Atmospheric density calibration using satellite drag observations

Thermospheric density models are currently the main source of error in the orbit determination and prediction of low Earth satellites. The empirical models which are in wide use today show an RMS accuracy of no better than 15-30%. This accuracy barrier is thought to be inherent in the model formulation, which is based on an imperfect correlation of density with space weather proxies. This barrier can be overcome by using model calibration. Selected correction parameters can be estimated using concurrent observations of satellite drag. We have investigated the derivation of accurate density values from satellite orbit data and tracking measurements, and the subsequent adjustment of the CIRA-72 model using these data. Two sources were investigated to compute integrated density values along satellite orbits. The first source is a limited number of satellites with highly accurate tracking systems, such as altimetry and gravity missions. The very large database of two-line element data can be used a second option. The influence on accuracy of uncertainties in other forces, the ballistic coefficients and thermospheric winds, has been assessed.