July 22, 2016


The T2L2 experiment is being developed by CNES in collaboration with the GeoAzur laboratory of the Observatoire de la Côte d'Azur (OCA), with Etienne Samain as Principal Investigator.

Development phase:

CNES is prime contractor for both the system and the instrument. OCA is not only playing a strictly scientific role but is also helping to design the instrument, as the metrology and time-tagging functions are inspired by prototypes developed by OCA.

Three manufacturers were chosen to produce the flight model under CNES supervision:

  • Erems was responsible for the electronics subsystem, producing the detection and time-tagging functions, designing and producing the instrument's management and power functions and then supervising qualification and validation of the Electronics Unit.
  • Seso produced the optical component and supervised qualification of the optics units assembly incorporated in the interface deck.
  • The BTS / Coriolis group was entrusted with the design and validation of the Active Thermal Control sub-system fitted to the optics units.

After it had been qualified and undergone metrology calibration tests and precise characterization, the instrument was delivered to Thalès Alenia Space for integration in the Jason-2 satellite.

Exploitation phase:

The T2L2 experiment will be jointly exploited by CNES and the participating scientists and particularly the Principal Investigator, through a T2L2 work group.

CNES ensures the operational exploitation of the instrument, i.e. the monitoring of its functioning in orbit, telecommand upload and telemetry collection, processing, and distribution.

The Observatoire de la Côte d’Azur develops and operates the scientific processing enabling to go from raw data to a real time in picosecond, to gather and sort the data supplied by the instrument and those delivered by the laser ground stations, and to compute the time transfers between the onboard clock and the ground clocks.

The T2L2 work group publicizes, organizes and coordinates scientific activities based on the T2L2 mission.
It is chaired by the Principal Investigator of the T2L2 mission. It includes a mission manager who represents CNES and liaises between the T2L2 working group and the operational ground segment.
The T2L2 working group is structured around five themes:

  • Ground stations and the ILRS, to organize and provide technical assistance to participating laser-ranging stations (from ensuring that they meet T2L2 standards to programming passes) and also managing the use of portable laser stations.
  • Scientific Mission Centre (CMS), concerning all issues related to the instrument's in-orbit commissioning, monitoring and exploitation, covering everything from updating the calibration tables and processing the onboard time-tagging data to expert assessment of any anomalies.
  • T2L2 time transfer validation, for developing the time transfer products (defining the processing algorithms, taking account of atmospheric and relativistic effects, etc.) and organizing their distribution.
  • Microwave transfer and time scales, for organizing activities concerning the use of T2L2 time transfer, comparison of primary frequency standard, timescales and the calibration of GPS / TWSTFT links.
  • DORIS, dealing with the in-flight characterization of the DORIS USO.