When you map the entire Earth every 5 days with the aim of generating high-quality time series over land, there is no room for geometrical error: the algorithms have to be stable, reliable, and precise. Rugged takes up this challenge, and is at the geometrical heart of the operational processing for Sentinel-2; it was used to generate the first images on 2015-06-26 at ESA’s ground segment in Matera.
In ESA’s words:
[the first results] demonstrated that the operational processor works flawlessly, paving the way for the mission’s data systematic generation to come
The full ESA article is available at Sentinel-2 delivers first imagesNews summary