SUSI is a sun simulator part of the optical ground support equipment (OGSE) for the calibration and characterization (C&C) of the Sentinel-5 instrument. The sun simulator is based on a Xenon continuous light source, a homogenizer, and a telescope. To meet the stringent spatial homogeneity requirements, a large homogenizer based on a kaleidoscope configuration was designed and manufactured. The proper collimation and large exit pupil are achieved through a mirror-based Offner telescope. SUSI covers a very wide spectral range, from 270 to 2385nm, with an irradiance of 80 mW/cm2. SUSI provides an illuminated exit pupil with a very high spatial uniformity. The collimated beam of 0.318º divergence illuminates an exit pupil 151mm diameter with continuous light and with a spatial non-uniformity better than 1% (according to IEC 60904- 9 definition) which is, to the best of our knowledge, the highest level of spatial uniformity for large aperture sun simulators.