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

"The test was very successful. We did not have any leaks, any issue or any anomaly," said NASA test director Charlie Blackwell-Thompson at a press conference on Wednesday.

On Thursday, Steve Payne, also a test director at the space agency, said the shuttle launch was on track for July 11 at 2339 GMT from the Kennedy Space Center at Cape Canaveral in Florida.

"I am pleased to report that our launch countdown operations are proceeding on schedule and without significant issues," he said.

NASA said a misaligned plate linking a hydrogen gas vent line with the external fuel tank had caused last month's leaks.

"Currently, our systems are in excellent shape, we have no issue whatsoever to report. The Endeavour crew and the launch team are ready to go," Payne said.

In addition to time pressures created by two cancelled launch attempts, the race is on to finish construction at the ISS before September 2010, when NASA is due to retire its shuttle program and start focusing on new space vehicles.

But ahead of the scheduled launch Saturday, there were questions about weather conditions

"We expect that we will see some afternoon thunderstorms in the area around launch time," said shuttle weather officer Kathy Winters.

"We are forecasting 60 percent (chance of) weather prohibiting launch -- which is of course, 40 percent chances for 'go' weather."

If the launch goes ahead, 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 voyage into space, though all have training experience as astronauts.

Endeavour is set 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.

The astronauts will also undertake other 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

The crew's first space walk is scheduled for the mission's fourth day, with the rest following on the sixth, eighth, 10th and 13th days the shuttle is in space.

The Endeavour is also carrying the latest addition to the ISS 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.

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