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The COROT small satellite project is a space mission dedicated to stellar seismology and search for telluric extra-solar planets. For the two programs a very high photometric precision is needed. The COROT seismology program will measure periodic variations with amplitude of 2.10-6 of the photon flux emitted by bright stars. COROT will also be able to detect the presence of exoplanets when they pass between the satellite and their parent star. Modifying both the integration time and the focus conditions, it allows to detect photons flux variations about 7.10-4 in one hour integration, compatible with an occultation detection on a very large number of stars (magnitude between 12 and 15.5). Between 10 and 40 telluric planets in the "habitable zone" and several hundreds of hot Jupiters should be detected depending on hypotheses about planets existence. To reach the required performances a stringent instrument stability is necessary. The satellite Preliminary Design Review will be held in November 2002 while the instrument is already in development phase for a delivery of the flight model in 2004. The launch is scheduled late 2005, by the first SOYUZ launcher to fly from the Guyana Space Center. The project activities are currently focused on the instrument and system engineering. Straylight rejection, pointing, thermal stability are the main critical points of the mission, on a LEO at 826 kms, for which cost-effective compromises have been found to 1mit their effects. This paper recalls the scientific program s, the main characteristics of the mission, describes the impact of the three main perturbators on the photometric precision and the technical solutions which reduce their contribution at an acceptable level.
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