Space agency officials said Tuesday they are confident they've solved mechanical problems that have dogged the mission since December. However, weather prospects for Thursday afternoon's launch are poor: a forecast for rain offers just a 40 percent chance of favorable conditions.
Launch director Doug Lyons said the countdown was going well, and "we're hoping it will stay that way."
"We're all thinking that Thursday's the day regardless of what the weather guy might tell you," he said.
Atlantis should have carried up the European Space Agency's lab, called Columbus, in December. But the flight was grounded by erratic fuel gauges in the shuttle's external tank. The problem was traced to a faulty connector.
Then just last week, a bent radiator hose posed a new problem. It was straightened, but engineers suspect the hose will bunch up again at the end of the 11-day flight. Most likely, astronauts could work around that.
The worst that could happen would be for the hose to burst and lose all its Freon, leaving Atlantis with just one good working coolant loop instead of two. That would require the shuttle to return quickly to Earth, said LeRoy Cain, chairman of the mission management team.
Some 300 Europeans will return to the launch site Thursday in hopes of seeing their space lab finally blast into orbit — after back-to-back disappointing mission scrubs in early December.
In the works for two decades, the $2 billion Columbus lab has endured many setbacks: space station design changes in the 1980s, delays by the shuttle and Russian station module in the 1990s, and the Columbia disaster in 2003 when seven astronauts died and all NASA missions were on hold until 2005.
After all that, two more months of waiting isn't so bad, observed Alan Thirkettle, the European Space Agency's station program manager.
"We've indeed waited a long time for this launch, and it's just going to make it all the better when it gets up there and it works," he said.
It will take a few weeks to determine the lab is in good shape and a few more weeks before science data start flowing, Thirkettle said.
Columbus, a 23-foot compartment, will join the U.S. Destiny lab at the space station. The even bigger Japanese lab, Kibo, will follow in sections, beginning with next month's shuttle launch.
