Characteristics of the LAGEOS and ETALON satellites orbits

Abstract

Satellite Laser Ranging (SLR) data to retroreflector carrying satellites allow the derivation of the details of their orbital evolution and behavioral characteristics. The semi-major axis monitors the effect of non-conservative forces, and the eccentricity is particularly affected by solar radiation pressure. The conservative forces of the geopotential and Earth and ocean tides influence the behavior of the inclination and the right ascension of the ascending node. The contrasting effects of these perturbations on the long-term evolution of the satellites LAGEOS I (circular, 12,000 km semi-major axis, 109 degree inclination orbit) and LAGEOS II (circular, 12,000 km semi-major axis, 53 degree inclination orbit), as well as ETALON I and ETALON II (both of which are in circular, 25,500 km semi-major axis 65 degree inclination orbits) will be presented. The major difference between the evolution of the LAGEOS satellites' orbits is caused by the difference in inclinations between LAGEOS I and LAGEOS II. There is no such contrast in the orbits of ETALON I and II and the observed dissimilarity in their response to direct solar radiation pressure must be caused by satellite area, mass or reflectivity differences. Although both LAGEOS satellites have observed solar radiation coefficients of about 1.13, using a 42 cm radius and a mass of 1346 kg for the ETALON satellites, the coefficient of solar radiation pressure for ETALON I has been determined to be 1.22, and 1.25 for ETALON II. The capability of these satellites to define a reference frame for Earth orientation measurements will improve with the models for their orbital evolution.