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\item Le site : The LSST will be constructed on El Pe\~nón Peak, in the Cerro Pachón mountains of the northern Chielan Andes, at an altitude of 2680 meters. This site benefits from the weather data taken over more than 10 years at the Cerro Tololo Inter-American Observatory (CTIO), located 10 km away. These data show that the more than 80\% of the nights are usable with excellent atmospheric condition. The ``seeing'' at 500 nm (the FWHM of the image of a point source) has for instance been measured as 0.67'' average (0.59'' median, with 25\% first and last quantiles at 0.44 and 0.81'', respectively). Furthermore, Cerro Pachón is also home of the Gemini South and SOAR telescopes, which have confirmed the site performance, and provide extensive infrastructure eventually usable by the LSST both at the summit and at the Base Facility, located 57 km away at La Serena. The summit has already been leveled off and construction has officialy started after the successful recent readiness reviews that the project undertook.  \item Le télescope : The telescope design is a three-mirror anastigmat, with the peculiarity that the primary and tertiary mirrors are polished from the same substrate. The primary mirror reach a diameter size of 8.4 meters (6.5 meter effective radius). All three mirrors will be actively supported to control wavefront distortions introduced by gravity and environmental stresses on the telescope. The dome that contains the telescope has been designed to reduce dome seeing and to maintain a uniform thermal environment over the course of the night.  \item La caméra  \item Le survey : As mentioned stated  in REF, ``The fundamental basis of the LSST concept is to scan the sky deep, wide, and fast with a single observing strategy, giving rise to a data set that simultaneously satisfies the majority of the science goals. This concept, the so-called “universal cadence”, will yield the main deep-wide-fast survey  (typical single visit depth of r ∼ 24.5) and use about 90\% of the observing time.'' This main survey will consist in series of pairs of 15-second exposures with each filter, optimized to cover the southern sky (20000 deg^2) in about 3 to 4 days, with a single visit reaching magnitude ~24.5 in the r band. As aften as possible, each field will be observed twice, with visits separated by 15 to 60 minutes, so as to optimize sampling of short-period variability. Over the planned 10 years of observations, this will represent about 2.8 million visits, or 5.6 15-secon long exposures.   ``The remaining 10\% of the observing time will be used to obtain improved coverage of parameter space such as  very deep (r ∼ 26) observations, observations with very short revisit times (∼ 1 minute), and  observations of “special” regions such as the ecliptic, Galactic plane, and the Large and Small  Magellanic Clouds''. Is also considered a third type of survey, micro-surveys, that would use  about 1\% of the time, or about 25 nights over ten years.  \item Le calcul  \end{enumerate}