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.