Calibrating the Apache Point Observatory Lunar Laser-ranging Operation (APOLLO) Apparatus
Lunar laser ranging has long provided precision tests of gravitational effects including, but not limited to, the strong equivalence principle (SEP), geodetic precession, secular evolution of the gravitational constant, gravitomagentism, and the inverse square law. The most recent ranging station, the Apache Point Lunar Laser-ranging Operation (APOLLO), achieves median lunar
range precision to the ∼ 2 mm level. However, the best model residuals (observed - predicted) are an order of magnitude larger than that, throwing into question whether APOLLO has gross systematic inaccuracies in its data collection, or the models are incomplete in some manner. The recent addition of an Absolute Calibration System (ACS), consisting of a high-repetition-rate, low jitter calibration laser slaved to a cesium clock, allows for independent assessment of APOLLO system accuracy and the ability to correct ranging data in-situ by delivering “truth” photons to the APOLLO detector at well-known time intervals. Initial ACS analysis suggested APOLLO is accurate to the ∼ 2 − 3 mm level, pushing primary suspicion of model residuals onto the models themselves. Further study, presented in the later chapters of this dissertation, has corroborated this story. A newer and more robust method of correcting those data runs containing ACS information has been developed, demonstrating the ability to remove range bias without significantly affecting the uncertainty of the range result. Additionally, this correction method has been extended to permit bias corrections to data runs without ACS information present, based on trends in ACS corrections overall and on a per-observation-night basis, given the presence of similar scale (∼ 2 − 3 mm) variations in range bias over the course of a year.