[S-GD01] Geodesy and Global Geodetic Observing System

[SGD01-11] Next Generation Lunar Retroreflector: Design, Fabrication and Special Requirements for Lunar Laser Ranging Observatories

★Invited Papers

*Douglas G Currie¹, Dennis Wellnitz¹, James Williams², Chensheng Wu^1,4, William Kleyman ¹, Laila Wise¹, Giovanni Delle Monache³, Simone Dell'Agnello ³ (1.University of Maryland, College Park, MD, USA, 2.Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA, 3.INFN-National Laboratory of Frascati, Frascati, Italy, 4.KBR, Inc., Greenbelt, MD, USA)

Keywords:Lunar, Laser, Ranging, NGLR, Astrophysics , Cosmology

For more than five decades Earth-based Lunar Laser Ranging Observatories (LLROs) have been performing ~daily laser range measurements to the Apollo Retroreflector Arrays (ARAs) that were deployed during the Apollo 11, 14 and 15 missions. The analysis of this archive of highly accurate range data by the Jet Propulsion Laboratory has produced many of the most accurate scientific results in lunar physics, astrophysics, cosmology and for tests of General Relativity. However, the combination of our use of an array of small Cube Corner Retroreflectors (CCRs) for the ARAs and the lunar optical librations have imposed a fundamental limit to the accuracy of a range measurement at the level of ~75 mm. A range normal point is made up of individual Single Range Measurements (SMRs). The SMRs scatter due to laser pulse width, timing uncertainty, and calibration at the ranging station plus scatter when bouncing off of a retroreflecting array on the Moon. New retroreflecting corner cubes greatly improve the latter. To address this, our Next Generation Lunar Retroreflector (NGLR) Project began in 2004 when NASA announced programs to return to the Moon. The NGLRs will support improved accuracy of a range measurement at the sub-millimeter level. This will be an improvement by a factor ~100 with respect to the current range measurement accuracy obtained by ranging to the ARAs and the Lunokhod retroreflector arrays deployed by the Soviet Union. The history and details of the design of our NGLRs will be described. In particular, the thermal changes are a particular challenge. With temperature of the housing more than 100 K above the temperature of the CCR, gradients in the CCR must be kept to below a few tenths of a degree Kelvin. Our approach to meeting these challenges, especially the Solar/Orbital/Optical/Thermal/Optical (SOOTO) suite of thermal simulation programs, will be described. The current status of the fabrication and the details of the deployment on the Blue Ghost Lanar lander built by Firefly Aerospace under the Commercial Lunar Payloads Service (CLPS) will be presented. However, the fundamental data for our Lunar Laser Ranging/NGLR (LLR/NGLR) project are the laser range measurements to be made by the Earth-based LLROs. We are working with four international LLROs, located in the US, France, Germany and Italy to perform the ranging to the NGLRs. Due to the greatly increased accuracy of the range measurement and various polarization effects, there are significant new requirements for ranging to the NGLRs. These requirements will require special modifications with respect to procedures and data processing methods currently being used by these LLROs for performing range measurements to the Apollos Retroreflector Arrays. There are also unique aspects of ranging to the NGLRs that may allow other Satellite Laser Ranging (SLR) stations that have not been involved in our LLR program to become contributors. These will be described and the reasons for these requirements considered.