Mean orbital motion of geodetic satellites and its applications

Averaging methods are convenient tools for studying long-periodic variations of the motion of artificial satellites. The main lines of a semi-analytical theory of the mean motion are given. We show how, when coupled with a careful reduction of the tracking data, this theory allows to determine parameters related to the temporal variations of the Earth gravity field (e.g. the amplitude of 18.6 years tide and the secular variation of even zonal harmonics). The theory is also very useful for other applications such as mission analysis.