Lunar Laser Ranging at the University of Texas at Austin

University Of Texas At Austin, Austin TX

Investigators

Abstract

AST-0204127 Shelus The Lunar Laser Ranging (LLR) experiment accurately measures the round-trip travel time for a laser pulse that is emitted from an observing station on the Earth and returns after bouncing off of a retroreflector array on the surface of the Moon. Such observations have been made at McDonald Observatory for more than 30 years. The data provide for varied, multi-disciplinary and inter-disciplinary science results in areas of solid Earth sciences, geodesy and geodynamics, solar system ephemerides, terrestrial and celestial reference frames, lunar physics, general relativity and gravitational physics. Standing alone or combined with data from other observing techniques, LLR expands the understanding of the precession of the Earth.s spin axis, the lunar nutation, Earth orientatation, the Earth.s obliquity to the ecliptic, the intersection of the celestial equator and the ecliptic, lunar and solar solid body tides, lunar tidal deceleration, lunar physical and free librations, the structure of the moon and energy dissipation in the lunar interior. LLR provides input into lunar surface cartography and surveying and helps determine Earth station and lunar surface retroreflector locations and motions, mass of the Earth-Moon system, lunar and terrestrial gravity harmonics and Love numbers, relativistic geodesic precession, and the equivalence principle of general relativity. Due to the passive nature of the reflectors and the improvement of observing equipment and data analysis capabilities with time, LLR data will continue to provide for improved results. Gains are steady and, as the data base expands, we are striving to learn even more by applying more clever observation strategies. Under this proposal, we continue the LLR observational effort at the McDonald Laser Ranging Station (MLRS). With routine single-person operation and a 24 hour/day, 7 day/week schedule, lunar coverage will be substantial in the years to come, as we share the use of the MLRS with artificial satellite laser ranging (SLR) efforts. We are cooperating with other observing efforts around the world, especially the French LLR/SLR station in the south of France. In addition to the observations, an analysis effort with world-wide communication, cooperation, and coordination will be ongoing here at the University of Texas at Austin. We cooperate with analysis efforts at the Jet Propulsion Laboratory, the Massachusetts Institute of Technology, the Paris Observatory, and the BKG in Frankfurt and Munich. Also, the University of Texas McDonald Observatory, since the inception of the International Laser Ranging Service (ILRS) in 1998, houses the ILRS LLR Operations and Analysis Center. The small size of the LLR observing network, and the relatively small number of LLR analysis centers, dictate the unique nature and operational procedures of this LLR Operations/Analysis Center. The responsibility of the LLR Operations Center has evolved to be one that assures the smooth flow of data through the LLR network, in a form and format that is useful for obtaining scientific results. The center also coordinates the observations and their scheduling in a manner to maximum the scientific gains. Predicts are coordinated on-site at each LLR station and the data are automatically transferred from all observing sites to the ILRS data centers. LLR data analysts can secure their data directly from the data centers as needed. Feed-back from these analysts often goes directly back to the individual observing stations. Under the auspices of this National Science Foundation Grant, we are looking forward to additional years of successful LLR observation and analysis, resulting in the steady and rapid expansion of scientific results. ***