Comparison of Air Densities Derived from the Orbits of 1966-51A, B and C
On 9 June 1966 three satellites were launched into polar orbits with perigee heights near 180 km and apogees near 3600 km. They were Secor 6 (1966-51B), a rectangular box of mass 17 kg and length O.33 m; ORS 2 (1966-51C), a regular octahedron of side O.23 m and mass 5 kg ; and the final-stage Agena rocket (1966-51A), of length at least 6 m. Analysis of the extensive orbital data now available on these three satellites gives 260 values of air density at heights near 190 km. Comparison of these values provides a severe test of the accuracy of the orbital data and methods of analysis, and shows that the accuracy is at least as good as has previously been estimated. The comparison also reveals that the effective crosssectional area of Secor 6 oscillated with an amplitude of about 10%, with minima when perigee was near the equator and maxima at latitudes near 70°. As a consequence, the amplitude of the semi-annual variation in air density previously obtained from Secor 6 should be reduced from 1.45 to 1.4O. Other findings are that the effective cross-sectional areas of the satellites never approached their extreme possible values, and that the effective area of 1966-51A changed by less than 10% from week to week.
KeywordsOrbit Determination Polar Orbit Break Curve Severe Test Regular Octahedron
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