Abdel Vetah, Saleh; (2022) Thermal dissipation force modelling for the Galileo constellation. Doctoral thesis (Ph.D), UCL (University College London).

Abstract

Radiation forces acting on GNSS (Global Navigation Satellite System) satellites have been studied, for the purposes of orbit prediction and determination, since the development of the initial solar radiation pressure models for the first generation of GPS (Global Positioning System) satellites. Over time, more detailed approaches were developed for the modelling of both the direct and thermal radiation forces. One of the components of thermal forces that has not been studied in great detail is the heat radiation due to the combination of the solar radiation, dissipation from internal units through the radiators and the heat exchange between the satellite components. In this project, an attempt is, therefore, made to develop an approach for modelling thermal radiation forces on the Galileo IOV (In Orbit Validation) and FOC (Full Operational Capability) satellites; resulting from solar illumination, heat dissipation and heat transfer. The approach consists of developing a thermal model based on the physical heat transfer and radiation momentum transfer mechanisms. The models are based on data supplied by ESA (European Space Agency). This model of thermal radiation forces is then used for the dynamical modelling of both the Galileo IOV and Galileo FOC satellites. Validation is done by comparing the orbit prediction performance of a model including the thermal effects against a model without. The performance is measured by the 24-hour 3D RMS (Root Mean Square) of the difference between predicted orbits and precise orbits obtained from the MGEX (Multi GNSS Experiment) dataset and taken as reference orbits. The whole Galileo constellation at the beginning of 2018 is studied. This consists of 3 active IOV satellites and 13 FOC satellites. For the IOV satellite, it was found that the inclusion of the thermal dissipation effect reduced the average 24 hour 3D orbit prediction RMS by circa 61% (from 1.14 m to 0.43 m). For the FOC, it was found that the RMS figures reduced by circa 74% (from 2.68 m to 0.68 m). The results showed consistent improvements for all satellites analysed. Based on these results, it is concluded that the thermal dissipation force modelling is relevant for precision force modelling for the Galileo satellites (and by extension to other similar GNSS satellites as well) and that the method developed here can successfully calculate it. Additional effects are also discussed, such as, the effect of transient heat transfer and the relevance of the thermal dissipation force to the Y-bias effect. The analysis suggests that the Y-bias of the Galileo satellites is likely of thermal origin, but no firm conclusions could be established. Finally, the Galileo FOC model showed how a simplified approach could be used when no detailed thermal data is available and that it could yield similar performance to a more detailed model.

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