LAGEOS Satellites: Relativistic Measurements in the Earth's Field
Peron, R.; Lucchesi, D.M.
IFSI-INAF

During the last 30 years, first LAGEOS (LAser GEOdynamic Satellite) and successively also LAGEOS II satellites have provided unique scientific results in the field of geophysics and geodynamics as well as – more recently – in fundamental physics. Indeed, the long–arc analysis of laser range data from such geodetic satellites rep resents a useful tool (by analysing the satellites orbital residuals) to extract relevant information concerni ng the Earth structure and relativistic gravity. Therefore, the accurate modelling of the orbit of the two LAGEOS satellites, together with the very accurate r ange measurements (station-to-satellite) provided by the powerful Satellite Laser Ranging (SLR) technique, rep resent the two fundamental ingredients in order to perform accurate long–arc analyses looking for relativistic effects in the satellites orbit. From this point of view, the Earth and its surroundings represent an interes ting reference in order to test the weak field and slow motion limit of general relativity. Under these conditions, mass–currents are responsible of gravitomagnetic effects similar to the electromagneti c effects produced by charges and electric currents. This results in a secular shift of both the satellite orb it pericenter and the longitude of the ascending node due to Schwarzschild point mass effect and the Lense–Thi rring effect produced by Earth’s spin. Moreover, deviations from the usual 1/r law for the gravitational potential, as in the hypothesis of a fifth–f orce of nature, may be bounded with LAGEOS satellites orbit analysis. These deviations, if measured, would lea d to new weak interactions between macroscopic objects. Very interesting, these supplementary interactions may be either consistent with Einstein Equivalence Principle or not. The characteristic of such interactions, whi ch are predicted by several theories and described through a Yukawa potential, is to produce deviations for ma sses separations ranging through several orders of magnitude, from the sub–millimeter level up to the astronom ical scale. Therefore, the accurate measurement of the pericenter shift of a binary system, such that provided by the Eart h-LAGEOS system, may be used to test for a long–range interaction with a characteristic range comparable with the system semimajor axis. We review the status of LAGEOS satellites orbit modelling with respect to SLR precision in order to (possibly) improve the last measurement of the Lense–Thirring effect and to (possibly) constrain a Yukawa–like interacti on at the two LAGEOS orbit scale.