  CoRoT is a space telescope dedicated to stellar seismology and the search for
extrasolar planets. The mission is led by CNES in association with French
laboratories and has a large international participation: the European Space
Agency (ESA), Austria, Belgium and Germany contribute to the payload, and Spain
and Brazil contribute to the ground segment. Development of the spacecraft,
which is based on a PROTEUS low earth orbit recurrent platform, commenced in
October 2000 and the satellite was launched on December 27th 2006.
  The instrument and platform characteristics prior to launch have been
described in ESA publication (SP-1306) . In the present paper we detail the
behaviour in flight, based on raw and corrected data. Five runs have been
completed since January 2007. The data used here are essentially those acquired
during the commissioning phase and from a long run which lasted 146 days, these
enable us to give a complete overview of the instrument and platform behaviour
for all environmental conditions. The ground based data processing is not
described in detail, the most important method being published elsewhere. It is
shown that the performance specifications are easily satisfied when the
environmental conditions are favourable. Most of the perturbations, and
consequently data corrections, are related to Low Earth Orbit (LEO)
perturbations: high energy particles inside the South Atlantic Anomaly (SAA),
eclipses and temperature variations, and line of sight fluctuations due to the
attitude control system. Straylight due to the reflected light from the earth,
which is controlled by the telescope and baffle design, appears to be
negligible.
