Live at KSC: Leak Troubleshooting Continues

LIVE IMAGES: The images above are from live video feeds from the Launch Complex 39 area at Kennedy Space Center, where Endeavour and seven astronauts are scheduled to blast off at 5:40 a.m. on an International Space Station assembly mission. They will automatically refresh to the most up-the-minute image every 30 seconds, and you can click to enlarge them.

Engineers have again stopped the flow of liquid hydrogen to Endeavour's external tank.

The same sort of leak that forced NASA to scrub a first launch attempt on Saturday has cropped up again.

NASA TV commentators say the signatures this time are different, including lower leakage levels after a vent line valve was cycled a second time.

But the leak remains at an "out of spec" parameter, commentators said.

About 15 minutes remain in a planned hold before the countdown to a 5:40 a.m. launch is supposed to pick up at the T-minus-3-hour mark.

No decisions have been made, but the timeline for a launch is becoming extremely tight and it's unclear how the launch team will make up time lost to earlier storms and now the leak.

Before the problem arose, Endeavour commander Mark Polansky wrote in his latests tweet that the crew was "putting on our game faces."