A new model for thermal thrust accelerations on LAGEOS satellites

Thermal thrust forces act on the surface of a satellite as a result of a non-uniform distribution of temperature across its surface. A new thermal model for the two LAGEOS satellites will be described with the goal of providing the thermal thrust accelerations acting on their surfaces. The thermal inertia of the satellite components together with the eclipses participate in the production of these perturbations. The main effects are due to the thermal inertia of the Corner Cube Retroreflectors (CCRs) of the satellite, being the direct solar visible radiation modulated by the eclipses and the Earth's infrared radiation the main sources. In addition to these sources, the solar radiation reflected by the complex Earth-atmosphere system, i.e. the Earth's albedo, is also responsible for a non-uniform heating of the surface of the satellite. Contrary to the models previously developed in the literature for the LAGEOS satellites, our new model, that we called LATOS (LArase Thermal mOdel Solutions), is not based on averaged equations. The attitude of the satellite plays an important role in this kind of analysis; we modelled it by means of the LASSOS (LArase Satellites Spin mOdel Solutions) model. This model for the spin was developed within the LARASE (LAser RAnged Satellites Experiment) research program. In our analysis, the CERES (Clouds and the Earth's Radiant Energy System) data have been used to account for the effects of the terrestrial albedo. The results for the thermal thrust accelerations acting on the two LAGEOS satellites will be presented together with their effects on their orbital elements. These effects will be then compared with the orbital residuals of the satellites in the same elements obtained by an independent Precise Orbit Determination (POD). The consequent improvements in the POD through the inclusion of the thermal thrust accelerations in the dynamic model, in such a way to replace the empirical accelerations, will be of fundamental importance for the geophysical products that are determined by analysing the orbits of the two LAGEOS satellites. At the same time, the fundamental physics measurements that are obtained with these satellites can benefit from a more precise determination of their orbit.