STS-115 was a Space Shuttle mission to theInternational Space Station (ISS) flown by Space Shuttle Atlantis. It was the first assembly mission to the ISS after the Columbia disaster, following the two successful Return to Flight missions, STS-114 and STA-121 STS-115 launched from Pad 39-B at the Kennedy Space Centre on 9 September 2006 at 11:14:55 EDT (15:14:55 UTC).
The mission is also referred to as ISS-12A by the ISS program. The mission delivered the second port-side trusssegment (ITS P3/P4), a pair of solar arrays (2A and 4A), and batteries. A total of three spacewalks were performed, during which the crew connected the systems on the installed trusses, prepared them for deployment, and did other maintenance work on the station.
STS-115 was originally scheduled to launch in April 2003. However, the Columbia accidentin February 2003 pushed the date back to 27 August 2006, which was again moved back for various reasons, including a threat from Tropical Storm Ernesto and the strongest lightning strike to ever hit an occupied shuttle launchpad.

Columbia's demise was due to a piece of foam, shed from its external tank, striking the shuttle's left wing during launch and causing a hole that was breached during re-entry.
The meeting also discussed problems with the bolts securing the shuttle's Ku-band antenna, which might not have been threaded correctly. The installation had been in place for several flights and hadn't experienced any problems. At the end of the two-day meeting, NASA managers had decided to proceed with the launch on 27 August 2006. However, on 18 August 2006, NASA decided to replace the antenna bolts with Atlantis still on the launch pad. NASA had no procedure to replace these on the pad, but the work was nonetheless completed by 20 August, without affecting the planned launch date.
On 25 August 2006, a direct lightning strike, the most powerful recorded at Kennedy Space Center, hit the lightning rod atop the launch pad. As a result, on 26 August the Mission Management Team ordered the mission postponed for at least 24 hours to assess damage. On 27 August, the decision was made to postpone the launch for another 24 hours, making the earliest possible launch date 29 August 2006, still unassured that there was no damage from the lightning strike and taking into account the possible threat from Hurricane Ernesto.
On 28 August 2006 it was decided to postpone the launch and rollback Atlantis to the VAB after updated forecasts projected Hurricane Ernesto would regain its strength and pass closer to Kennedy Space Center than previously anticipated. NASA began rolling back the shuttle on 29 August 2006 in the late morning, but by early afternoon the decision was made to move Atlantis back to the launch pad (something that has never been done before) to weather out Tropical Storm Ernesto instead. The change came after weather forecasters determined that the storm wouldn't hit Kennedy Space Center as forcefully as they once thought. Its peak winds were expected to be less than 79 mph (126 kilometers per hour), NASA's limit for keeping the shuttle outdoors.
By the early morning of 31 August 2006, the storm had passed and inspection teams began a survey for damage to the launch facilities. Only three problems were discovered, all of which were simple repairs. A target date for launch was set for 6 September with the option to launch for another two days after NASA and Russian space managers agreed to extend the launch window by one day. On the morning of 3 September 2006, the official countdown began at the T minus 43-hour mark, with about 30 hours of scheduled holds. In the early morning of 6 September 2006, engineers observed an apparent internal short when one of the three electricity producing fuel cells was powered up. When engineers couldn't figure out the problem in time, the launch was scrubbed for the day to further analyze the fuel cell problem. Late Wednesday evening NASA managers decided that they would not attempt a launch on Thursday, and scheduled the next launch attempt for 8 September 2006. Originally they had ruled out 9 September as a potential launch date due to a conflict with the planned Russian Soyuz mission Soyuz TMA-9, which was scheduled to, and did, launch on 18 September 2006. This caused some news agencies to report that Friday as the last chance for a launch until October.

Atlantis was rolled out from the Orbiter Processing Facility to the Vehicle Assembly Building (VAB) on 24 July 2006. It was lowered onto the mobile launcher platform on 26 July and rolled out to Pad 39B in the early morning hours of 2 August. The rollout was scheduled for 31 July, but a storm in the vicinity of the Kennedy Space Center resulted in a delay of two days from fears of the orbiter being hit by lightning, which could cause immeasurable damage.
Top NASA managers held a Flight Readiness Review (FRR) meeting 15–16 August 2006 to finalize the launch date. Foam loss from the external tank was a key issue at this meeting because on 13 August 2006, NASA announced there was an average amount of loss from the external tank of STS-121, the previous mission.