Orbit Evolution and Uncontrolled Re-Entry of the "Molniya" Type Satellites

The Russian telecommunication satellites of the "Molniya" series are inserted into special high elliptical orbits with a period of ~ 12h and typical minimal altitude of about 500 km. Such kinds of satellites have been launched since the mid of 1960s. At present more than 160 spacecrafts of this type were inserted into orbits. After the end of mission (or a spacecraft emergency) the satellite turns into an uncontrolled mode and the parameters of its orbit are changing due to the perturbing forces action. With the lapse of time the perigee altitude can become so low, that a spacecraft cannot orbit the Earth and it re-entries. The conditions of the final phase of the flight and the re-entry of the "Molniya" type satellite as a rule have the other character, than the re-entry of the space objects which were flying on circular (or near circular) orbits.In the paper the influence of the perturbation forces (first of all the luni-solar attraction) on changing the parameters of "Molniya" type orbit is researched. In the example of a concrete "Molniya" spacecraft the orbit evolution of such a kind of satellites is examined. The variation of the main parameters, determining the lifetime of space vehicle, and a condition at which the satellite re-enters are studied.