A paper describes how, based on a structural-thermal-optical-performance analysis, it has been determined that a single, large, hollow corner cube (170-mm outer diameter) with custom dihedral angles offers a return signal comparable to the Apollo 11 and 14 solid-corner-cube arrays (each consisting of 100 small, solid corner cubes), with negligible pulse spread and much lower mass. The design of the corner cube, and its surrounding mounting and casing, is driven by the thermal environment on the lunar surface, which is subject to significant temperature variations (in the range between 70 and 390 K). Therefore, the corner cube is enclosed in an insulated container open at one end; a narrow-bandpass solar filter is used to reduce the solar energy that enters the open end during the lunar day, achieving a nearly uniform temperature inside the container. Also, the materials and adhesive techniques that will be used for this corner-cube reflector must have appropriate thermal and mechanical characteristics (e.g., silica or beryllium for the cube and aluminum for the casing) to further reduce the impact of the thermal environment on the instrument’s performance.
The instrument would consist of a single, open corner cube protected by a separate solar filter, and mounted in a cylindrical or spherical case. A major goal in the design of a new lunar ranging system is a measurement accuracy improvement to better than 1 mm by reducing the pulse spread due to orientation. While achieving this goal, it was desired to keep the intensity of the return beam at least as bright as the Apollo 100-corner-cube arrays. These goals are met in this design by increasing the optical aperture of a single corner cube to approximately 170 mm outer diameter. This use of an “open” corner cube allows the selection of corner cube materials to be based primarily on thermal considerations, with no requirements on optical transparency. Such a corner cube also allows for easier pointing requirements, because there is no dependence on total internal reflection, which can fail off-axis.
This work was done by Slava G. Turyshev, William M. Folkner, Gary M. Gutt, James G. Williams, Ruwan P. Somawardhana, and Richard T. Baran of Caltech for NASA’s Jet Propulsion Laboratory. NPO-47489
This Brief includes a Technical Support Package (TSP).
Corner-Cube Retroreflector Instrument for Advanced Lunar Laser Ranging
(reference NPO-47489) is currently available for download from the TSP library.
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Overview
The document is a Technical Support Package for the Corner-Cube Retroreflector Instrument used in the Advanced Lunar Laser Ranging Experiment, developed by NASA's Jet Propulsion Laboratory (JPL). It serves as a comprehensive resource detailing the advancements and applications of lunar laser ranging technology, which has its roots in the Apollo program.
The Apollo missions, particularly Apollo 11 and Apollo 14, deployed retroreflectors on the lunar surface, enabling precise measurements of the distance between the Earth and the Moon. This technology marked a significant shift from analyzing lunar position angles to measuring ranges, establishing a foundation for ongoing lunar research. The document emphasizes that Lunar Laser Ranging (LLR) is the only continuing experiment from the Apollo era, showcasing its enduring relevance in space science.
The Advanced Lunar Laser Ranging Experiment, which achieved its first light on July 24, 2005, aims to enhance the accuracy of distance measurements to the Moon. This experiment utilizes advanced technology to improve the precision of LLR, which has applications in various fields, including geodesy, fundamental physics, and tests of general relativity.
The document also outlines the technical specifications and operational details of the Corner-Cube Retroreflector, which is a critical component of the LLR system. The retroreflector's design allows it to reflect laser beams sent from Earth back to their source, facilitating accurate distance measurements. The information provided is intended to support researchers and engineers involved in lunar exploration and related technological developments.
Additionally, the document includes contact information for further inquiries and assistance related to the research and technology discussed. It highlights NASA's commitment to sharing knowledge and fostering innovation through its Commercial Technology Program, which aims to make aerospace-related developments accessible for broader scientific and commercial applications.
In summary, this Technical Support Package serves as a vital resource for understanding the advancements in lunar laser ranging technology, its historical significance from the Apollo missions, and its ongoing contributions to space science and technology.
