Astronauts Anticipate Launch

The countdown for NASA's return to space began Sunday amid sky-high anticipation, although Hurricane Dennis (search) threatened to interfere with the liftoff of the first shuttle mission in more than two years.

At precisely 6 p.m., the multitude of countdown clocks started ticking down to a Wednesday launch of Discovery (search). The last time they flashed the hours, minutes and seconds remaining before a blastoff was in 2003, for Columbia's disastrous flight.

Test director Jeff Spaulding (search) said excitement had been "building and growing" ever since the space agency overcame fuel-tank difficulties that prompted a launch delay a few months ago.

"It's only recently, I think, that it's all come to fruition where we can see the light at the end of the tunnel," Spaulding said.

"There's some excitement for people to get back to launching again and also, I think, maybe a quiet reserve as well, just remembering where we've been. But we all do feel confident that we've done it right."

Added payload manager Scott Higginbotham: "It sure does feel good to be back in the saddle again. It's been too long."

The effects of Hurricane Dennis, which roared ashore on the Florida Panhandle off to the northwest, could be felt at the launch site Sunday as the sky was gray and solidly overcast.

Thunderstorms were forecast throughout the week. However, a ridge of high pressure offered hope that the storms may stay away at launch time Wednesday afternoon. Forecasters put the odds of acceptable weather at 70 percent, with conditions expected to worsen as the week wears on.

Because of the hurricane, the mission's seven astronauts flew in from Houston on Saturday evening, a day early.

Discovery will be making its first flight in four years when it takes off for the international space station with much-needed supplies and replacement parts.

Even before Columbia broke up during re-entry on Feb. 1, 2003, Discovery had been undergoing an extensive overhaul. The catastrophe prompted nearly 50 additional modifications, all of which will be demonstrated for the first time on this 12-day test flight. Techniques for inspecting the shuttle's thermal shield and fixing any holes also will be tested by the crew.

The biggest change, by far, is the redesigned external fuel tank.

Columbia's fuel tank lost a large chunk of foam insulation at liftoff. The debris slammed into the left wing, smashing a hole that proved catastrophic during re-entry. All seven astronauts were killed.

NASA removed the responsible section of foam and installed heaters in its place to prevent ice buildup from the super-chilled fuel. Just 11/2 months ago, engineers added a heater in another ice-prone spot on the tank; the work delayed the launch from May to July.

Managers also added extra checks for fuel-tank ice during the final portion of the countdown. Any significant patches of ice — which could be as lethal as flying foam — will mean a launch delay. Engineers considered putting infrared lamps at the pad to melt ice and covering vulnerable brackets with bags, but the ideas were scrapped, at least for now.

"With all the modifications, with all the improvements and changes and upgrades," Spaulding said, "certainly we can, without hesitation, say this will be the safest vehicle that we've ever had to launch."

That doesn't mean the tension level isn't high.

"It's a risky business so we're all sort of apprehensive," astronaut John Phillips said from the space station late last week. But he added, "I am fully confident that we've done what it takes to get this shuttle up here and I'm very anxious to see them come up here."