Time Transfer by Laser Link (T2L2) experiment on Mir

The experiment on Time Transfer by Laser Link (T2L2) under development at the OCA (Observatoire de la Cote d'Azur) and the CNES (Centre National d'Etudes Spatiales) will permit the synchronization of remote clocks. To perform a T2L2 time transfer, laser stations and a satellite are needed, all equipped with a clock and a time-tagging unit. We have the opportunity to put a T2L2 payload on the Russian space station Mir in 1999. The T2L2 is based on the propagation of light pulses in space. It will make it possible to synchronize remote ground clocks, several thousand kilometres apart, with an uncertainty of about 100 ps, and to measure the performance of ground clocks having a relative frequency stability of about 3 × 10 -15 over the station visibility period (around 200 s). Accumulation of the data from several successive passages of Mir will allow a stability of about 3 × 10 -17 over ten days to be reached. The uncertainty budget of the T2L2 time transfer is analysed, and the on-board optical equipment that will allow us to achieve these time-transfer performances is presented.