They have determined that the Shuttle replacement is the agency's number one priority right now and have moved its first test flight up even though that will push the first available launch date for STS-129 back to a date when it can not be launched unless another launch is postponed.
It takes two days to reconfigure all of the tracking hardware the Air Force uses to support launches and right now there is a military launch scheduled for 14 or 15Nov09, which means that STS-129 couldn't be launched before 17Nov09. The launch window for STS-129 is 16-19Nov09. After 19Nov09 NASA will have to stand down until 6-11Dec09 because of thermal concerns at ISS and a subsequent Russian satellite docking at ISS.
