NASA to make sixth attempt for space shuttle launch

NASA is poised to try to get the Endeavour space shuttle off the ground and into orbit on Wednesday, after bad weather and technical trouble blighted five previous launch attempts.

Fueling of Endeavour's massive external fuel tank, which began at 8:38 am (1238 GMT), showed no early signs of problems, but experts noted that the same rainy weather systems that hampered prior attempts continue to linger in the area.

"The weather is looking better but I am being a little bit optimistic -- it's about the same as we had over the last couple of days," said launch integration manager Mike Moses.

The shuttle is scheduled for a 6:03 pm (2203 GMT) lift-off, carrying seven crew members to the orbiting International Space Station (ISS) where they are to complete the assembly of the Japanese Kibo laboratory.

Endeavour's launch has been cancelled three times since Saturday due to inclement weather. Two earlier attempts were aborted after potentially hazardous fuel leaks were discovered, apparently caused by a misaligned plate linking a hydrogen gas vent line with the external fuel tank.

In the summer, Florida weather is often unstable in the afternoon, with violent storms and heavy rains that can prevent launches.

The previous lightning storms and fuel tank problems left the cash-strapped US space agency footing 4.5 million dollars in extra costs attached to the scrapped launch attempts, as officials kept their fingers crossed that they would finally have a success.

"The cost of a scrub is approximately one million dollars," said spokesman Allard Beutel at NASA's Kennedy Space Center at Cape Canaveral, Florida.

Along with the cost of filling, draining and then refilling the external tank so many times with specialized liquid hydrogen and oxygen fuel, expenses also sky-rocketed due to overtime pay for NASA employees and other workers at the space centers here.

But Beutel said the added costs were "marginal" in NASA's overall operating budget. The agency says Endeavour alone, built to replace the shuttle Challenger, cost some 1.7 billion dollars.

Endeavour was originally scheduled to launch June 13 but a liquid hydrogen leak twice postponed it last month.

In addition to the potential Wednesday blast-off, a launch was also being considered for Thursday, the last possible date before interfering with the July 24 lift-off of the Russian cargo craft Progress to the ISS, Moses said.

A Thursday launch date would force NASA to abandon one of five space-walks planned for Endeavour's mission.

If the shuttle does not take off on Wednesday or Thursday, the next launch window would begin on July 26.

Endeavour's crew of six Americans and one Canadian is scheduled to install a platform on the ISS for astronauts to conduct experiments in the vacuum of space, 350 kilometers (220 miles) above Earth's surface.

The ISS should be completed in 2010, also the target date for the retirement of the US fleet of three space shuttles.

The crew of the Endeavour mission includes Canadian Julie Payette, an electrical and information engineer who has been in space before and is the only woman on board.

Two other members of the crew, including Polansky, have previously traveled in space, while four of the astronauts will be on their maiden space voyage.

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

He would be the latest addition to the permanent crew of the ISS, which is a joint collaboration between 16 different countries.

The US space agency has been extra cautious about conditions for the exit and return of space shuttle missions since the Columbia blew apart some 20,000 meters (65,500 feet) above the Earth in 2003 as it was returning from a 16-day space mission to land in Florida.

A chunk of insulation that broke off from the shuttle's external fuel tank during takeoff had gouged Columbia's left wing heat shield, allowing superheated gases to melt the shuttle's internal structure, leading to its explosion and the death of its seven astronauts.

The Columbia tragedy was the second shuttle accident since the program was launched in 1981. On January 28, 1986 the Challenger shuttle blew up 73 seconds after lift-off, also killing seven astronauts on board.