The most important and biggest input is the telemetry data from the Gaia satellite. Originating from the spacecraft, they enter the data processing after several transmission and transformation steps: through the spacecraft-to-Earth telemetry link, the three ESA ground station antennas at Cebreros (Spain), New Norcia (Australia) and Malargüe (Argentina) to the Mission Operations Centre (MOC) at ESOC, Darmstadt (Germany), into the Telemetry Archive at the Science Operations Centre (SOC) at ESAC, Villafranca (Spain) and into the DPAC’s live pre-processing database via the DPAC’s MOC–SOC Interface Task (MIT) software.
The telemetry consists of housekeeping and science data. The former contains a variety of on-board status information, subsystem working logs, etc., including the autonomous on-board attitude determination results. The housekeeping data is not described further in the present chapter, although it enters the processing in many critical ways.
The science telemetry data are described in Section 2.2.2. Section 2.2.3 explains the usage of
the Attitude Star Catalogue (ASC) for the continual on-ground attitude reconstruction.