The problem is in assembling the shuttle's external tanks at the Michoud assembly plant in New Orleans. After the Columbia accident, numerous changes were made in the way that the now-notorious orange insulating foam is applied to parts of the tank.
They've fallen behind. The people at Michoud had to redo much of the work on existing fuel tanks -- and then they took a direct hit from Hurricane Katrina in 2005. Some workers moved elsewhere. The program has never recovered.
The tank for the next flight, STS-124 in May, has just been shipped to the Kennedy Space Center--but tanks for later missions may not be there in time.
One particularly sensitive case is STS-125, the mission by the shuttle Atlantis to repair the Hubble telescope, currently scheduled for the end of August. It's the one remaining shuttle flight that does not bring astronauts to the space station -- so if history repeats itself and Atlantis is damaged on launch the way Columbia was, a second shuttle will have to be on the launch pad, ready to go in case Atlantis' crew needs rescue.
That would mean two shuttles -- and two external tanks. Sources tell Gina that for now, that's a squeeze. They differ on how much the delays could be. A few months may not matter -- but if it's a lot more than that, the Hubble may give out for lack of new gyroscopes and batteries.
This story is developing. More as we get it.
UPDATE, Sunday evening:
We now have a couple of sources saying they can work through the delays. STS-124 still launches in May, though STS-125, the Hubble servicing mission, may slip from August to October.
(Photo: External Tank for STS-123, the shuttle mission currently on orbit, leaving Michoud last year. Courtesy: Lockheed Martin)