Total densities derived from accelerometer data

The German satellite Challenging Minisatellite Payload (CHAMP), carrying the STAR accelerometer onboard, was launched in July 2000. The CHAMP mission profile is compatible with studies of the thermosphere: it will provide good geographical and altitude coverage over a period of five years. The preprocessing of the accelerometer data consists of correcting them for maneuvers, specific events, and instrumental bias. The total density can then be reconstituted, employing a model for the aerodynamic coefficient. We have employed a theory based on diffuse reemission applied to a 15-plate macromodel. The accuracy of the observed densities depends mainly on the uncertainties of the estimated accelerometer calibration parameters and of the aerodynamic coefficient, as well as on geomagnetic activity. The six weeks of data analyzed in this preliminary study showed their high precision and model shortcomings. Assimilation of at least one year of data in a thermosphere model will significantly increase its accuracy, which, in turn, will improve satellite drag modeling.