Abstract. The West Ford package placed in orbit in 1963 contained almost 500 million copper dipoles. Due to a delay in releasing the needles in orbit a number of clusters of needles formed. Analysis of 34 years of mean orbital elements of 20 different clusters has revealed perturbations of 10 km or more in the semimajor axis due to direct solar radiation pressure, atmospheric drag, and Earth albedo pressure. The orbits have perigee heights ranging from 1500 km to 3600 km. A simplified Earth albedo model has been adopted to account for the long periodic perturbations observed in the semi-major axis. The periodic terms are a function of the sun and cluster nodal longitude angles. The atmospheric drag perturbation was modeled by extending the CIRA72 model atmosphere to heights above 2000 km. Cluster area-to-mass ratios were determined from fitting direct solar radiation pressure coefficients over 25 to 30 year data spans. Twenty to thirty year semi-major axis fits produced mean atmospheric density factors for hydrogen and helium for each cluster. These factors show a very high correlation with average perigee height. The results show that average hydrogen concentrations are from 3 to 5 times greater than given by the CIRA72 model. Helium concentrations also are from 1.5 to 4 times greater than predicted for these heights.
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