Geodynamics from the analysis of the mean orbital motion of geodetic satellites

Secular and long periodic perturbing forces acting on the orbit of an artificial satellite are modelled and included in a semi-analytical theory of the mean orbital motion. Gravitational and nongravitational forces are averaged using analytical transformations and numerical quadratures, respectively. As non-gravitational modelling is the first source of problems arising in the determination of geodynamical parameters, special attention is given to this question. Resulting averaged equations of motion are integrated numerically allowing the visualization and deconelarion of long periodic signals in the classical mean orbital elements. Observed mean orbital elements of LAGEOS (18 years) and Starlette (14 years) have been computed from Satellite Laser Ranging (SLR) measurements which had fast been reduced by classical orbit fits on short arcs. The results of these long arc solutions exhibit variations of geodynamical coefficients at different periods ranging from semi-annual and annual to 9.3 and 18.6 years. Values of coefficients are compared to other results obtained recently in this field.