Several analyses of LLR observations have been performed using the lunar theory ELP2000-96 (Chapront & Chapront-Touzé 1997) and an improved version of the lunar libration theory of Moons (1984) with numerical and analytical complements (Chapront et al. 1999a). A previous analysis, described in (Chapront et al. 1999b), covered the time span January 1972 until March 1998. It is referred to below as the solution S1998. We refer to this paper for the presentation of the principles of the analysis, discussion of the methods and results of the comparisons. More recently a new analysis was performed using LLR observations of McDONALD and CERGA before May 2000 (Chapront et al. 2000). Several improvements were introduced in the lunar ephemerides, mainly in the libration model, and also in the program of reduction (an up-to-date nutation model) and in the statistical treatment of the data (an adequate distribution of weights among the various observing stations and periods of observations). This solution is referred to as S2000. Now, on the same basis, we have enlarged the time span of observations until April 2001 and added a few parameters in the program of reduction (positions and velocities of the observing stations). This last solution is referred to as S2001.
In this paper, we shall also mention intermediate solutions in which the characteristics of the fit are the same as in S2001; the only change is the upper limit of the time span covered by the observations, which may vary within 5 years (1996-2001). This interval has been chosen considering that recent observations, more accurate than earlier ones, have a much larger weight in the determination of the fitted parameters. These intermediate solutions were done to study the evolution of the fitted values with the time interval of observations, in particular for tidal acceleration (Fig. 3), precession constant (Fig. 4), and obliquity (Fig. 5).
Copyright ESO 2002