30 years of lunar laser ranging and the gravitational interaction

The main oscillation amplitudes of the lunar orbit have been measured to precisions of a few millimetres, using data from 30 years of laser ranging to the Moon. Several key tests of the general relativity theory of gravity result. Earth and Moon, differently composed bodies, fall toward the Sun at rates equal to one part in 1013, thereby confirming the universal coupling of gravity to matter's energy tensor, and gravity's nonlinear self-coupling structure to one part in 104. The expected de Sitter precession of the Earth - Moon system's local inertial frame with respect to distant frames is confirmed to a precision of three parts in 1000, and Newton's constant indeed shows no cosmological time variation at the few parts in 1012 per year level. Almost every term in the N-body relativistic equation of motion contributes to the measured perturbations of the Moon's orbit, so lunar laser ranging (LLR) can be said to be a `near-complete' gravity experiment. The precision of these measurements should improve further, especially those connected with determination of lunar orbit frequencies and their time evolutions, as this active experiment continues.