Impact of thermal imbalanced radiation forces on GNSS satellite orbits

An accurate model of all the forces acting on a satellite is an essential precondition of achieving high orbit accuracy. Solar radiation pressure (SRP), the largest non-gravitational perturbation for GNSS satellites is typically modeled by an empirical model (i.e., Empirical CODE Orbit Model, ECOM/ECOM2). If satellite metadata information is available, an analytical box-wing model can be formed to reinforce the ECOM models. However, the current GNSS satellite orbits show notable degradation during eclipse seasons in particular for long-arc solutions and orbit predictions. The reason is proven to be mostly due to the ignoring of the thermal imbalanced forces (i.e., radiator emission and thermal radiation of solar panels). The ECOM parameters can compensate these thermal radiation forces fairly well outside eclipse seasons, while this is not true when satellites are inside eclipse seasons, because the Earth’s shadowing of a satellite in orbit causes periodic changes of the thermal environment. On one hand, these thermal imbalanced forces contribute also inside the shadow while inside the shadow all the ECOM parameters are deactivated. On the other hand, satellite attitude could be far from the nominal inside the shadow, making that these thermal imbalanced forces cannot be well absorbed by the ECOM parameters. To capture these thermal forces, we set up physical thermal force models for each Block type of GNSS satellites. In the absence of published thermal properties, we estimate necessary thermal modeling parameters using tracking data over long time period. With the use of the physical thermal force models, satellite orbits inside eclipse seasons are greatly improved. For instance, orbit misclosures are improved by a factor of two for BDS-3 and Galileo satellites when using the 5-parameter ECOM model.