COPERNICUS POD SERVICE: Radiation modelling based on 3-D model

The Copernicus Precise Orbit Determination (CPOD) Service is key to the Copernicus Sentinel missions, supporting Sentinel-1, -2, -3, and -6 with precise orbit products and auxiliary data. These products enable the operational generation of scientific data at ESA and EUMETSAT and are distributed via the Copernicus Data Space Ecosystem (https://dataspace.copernicus.eu/).

For high-accuracy POD, radiation pressure modelling is a major contributor to orbit errors, particularly for platforms with complex geometries. Sentinel-6 represents a challenging case, as its structural configuration is poorly represented by conventional macro-models, leading to persistent signatures in the estimated empirical accelerations used to absorb unmodelled dynamical effects.

Within the CPOD context, GMV has been investigating an alternative radiation modelling strategy using the GMV Grial tool. The approach relies on a surface projection algorithm that computes radiation forces directly from a detailed spacecraft three-dimensional model, provided in CAD format, together with associated optical and infrared material properties. The resulting adimensional force coefficients are tabulated in the satellite reference frame as a function of the azimuth and elevation of the incident ray, allowing efficient integration into operational POD workflows. The methodology targets improved modelling of solar radiation pressure, as well as Earth albedo and infrared radiation pressure effects.

The methodology has been successfully applied and validated for Sentinel-3, demonstrating good agreement between modelled and estimated accelerations for box-wing-type spacecraft. Its extension to Sentinel-6 is currently under assessment. This work presents the modelling framework, validation strategy, and first Sentinel-6 results. While no significant reduction of empirical acceleration signatures is yet observed, the results indicate a strong sensitivity to assumed geometry and surface properties, highlighting the need for improved spacecraft characterisation from spacecraft manufacturers to fully exploit advanced radiation modelling techniques.