Integrated Truss Structure
International Space Station assembly took a dramatic turn in late 1999 as a pre-integrated truss segment began sprouting from the top of U.S. Node 1 Unity .
Space Shuttle Discovery delivered truss segment "Z1" in October, 1999, signaling the beginning of work on the major elements that make the Station more than a unique vision with a good start.The integrated truss segments started with Starboard zero (S0) as the center assignment and were numbered in ascending order outward to the port (P) and starboard (S) sides. Starboard is the right side and port is the left side of the truss structure. Zenith (Z) is up, when the station is flying in its normal direction, in its normal orientation. At one time, there was an S2 and a P2 planned, but they were eliminated when the station design was scaled back. From S0, the truss segments are P1, P3, P4, P5 and P6 and S1, S3, S4, S5 and S6.
The first U.S. solar arrays called Port 6 were temporarily attached to Z1 a month later. They provided power for the initial work on assembly of the Integrated truss Structure -- the backbone of the ISS.
When it is completed, the truss will be the length of a football field, with its axis perpendicular to the Station's main axis. Its simple, girder-like appearance will mask its multiple ISS roles. When the P4 element was launched, NASA deployed a new External Wireless Instrumentation System (EWIS) (PDF) for the first time. The system consists of accelerometers placed around the outboard integrated truss structure to monitor the health of this complex truss structure. Labs, living quarters, payloads and systems equipment are directly or indirectly connected to it. Depending on demand, the U.S. solar arrays supply 84 to 120 kW of ISS usuable power -- enough to light a town.
Wires and cables will snake through the truss to carry energy and information to the Station's farthest reaches. Canada's Mobile Servicing System will move its 55-ft. robotic arm and hand along tracks attached to the truss. It also will house batteries, radiators, antennas and gyros.
Eight Space Shuttle missions will be required to deliver and assemble the Structure's eleven pre-integrated truss segments. Assembly of the International Space Station resumed with delivery of the the Boeing built Port 3/Port 4 truss (PDF) on STS-115 mission in August 2006. The final segment of the ISS truss segment, called Starboard 6 (PDF), was delivered on the STS-119 mission.
Learn more about the 11 Integrated Truss Segments at www.nasa.gov.