Preliminary results of the LARES mission to test general relativity

The LARES mission was conceived to put an almost perfect test particle into an orbit around Earth that, when the known non-gravitational perturbations are removed, will approximate a geodesic of pacetime. Accurate orbit determination along with the accurate modeling of classical perturbation effects on the orbital dynamics of the satellite are key factors for the success of the mission. According to the theory of General Relativity a current of mass-energy, such as a rotating mass, induces an additional deformation to the spacetime. Thus the Earth, with its rotation, produces a very small perturbation on the node of the orbit. This phenomenon is caused by the gravitomagnetic field and in the case of an orbiting satellite is known as frame dragging or Lense-Thirring effect. To measure this effect with a reasonable accuracy, analysis of LAGEOS and LAGEOS 2 data was already performed back in 2004. For a very accurate test of the Lense-Thirring effect, a third specifically designed satellite was required. Many years after the proposal was submitted, in the year 2008 the Italian Space Agency supported the mission and the European Space Agency Launcher Programme Board approved LARES (LAser RElativity Satellite) as the primary payload to be accommodated for the VEGA Launcher qualification flight. Several university satellites were selected to be launched as secondary payload passengers. The launch, on the 13th of February 2012, was very successful for both the VEGA and LARES teams, the satellite being released with a very high accuracy into the nominal orbit. In this paper it will be shown that LARES, once the known non-gravitational perturbations are removed, behaves as the best test particle available in the solar system. So it turns out to be the ideal instrument for testing not only fundamental physics, but also for carrying out studies on geodesy and geodynamics. Accurate measurement of the Lense-Thirring effect requires several years of data acquisition because of the presence of some periodical perturbations, but some improvements are expected in the next years over the 2004 measurements obtained with only the two LAGEOS satellites.