Three looks at Gaia data volumes

In this paper we discuss a few aspects of the data volume to be generated by the ESA space astrometry mission Gaia. This volume is assessed first from the on-board point of view in the form of the instantaneous number of sources in the combined astrometric fields of view as a function of time. Then one focuses on the data flow for the data processing itself measured by the number of objects entering the pipeline every day. Finally the combination of the on-board acquisition scheme with the number of stars per day gives the actual telemetry volume to be transferred to the ground and its variation during the mission.