Tuning thermal reradiation pressure accelerations for Sentinel-6

For radar altimetry missions such as Sentinel-6, a precise orbit is mandatory for deriving reliable sea surface heights. In addition to accurate tracking measurements, precise orbit determination relies on high-fidelity non-gravitational force models. At 1300km the solar radiation pressure (SRP), which varies mainly with the satellite’s orientation towards the Sun, is the dominating non-gravitational force. Additionally, the acceleration due to the Earth radiation pressure (ERP) acts on the satellite and decreases with increasing satellite altitude. As the radiation of Sun and Earth is partly absorbed at the satellite’s surface, the satellite experiences an additional force due to the thermal reradiation of heat (thermal reradiation pressure, TRP). Aerodynamic forces are in constrast negligible at around 1300km altitude.

In previous investigations, we extended the conventional radiation pressure force models with a focus on a GRACE-like satellite. Our SRP and ERP model extensions can be easily applied to other satellites with available geometry and thermo-optical material properties. However, transferring the heat-conductive TRP model to other satellites is more challenging, as assumptions on the materials’ thermal diffusivity and thickness as well as inner heat sources need to be made to adequately model the satellite’s surface temperature.

In this study, we attempt to develop a TRP force model for Sentinel-6. We depart from GRACE settings and refine our model stepwise. Boundary conditions are updated and the material properties are replaced with available information or assumptions. Then, a stepwise tuning is necessary to match the modelled surface temperatures with thermistor measurements. We choose one beta cycle during the year 2023 for our experiments. Preliminary investigations reveal that the tuning of the satellite’s thermal properties varies strongly with the beta angle.