These rather fascinating photos were found originally on a NASA website. While one can only speculate on the true origin of the craft, my inclination is that it really is from "elsewhere".

http://www.dumpert.nl/mediabase/587491/87867201/nasa_sts_88_pics_unknown_spacecraft_%28ufo%29.html

This may be a helpful "explanation", but not necessarily :)

http://www.forbiddenhistory.info/?q=node/57