Apollo ASTP / DM - Credit: NASA. 9,264 bytes. 354 x 158 pixels.

The ASTP docking module was basically an airlock with docking facilities on each end to allow crew transfer between the Apollo and Soyuz spacecraft. The docking module was 3.15 m long, 1.4 m maximum diameter, and weighed 2,012 kg. Apollo's cabin atmosphere was 100 percent oxygen at 0.34 atmosphere pressure, while that of Soyuz was nitrogen/oxygen at 1.0 atmosphere. Transfer between these two atmospheres would require pre-breathing of pure oxygen to purge the blood of suspended nitrogen. This was avoided by lowering the Soyuz pressure to 0.68 atmospheres pressure. The docking module served mainly as an airlock to raise or lower the pressure between 0.34 and 0.68 atmospheres when moving from one spacecraft to the other. This was done through the use of pressure equalisation valves with both hatches closed.

The docking module pressure vessel was formed from a welded cylinder of 1.58 cm thick aluminium, with a tapered bulkhead and tunnel section on the command module and a machined base assembly and bulkhead on the Soyuz end.

A systems module inside the docking module contained control and display panels, VHF/FM transceiver, environmental control system, and storage compartments. Other equipment included oxygen masks, fire extinguisher, floodlights and handholds, a junction box for linking Soyuz communications circuits to Apollo, the MA-010 Multipurpose Furnace and two removal stowage lockers containing TV equipment and spare equipment.

The docking module pressure vessel and external gas tanks were covered with an external insulation cover made of thin Inconel over a multi-layer insulation blanket separated from the vessel by a framework.

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Apollo ASTP DM Credit: NASA. 23,485 bytes. 650 x 457 pixels.

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The universal docking system was a Soviet design. It consisted of an extendible guide ring with three petal-shaped guide plate, three capture latches, and six hydraulic attenuators for soft dock. Hard dock was achieved by retracting the guide ring with a cable-drive system, which compressed the seals between the Apollo and Soyuz, followed by engagement of eight structural latches.

All docking module electrical power was supplied by umbilical from the Apollo CSM. There were no provisions for carbon dioxide removal; this was done by the exiting Apollo CSM or Soyuz environmental control systems.

The docking module was built by Rockwell International Division, Downey, California (prime contractor for the Apollo spacecraft itself).