Discovery is off! Orbit in 8.5 minutes

ON A ROLL: Discovery is the third shuttle to launch without a delay. Atlantis will launch Dec. 6. NASA photo.

With a shrinking piece of ice on a fuel line and clouds moving in on the launch pad, Discovery launched on time at 11:38 a.m EDT, bound for the International Space Station on the most complex construction mission of the program's history.

The 14-day mission ends Nov. 6.

All launch teams cleared the shuttle for launch, despite the ice. Shuttle Weather Officer Kathy Winters cleared Discovery for launch, though clouds are approaching.

"The ice is diminishing in size. It is dissipating. All appears to be go," said the NASA TV commentator shortly before launch.

The final inspection team completed their check of a four-inch piece of ice on the fuel line bracket. Pictures from cameras at the pad seem to indicate less ice than was present before.

The ice was found on the 17-inch liquid hydrogen umbilical fuel line that goes into the tank. The ice appeared to be 4 inches by 1.5 inches in diameter, NASA said.

The shuttle team is also looked into a slight reading of hazardous gas in the aft of the orbiter. An "extremely minor" measurement of liquid hydrogen gas in the aft compartment is the issue. The early analysis is that it won't be an issue for launch because the amount is so tiny.

The crew is led by the second female commander, Pam Melroy, and will deliver Dan Tani to the ISS, while bringing flight engineer Clay Anderson home.