US Orbital Segment

Modules

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.

Nodes

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.

Unity

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, Leonardo on the nadir, 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.

Harmony

The Harmony node is the central connecting node of the USOS. Harmony connects to the Destiny lab aft end, Kibo lab to the port side, and Columbus lab to the starboard side. The Harmony node's nadir and zenith ports also serves as the berthing port for H-II Transfer Vehicle (HTV), Dragon and Cygnus resupply vehicles. On the forward end of Harmony is PMA-2, which was used by visiting Space Shuttles as a mating adapter and by future manned missions to the ISS. Harmony was delivered by the STS-120 mission on October 23, 2007.

Tranquility and Cupola

The Tranquility node houses the USOS life support systems. Tranquility also hosts the seven windowed Cupola module. The Cupola is used for Earth observation and robotic operations. The forward facing port of Tranquility is blocked by the station's truss structure, while the aft facing port is free for use. While the nadir port is used by the Cupola, the zenith port is used by some exercise equipment inside the node. The port side port is occupied by the PMA 3, and the starboard port is connected to node 1. The Cupola and Tranquility modules were delivered by STS-130 in February 2010.

Destiny

The Destiny laboratory is the American built laboratory module. It is used for medical, engineering, biotechnological, physics, materials science and Earth science research. Destiny also houses a back-up robotic work station, and was the first of the USOS laboratories to be delivered. It was delivered by STS-98 on February 7, 2001. The Destiny lab is managed by mission control centers in Houston, Texas and Huntsville, Alabama.

Columbus

Columbus is a laboratory module built by the European Space Agency. It is host to scientific research in fluids, biology, medicine, materials and Earth sciences. Columbus also has four external payload locations, used to expose experiments to the vacuum of space. The Columbus module was delivered to the ISS by STS-122 on February 7, 2008. The Columbus Control Center, located in Germany, is responsible for the Columbus module.

Kibo

The Kibo laboratory is the Japanese component of the USOS. Kibo has four main parts: the Kibo lab itself, a pressurized cargo container, an exposed science platform and two robotic arms. The module is unique in that it has a small airlock, which can be used to pass payloads to the robotic arms or astronauts outside the station. The robotic arms are controlled from a work station inside the lab. The lab is used for research in medicine, engineering, biotechnology, physics, materials science and Earth science. The logistics container was the first part of Kibo to arrive. It was delivered by STS-123 in March 2008. The Kibo lab itself was delivered to the ISS by the STS-124 mission in May 2008. The exposed facility was brought to the ISS by the STS-127 mission in July 2009. The JEM Control center in Tsukuba, Japan is responsible for all elements of the Kibo laboratory.

Quest

The Quest Joint Airlock is used to host spacewalks from the USOS segment of the ISS. It consists of two main parts: the equipment lock and the crew lock. The equipment lock is where the Extravehicular Mobility Units are stored and preparations for spacewalks are carried out. The crew lock is depressurized during spacewalks. The Quest airlock was delivered and installed by the STS-104 crew in July 2001.

Leonardo

The Leonardo module, also known as the Permanent Multipurpose Module (PMM), is a module used for stowage space on the ISS. Leonardo is attached to the forward-facing side of the Tranquility node. The PMM was delivered to the ISS by the STS-133 mission in early 2011. Originally the Multi-Purpose Logistics Module (MPLM) Leonardo, it was converted to stay on orbit for an extended period of time prior to being installed on the ISS.

Pressurized Mating Adapter

The Pressurized Mating Adapters (PMA) serve as docking ports on the USOS portion of the ISS. Currently PMA-1 is used to connect the Unity node with the Zarya module on the ISS. Pressurized Mating Adapter-2 is located on the forward end of Harmony, and was used by the Space Shuttle to dock with the ISS. Any future manned American spaceflights to the ISS will use PMA-2. The third Pressurized Mating Adapter is located on the aft end of the Tranquility node. Currently, PMA-3 serves only as a storage location, and serves as a back up to PMA-2. PMA-1 and PMA-2 were delivered with the Unity node on STS-88 in December 1998. The third PMA was delivered by STS-92 on October 11, 2000.