GPS based orbit determination using accelerometer data

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Ongoing and future geopotential space missions are equipped with one or more accelerometers. In order to use these observations, the accelerometer measurements have to be calibrated before processing them. In this paper they are introduced in the GPS based precise orbit determination, by replacing the non-gravitational force models for atmospheric drag and solar radiation pressure. Empirical accelerations are still estimated to account for deficiencies in the applied conservative force models. The in-orbit calibrated accelerometer observations are used to validate the accelerations determined by force modeling. In along-track direction they show the best agreement. During days of high solar activity the benefit of using accelerometer observations is clearly visible. The observations during these days show high frequency fluctuations which the modeled and empirical accelerations cannot follow. A long period of GRACE (second half of 2003) and of CHAMP (2004) data is processed. This results for GRACE in a mean orbit fit of a few centimeters with respect to high-quality JPL reference orbits, showing a slightly better consistency compared to the case when using force models, which is also supported by SLR residual analysis. The daily calibration factors determined with this technique show a small variation. When not including empirical accelerations in the estimation procedure, the calibration factors in radial and cross-track direction show a bigger spread, with an orbit fit below the decimeter level.