HR: 13:40h
AN: P43C-01    [Abstracts]
TI: Lunar Laser Ranging Science: Recent Progress and Future Plans
AU: * Turyshev, S G
EM: turyshev@jpl.nasa.gov
AF: Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, United States
AU: Williams, J G
EM: James.G.Williams@jpl.nasa.gov
AF: Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, United States
AU: Boggs, D H
EM: Dale.Boggs@jpl.nasa.gov
AF: Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, United States
AB: Since it's initiation by the Apollo 11 astronauts in 1969, lunar laser ranging (LLR) has strongly contributed to our understanding of the Moon's internal structure and the dynamics of the Earth-Moon system. LLR science results include tests of gravitational physics and ephemeris information from the orbit, lunar science from rotation and solid-body tides, and Earth science. \underline{Science from the orbit}: LLR data provide for high-accurate research in gravitational physics including tests of the equivalence principle (EP), search for the time variation of the gravitational constant G, and geodetic precession. The EP test is used for an accurate determination of the Eddington parameter beta. The analysis is sensitive to astronomical parameters such as orbit, masses, and obliquity. The dissipation-caused acceleration in orbital longitude is -25.9 {"/cent}², dominated by tides on Earth with a 1% lunar contribution. Lunar ephemerides are a product of the LLR analysis used by current and future spacecraft missions. \underline{Lunar science}: variations in the lunar orientation and rotation plus tidal deformation provide unique information on lunar interior structure, physical properties, and energy dissipation. Analyses of the LLR data determine the second-degree lunar tidal Love numbers k₂ (potential) and h₂ (vertical displacement), tidal dissipation related Q, and two interactions at the fluid-core/solid-mantle boundary. The determined Love numbers are k₂=0.0199±0.0025 and h₂=0.043±0.008, consistent with elastic models of the interior. Tidal dissipation is strong, Q has a weak dependence on tidal frequency and is about 29 at a one month period and 36 at one year. The core/mantle interactions are dissipation, indicating a fluid core of about 20% the Moon's radius, and an oblateness interaction. \underline{Earth science}: Station positions and motions, Earth rotation variations, and precession are determined from analyses. At the same time, the current distribution of the retroreflectors is not optimal and signals are weak. We discuss a recently proposed next-generation of LLR experiment. In particular, we suggest that upcoming missions to the Moon should carry either new sets of laser retroreflector arrays or laser transponders pointed at Earth or both of these instruments. A wider geographic distribution of new instruments on the lunar surface than the current distribution would improve the accuracy of the lunar science parameters several times. A bright transponder source on the Moon would open LLR to dozens of satellite laser ranging stations which cannot detect the current weak signals from the Moon. Properties of the lunar interior, including liquid core and solid inner core, can be determined from lunar rotation, orientation, and tidal response. Anticipated improvements in Earth geophysics and geodesy would include the positions and rates for the Earth stations, Earth rotation, precession rate, nutation, and tidal influences on the orbit. Improvements are also expected in several tests of general relativity. Science investigations with optical transponders on the Moon can also be used as a prototype demonstration for later laser ranging to Mars; a lunar installation would provide valuable early feedback on their operational characteristics. The work described here was carried out at the Jet Propulsion Laboratory, California Institute of Technology under a contract with the National Aeronautics and Space Administration.
DE: 1221 Lunar and planetary geodesy and gravity (5417, 5450, 5714, 5744, 6019, 6250)
DE: 2194 Instruments and techniques
DE: 5417 Gravitational fields (1221)
DE: 5450 Orbital and rotational dynamics (1221)
DE: 5770 Tidal forces
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting