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IAA Transactions, No. 8, ``Celestial Mechanics'', 2002
Selenodynamical parameters from analysis of LLR
observations of 1970--2001
G. A. Krasinsky
Institute of Applied Astronomy, St.Petersburg, Russia
LLR observations of 1969--2001 are processsed to estimate a set of parameters
of the Earth--Moon system. The dynamical model accounts for effects of elasticity
of the lunar body, tidal dissipation in the Moon, and friction coupling between
the lunar mantle and its fluid core. A Poincare's type model is developed to
describe effects of the fluid core assumed to be a three--axis ellipsoid. Estimated
selenodynamical parameters include Love numbers h 2 , l 2 , k 2 , dissipation factor Q,
undimensional moment of inertia, coefficients of the lunar gravitational potential
of the orders 2 and 3, coupling parameter џ and three parameters describing
the fluid core. Except these three parameters the obtained estimates seem to
be reliable. So no evidences of direct effects of the fluid core is found. For the
dissipation factor Q (defined by the relation Q = 1=2ffi where ffi is the tidal lag)
the estimates vary in the range from Q = 13 to Q = 18 depending on solution.
They are of the same order as the value Q = 11:032 \Sigma 0:004 obtained for the
Earth, which means that the tidal dissipation in the Moon is close to that in the
Earth (notwithstanding that there are no oceans on the Moon to contribute to
the dissipation). Thus a widespread opinion that the largest contribution to the
dissipation of energy in the Earth is due to the ocean tides becomes doubtful.
Analysis of residuals reveals a sharp change of their time behavior after March
1998. This effect could not be modeled by other ways but including corrections to
coordinates of the reflectors after this date as independent solve--for parameters.
Because the corrections derived for all four observed reflectors appear to be rather
close it is conjectured that near this date a jump of a few centimeters in the
position of the lunar barycenter with respect to the lunar crust has occurred.
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