Clark McClelland claims to have observed the eight to nine-feet tall being in an astronaut's suit in the bay of the shuttle.
The story, which has emerged on paranormal websites and YouTube, is true he said, giving a testimony about the supposed sighting in a vide for YouTube channel Paranormal Crucible.
The channel produced mock-up video of the oversized "alien entity" interacting with NASA astronauts in the bay.
Mr McClelland claims he was monitoring the shuttle from the Kennedy Space Centre in Cape Canaveral, Florida, at the time of the sighting in 1991.
That might be why he's a "former" NASA engineer. ;-) To read more, click here.