Orbit determination and estimation of non-gravitational accelerations for the GOCE reentry phase

A reduced-dynamic orbit determination based on an extended Kalman filter approach was adopted to cope with the estimation of the orbit parameters, including the exponentially growing non-gravitational accelerations. The orbits were found to be consistent with Satellite Laser Ranging (SLR) observations at a level of just a few centimeters for a few passes collected up to 2 November 2013. Also orbit overlap comparisons and comparisons with external orbit solutions indicate a 3-dimensional orbit quality at the dm level or better. In addition, high correlations were found between the estimated non-gravitational accelerations and those from the accelerometers during all periods when they were not saturated: typically close to 0.99 for the X axis of the gradiometer reference frame (close to the flight direction), for which the non-gravitational acceleration signal is by far the largest. High correlations were found as well for the Y axis (0.68-0.96) and Z axis (0.61-0.93), predominantly aligned with respectively the cross-track and height direction. The highest correlations were found for the last days, as long as the accelerometers were not saturated.