High-Precision Lunar Laser Ranging Achieves Millimeter Accuracy

This paper details the metrology and covariance layer for high-power amplitude-modulated continuous-wave (AM-CW) Lunar Laser Ranging (LLR). It addresses limitations of current pulsed systems by focusing on RF-envelope phase observables, multi-tone ambiguity removal, range and range-rate estimators, and observation-level covariances. The analysis indicates that a dedicated station can plausibly reach 0.08 mm absolute range precision under favorable conditions. Differential LLR between nearby lunar reflectors can suppress common-mode station and atmospheric terms, but not independent photon noise. Robust design bands are projected to be ~45-90 um for the dedicated AM-CW case and ~35-60 um in photon-rich excellent-seeing operation. The study outlines requirements on link SNR, Doppler derotation, detector mode, instrument PSD/Allan stability, oscillator slew, multi-tone nonlinearity, and differential CONOPS. This advancement promises to enhance tests of relativistic gravity and provide more detailed insights into the lunar interior. The technology's success hinges on overcoming atmospheric variability and instrumental limitations, which could impact the achievable precision in real-world applications.

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