Recent improvements to reference frames from Lunar Laser Ranging data analysis

Abstract

Lunar Laser Ranging (LLR) has been measuring the distance between the Earth and the Moon since 1969. Until the end of 2021, more than 29000 normal points (NPs) are included in our analysis. The LLR analysis procedure is an iteration of the calculation of ephemeris of the solar system followed by the estimation of parameters. The initial orbit of the Moon (Euler angles and angular velocity of the lunar mantle, Euler angles of the lunar core, and the position and the velocity of the selenocenter), amongst many other parameters, is estimated in a standard solution. In our previous standard calculation, the initial orbit of the Moon was estimated for June 28, 1969 and ephemeris was calculated from this time until June 2022. Now, we estimate the initial orbit of the Moon for Jan 1, 2000 to be able to benefit from the higher accuracy of the NPs in the last decade; calculating ephemeris in the forward direction until June 2022 and backwards until June 1969. When comparing the uncertainty obtained from a least-squares adjustment of this study with the previous standard calculation, preliminary results show an improvement of over 50% in the initial position and the initial velocity of the Moon, a deterioration of about 20% in the Euler angles of the mantle and the core, and an improvement of over 15% in the angular velocity of the mantle. Using the new ephemeris, we estimate the benefit of the new highly accurate LLR NPs for the determination of the Earth rotation parameters (terrestrial pole offsets, xp and yp, and Earth rotation phase, deltaUT1). Recent results show the uncertainty of deltaUT1 staying less than 20 µs (to be used for verifying VLBI results independently), less than 2.5 mas for xp, and less than 3 mas for yp for nights selected when at least 15 NPs were observed. Recent results will be presented and major changes would be discussed.