Title: Lunar Ephemerides and Lunar Laser Ranging

Authors: X X Newhall, E. M. Standish, Jr., and J. G. Williams
         Jet Propulsion Laboratory,
         California Institute of Technology
         Pasadena, California  91109-8099

         Phone:  (818) 354-0000 
         Fax:    (818) 393-6890
         E-mail: xxn@logos.jpl.nasa.gov

Abstract:

>From 1969 through 1972, lunar space missions placed four functioning laser
retroreflector arrays on the Moon. Several observatories have ranged the
reflectors from 1969 to the present. Beginning in March, 1970, ranging data
were accurate enough to be used for parameter estimation. Approximately 9500
normal points have been acquired from three observatories over the past 25
years, with accuracies over the past five years being 2-3 cm. 

The implementation of lunar laser ranging (LLR) ushered in a new era of lunar
ephemerides. After only eight years of ranging data acquisition, the ephemeris
accuracy improved by three orders of magnitude and obviated the need for any
other data type. In addition, ranging data are sufficiently accurate to permit
the estimation, modelling, and integration of the lunar physical librations. 

JPL has recently generated the lunar and planetary ephemeris DE403. This paper
discusses the modelling, numerical integration, and polynomial representation
of the ephemeris. A significant recent modelling improvement is the lunar
elastic dissipation. This feature requires the implementation of retarded-time
differential equations, which, when integrated backward, function
mathematically as advanced-time equations. 

Also given is a comparison of DE403 with earlier JPL ephemerides, notably DE102
(produced in 1978), to illustrate the effects of a more refined physical model
and of the inclusion of 17 more years of LLR data. 

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