Here you can see how they were built up:
http://forum.nasaspaceflight.com/for...d=4538&start=1
http://forum.nasaspaceflight.com/for...d=7231&start=1
There's a pressure hull like on a submarine that is placed inside the outer unpressurised hull that we see. The cabin is a capsule and is connected to the airlock with the docking mechanism.
Good view of the capsule:
http://forum.nasaspaceflight.com/for...chmentid=13200
And the outer hull where it will be placed:
http://forum.nasaspaceflight.com/for...chmentid=13206
Hope it helps
