A Numerical Study of the Effects of Fourth Degree Terms in the Earth-Moon Mutual Potential on Lunar Physical Librations

Abstract

Lunar laser Ranging Data (LURE) is currently available with a range accuracy of 10 cm. Accuracies of 2 to 3 cm are ultimately expected. Previous analyses have shown that for an Earth-Moon range precision of 10 cm, certain fourth degree lunar harmonic gravity coefficients must be included in the lunar physical libration model. An order-of-magnitude calculation shows that some torques arising from previously neglected fourth-degree “figure-figure interaction” terms of the Earth-Moon mutual potential could produce effects on the physical librations that should be modeled for range accuracies of 2 to 3 cm.