I discuss some aspects of a recent frame-dragging test performed by exploiting the Root-Mean-Square (RMS) orbit-overlap differences of the out-of-plane component (N) of the Mars Global Surveyor (MGS) spacecraft’s orbit in the gravitational field of Mars. A linear fit to the complete time series for the entire MGS data set (4 February 1999–14 January 2005) yields a normalized slope 1.03 ± 0.41 (with 95% confidence bounds). Other linear fits to different data sets confirm agreement with general relativity. Huge systematic effects induced by mismodeling the martian gravitational field which have been claimed by some authors are absent in the MGS out-of-plane record. The same level of effect is seen for both the classical non-gravitational and relativistic gravitomagnetic forces on the in-plane MGS orbital components; this is not the case for the out-of-plane components. Moreover, the non-conservative forces experience high-frequency variations which are not important in the present case where secular effects are relevant.
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