Atmospheric Density Corrections Estimated from Fitted Drag Coefficients

Fitted drag coefficients estimated using GEODYN, the NASA Goddard Space Flight Center Precision Orbit Determination and Geodetic Parameter Estimation Program, are used to create density corrections. The drag coefficients were estimated for Stella, Starlette and GFZ using satellite laser ranging (SLR) measurements; and for GEOSAT Follow-On (GFO) using SLR, Doppler, and altimeter crossover measurements. The data analyzed covers years ranging from 2000 to 2004 for Stella and Starlette, 2000 to 2002 and 2005 for GFO, and 1995 to 1997 for GFZ. The drag coefficient was estimated every eight hours. The drag coefficients over the course of a year show a consistent variation about the theoretical and yearly average values that primarily represents a semi-annual/seasonal error in the atmospheric density models used. The atmospheric density models examined were NRLMSISE-00 and MSIS-86. The annual structure of the major variations was consistent among all the satellites for a given year and consistent among all the years examined. The fitted drag coefficients can be converted into density corrections every eight hours along the orbit of the satellites. In addition, drag coefficients estimated more frequently can provide a higher frequency of density correction.