Abstract. The Lunar Laser Ranging station at the Observatoire de la Côte d'Azur, France, permits to measure the Earth-Moon distance with millimetric precision. Applications in astronomy, lunar science, geodesy, and gravitation are summarised. Expected scientific results with millimetric Lunar Laser Ranging data are presented. A complete error budget is given, showing that the precision is mainly limited by the orientation and the size of the corner cube arrays placed on the Moon. The measurement accuracy is degraded by the bad knowledge of the air index. The time stability, computed from the lunar echoes, permits to extract the real precision of the EarthMoon distance and to optimise the integration time of the normal points.

The Time Transfer by Laser Experiment (T2L2) on the Jason 2 satellite is a mission allowing remote clocks synchronization at the picosecond level. It is based on laser ranging technologies, with a laser station network on the ground and a dedicated instrument on board the satellite. It was launched in June 2008 and has been working continuously since then. T2L2 performances are very promising for time and frequency metrology and also for fundamental physics. The scientific objectives of the whole experiment rely on a rigorous uncertainty budget. This is governed by the characteristics of the space instrument and the laser stations network, the post treatment done on the ground, and also the process used to calibrate the laser stations. The uncertainty budget demonstrates that T2L2 is able to perform common-view time transfers between remote sites with an expanded uncertainty better than 140 ps (coverage factor = 2).

We present a direct comparison between two different techniques for the relative calibration of time transfer between remote time scales when using the signals transmitted by the Global Positioning System (GPS). Relative calibration estimates the delay of equipment or the delay of a time transfer link with respect to reference equipment. It is based on the circulation of some travelling GPS equipment between the stations in the network, against which the local equipment is measured. Two techniques can be considered: first a station calibration by the computation of the hardware delays of the local GPS equipment; second the computation of a global hardware delay offset for the time transfer between the reference points of two remote time scales. This last technique is called a ‘link’ calibration, with respect to the other one, which is a ‘receiver’ calibration. The two techniques require different measurements on site, which change the uncertainty budgets, and we discuss this and related issues. We report on one calibration campaign organized during Autumn 2013 between Observatoire de Paris (OP), Paris, France, Observatoire de la Côte d'Azur (OCA), Calern, France, and NERC Space Geodesy Facility (SGF), Herstmonceux, United Kingdom. The travelling equipment comprised two GPS receivers of different types, along with the required signal generator and distribution amplifier, and one time interval counter. We show the different ways to compute uncertainty budgets, leading to improvement factors of 1.2 to 1.5 on the hardware delay uncertainties when comparing the relative link calibration to the relative receiver calibration.

T2L2 (Time Transfer by Laser Link), developed by both CNES and OCA permits the synchronization of remote ultra stable clocks over intercontinental distances. The principle is derived from laser telemetry technology with dedicated space equipment deigned to record arrival time of laser pulses at the satellite. Using laser pulses instead of radio frequency signals, T2L2 permits to realize some links between distant clocks with a time stability of a few picoseconds and accuracy better than 100 ps. The T2L2 space instrument is in operation onboard the satellite Jason 2 since June 2008. Several campaigns were done to demonstrate both the ultimate time accuracy and time stability capabilities. It includes some experiments implemented in co-location to directly compare T2L2 time transfer residuals with the direct link between stations, and some ground to ground time transfer between ultra stable clocks. Important works have been done, between OCA and OP, to accurately compare T2L2 with microwave time transfer GPS and TWSTFT. These comparisons are based on laser station calibrations with a dedicated T2L2 calibration station designed to accurately set the optical reference of the laser station within the PPS reference of the microwave systems. Other experiments are also planned in the future: 3D localization with the lunar space vehicle LRO, T2L2 coverage extension over the Pacific Ocean (Tahiti), DORIS comparison and a third international campaign.