ISS Pressurized Mating Adapter (PMA)
There are three PMAs located on the International Space Station (ISS). 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.
PMA-1 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.
After activation of Tranquility, PMA-3 was moved on February 16, 2010 to the port location on Tranquility where the Cupola had been docked for launch.