System

The purpose of the T2L2 system is to interconnect an instrument in orbit and a worldwide network of laser stations to deliver data to the scientific community enabling scientific progress in time-frequency, laser telemetry and basic physics domains. To fulfil these objectives, T2L2 system is made up of four main elements:

• The onboard segment, including the instrument, the DORIS USO and the LRA retro-reflector.
  This is the element which time-tags pulses of light as they arrive on board and reflects them back to the laser stations.

• The operations ground segment, which controls the instrument (by sending commands and monitoring operational telemetry data), receives the scientific telemetry data and provides Level 1 processing (data formatting).

• The scientific ground segment, which request and collect data from the laser stations and undertakes more detailed processing, particularly by calculating triplets.

• The optical link budget, a method of guaranteeing the link between the laser stations and the onboard segment.

Architecture of the T2L2 system