ISS Docking Mechanism plans for Discovery, other Shuttles and this first logistics mission call for Discovery to dock at the ISS on Day 3 and remain there for six days. The Shuttle’s external airlock will be connected to Unity’s Pressurized Mating Adapter (PMA) 2 using an interlocking system designed in Russia. It is termed an Androgynous Peripheral Attach System. Discovery’s crew will control PMA-2’s docking mechanism from the cockpit.


Pressurized Mating Adapters

Two PMAs are attached to Unity, one at each end. They provide passageways for crew, equipment and supplies. They also feature docking mechanisms for space shuttles at one end and Zarya at the other.

Because they are pressurized, heated and supplied with hand-hold grips, the 8-ft-long, tunnel-like PMAs permit shirt-sleeved crews to pass between Discovery and the ISS.


Androgynous Peripheral Attach System

A structural ring, a movable ring, alignment guides, latches, hooks, dampers and fixers are integrated to form the Androgynous Peripheral Attach System. It mates with an exact copy, and each can act as the passive or active half.

During docking, the active half’s capture ring extends outward from the structural ring toward the passive half. Upon contact, the system dampens out any relative motion between the docking vehicles. Once that is accomplished, the capture ring aligns the two vehicles. It is then retracted with the passive ring still attached. Twenty-four structural hooks snug the connection down to form an airtight seal.