MG14 - Talk detail

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The International Laser Ranging Service (ILRS) provides range measurements of passive satellites around the Earth through the powerful Satellite Laser Ranging (SLR) technique. These very precise measurements of the distance between an on-ground laser station and a satellite equipped with cube corner retro-reflectors (CCRs) make possible precise tests and measurements in fundamental physics and, in particular, in gravitational physics. The LAGEOS (NASA 1976) and LAGEOS II (NASA/ASI 1992) satellites are outstanding examples of very good test particles because of their very low area-to-mass ratio as well as the high quality of their tracking data and, consequently, of the precise orbit determination (POD) we can obtain after a refined modeling of their orbit. The aim of our research program LARASE (LAser RAnged Satellites Experiment) is to go a step further in testing gravitation in the field of Earth by means of the joint analysis of the orbits of the two LAGEOS satellites together with that of the most recently launched LARES (ASI, 2012) satellite. Therefore, our work falls in the so-called weak field and slow motion (WFSM) limit of Einstein’s general relativity (GR) where, in terms of Newtonian physics, relativistic effects appear as two new fields to be added to the classical gravitational field: the gravitoelectric and the gravitomagnetic fields. A fundamental ingredient to reach such a goal is to provide high-quality updated models for the perturbing non-gravitational perturbations (NGP) acting on the surface of these satellites. In fact, regardless of their minimization thanks to a smaller value for the area-to-mass ratio, the subtle and complex to model perturbing effects of the NGP play a crucial role in the POD of the considered satellites, especially in the case of the thermal thrust effects. A large amount of SLR data of LAGEOS and LAGEOS II has been worked out using a set of dedicated models for the satellite dynamics and the related post-fit residuals have been analyzed. A parallel work is on-going in the case of LARES. The effects predicted by GR leave a peculiar imprint on the satellite orbit, namely in the precession of the three Euler angles that define the orbit orientation in the inertial space: the right ascension of the ascending node, the argument of pericenter and the inclination. Our recent work on the orbit modeling and on the data analysis of the orbit of such satellites will be presented together with new measurements of the relativistic precessions and updated constraints on non-Newtonian gravitational dynamics. The measurement error budget will be also discussed, emphasizing the role of the modeling of both gravitational and non-gravitational forces on the overall precise orbit determination quality.

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Session

Accepted

Yes

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Time

Talk

Title

Abstract

Laser ranging to passive satellites 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. Moreover, the precise range measurements of the Satellite Laser Ranging (SLR) technique have allowed to reach significant tests and measurements in gravitational physics, as in the case of gravitomagnetic and gravitoelectric precessions of the orbits of the two LAGEOS satellites and significant constraints on non-Newtonian physics. Therefore, the improvement in the orbit determination of such satellites represents a basilar goal to be reached in order to gain more precise and accurate results in the fields of space geodesy and of fundamental physics. The satellite precise orbit determination (POD) requires two main features: i) high-quality observations and ii) high-quality dynamical models. The availability of high-quality tracking data is provided by the International Laser Ranging Service (ILRS) by means of the very precise SLR technique. With regard to the second issue, a big effort has been done to develop models for the non-gravitational forces on passive satellites, especially for the two LAGEOS with significant results in the literature as already highlighted. However, some of the models built in the past 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. Further, in order to account for such effects and also to extend/apply the models to the new LARES satellite, new efforts are needed in the field of the non-gravitational forces modeling. The aim of the LARASE (LAser RAnged Satellites Experiment) program is to go a step further in the tests of the gravitational interaction in the field of the Earth by developing high-quality updated models for the perturbing non-gravitational forces. Such an effort is also required in order to provide a reliable error budget with a correct evaluation of the systematic error sources, both gravitational and non-gravitational in their nature. Consequently, 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 modeling 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. Concerning the gravitational perturbations, a comparison among a few models for the background gravitational field will be discussed together with the impact of the tidal errors on the orbits of the satellites. Finally, our recent results on the data analysis of the orbit of the two LAGEOS satellites and of LARES will be shown.

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