Characteristics of differential lunar laser ranging

Abstract

Context. To obtain more details about the lunar interior, a station at Table Mountain Observatory of JPL will enable a new measurement of lunar laser ranging (LLR), known as differential lunar laser ranging (DLLR). It will provide a novel type of observable, namely, the lunar range difference, which is the difference of two consecutive ranges obtained via a single station swiftly switching between two or more lunar reflectors. This previously unavailable observation will have a very high level of accuracy (about 30 µm), mainly resulting from a reduction in the Earth's atmospheric error. In addition to the intended improvements for the lunar part, it is expected to contribute to improved relativity tests, for instance, the equivalence principle (EP). Aims. This paper focuses on the simulation and investigation of the characteristics of DLLR. Methods. Using simulated DLLR data, we analyzed and compared the parameter sensitivity, correlation, and accuracy obtained by DLLR with those attained by LLR. Results. The DLLR measurement maintains almost the same sensitivity to certain parameters (called group A) as that of LLR, such as the lunar orientation parameters. For other parameters (called group B), such as station coordinates, it is shown to be less sensitive. However, owing to its extraordinary measurement accuracy, it not only retains nearly the same level of accuracy of group B as LLR, but it also improves the estimation of group A significantly (with the exception of reflector coordinates, due to the DLLR measuring mode). Also, DLLR increases the correlations among the reflectors and between stations and reflectors caused by its constellation. Additionally, we compared different switching intervals with respect to sensitivity and correlation. Large switching intervals are more beneficial for group B and the decorrelation of stations and reflectors. Furthermore, DLLR enhances the accuracy of EP tests.

Advantages of combining Lunar Laser Ranging and Differential Lunar Laser Ranging

“…The observatories are the McDonald Laser Ranging Station (MLRS) conducting LLR at three stations (denoted as McDonald, MLRS1 and MLRS2), which are very close to each other (Hofmann 2017), the Lunar Ranging Experiment Observatory (LURE; Müller et al 2019), the Apache Point Observatory Lunar Laser ranging Operation (APOLLO; Murphy et al 2008), the Observatoire de la Côte d'Azur (OCA; Courde et al 2017), the Wettzell Laser Ranging System (WLRS; Schreiber et al 2019) and the Matera Laser Ranging Observatory (MLRO; Dequal et al 2021). More details on the real LLR data, for instance, the data accuracy, can be found in Zhang et al (2022). The simulated LLR data (Zhang 2023) were generated by a simulation program (Hofmann 2017) as one component of the LUNAR software, using the range model of Eq.…”

“…After a short time interval, another range, ρ ref2 , to the second reflector is measured by the same station. Thus, DLLR data were simulated by the difference ∆ρ of the ranges (based on the range model used in LUNAR) to the two reflectors with white noise ε added (Zhang et al 2022):…”

“…By using the same long data time span (more than 50 yr) as LLR, the parameters related to the lunar orientation, rotation, and interior have been investigated using the simulated DLLR data from our previous research (Zhang et al 2022). It has been shown that their estimated accuracies can really be improved largely, by about two orders of magnitude, if DLLR can indeed reach the high observation accuracy that is expected for it.…”

“…It has been shown that their estimated accuracies can really be improved largely, by about two orders of magnitude, if DLLR can indeed reach the high observation accuracy that is expected for it. Furthermore, using highly accurate DLLR data in Zhang et al (2022), the lunar orbit can be determined at a similarly good level as via LLR.…”