Analysis of the Orbit of Cosmos 387 (1970-111A) near 15th-Order Resonance

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Analysis of the Orbit of Cosmos 387 (1970-111A) near 15th-Order Resonance

D. G. King-Hele

Cosmos 387 (1970-111A) was launched on 16 December 1970 into a near-circular orbit with an average height of 540 km and an inclination of 74.0 degrees. On 5 Nobember 1971 the orbit, in its slow contraction under the influence of air drag, passed through 15th-order resonance, when the ground track repeats after 15 revolutions. The orbit has been determined with the aid of the RAE orbit refinement program PROP at 19 epochs between May 1971 and June 1972, using 1500 optical and radar observations. The average accuracy is about 70 m in perigee height and 0.001 degrees in inclination. The variation of orbital inclination while the satellite was experiencing 15th-order resonance, as given by these 19 orbits and 55 US Navy orbits, has been analysed to obtain equations accurate to 4% for the geopotential coefficients of order 15 and odd degree (15, 17, 19 ....). These equations have subsequently been used (with others) in determining individual coefficients of order 15 and odd degree.