Benefit of New High-Precision LLR Data for the Determination of Relativistic Parameters

From 1969 on, Lunar Laser Ranging data are collected by various observatories and analyzed by different analysis groups. In the past years observations with bigger telescopes (APOLLO) and at infrared frequencies are carried out, which resulted in a better spread of precise LLR data over the lunar orbit and the observed reflectors on the Moon. In Germany, from the early 80ies on, the software package LUNAR has been developed to study the Earth-Moon system and to determine several related model parameters. Research covered physical libration and orbit of the Moon, coordinates of observatories and retro-reflectors, Earth orientation parameters and, with special modifications, tests of Einstein's theory of relativity. Including the new data, we show recent results for relativity parameters related to the equivalence principle, temporal variation of the gravitational constant and for a selection of PPN (Parametrized Post-Newtonian) parameters.

With the construction of the new LLR facility at Table Mountain Observatory (JPL's Optical Communication Testbed Laboratory - OCTL) in California, for the first time, it will be possible to conduct differential LLR with an expected range precision of less than 30 micrometers - a factor of 200 better than the current accuracy. This opens new possibilities for improved analysis of the whole LLR parameter set and allows to address further effects, e.g., related to the deep lunar interior. In order to quantify the potential benefit of this novel high-precision data on the determination of the relativistic parameters, simulations are performed using our LUNAR software. The results are compared to those of the classical analysis mentioned before and will be critically discussed.