Lunar Laser Ranging (LLR), which has been carried out for more than 35 years,
is used to determine many parameters within the Earth-Moon system. This
includes coordinates of terrestrial ranging stations and that of lunar
retro-reflectors, as well as lunar orbit, gravity field, and its tidal
acceleration. LLR data analysis also performs a number of gravitational physics
experiments such as test of the equivalence principle, search for time
variation of the gravitational constant, and determines value of several metric
gravity parameters. These gravitational physics parameters cause both secular
and periodic effects on the lunar orbit that are detectable with LLR.
Furthermore, LLR contributes to the determination of Earth orientation
parameters (EOP) such as nutation, precession (including relativistic
precession), polar motion, and UT1. The corresponding LLR EOP series is three
decades long. LLR can be used for the realization of both the terrestrial and
selenocentric reference frames. The realization of a dynamically defined
inertial reference frame, in contrast to the kinematically realized frame of
VLBI, offers new possibilities for mutual cross-checking and confirmation.
Finally, LLR also investigates the processes related to the Moon's interior
dynamics. Here, we review the LLR technique focusing on its impact on Geodesy
and Relativity. We discuss the modern observational accuracy and the level of
existing LLR modeling. We present the near-term objectives and emphasize
improvements needed to fully utilize the scientific potential of LLR.Comment: 7 pages, 7 figures, 2 tables. Talk given at `Dynamic Planet 2005:
Monitoring and Understanding a Dynamic Planet with Geodetic and Oceanographic
Tools,'' a Joint Assembly of International Associations: IAG, IAPSO and IABO,
Cairns, Australia, 22-26 August 200