As you can see in this animationtime 11:45 >, during latter Shuttle missions EVA airlock was placed in payload bay and used both for docking with ISS (with orbital docking system on top of it) and for astronauts spacewalks. All while orbiter was turned upside down to protect crew against debris strike and payload bay was open to allow radiators to radiate heat. During missions with spacelab, Crew cabin was always connected through access tunnel with spacelab and between them was EVA airlock with ODS. https://lh5.ggpht.com/_1wtadqGaaPs/TF6EG3y7VlI/AAAAAAAAPAk/zBp7Hd2AvtU/tmp3D23_thumb1_thumb1.jpg?imgmax=800
But for early Shuttle missions orbiter EVA airlock was placed inside the Crew Cabin (next to entry to payload bay) and they made spacewalks through this entry to the payload bay. Where was then ODS (orbital docking system) placed on missions with internal airlocks ?
During spacelab missions, Crew cabin must be connected with spacelab through access tunnel, which had already EVA airlock mounted on tunnel adapter to orbiter, so were internal airlocks ever used for missions with spacelabs ? Why would they need two ?