their optical properties. As long as the satellites have simple shapes the box-wing models are fully sufficient for a precise modelling. However, if a satellite has a complex shape where self-shadowing significantly impacts the resulting non-gravitational accelerations the box-wing modelling is limited.Compared to other low-Earth orbiting satellites Sentinel-1 has a quite complex shape with self-shadowing of, e.g., the solar panel on the back of the SAR antenna. In the case of Sentinel-2 the solar panel is also shadowing one side of the satellite. Therefore, an improved box-wing modelling taking the self-shadowing into account is proposed to improve the orbit parameter estimation and the orbit determination results. Affected satellite surfaces are scaled based on the incident angle of the sun or the angle of the atmospheric drag acting on the satellite. The proposed improved box-wing modelling is presented in detail. Improved results for Sentinel-1 and Sentinel-2 are shown in terms of estimated orbit parameters, cross-comparisons to other orbit solutions provided by the Copernicus POD QWG (Quality Working Group) and in terms of orbit extrapolations.