The 1970–1984 lunar laser ranging observations in the Crimean Astrophysical Observatory

The Lunar Laser Ranging (LLR) has been the main method of study of the dynamics of the Sun-Earth-Moon system since 1969 to present. Lunar parts of the three modern high-precision ephemerides of the Solar system bodies are based solely on LLR measurements: DE (USA), EPM (Russia), INPOP (France). LLR measurements allow to determine parameters of lunar orbital and rotational motion, as well as some parameters related to terrestrial and lunar tides, and also fundamental relativistic parameters. Those parameters were determined from LLR with high accuracy by different authors. In USSR, LLR measurements were performed in the Crimean Astrophysical Observatory (CrAO) in Nauchny, on the 2.6 m Shajn’s Zenith telescope (ZTSh) with an automated laser ranging system developed by the Russian Lebedev Physical Institute (LPI). Within the time span of 1969–1984, 1400 measurements were obtained. Unlike LLR measurements done in other observatories, they were eventually forgotten and have not made their way into the dataset that is used by scientists worldwide to build lunar ephemerides and conduct other lunar research. The main reason for writing this paper was the discovery by Tryapitsyn, a researcher at the Katziveli station of CrAO, of old printouts containing the 1970–1984 LLR observations made with the ZTSh 2.6 m telescope. Some details were missing from the printouts, which required careful restoration work. In this paper the history of those LLR observations with surrounding historical events is presented, and some details of the analysis these observations are described. Of particular interest is the finding related to the three normal points of Lunokhod-1 ranges obtained in 1974 that allowed Odile Calame to determine the rover’s position with a few kilometers accuracy. Unfortunately, the accuracy was not sufficient for other researchers to confirm and pin down the location of the rover.