Results from Lunar Laser Ranging Data Analysis

The lunar laser range data taken at McDonald Observatory between August 1969 and May 1980 has been analyzed. The simple rms residual for the 2954 ranges is 31 cm. Results of the analysis include GMearth = 398600.45±0.02 km3/sec2 and a secular acceleration of the lunar orbital mean longitude of ṅ = −23.8±1.5“/century2 which yields a Q of 12.3 at semidiurnal frequencies. The lunar harmonic C30 is (−8.7 ± 1.1) × 10−6 and the lunar rotational dissipation k2mT = (4.7 ± 0.5) × 10−3 day. Also resulting from the solution are geocentric coordinates of McDonald accurate to 30 cm, including the first value for the longitude with the new IAU constants and a dynamical equinox.

Expected Use of Lunar Range Data to Determine Modified Nutation Terms

The lunar laser range data from the McDonald Observatory in Texas have been used so far to determine major improvements in the lunar ephemeris and librations, to provide a new test of gravitational theory, and to determine single-day UT0 values on about 200 days during the period 1970-1974. The mean uncertainty in the UT0 values is 0.5 msec, and the smallest uncertainty is 0.2 msec (Stolz et al. 1976). The changes in the angular position of the moon with time are believed to be well enough known so that their uncertainty does not substantially degrade the accuracy of the UT0 values.

Results from lunar laser ranging (summary only)

Over 1500 lunar laser range measurements have been made during the past six years at McDonald Observatory. These data have been fitted with a 41 cm r. m. s. residual. The geocentric coordinates of McDonald Observatory are now known to better than 1 m, the three-dimensional coordinates of the Moon and the selenocentric coordinates of the retroreflectors are accurate to about 25 m, and the mass ratio Sun/(Earth + Moon) is determined to 2 parts in 107. A search for the Nordtvedt term in the Moon’s orbit, a term predicted by some relativity theories, gives a null value, a result consistent with general relativity. The measurement of the physical librations determines very accurately the moment of inertia parameters β = (C - A)/B and γ = (B - A)/C, and significantly determines the third degree gravitational harmonics C 30 , C 32 , S 32 and S 33 The postfit residuals are not random but yield corrections to the rotation of the Earth, values of U. T. 0 for individual days having typical accuracies of 0.5 ms (20cm). The anticipated regular operation of two or more stations will allow the separation of U. T. 1 and polar motion.