The Pressurized Mating Adapter (PMA) is a class of spacecraft adapters that convert the Common Berthing Mechanism (CBM) used on the US Orbital Segment to APAS-95 docking ports. There are three PMAs located on the International Space Station (ISS); the first two were launched with the Unity connecting module in 1998 aboard STS-88, and the third was launched in 2000 aboard STS-92. All three of the PMAs are now used to permanently connect parts of the ISS, so they are no longer available as docking ports for visiting spacecraft. Design/History Its origins lie in designs for the Pressurized Docking Mast, consisting of an off-axis frustoconical docking tunnel contained within a framework and a retractable coupling mechanism, later part of the Pressurized Berthing Adapter assembly that appeared in designs for Space Station Freedom 1987, and the reduced design referred to as 'Fred' 1991. After 1992-93 and the Russian integration into the International Space Station Alpha project, this NASA docking design abruptly disappeared from all concepts. This was due to the availability of Russian docking hardware and experience, brought together during the Shuttle-Mir program. Russian APAS docking technology originally planned for the then defunct Soviet space shuttle program was integrated into the US Space Shuttle ODS (Orbital/Orbiter Docking System). This could hard dock with the space station through a structural interface, which became the PMA. With both the Russian docking ring and the CBM integrated into the PMA, this became the link between the USOS and the ROS from 1993. Fabrication completed in 1995 with tests and mating tests with Node STA throughout 1996-97. Uses The three PMAs are identical, but they have slightly different uses. All three perform the same basic function of connecting a CBM port of an ISS module to an APAS-95 docking port of another module or visiting spacecraft. For this purpose, the PMAs carry a passive CBM port and a passive APAS port. The PMAs are pressurized and heated from the inside, and they allow for power and data communications transfer through docking rings and external connections. PMA-1 This was one of the first components of the International Space Station. PMA-1 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. These first two station components are permanently