This illustration is a cutaway view of the internal arrangement of the Airlock Module (AM). The aft end of the Docking Adapter mated to the AM, and served as the environmental, electrical, and communications control center. The docking adapter also contained the port through which the astronauts exited to perform extravehicular activity. The AM contained a turnel section through which Skylab crewmen could move between the workshop and the forward end of the airlock. It was encircled, for part of its length, at its aft end by the fixed Airlock Shroud (FAS), that had the same diameter as the workshop (22 feet) and was attached to the workshop's forward end. High pressure containers for oxygen and nitrogen providing Skylab's atmosphere, were mounted in the annular space between the outside of the tunnel and the inside of the shroud. The forward end of the FAS was the base on which the tubular structure supporting the solar observatory was mounted. Many of the supplies, and most of the control systems for Skylab were located in the AM; this module could well be the "utility center" of the Skylab cluster. McDonnell Douglas fabricated the module with close Marshall Space Flight Center's involvement in design, development, and test activities.