UFO Recorded by Space Shuttle Atlantis
In April 1991 the Space Shuttle Atlantis recorded this video of an unidentified object in relatively close proximity to the spacecraft. NASA speculated that the object may have been a block of ice, but to date no convincing explanation has been offered.
Note that some versions of this video are zoomed in and slowed down, making them appear somewhat more "UFO-like". This video is a better representation of what was actually recorded.