This mod will be a few add on airlocks, mostly as surface attachable parts.  Over on the G+ community for KSP someone mentioned it would be nice to be able to add hatches to parts.  That's a task I leave to someone who wants lots of coding headaches.  However, and Airlock is quite fine.  Basically a small part, with a crew capacity of one, with a hatch.  I'll be adding in the MM config for Connected Living Space, so if you're using that, they'll be usable.  For us non-realism type users, th