The orbit of Proton 4 redetermined, with geophysical implications

The orbit of Proton 4, 1968-103A, was redetermined, in greater detail and with better accuracy, to clarify previously puzzling features in the variation of orbital inclination. Orbital parameters were determined at 25 epochs between December 1968 and July 1969, using the RAE orbit refinement program PROP6. During January 1969 the orbit passed through 31:2 resonance--when the ground track over the Earth repeats every two days after 31 revolutions of the satellite. A simultaneous least-squares fitting of theoretical curves to the values of inclination and eccentricity between 14 December 1968 and 6 March 1969 yielded values for two pairs of lumped 31st-order geopotential coefficients, appropriate to an inclination of 51.5 deg -- the first specific evaluation of 31st-order coefficients. The 15 values of inclination after the resonance, from March to near decay in July 1969, were used to determine mean, morning and afternoon-evening values for the rotation rate of the atmosphere at a height near 260km; the values of rotation rate, namely 1.1, 0.9 and 1.3rev/day respectively, confirm trends already established from analysis of other satellite orbits.