Sensitivity of Simulated LRO Tracking Data to the Lunar Gravity Field

The Lunar Reconnaissance Orbiter (LRO) is the first spacecraft in interplanetary space routinely tracked with 1-way optical laser ranges. Therefore, the mission is a suitable testbed to investigate the potential of laser ranging for precise orbit determination and lunar gravity field recovery compared to radiometric observations. As a first step, we simulated laser ranges and range-rates from various ground stations to LRO. The synthetic data were used to retrieve the satellite orbit. Further, we estimated three sets of spherical harmonic coefficients representing the lunar gravity field: one set based on laser ranges, one set based on range-rates, and one set based on laser ranges and range-rates. We found laser ranging to be capable of recovering the coefficients up to degree and order ≈ 12 without applying regularization. From a joint inversion we conclude that laser ranges only slightly improve the findings obtained from range-rates. Preliminary real data results based on twelve days of laser ranging observations show a range residual root mean square (RMS) value of 2.3 m. The RMS value in total position between our solution and a published LRO orbit derived from radiometric data and altimetric crossovers is about 550 m.