1 Introduction

In 1969, during the Apollo XI mission, the astronauts placed on the Moon the first corner cube array permitting to measure the Earth-Moon distance with the laser ranging technique. As early as in 1970, some Earth-Moon distances have been obtained with a precision in the 25 cm range at the McDonald laser station (Texas). Four other retroreflector arrays have been placed during the following Apollo XIV and XV, and Lunakhod 1 and 2 missions Faller 1972); (Chang et al. 1972); (Fournet 1972). McDonald was the only laser station ranging to the Moon on a routine basis for many years starting from 1970. In France, some lunar echoes were obtained at Pic du Midi Observatory in 1970. In 1984, two additional laser stations were built, one in Hawaii, the other in France, whereas the McDonald station came to a stop and was replaced by a smaller one. The French station, located at the Observatoire de la Côte d'Azur (OCA), is dedicated to Earth-Moon measurements. Its precision, in the 15 cm range at the beginning, reached the centimetre level in 1987 (Veillet 1987); (Veillet et al. 1993). The principle of Lunar Laser Ranging (LLR) is based on time propagation measurements of a light pulse between the Earth and the Moon. The start time of a laser pulse sent in the direction of the Moon is measured. A lunar retroreflector returns a fraction of the incident photons to the telescope and the return time is measured. The time interval between the start and return times permits to deduce the distance between the telescope and the retroreflector array, if the propagation velocity of the light pulses is known. In 1992, a millimetric Lunar Laser Ranging project started at OCA. This program aimed to improve both precision and accuracy of the OCA Lunar ranging station by one order of magnitude. Since 1995, observational results have been obtained with these "millimetric'' performances (Samain 1995). After a brief review of the (LLR) scientific applications, we present the instrumental configuration of the station, the complete error budget and the current precision, and accuracy limitations.