Published: Nov 05, 2010 1:36 PM EDT
Updated: Nov 05, 2010 10:36 AM EDT

CAPE CANAVERAL, Fla. (AP) - Space shuttle Discovery has a fuel leak that threatens to delay Friday's planned launch.

Hydrogen fuel began leaking Friday morning, midway through the fueling process. NASA says it's the same type of problem that prevented a space shuttle from flying last year. It's considered a serious problem.

Launch controllers are considering their options as the countdown continues toward a 3:04 p.m. liftoff. The six astronauts have yet to board. The weather, meanwhile, is holding at 70 percent "go."

Discovery's final mission is already running four days late because of technical and weather problems. NASA has until Sunday to send the shuttle to the International Space Station. Otherwise, the flight will be off until December because of unacceptable solar angles.