The analysis of the orbit of 1975-22B at 14th-order resonance

The orbit of Intercosmos 13 rocket (1975-22B) passed through exact 14th-order resonance during December 1977. The variations in orbital eccentricity and inclination are analyzed to evaluate four lumped geopotential harmonics, using 21 orbits determined by Brookes and Swinerd (1986, Planet. Space Sci. 34, 1263). In the analysis of eccentricity an acceptable result was recoverable only by the careful removal of the drag perturbation, due to an increase in solar activity during the latter half of the period considered. The inclination variation had been analyzed previously by Brookes and Swinerd, but the discovery of an inaccuracy in their results led to a re-evaluation of the lumped harmonic values in this paper.