US Orbital Segment

The US Orbital Segment (USOS) is the name given to the components of the International Space Station (ISS) constructed and operated by the United States National Aeronautics and Space Administration (NASA), European Space Agency (ESA), Canadian Space Agency (CSA) and Japan Aerospace Exploration Agency (JAXA). The segment currently consists of eleven pressurized components and various external elements, all of which were delivered by the Space Shuttle.

The segment is monitored and controlled from various mission control centers on the world including Lyndon B. Johnson Space Center in Houston, Texas, Columbus Control Center in Oberpfaffenhofen, Germany, Tsukuba Space Center in Tsukuba, Japan, and Marshall Space Flight Center in Huntsville, Alabama.

The US Orbital Segment consists of 11 pressurized modules. Of these, eight are habitable, one is for observation and three are for docking and mating.

All three nodes have 4 ports around its exterior, and 1 port on each end. Each of the ports are called Common Berthing Mechanisms, or CBM's.

The first component of the USOS pressurized segment is the Unity node. On the aft end of Unity is the Pressurized Mating Adapter (PMA) 1. The PMA-1 connects Unity with the Russian segment. Unity is also connected to the Quest airlock on the starboard side, Tranquility on the port side, and the Z1 truss on the zenith. The Destiny lab connects to the forward end, leading to the rest of the USOS. Unity is also used by the crews on board the ISS to eat meals and share some downtime together. The Unity node was delivered to the station by STS-88 on December 6, 1998.

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