Obama's Space Summit Coming Amid Discovery's Mission, 13 News

"Even if the shuttle program were extended today, there would still be some a gap. "The real issue we would have is just in manufacturing," [space shuttle program manager John] Shannon explained. "While you have a supply chain, while you can get a workforce back to build things like external tanks, there would be some type of a gap -- and right now, we estimate that gap would be about two years, from when we're told to when we would have the first external fuel tank rolling off the assembly line."

If shuttles kept flying, what would mission be?, Orlando Sentinel

"In response, NASA has reached out to shuttle suppliers and vendors to check whether there would be any issues, beyond the cost of restarting production lines, should NASA keep flying the orbiter fleet. The agency is also examining whether there will be enough spares on the station to continue operations until 2020."