Thermosphere Density Variability , Drag Coefficients , and Precision Satellite Orbits

Precision orbit ephemerides (POE) are used to estimate atmospheric density along the orbits of CHAMP (Challenging Minisatellite Payload) and GRACE (Gravity Recovery and Climate Experiment). The densities are calibrated against accelerometer derived densities and considering ballistic coefficient estimation results. The 14-hour density solutions are stitched together using a linear weighted blending technique to obtain continuous solutions over the entire mission life of CHAMP and through 2011 for GRACE. POE derived densities outperform the High Accuracy Satellite Drag Model (HASDM), NRLMSISE-00 model, and Jacchia 71 model densities when comparing cross correlation and RMS with accelerometer derived densities. Cross correlations for all other data sets with accelerometer derived densities are lower when the satellite’s orbit planes are near the terminator. Additional research showed that the high frequency variations in density observed only be accelerometers have little effect on orbit propagation accuracy. CHAMP and GRACE precision orbit data were decimated to 8 and 15 minutes per orbit and had noise levels up to 100 m added to them to observe the effects of limited data of lower accuracy on density estimation. As expected, the accuracy decreased as higher levels of noise were added to the data, but the even with limited data of moderate accuracy, the estimated densities were of usable accuracy. The Direct Simulation Monte Carlo was used to estimate drag coefficients for the GRACE, Stella, and Starlette satellites. The resulting drag coefficients showed good agreement with existing drag coefficient techniques. The models were also used to develop a new empirical drag coefficient model for GRACE, which can be easily extended to other satellites. The empirical model allows computationally efficient determination of drag coefficients for complex satellites.