Progress in Lunar Laser Ranging Tests of Relativistic Gravity

Analyses of laser ranges to the Moon provide increasingly stringent limits on any violation of the equivalence principle (EP); they also enable several very accurate tests of relativistic gravity. These analyses give an EP test of Δ(M_G/M_I)_EP=(-1.0±1.4)×10^-13. This result yields a strong equivalence principle (SEP) test of Δ(M_G/M_I)_SEP=(-2.0±2.0)×10^-13. Also, the corresponding SEP violation parameter η is (4.4±4.5)×10^-4, where η=4β-γ-3 and both β and γ are post-Newtonian parameters. Using the Cassini γ, the η result yields β-1=(1.2±1.1)×10^-4. The geodetic precession test, expressed as a relative deviation from general relativity, is K_gp=-0.0019±0.0064. The search for a time variation in the gravitational constant results in G˙/G=(4±9)×10^-13 yr^-1; consequently there is no evidence for local (∼1 AU) scale expansion of the solar system.