NASA begins countdown for launch

CAPE CANAVERAL, Florida (Reuters) - Clocks at the Kennedy Space Center in Florida began ticking down on Saturday toward Tuesday's planned launch of the space shuttle Discovery on a construction mission to the International Space Station.

The traditional three-day countdown was expected to culminate with the shuttle blasting off its seaside launch pad at 11:38 a.m. EDT on Tuesday.

"All of our systems are in good shape, said Charlie Blackwell-Thompson, a NASA launch manager said at a news conference. "I have no issues to report."

NASA's only impediment at this point might be the weather. Meteorologists predicted a 40 percent chance of a launch delay due to possible rain and clouds.

The U.S. space agency has until December 11 to launch Discovery, which is ferrying a critical connection hub to the outpost. The installation of the module, called Harmony, will provide a docking port for additional laboratories built in Europe and Japan.

NASA would like to fly two missions before that date, when launch opportunities close for the rest of the year. Europe's laboratory Columbus is scheduled for launch on December 6.

The shuttle's crew includes Dan Tani, who will replace NASA astronaut Clay Anderson as a live-in member of the space station crew. Anderson is to return home aboard Discovery.