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ITS-P3/4 [NASA]

ITS-S3/4 and ITS-P3/4 (Integrated Truss Structure) are elements of the International Space Stations main truss structure.

The Integrated Truss Structure of the ISS consists of a linearly arranged sequence of connected trusses which is used to mount various unpressurized components, such as ELC logistics carriers, radiators, solar arrays, and other equipment.

These elements were originally planned as two seperate truss structures, but were finally built as joint elements, hence the 3/4 designation. Each element together contain a pair of solar arrays, a radiator and a rotary joint that will aim the solar arrays, and connects P3 to P4 and S3 to S4 respectively.

Following major subsystems are located on P3 and S3 respectively: the Segment-to-Segment Attach System (SSAS), Solar Alpha Rotary Joint (SARJ), and Unpressurized Cargo Carrier Attach System (UCCAS). The primary functions of the P3/S3 truss segment are to provide mechanical, power and data interfaces to payloads attached to the two UCCAS platforms; axial indexing for solar tracking, or rotating of the arrays to follow the sun, via the SARJ; movement and work site accommodations for the Mobile Transporter. The P3/S3 primary structure is made of a hexagonal shaped aluminum structure and includes four bulkheads and six longerons. The P3/S3 truss also supports ELC (EXPRESS Logistics Carrier) locations.

The P4 and S4 segments photovoltaic Modules (PVM) include the two Solar Array Wings (SAW), the Photovoltaic Radiator (PVR), the Alpha Joint Interface Structure (AJIS) and Modified Rocketdyne Truss Attachment System (MRTAS), and Beta Gimbal Assembly (BGA).

The S3/4 truss was launched on STS-115 in September 2006 and the P3/4 truss was launched on STS-117 in June 2007.