Pressurized Mating Adapter

The Pressurized Mating Adapter (PMA) is a spacecraft adapter that converts the Common Berthing Mechanism (CBM) to APAS-95. There are three PMAs located on the International Space Station (ISS). The first two PMAs were launched with the Unity module in 1998 aboard STS-88. The third was launched in 2000 aboard STS-92.

All the PMAs on the ISS are identical but used slightly differently, and all three perform the same basic function of connecting a Common Berthing Mechanism port of an ISS module to an APAS-95 docking port of another module or visiting spacecraft. For this the PMAs carry a passive CBM port and a passive APAS port. They are pressurized and heated from the inside, and through docking rings as well as external connections allow for power and data communications transfer.

This was one of the first components of the International Space Station and joins the Russian side of the station with the US side. On STS-88 the crew used the shuttle's robotic arm to attach the Zarya control module to PMA-1, which was already connected to the aft berthing port of Unity. PMA-1 now permanently connects these first two station components.

PMA-2 is currently mounted on the forward port of the Harmony connecting node and was used when Space Shuttle orbiters docked at the station. It is the only PMA that has been outfitted with Station-to-Shuttle Power Transfer System (SSPTS) hardware, which allowed shuttles to stay docked longer to the space station.

Due to space station assembly PMA-2 has been moved several times. It was originally connected to the forward hatch of Unity, but when STS-98 delivered the Destiny in February 2001, Destiny was berthed to that hatch while PMA-2 was moved to the forward hatch of the Z1 truss. It was finally moved to the forward hatch of "Destiny". (The removal of PMA-2 from Unity was the first time the Common Berthing Mechanism (CBM) was used to disconnect two ISS components.) After STS-120 had delivered Harmony at the station in October 2007, Canadarm2 relocated PMA-2 to its final location at the forward hatch of Harmony on November 12, 2007. Two days later, the combined package of Harmony and PMA-2 was moved to its final location, the forward hatch of Destiny. PMA-2 will stay berthed at the forward port of Harmony for the remaining duration of the ISS.

...
Wikipedia