NASA is discussing International Space Station (ISS) scheduling conflicts with the Russian Federal Space Agency because the US agency's mission managers have decided to roll back Atlantis and that will see its launch delayed till next week, which means the shuttle could still be docked to the ISS, on its 11-day STS-115 mission, when a manned Soyuz vehicle is planned to arrive there.
At a midmorning briefing, local time today, the NASA mission manager's announced that rollback preparations are proceeding to ensure Space Shuttle Atlantis would be safely back in the vehicle assembly building (VAB) before the effects from tropical storm Ernesto would be felt at the Kennedy Space Center (KSC).
At the briefing shuttle weather officer Kathy Winters explained that KSC could expect tropical storm force winds Wednesday morning, local time, and hurricane force winds by 1700EDT (2100GMT) if Ernesto's current track and strength holds.
"We'd like to get off the pad tomorrow morning if at all possible," says NASA launch director Mike Leinbach, "based on tomorrow afternoon's local weather, we'd much rather be back in the VAB earlier rather than later."
Once rolled back to the VAB this time Atlantis will need eight days of launch preparations once it is returned to launch pad 39B, giving a possible launch date of  7 September or later. The launch window extends to 13 September but NASA needs a 7 September lift off to avoid the scheduling conflict with the Soyuz vehicle also bound for the ISS.
The Soyuz is to launch on 18 September and would reach the ISS on the following day. Atlantis has an 11-day mission planned and would undock from the ISS on the tenth day, which would be the same day as the Soyuz's arrival if Atlantis were to launch on 9 September.

 Atlantis rolls from the VAB for STS-115

 Above: Atlantis is rolled by the mobile transporter with launch pad 39B behind

The last time a shuttle was rolled back to the VAB was Shuttle Discovery on 26 May 2005. A new modified external fuel tank was needed for that mission, STS-114, which was the first return to flight following the 2003 Columbia disaster. Before that Atlantis had to be rolled back twice for mission STS-98 on 2 January and 19 January 2001. The first roll out to the launch pad was stopped and a roll back ordered after a malfunction on the transporter and the second roll back was caused due to uncertainty involving the integrity of the solid rocket booster cables.