  Euclid is a space-based optical/near-infrared survey mission of the European
Space Agency (ESA) to investigate the nature of dark energy, dark matter and
gravity by observing the geometry of the Universe and on the formation of
structures over cosmological timescales. Euclid will use two probes of the
signature of dark matter and energy: Weak gravitational Lensing, which requires
the measurement of the shape and photometric redshifts of distant galaxies, and
Galaxy Clustering, based on the measurement of the 3-dimensional distribution
of galaxies through their spectroscopic redshifts. The mission is scheduled for
launch in 2020 and is designed for 6 years of nominal survey operations. The
Euclid Spacecraft is composed of a Service Module and a Payload Module. The
Service Module comprises all the conventional spacecraft subsystems, the
instruments warm electronics units, the sun shield and the solar arrays. In
particular the Service Module provides the extremely challenging pointing
accuracy required by the scientific objectives. The Payload Module consists of
a 1.2 m three-mirror Korsch type telescope and of two instruments, the visible
imager and the near-infrared spectro-photometer, both covering a large common
field-of-view enabling to survey more than 35% of the entire sky. All sensor
data are downlinked using K-band transmission and processed by a dedicated
ground segment for science data processing. The Euclid data and catalogues will
be made available to the public at the ESA Science Data Centre.
