Androgynous Peripheral Attach System
The Androgynous Peripheral Attach System, or Androgynous Peripheral Assembly System, is a spacecraft docking mechanism used on the International Space Station
International Space Station
The International Space Station is a habitable, artificial satellite in low Earth orbit. The ISS follows the Salyut, Almaz, Cosmos, Skylab, and Mir space stations, as the 11th space station launched, not including the Genesis I and II prototypes...

. It is used to dock the Space Shuttle
Space Shuttle
The Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...

 orbiter and to connect the Functional Cargo Block (Zarya
Zarya , also known as the Functional Cargo Block or FGB , was the first module of the International Space Station to be launched. The FGB provided electrical power, storage, propulsion, and guidance to the ISS during the initial stage of assembly...

) to Pressurized Mating Adapter
Pressurized Mating Adapter
The International Space Station uses three Pressurized Mating Adapters to interconnect spacecraft and modules with different docking mechanisms. The first two PMAs were launched with the Unity module in 1998 aboard STS-88...

-1. A system compatible with APAS is used by the Chinese Shenzhou spacecraft
Shenzhou spacecraft
Shenzhou is a spacecraft developed and operated by the People's Republic of China to support its manned spaceflight program. The name is variously translated as "Divine Craft," "Divine Vessel of God," "Magic Boat" or similar and is also homophonous with an ancient name for China...

 making it possible for that spacecraft to dock with the ISS.


APAS was designed by Vladimir Syromyatnikov
Vladimir Syromyatnikov
Vladimir Sergeevich Syromyatnikov was a Soviet and Russian space scientist best-known for designing docking mechanisms for manned spacecraft; it was his Androgynous Peripheral Attach System which, in the 1970s, linked the Soviet and American space capsules in the Apollo-Soyuz test...

 of the Moscow-based RSC Energia
S.P. Korolev Rocket and Space Corporation Energia
OAO S.P. Korolev Rocket and Space Corporation Energia , also known as RKK Energiya, is a Russian manufacturer of spacecraft and space station components...

 and has roots in the Apollo-Soyuz program
Apollo-Soyuz Test Project
-Backup crew:-Crew notes:Jack Swigert had originally been assigned as the command module pilot for the ASTP prime crew, but prior to the official announcement he was removed as punishment for his involvement in the Apollo 15 postage stamp scandal.-Soyuz crew:...

. 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 however, an active and a passive side, but both sides can fulfill either role. There are 3 basic variations of the APAS system.


APAS-75 was developed for the Apollo–Soyuz Test Project (ASTP). Unlike previous docking systems, both units could assume the active or passive roles 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.
Russia built five Soyuz spacecraft that used APAS-75. The first three flew as test systems (Cosmos 638
Cosmos 638
Kosmos 638 was an unmanned test of the ASTP Soyuz. It carried an APAS-75 androgynous docking system.-Mission parameters:*Spacecraft: Soyuz-7K-TM №71*Mass: 6510 to 6680 kg*Crew: None*Launched: April 3, 1974*Landed: April 13, 1974-References:...

, Cosmos 672
Cosmos 672
Kosmos 672 was the second unmanned test of the ASTP Soyuz spacecraft. Also had APAS-75 androgynous docking system.-Mission parameters:*Spacecraft: Soyuz 7K-OK*Mass: 6510 to 6680 kg*Crew: None*Launched: August 12, 1974*Landed: August 18, 1974...

 and Soyuz 16
Soyuz 16
Soyuz 16 was a 1974 manned test flight for a joint Soviet-US space flight which culminated in the Apollo-Soyuz mission in July, 1975. The two-man Soviet crew tested a docking ring and other systems to be used in the joint flight.-Crew:-Backup crew:...

). One was used for the Apollo-Soyuz Test Project, Soyuz 19 the only Soyuz to actually use the docking system, and the last one flew as Soyuz 22
Soyuz 22
Soyuz 22 was 1976 Soviet manned spaceflight. It was an earth-sciences mission using a modified Soyuz spacecraft, and was also, some observers speculated, a mission to observe NATO exercises near Norway....

. On the American side the ASTP Docking Module carried one APAS-75 docking collar and one Apollo docking collar.


When the USSR started working on Mir
Mir was a space station operated in low Earth orbit from 1986 to 2001, at first by the Soviet Union and then by Russia. Assembled in orbit from 1986 to 1996, Mir was the first modular space station and had a greater mass than that of any previous spacecraft, holding the record for the...

 they were also working on the Buran shuttle program. APAS-89 was envisioned to be the docking system for Buran with the Mir space station. The original design was heavily modified. The outer diameter was reduced from 2030 mm to 1550 mm and the alignment petals were pointed inward instead of outward. This limited the internal diameter of the docking port to about 800 mm. The Buran shuttle was finally canceled in 1994 and never flew to the Mir space station, but Mir's Kristall
The Kristall module was the fourth module and the third major addition to the Mir space station. As with previous modules, its configuration was based on the 77K module, and was originally named "Kvant 3". It was launched on May 31, 1990 on a Proton rocket...

 module was outfitted with two APAS docking collars. The Mir Docking Module
Mir Docking Module
The Stykovochnyy Otsek , GRAU index 316GK, otherwise known as the Mir docking module or SO, was the sixth module of the Russian space station Mir, launched in November 1995 aboard the...

, basically a spacer module between Kristall and the Shuttle also used APAS-89 on both sides. This design is sometimes called Androgynous Peripheral Docking System.


When the Shuttle-Mir Program
Shuttle-Mir Program
The Shuttle–Mir Program was a collaborative space program between Russia and the United States, which involved American Space Shuttles visiting the Russian space station Mir, Russian cosmonauts flying on the shuttle and an American astronaut flying aboard a Soyuz spacecraft to engage in...

 began APAS was selected as the docking system. The visiting US Space Shuttles used an Androgynous Peripheral Attach System docking collar originally designed for Buran, mounted on a bracket originally designed for use with the American Space Station Freedom
Space Station Freedom
Space Station Freedom was a NASA project to construct a permanently manned Earth-orbiting space station in the 1980s. Although approved by then-president Ronald Reagan and announced in the 1984 State of the Union Address, Freedom was never constructed or completed as originally designed, and after...

. Although Energia's code for the Shuttle APAS is APAS-95, it is basically the same as APAS-89. The APAS on the Shuttle's Orbiter Docking System remained unchanged when it began to be used for ISS dockings. The active capture ring that extends outward from the orbiter will capture the passive mating ring on the space station's Pressurized Mating Adapter
Pressurized Mating Adapter
The International Space Station uses three Pressurized Mating Adapters to interconnect spacecraft and modules with different docking mechanisms. The first two PMAs were launched with the Unity module in 1998 aboard STS-88...

s. The capture ring aligns them, pulls them together and deploys 12 structural hooks, latching the two systems with an airtight seal. The Pressurized Mating Adapters are permanently passive.

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