Lunar laser ranging (LLR) has made major contributions to our understandingof the Moon's internal structure and the dynamics of the Earth-Moon system.Because of the recent improvements of the ground-based laser rangingfacilities, the present LLR measurement accuracy is limited by theretro-reflectors currently on the lunar surface, which are arrays of smallcorner-cubes. Because of lunar librations, the surfaces of these arrays do not,in general, point directly at the Earth. This effect results in a spread ofarrival times, because each cube that comprises the retroreflector is at aslightly different distance from the Earth, leading to the reduced rangingaccuracy. Thus, a single, wide aperture corner-cube could have a clearadvantage. In addition, after nearly four decades of successful operations theretro-reflectors arrays currently on the Moon started to show performancedegradation; as a result, they yield still useful, but much weaker returnsignals. Thus, fresh and bright instruments on the lunar surface are needed tocontinue precision LLR measurements. We have developed a new retro-reflectordesign to enable advanced LLR operations. It is based on a single, hollowcorner cube with a large aperture for which preliminary thermal, mechanical,and optical design and analysis have been performed. The new instrument will beable to reach an Earth-Moon range precision of 1-mm in a single pulse whilebeing subjected to significant thermal variations present on the lunar surface,and will have low mass to allow robotic deployment. Here we report on ourdesign results and instrument development effort.
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