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Lunar University Network for Astrophysics Research Jack Burns, Director A LUNAR LASER RANGING RETRO-REFLECTOR ARRAY for the 21 st CENTURY Professor Douglas Currie University of Maryland, College Park, MD, USA NASA Lunar Science Institute, Moffett Field, CA INFN LNF, Laboratori Nazionali di Frascati, Italy & The LLRRA-21 Teams with the 1

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OUTLINE Outline of Talk Brief History of Lunar Laser Ranging Original Science Objectives of Our LLR Project Concept > Apollo 11, 14, 15 Improvement Kilometers -> 30 cm Not one by Time Series of Measurements Limiting Accuracy Continuing Science Due to 40 year Baseline Lunar Physics from Apollo Arrays Lunar Core Discovery Size and Shape Confirmed Other Relativity Physics from Apollo Arrays Inertial Properties of Gravitational Energy Temporal Change of G Spatial Change of G General Review Apollo Array Problem Due to Librations Ground Station Improvement Factor of 100 Illustration Decadal Remarks w.r.t. Lunar Laser Ranging Planetary - Astronomy Panel Discovery Mission Astronomical - LLRRA-21 Proposal New Interest in the Moon LLRRA-21 Concept Why is a Single CCR a Solution Design of LLRRA-21 Challenges Signal Performance Emplacement Issues Advantages Higher Accuracy More Stations Accuracies for Various Deployment Methods Lander Surface Anchored Expected Science Results Lunar Physics Relativity Science Possible Flight Opportunities Google Lunar X Prize Lunette ILN LGN Lunar Geophysical Network Discovery Mission Thank You & Acknowledgements NASA LSSO Lunar Science Institute > LUNAR Team at UC INFN-LNF 2

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To be done Simulation Results More pictures Find Charts of Accuracy Lunar with periods Relativity Statement about Heritage Science Technology 3American Geophysical Union 5 December 2011

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OUTLINE Brief History of Lunar Laser Ranging Lunar Physics from the Apollo Arrays Relativity Physics from the Apollo Arrays Apollo Array Problem Due to Librations Decadal Remarks w.r.t. Lunar Laser Ranging LLRRA-21 Proposal Accuracies for Various Robotic Deployment Methods Expected Science Results Possible Flight Opportunities Acknowledgements 4American Geophysical Union 5 December 2011

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Brief History of Lunar Laser Ranging Operational Procedure Transmit Narrow Laser Pulse from Earth Pulse is Reflected from a Fixed Point on the Moon Measure the Light Travel Time Analyze Time Series of Measurements for Frequencies Range Improvement due to Apollo LLR Kilometers (Radar) would go to ~300 mm Continue Measurements for Long Time Series Originally 3 Measurements per Day 5American Geophysical Union 5 December 2011

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Lunar Physics from the Apollo Arrays Discovery of Liquid Core Ten years Ago Confirmed This Year by Seismometer Properties of Liquid Core Size, Shape Moment of Inertia 6 American Geophysical Union 5 December 2011

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LLR LUNAR SCIENCE OVERVIEW Elastic Tides of the Moon Tidal Dissipation Size and Oblateness of Liquid Core Dissipation at Liquid-Core/Solid-Mantle Interface Lunar Moment of Inertia Fluid Core Moment of Inertia Evolution and Heating Existence of a Smaller Solid Inner Core Selenodetic Site Positions 7 American Geophysical Union 5 December 2011

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Relativity Physics from the Apollo Arrays Inertial Properties of Gravitational Energy Does Gravitational Energy Resist Acceleration Earth and Moon have Different Gravitational Energy Do They Fall to the Sun at the Same Rate? Measurement of Temporal Change in G Addresses Alternative MOND Theories of Gravitation Measurement of Spatial Change in G Fundamental Inconsistency of General Relativity and Quantum Mechanics 8American Geophysical Union 5 December 2011

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What have the Apollo Arrays Done Relativity Science The Earth-Moon System Provides an Ideal System To Evaluate Relativity and Einsteins Theory Moon is Massive enough to Resist Drag/Pressure Moon is Far Enough to be in a Solar Orbit (Weakly Bound) LLR Currently Provides our Tests of: The Weak Equivalence Principle (WEP)*: a / a < 1.3 10-13 The Strong Equivalence Principle (SEP): < 4 10 4 Time-Rate-of-Change of G to < 7 10 13 per year Inverse Square Law to 3 10 11 at 10 8 m scales Geodetic Precession to 0.6 % Gravitomagnetism to 0.1 % 9 American Geophysical Union 5 December 2011

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Apollo Array Problem Due to Librations Apollo Arrays Consisted of 100 CCR Arranged in a10 by 10 flat panel Accuracy of Ground Stations Improved by a Factor of 200 w.r.t. 1969 Lunar Librations Rotation of Moon w.r.t. Earth-Moon Axis +/- 8 degrees in Latitude and Longitude We Cannot Distinguish between Near & Far CCRs A Very Short Laser Pulse is Spread Return Pulse is ~20 mm Therefore Limiting Accuracy 10American Geophysical Union 5 December 2011

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Decadal Remarks w.r.t. Lunar Laser Ranging 2010 Planetary Decadal Survey Recommended NGL as Discovery Mission Including Lunar Laser Retroreflectors Astro2010 Gravitational and Astrophysics Panel Specifically Recommended LLRs improvements in Lunar Laser Ranging promise to advance this area G (< 10 -12 /yr) from lunar laser ranging So far, LLR has provided the most accurate tests of the weak equivalence principle, the strong equivalence principle and the constancy in time of Newtons gravitational constant recommendation below in the context of a recommendation to augment the Explorer program 11American Geophysical Union 5 December 2011

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LLRRA-21 Proposal NASA Revives Interest in Moon 2006 LSSO Proposal for Improved Lunar Retroreflector Lunar Laser Ranging Retroreflector Array for the 21 st Century Large Single Solid Cube Corner Reflector Accuracy to be Improved by Factor of 10 to 100 Great Reduction in Weight w.r.t. Apollo Arrays No Power or Communication Required Very Long Operational Lifetime - Centuries Great Heritage to Assure Risk Reduction Same Design on the Moon has Provided Excellent Science for 40 years Thousands of Smaller Solid CCRs Operating in Earth Orbit for over 40 years 12American Geophysical Union 5 December 2011

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Why Consider a Single CCR No Spreading of Laser Return Pulse 20 mm Uncertainty due to Librations Goes to ~0 Larger Return Signal Level Similar to Apollo 15 Available to More Laser Ranging Ground Stations 13

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CHALLENGES for SOLID CCR Fabrication of the CCR to Required Tolerances Sufficient Return for Reasonable Operation Ideal Case for Link Equation Thermal Distortion of Optical Performance Absorption of Solar Radiation within the CCR Mount Conductance - Between Housing and CCR Tab Pocket Radiation - IR Heat Exchange with Housing Solar Breakthrough - Due to Failure of TIR Stability of Lunar Surface Emplacement Problem of Regolith Heating and Expansion Drilling to Stable Layer for CCR Support Thermal Blanket to Isolate Support Housing Design to Minimize Thermal Expansion 14 LUNAR Workshop 6 October 2010

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Thermal Simulation Results 154th Allahabad Science Conclave 28 November 2011

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164th Allahabad Science Conclave 28 November 2011

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ROBOTIC DEPLOYMENT Alterative Deployment Methods Lander Mounting Few Millimeters Motion Due to Thermal Cycling Thermal Expansion of Lander during Lunation Surface Deployment Sub-Millimeter Motion Due to Thermal Cycling Regolith Expansion Requires an Arm Anchored Deployment Tens of Microns 17 American Geophysical Union 5 December 2011

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Regolith Drilling in Apollo 18

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Kriz Zacny at HoneyBee 19American Geophysical Union 5 December 2011

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CURRENT STATUS Preliminary Definition of Overall Package Completed Preliminary Simulations LSSO Lunar Science Surface Opportunities Thermal (CCR, Regolith, Housing), Optical Completed Phase I Thermal Vacuum Tests Solar Absorption Effects on CCR CCR Time Constants IR Camera Front Face Thermocouples Volume Preliminary Optical FFDP 20

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LLRRA-21 PACKAGE 21American Geophysical Union 5 December 2011

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LUNAR Science Fluid Core Moment of Inertia LLR Detection of Liquid Inner Core has very Recently been Confirmed by Seismometry Whole Moon Moment of Inertia Core Oblateness: LLR detects fluid-core/solid-mantle boundary (CMB) Inner Core: A solid inner core apparently exists and can be confirmed by LLRRA-21 Elastic Tides: Solid-body tidal displacements depend on the Moons elastic properties. Typical monthly variations are 9 cm. Lunar Tidal Dissipation: The tidal specific dissipation Q depends on the radial distribution of the material Qs. Core/Mantle Boundary Dissipation: LLR first demonstrated that the Moon has a fluid core by Free Physical Librations Selenodetic Site Positions: The Moon-centered locations of four retroreflectors are known with submeter accuracy Tidal Acceleration and Orbit Evolution: LLR is very sensitive to the tidal acceleration of the lunar orbit. 22

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Detailed Lunar Science Results 1 Fluid Core Moment of Inertia: LLR is sensitive to the fluid core moment of inertia, which depends on core density and radius. This is a new LLR lunar science result for the core. The solution for the ratio of fluid moment to total moment gives Cf/C = (124)x104, where the subscript f indicates the fluid core (Williams et al., 2009). For a uniform liquid iron core without an inner core this value would correspond to a radius of 39030 km. Lower fluid densities or presence of A Planetary Science Decadal Survey White Paper: Lunar Science and Lunar Laser Ranging Page 2 of 7 Retroreflector arrays on the Moon. an inner core would give larger outer radii for the fluid. Weakly determined at present, an accurate determination of core moment depends on a long time span of high accuracy range data. There is very little information on the core and it is very important to improve this determination. Whole Moon Moment of Inertia: The whole Moon moments of inertia A10 m) which implies active or geologically recent stimulation (Newhall and Williams, 1997; Chapront et al., 1999; Rambaux and Williams, 2009). The 2.9 yr longitude mode with an 11 m amplitude is stimulated, at least in part, by resonance passage (Eckhardt, 1993). The wobble mode, analogous to the Earths Chandler wobble, is a large elliptical (28x69 m) 74.6 yr motion of the pole direction. If wobble is stimulated by eddies at the CMB as suggested by Yoder (1981), then ongoing activity might be revealed by future LLR measurements as irregularities in the path of polar wobble. The third mantle mode, a free precession in space, and the liquid core free core nutations are small (