Space Shuttle Atlantis launched successfully from Kennedy Space Center's pad 39B today for its 11-day International Space Station (ISS) assembly mission STS-115, during which its crew will install the P3/P4 trusses to provide more solar arrays and therefore more power for the orbital outpost.

During its ascent main engine shut off will occur at 11:23 local time and once in orbit the crew, commander Brent Jett, pilot Christopher Ferguson and mission specialists Heidemarie Stefanyshyn-Piper, Joseph Tanner, Daniel Burbank and the Canadian Space Agency's Steven MacLean,  will conduct system checks before going to sleep at 21:15GMT. STS-115 will re-start the assembly sequence of the ISS, stopped after the 1 February 2003 Shuttle Columbia disaster that halted Shuttle flight operations for more than two years. The launch of Atlantis has been delayed since its planned 27 August lift off due to a lightning strike, tropical storm Ernesto and technical problems.

Shuttle Atlantis's launch today followed a successfull re-fuelling operation that saw the Shuttle's external tank's (ET) engine cut-off (ECO) sensors perform correctly. Yesterday's launch attempt was cancelled due to the number three ECO sensor, which monitors hydrogen fuel levels, showing an incorrect reading. ECO sensors help ensure Shuttle main engines shut down at the correct time, while there is still some propellant left, so the engines can't run dry and damage themselves.

Atlantis's 8 September launch was cancelled because of countdown rules developed due to ECO sensor problems with Shuttle Discovery's propellant tank in 2005. The rules mean pad 39B workers drain the ET of fuel if a sensor is malfunctioning and then re-fuel it for a following day lift off.  If one sensor still shows an incorrect reading, the launch countdown would go ahead but further sensor problems would have meant the Shuttle being rolled back to the vehicle assembly building and the failed sensors removed and replaced.

Despite the resolution of the ECO sensor issue Atlantis still has a problem with its number one fuel cell, which is one of three cells providing onboard Orbiter power. The cell's coolant pump has had electrical problems but the NASA mission management team decided it could launch with two functioning fuel cells.

If NASA had had to remove Atlantis's ET's ECO sensors a September launch would have been abandoned and re-scheduled for the next daylight window, which starts on 26 October. Because NASA wants to image the ascending Shuttle to monitor ET foam debris loss it currently requires Shuttle to launch in daylight. The daylight requirement affects the launch window times and dates.

NASA has been able to launch today because of Russian agreement. Russia's Federal Space Agency (FSA) agreed that the arrival at ISS of its Soyuz TMA-9 spacecraft, carrying the first female space tourist Anousheh Ansari and two ISS expedition 14 crew members, on 20 September would be possible despite Shuttle only having left the space station hours before.

With a 9 September launch Atlantis's 11-day mission means it departs on 20 September. Soyuz TMA-9 is launched on 18 September and arrives two days later. The Soyuz TMA-8 spacecraft is already docked at the ISS and has been since its 1 April arrival. It will return to Earth in late September with Ansari and two of the current ISS expedition 13 crew members. TMA-9 will remain docked until next March, acting as the ISS's emergency return vehicle.

If today's launch had been cancelled for any reason NASA could attempt to launch in late September if they chose to relax the daylight launch rules.