re: Big "Open Door" Value on Space Station
Done a lot of work on Alternate Access type projects, and the Common Berthing Mechanism (CBM) is indeed attractive for its "barn door" hatchway. Of course the catch is that this particular system can't "dock" on its own, but has to be manually placed by a robot arm into the latching position.
The CBM:
<img src="http://www.boeing.com/defense-space/space/spacestation/components/images/iss_cbm_250X200.jpg";
The barn door, open: