Lunar Laser Ranging Retroreflectors: Velocity Aberration and Diffraction Pattern

The Lunar Laser Ranging (LLR) retroreflector arrays have been on the Moon for half a century. During that time, the laser range uncertainty has improved by a factor of 100. Consequently, the science results have also improved by orders of magnitude. New retroreflectors are scheduled to go to the Moon on Commercial Lander Payload Services missions and the Lunar Geophysical Network mission. The new retroreflectors are single 10 cm corner cube retroreflectors that will not spread the laser pulse during reflection like the existing arrays do. Due to the orbital and Earth rotational speeds, there is a velocity aberration of 0.'' 8-1.'' 5 for existing stations. Larger corner cubes require attention to ensure that the spread of possible velocity aberration displacements is optimally contained within the diffraction pattern. The diffraction pattern can be changed by making one or more of the rear dihedral angles slightly different from 90 degrees. Improvements in the equipment at the LLR stations and improvements in the data analysis software are also desirable. Future possibilities are described.

Automated summary

The Lunar Laser Ranging (LLR) retroreflector arrays have been on the Moon for 50 years, with improved laser range uncertainty and science results. New retroreflectors are planned to be sent to the Moon, which are single 10 cm corner cube retroreflectors without laser pulse spreading during reflection. Attention is needed for larger corner cubes to ensure optimal containment of velocity aberration displacements within the diffraction pattern. Improvements in equipment and software are desirable, and future possibilities are described.