Androgynous Peripheral Attach System

The terms Androgynous Peripheral Attach System (APAS), Androgynous Peripheral Assembly System (APAS) and Androgynous Peripheral Docking System (APDS), are used interchangeably to describe a family of spacecraft docking mechanisms, and are also sometimes used as a generic name for any docking system in that family. A system similar to APAS-89/95 is used by the Chinese Shenzhou spacecraft.

The name of the system is Russian in origin, and is an acronym, АПАС, in the Cyrillic alphabet, from the Russian, Андрогинно-периферийный агрегат стыковки. The English acronym was designed to be just the same letters but in the Latin alphabet, for which the first two words are direct counterparts of those in the original. The third word in Russian comes from the German aggregat, meaning "complicated mechanism", and the last means "docking". The last two words in the English name were picked to begin with the same equivalent letters as in the Russian name.

The idea behind the design is that unlike with the probe-and-drogue docking system, any APAS docking ring can mate with any other APAS docking ring; both sides are androgynous. In each docking there is an active and a passive side, but both sides can fulfill either role. There are three basic variations of the APAS system.

Co-developed by American and Soviet engineers though a series of in-person meetings, letters and teleconferences, APAS-75 was initially planned to be used on an American mission to a Salyut space station which instead became the Apollo–Soyuz Test Project (ASTP). There were differences between the American and Soviet version of the docking mechanism, but they were still mechanically compatible. Early on, the Americans called the device both the International Rendezvous and Docking Mission (IRDM) Docking Mechanism and the International Docking System. The device is called the Androgynous Peripheral Docking System (APDS) in the NASA press packet for ASTP.

Unlike previous docking systems, either APAS-75 unit could assume the active or passive role as required. For docking, the spade-shaped guides of the extended active unit (right) and the retracted passive unit (left) interacted for gross alignment. The ring holding the guides shifted to align the active unit latches with the passive unit catches. After these caught, shock absorbers dissipated residual impact energy in the American unit; mechanical attenuators served the same function on the Soviet side. The active unit then retracted to bring the docking collars together. Guides and sockets in the docking collars completed alignment. Four spring push rods drove the spacecraft apart at undocking.

...
Wikipedia