Subject: VRD: Variations in the path of the space shuttle?

My roommate and I were up late one night discussing a feature of the
orbit of satellites around the earth.  While observing the path of the 
space shuttle in orbit, we noticed that the shuttle did not use the exact 
same orbital path every time it circled the earth.  Instead, each orbit 
around the earth was offset from the previous one, producing slightly 
different tracks after each orbit.  For example, one path would have the 
shuttle passing over the New York City area, the next orbit would be over 
Chicago, the next over Denver, and so on.  What exactly causes this orbital 
shift, and why?  We thank you for your time.

Re: VRD: Variations in the path of the space shuttle?