Thermal-vacuum optical characterization of next-generation lunar laser retroreflectors

The SCF_Lab (Satellite/lunar/GNSS laser ranging/altimetry and Cube/microsat Characterization Facilities Laboratory) is a brand new ISO 7 Clean Room, dedicated to design, characterization and modelling of the space segment of Satellite Laser Ranging (SLR), Lunar Laser Ranging (LLR) and Planetary Laser Ranging and Altimetry (PLRA) for industrial and scientific applications. The role of SCF_Lab is fundamental to study and characterize cube corner retroreflectors (CCRs) necessary for laser ranging. CCRs are special “mirrors” that reflect light in the same direction it came from as it was a normal flat mirror but always orthogonal to the beam no matter where the beam actually came from. It happens thanks to a triple rebound of photons, over the three faces of the corner. In SCF_Lab, thanks to an innovative thermal-vacuum-optical test (SCF-Test), we characterize and model the thermal behaviour and the optical performances of CCRs. The laboratory procedures are approved by the international organization that coordinates all laser ranging activities, the International Laser Ranging Service (ILRS). Our key experimental innovation is the concurrent measurement and modelling of the optical Far Field Diffraction Pattern (FFDP) and the temperature distribution of the SLR/LLR payload of retroreflectors under thermal conditions produced with a solar simulator. The primary target is to provide critical design and diagnostic capabilities for SLR to Galileo and other GNSS (Global Navigation Satellite System) constellations. New retroreflectors designs will be fundamental to improve GNSS orbits, increasing, this manner, accuracy, stability, and distribution of the International Terrestrial Reference Frame (ITRF), in order to provide a more precise definition of the geocenter (origin) and the scale (length unit). The SCF_Lab is also developing, validating and optimizing a next-generation LLR arrays for precision tests of GR with the MoonLIGHT-2 (Moon Laser Instrumentation for General relativity High-accuracy Tests - Phase 2) experiment.