Orbital differences

Finally, the radial orbit error of the DUT operational JGM-2 orbits can be monitored by looking at the orbital height differences between consecutive overlapping arcs. Over all ten 2-day overlaps the total RMS radial orbit difference amounts to 13.4 cm.

The general assumption that the errors on different arcs are uncorrelated is not valid, because the ends of both arcs are generated with the same dynamic model and are for a major part determined by the same tracking data. Hence, a reduction by a factor is not applicable. On the other hand, the 1-day extensions of the arc will usually be less precise than the central 3.5 days, suggesting that the RMS overlap difference at least provides an upper limit of the radial orbit error.

More likely to be uncorrelated are the orbits generated by D-PAF and DUT: both are computed with different gravity models (PGM035 and JGM-2, respectively) and the D-PAF orbits incorporate crossover height differences as additional tracking data. The statistics of the radial orbit difference (0.3 cm mean and 12.8 cm RMS over the full 36-day period) are very encouraging and indicate a radial orbit error of the order of 10-13 cm.