Unidentified Flying Object near the ISS Space station

This video was recorded 20 June 2007 from the docking cam on board Atlantis Space Shuttle. An object that seem to be rolling more then flying appears just behind the ISS Space station. What could we be looking at. ? If its an astronaut on spacewalk i would dare to say its the most craziest and dangerous spacewalk ever. But Truth is.... I don't think its an astronaut on spacewalk. What could this Unidentified Flying Object be ?

Space debris ? Swamp gas ? Weather balloon ? Space worm ?

Until now it remains an Unidentified Flying Object...