I just ran across this. NASA has produced an ebook on the Cassini mission to Saturn. The book is available in MOBI, EPUB and PDF formats. I've only just downloaded it (in both EPUB and MOBI formats) and a quick glance with Calibre's ebook viewer looks pretty good. There are a lot of photos, so this might be best viewed on a tablet.
EDIT: And I did just download the PDF for the photos. They look very good on the desktop's large monitor.
The Saturn System Through the Eyes of Cassini