English: This photograph shows the flight article of the mated Airlock Module (AM) and Multiple Docking Adapter (MDA) being lowering into horizontal position on a transporter. Although the AM and the MDA were separate entities, they were in many respects simply two components of a single module. The AM enabled crew members to conduct extravehicular activities outside Skylab as required for experiment support. Oxygen and nitrogen storage tanks needed for Skylab's life support system were mounted on the external trusswork of the AM. Major components in the AM included Skylab's electric power control and distribution station, environmental control system, communication system, and data handling and recording systems. The MDA, forward of the AM, provided docking facilities for the Command and Service Module. It also accommodated several experiment systems, among them the Earth Resource Experiment Package, the materials processing facility, and the control and display console needed for the Apollo Telescope Mount solar astronomy studies. McDonnell Douglas built the AM and Martin Marietta built the MDA. The Marshall Space Flight Center was responsible for the design and development of the Skylab hardware and experiment management.