The european laser timing (ELT) experiment on-board ACES

The development of techniques for the comparison of distant clocks and for the distribution of stable and accurate time scales has important applications in metrology and fundamental physics studies. Additionally, the rapid progress of frequency standards in the optical domain is presently demanding additional efforts for improving the performances of existing time and frequency transfer links. Present clock comparison systems in the microwave domain are based on GPS and TWSTFT (Two-Way Satellite Time and Frequency Transfer). ELT (European Laser Timing) is an optical link presently under study in the frame of the ESA mission ldquoAtomic Clock Ensemble in Spacerdquo. The on-board hardware consists of a corner cube retro-reflector (CCR), a single-photon avalanche diode (SPAD), and an event timer board connected to the ACES time scale. Light pulses fired towards ACES by a laser ranging station will be detected by the SPAD diode and time tagged in the ACES time scale. At the same time, the CCR will re-direct the laser pulse towards the ground station providing precise ranging information. This paper will present the ELT scientific objectives, the recent studies performed on the ELT hardware, and the dedicated test campaign carried out at the Wettzell laser ranging station to demonstrate the experiment feasibility. Recent test results will be also discussed.