Professor Douglas Currie (University of Maryland, NASA Lunar Science Institute, Istituto Nazionale di Fisica Nucleare Laboratori), Dr. Simone DellAgnello (Istituto Nazionale di Fisica Nucleare Laboratori, Nazionali di Frascati), Dr. Giovanni Delle Monache (Istituto Nazionale di Fisica Nucleare Laboratori)
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Abstract:
Over the past forty years, Lunar Laser Ranging (LLR) to the Apollo Cube Corner (CCR) Retroreflector arrays has supplied almost all of the significant tests of General Relativity. The LLR program has evaluated the PPN parameters and addressed, for example, the possible change in the gravitational constant and the properties of the self-energy of the gravitational field. In addition, LLR has provided significant information on the composition and origin of the moon. These arrays are the only experiment of the Apollo program that are still in operation. Initially the Apollo Lunar Arrays contributed a negligible portion of the error budget used to achieve these results. Over the decades, the performance of ground stations has greatly upgraded so that the ranging accuracy has improved by more than two orders of magnitude, i.e., a factor of 140. Now, after forty years, because of the lunar librations the existing Apollo retroreflector arrays contribute significant fraction of the limiting errors in the range measurements. The University of Maryland, as the Principal Investigator for the original Apollo arrays, is now proposing a new approach to the Lunar Laser CCR array technology. The investigation of this new technology, with Professor Currie as Principal Investigator, is currently being supported by two NASA programs and, in part, also by INFN/LNF. Thus after the proposed installation on the next Lunar landing, the new arrays will support ranging observations that are a factor 100 more accurate than the current Apollo LLRRAs, from the centimeter level to the micron level. The new fundamental physics and the lunar physics that this new LLRRA can provide will be described. In the design of the new array, there are three major challenges: 1) Validate that the specifications of the CCR required for the new array, with are significantly beyond the properties of current CCRs, can indeed be achieved. 2) Address the thermal and optical effects of the absorption of solar radiation within the CCR, reduce the transfer of heat from the hot housing to the CCR and 3) Define a method of emplacing the CCR package on the lunar surface such that the relation between the optical center of the array and the center of mass of the moon remains stable over the lunar day/night cycle. The design approach, the computer simulations using Thermal Desktop, Code V and locally developed IDL software, and the results of the thermal vacuum testing conducted at the INFN/LNF’s SCF facility at Frascati, Italy of the new array will also be presented. For example, the new lunar CCR housing has been built at INFN/LNF. The innovations in the LLRRA-21 with respect to the Apollo LLRR Arrays and current satellite retroreflector packages will be described. The new requirements for ground stations will be briefly addressed. This new concept for the LLRRA-21 is being considered for the NASA Manned Lunar Landings, for the NASA Anchor Nodes for the International Lunar Network and for the proposed Italian Space Agency’s MAGIA lunar orbiter mission.
Date of Conference: September 1-4. 2009
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