Knowledge of the forces affecting mostly the description of the artificial satellites motion is very important task at present. This is valid especially for the forces of the non-gravitational origin. Their description is done at best via the in-situ measurements of their dynamlcs manifestations, i.e., to use the high-sensitive microaccelerometers. We already built and proved one such a device consisting of a cubic proof-mass free-flowing within an external cubic cavity. Our accelerometer has been succesfully tested on the RESOURCE F-1 satellite on June 1992. A project
of another experiment is now being prepared under the náme of
”CESAR” with a participation of five central-European countries. The launch of the proposed satellite is envisaged for 1997.
The analytical second-order theory of the motion of an arificial satellite in the Earth’s atmosphere is used to determine the satellites’ lifetime. The analytical theory is unique in the sense that it determines the secular changes of the semi-major axis and the eccentricity for a longer time-interval, characterized by the time of revolution. To establish the analytical theory, a special thermospheric model is used, which expresses directly the thermospheric total density. The theory is developed to the
second-degree in small parameters (coefficients of the density model); this enables to determine analytically the changes of the elements over an interval of several days. The gravitational effects of the Earth’s oblateness are taken into account, too. The whole theory is used for the lifetime determination of the satellite "CESAR" supposed to be launched in 1997.
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.