When i first saw this footage i presumed it was a lens or light anomaly from the ISS camera, but after running it through several filters i changed my mind.
Object starts off quite translucent as it comes into view, and then becomes more solid and defined.
This could indicate the object is a dimensional craft, phasing into our reality from an alternate one. This of course is only an opinion, but please note, sightings of these ring shaped UFOs are increasing, some are quite small, and others, especially ones seen around the sun are massive, only question is what are they?
NASA Footage Here: http://www.ustream.tv/recorded/40481898