Im going to play a Self aware AI that wishes to expand it's knowledge base, through exploration. I feel that sounds perfectly logical as an explanation since it machines often go the route of finding knowledge and new technology in a lot of sci-fi lor. Im going to work out more details and elaborate on my story further though just haven't got that far.
I guess I would aprouch it some what like this though . Say I was in texas or a similar system and get stopped by the military I would tell them I'm not a threat and explain to them my ideas for obtaining more information about the universe and the places and things within it. Knowledge will be my main concern as a machine and expanding it till it is no longer possible to expand it any further.