Istituto di Scienza e Tecnologie dell'Informazione     
Lucchesi D., Anselmo L., Pardini C., Peron R., Pucacco G., Visco M. Satellite laser ranging and the modelling of non-gravitational perturbations: the Larase experiment. In: COSPAR 2014 - 40th COSPAR Scientific Assembly (Moscow, Russia, 2-10 August 2014).
Laser ranging to passive (cannonball) satellites like the two LAGEOS still represents a way to extract relevant information on Earth's internal structure, its surface and the way it interacts with the surrounding medium, the atmosphere. The related precise orbit determination (POD) represents the first issue to be fulfilled, to be followed by a solve for the unknown global parameters. The POD requires two main features: i) high-quality observations and ii) high-quality dynamical models. The first item, i.e., the availability of high-quality tracking data, is provided by the International Laser Ranging Service (ILRS) by means of the very precise Satellite Laser Ranging (SLR) technique. With regard to the second point, a big effort has been done to develop models for the non-gravitational forces (i.e., non-conservative forces) on passive satellites, especially for the two LAGEOS, since early '80s, with significant results in the literature. However, some of the models built were valid only under particular approximations or simplifications, as for the spin model and the thermal thrust forces, and have not been generalized or tested under different conditions. Other aspects, such as the asymmetric reflectivity of the two LAGEOS satellites, are not fully understood. For instance, one of the main parameters that enters in these models is the spin rate of the satellite and its slowing down due to the coupling of the induced magnetic moment produced by eddy currents with the external geomagnetic field. Once the value of the spin period is close to other characteristics time scales, as the thermal inertia of the cube corner retroreflectors or the orbital period of the satellite, resonances are present and more complicated (non-averaged) equations have to be considered for a reliable model of the spin evolution. In order to account for such effects and also to extend/apply (correctly) the models to the new LARES satellite, new efforts are needed in the field of the non-gravitational forces modelling. This is also particularly important for the role played by these satellites in general relativity theory tests in the field of the Earth, wherever the tiny predictions of Einstein's geometrodynamics need a quite reliable and robust POD. The aim of LARASE (LAser RAnged Satellites Experiment) is to go a step further in the tests of the gravitational interaction in the field of the Earth and, as highlighted above, a key role to reach such a goal is played by high-quality updated models for the perturbing non-gravitational forces acting on the surface of the satellites. Therefore, in the context of the LARASE collaboration, we started an activity dedicated to revisit, extend and improve current models for the non-gravitational perturbations in the case of LAGEOS-type satellites. We discuss the spin modelling problem and its intimate relationship with the thermal thrust forces; also the atmospheric drag impact on the orbit will be discussed, especially in the case of LARES due to its much lower altitude with respect to that of the two LAGEOS. Finally, we present our recent results on the data analysis of the orbit of the two LAGEOS satellites and on that of LARES.
Subject LARASE
Non-gravitational Perturbations
General Relativity
Fundamental Physics
70F15 Celestial mechanics

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