 So P2 and S2 were canceled.The P3/P4 truss assembly was installed by the Space Shuttle "Atlantis" STS-115 mission, launched September 9, 2006, and attached to the P1 segment.The P3 and P4 segments together contain a pair of solar arrays, a radiator and a rotary joint that will aim the solar arrays, and connects P3 to P4.