Gravitomagnetism and lunar laser ranging

The problem of measuring gravitomagnetic effects by means of lunar laser ranging (LLR) is investigated. The relevant terms in the Einstein-Infeld-Hoffmann equations of motion in barycentric coordinates are parametrized by a parameter ${\eta }_G$, which is fitted along with other parameters to LLR data and not derived from postfit residuals as it was done by other authors. The physical relevance of ${\eta }_G$ and its relation to the preferred frame parameter ${\alpha }_1$ are discussed. Finally, ${\alpha }_1$ is fitted to LLR data by choosing the Barycentric Celestial Reference System as preferred frame instead of the cosmic rest frame determined via the temperature anisotropy of the cosmic microwave background radiation.

Figure 1

(a) Sensitivity of the Earth-Moon distance with respect to ${\eta }_G$ assuming ${\eta }_G=1.5\times {10}^{-3}$ according to Eq. (14) (b): the corresponding power spectrum.