  The Ultraviolet Transient Astronomy Satellite (ULTRASAT) is a space-borne
near UV telescope with an unprecedented large field of view (200 sq. deg.). The
mission, led by the Weizmann Institute of Science and the Israel Space Agency
in collaboration with DESY (Helmholtz association, Germany) and NASA (USA), is
fully funded and expected to be launched to a geostationary transfer orbit in
Q2/3 of 2025. With a grasp 300 times larger than GALEX, the most sensitive UV
satellite to date, ULTRASAT will revolutionize our understanding of the hot
transient universe, as well as of flaring galactic sources. We describe the
mission payload, the optical design and the choice of materials allowing us to
achieve a point spread function of ~10arcsec across the FoV, and the detector
assembly. We detail the mitigation techniques implemented to suppress
out-of-band flux and reduce stray light, detector properties including measured
quantum efficiency of scout (prototype) detectors, and expected performance
(limiting magnitude) for various objects.
