Variation in eccentricity for the orbit of cosmos 373, 1970-87A

Abstract

The orbital parameters of the satellite Cosmos 373, 1970–1987 A, have been determined at 105 epochs during a 9 year period prior to its decay in March 1980. With an initial perigee height of 472 km and an orbital plane inclined at 62.9° to the equator, the satellite was regarded as emminently suitable for the study of the gravitational field of the Earth, since the amplitude of the oscillation in eccentricity becomes very large for inclinations close to the critical angle of 63.4°. The analysis has yielded extremely accurate values of eccentricity, with standard deviations (S.D.s) down to 0.000004. In paricular, 80 values of eccentricity were examined, covering a complete cycle of the argument of perigee, and corrections incorporated for the effects due to lunisolar perturbations, solid-Earth tides, solar radiation pressure and air drag. The analysis of the modified data has indicated an amplitude of oscillation of 0.00836 ± 0.00001, equivalent to almost 60 km in perigee height—the largest yet recorded for any near-Earth orbit of high accuracy.