  This document describes the uplink commanding system for the ESA Gaia
mission. The need for commanding, the main actors, data flow and systems
involved are described. The system architecture is explained in detail,
including the different levels of configuration control, software systems and
data models. A particular subsystem, the automatic interpreter of
human-readable onboard activity templates, is also carefully described. Many
lessons have been learned during the commissioning and are also reported,
because they could be useful for future space survey missions.
