Models of the variations and distribution of the upper atmosphere density are constructed, using modelled as well as observed data. Theoretical expression of the model is used in the equations of motion to study the drag effects of the atmosphere.
The semianaytical theory of the motion ol the resonant Earth satellite under the inlluence of Sun and Moon is constructed in nonsingular variables by Lie transforms. The explicit expressions tor the general terms of the combined perturbations are obtained up to the third order with resped to C20. The account ol the additional perturbations is exemplified by the calcuiaiion of the corrections due to the precession and the nutation.