All you need is one point of reference..If you know were your location is ( lets say before they shut down all comms to ground control ) and you have a watch..then you can determine your location anytime after that.
Its simple navigation m8.
Like I said..all they have to do it be able to SEE NY and then its fly bye sight after that.
LOL..that made me laugh..really Im still smiling..good to see some sense of humor still alive :-D
There was a sense of humor until you arrived.