Weather worries cloud Endeavour launch attempt

Inclement weather loomed over the space shuttle Endeavour's third launch attempt, as NASA moved ahead with preparations for the mission to blast off to the International Space Station.

The shuttle is now scheduled to lift off with seven astronauts onboard at 7:39 pm (2339 GMT) from the Kennedy Space Center at Cape Canaveral in Florida.

"Everybody is 'go' for launch; we have no major issues at all," said Mike Moses, chairman of the mission management team, which completed its final review Friday.

But one problem remained: weather.

Shuttle weather officer Kathy Winters warned that showers, thunderstorms and icy cloud could interfere with the final countdown.

There is 60 percent chance of inclement weather conditions "prohibiting" the shuttle's latest launch attempt, she said.

The rotating service structure at the shuttle's Launch Pad 39A was set to begin rolling back late Friday, paving the way for Endeavour's external fuel tank to be filled starting at 10:14 am (1414 GMT) Saturday, NASA said.

It is a long process, taking three hours for technicians to fill the fuel tank with two million liters (half a million gallons) of liquid hydrogen and oxygen at very low temperatures.

Two previous launch attempts were scuttled by potentially hazardous hydrogen leaks, but NASA said tests to the Endeavour following repairs to an external fuel tank proved problem-free.

NASA said a misaligned plate linking a hydrogen gas vent line with the external fuel tank had caused the leaks on June 13 and 17.

If the launch is moved to Sunday, chances of good weather jump to 60 percent, rising to 70 percent on Monday.

Endeavour is due to conduct a 16-day voyage to install a platform on the ISS that will allow astronauts to conduct experiments in the vacuum of space, 350 kilometers (220 miles) above Earth's surface.

Endeavour will carry into space a seven-person crew, including six Americans and one Canadian -- Julie Payette, an electrical and information engineer and the only woman on board.

Payette has been into space before, as have two other members of the crew, including shuttle commander Mark Polansky.

The crew's four other members will be on their maiden space voyage.

It is also expected to carry the latest additions to the ISS's permanent crew, which is made up of astronauts from 16 countries.

American Tim Kopra, 46, an aerospace engineer, will replace Japanese astronaut Koichi Wakata, spending several months aboard the floating space station.

The rest of the crew is scheduled to head back to Earth on July 27, with a planned landing at the Kennedy Space Center and back up landing sites in case of bad weather in Edwards, California or White Sands, New Mexico.

The astronauts will undertake repair and replacement work, including installing six new batteries in the ISS.

The mission, which will require two astronauts to conduct five space walks totaling 32.5 hours, is the last of three trips being undertaken to assemble the Japanese Kibo laboratory aboard the orbiting space station.

Kibo's two pressurized modules were attached to the ISS in 2008, along with the European lab Columbus.