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.