Time Transfer by Laser Link - T2L2: An Opportunity to Calibrate RF Links

Abstract

The T2L2 instrument, The “Time Transfer by Laser Link” experiment T2L2 [1], under development at OCA (Observatoire de la Cote d’Azur) and CNES (Centre National d’Etudes Spatiales), France, has been successfully launched with the Jason-2 space vehicle on 20 June 2008 and switched on 5 days later. Besides the validation of the laser link time transfer scheme, T2L2 on Jason 2 has a whole panoply of science goals, including a possible contribution to the construction of international timescales such as TAI through the calibration of existing systems such as GNSS and TWSTFT, with an improvement of at least one order of magnitude as compared to the best calibrations performed so far (about 1 ns exactitude). It will further permit performing fundamental physics tests such as the measurement of a possible drift in the fine structure constant by comparing clocks of various atomic species over the Jason 2 mission lifetime. T2L2 will also permit precise characterization of the DORIS Ultra Stable Oscillator aboard Jason 2 and demonstrate for the first time in orbit one-way laser ranging. After a short reminder of principles and of foreseen and measured performances of the T2L2 experiment, we present the first preliminary in-orbit results, including space-to-ground and ground-to-ground time transfer. We then conclude with an overview of the future exploitation campaigns, such as the comparison of different Cs fountains of the Observatoire de Paris, including the mobile fountain FOM and the French transportable laser station.