NASA TV image of launchpad and virtual clock
In this image from NASA TV, a virtual countdown clock is superimposed over a view of the shuttle launch pad. The clock shows one day, 18 hours, 56 minutes and 21 seconds. The time is less than the amount of time until the schedule liftoff, because of a series of built-in pauses that halt the countdown.
By Alan Boyle Science editor
updated 7/10/2005 6:55:17 PM ET 2005-07-10T22:55:17

The countdown is under way for the first space shuttle mission in 2 1/2 years — a mission whose main aim is to make sure the problems of the last disastrous shuttle flight can be caught and perhaps corrected.

After fits and starts, NASA says it has changed its hardware and its "safety culture" enough to resume flights after the breakup of the shuttle Columbia on Feb. 1, 2003, which killed all seven astronauts and brought America's human spaceflight program to a halt.

Investigators say flying foam insulation from Columbia's external fuel tank knocked out a portion of the orbiter's left wing just after launch. During re-entry, 16 days later, superheated gases entered through the hole and destroyed the shuttle from within, the investigation concluded.

"A lot has happened over the last 2½ years", NASA test director Jeff Spaulding told journalists Sunday. "Our focus during that time frame has shifted, from recovery and investigation, to one of redesign and improvement, to mission processing and now to launch."

Discovery's countdown began at 6 p.m. ET Sunday, starting at T-minus 43 hours. In a sign of changing times, as well as the intense interest in the mission, NASA TV used some electronic tricks to display a countdown from 1:19:00:00 — one day and 19 hours — even though Kennedy Space Center's Apollo-era outdoor clock is incapable of showing times of more than 24 hours. The virtual clock was superimposed on a view of the launch pad.

If all goes as planned, the countdown will climax with liftoff at 3:51 p.m. ET Wednesday. NASA's official clock does not match the actual amount of time before the scheduled liftoff because it takes into account a series of built-in pauses, during which time the clock simply freezes.

Spaulding pronounced the shuttle to be in "excellent shape," with weather looming as the biggest uncertainty. Earlier worries about Hurricane Dennis led NASA to bring the shuttle crew in a day early, and at one point launch managers even considered moving Discovery off the pad. But the hurricane made landfall Sunday well to the west, and launch weather officer Kathy Winters said there was a 70 percent chance of favorable conditions for liftoff.

"Our main threat will be inland thunderstorms" that may stir up near the space center, she said.

Winters said prospects for launch could worsen slightly later in the week, partly as a consequence of Dennis' passage. If Wednesday's weather is unacceptable, NASA could reschedule the launch for Thursday. After that, the next backup launch day is Saturday, Spaulding said.

If Discovery is unable to launch by July 31 due to weather or mechanical problems, the mission would have to be put off until September. That timing is dictated by the requirements for a just-right rendezvous with the international space station, as well as a daytime launch that will make it easy for more than 100 cameras to monitor the shuttle's ascent to orbit.

Long wait for the crew
It's already been a long wait for Discovery's crew of seven, headed by Eileen Collins, NASA's only experienced woman commander. But former astronaut Rick Hauck, who commanded Discovery in 1988 on the first shuttle mission after the 1986 Challenger explosion, said Collins is as steady as they come.

"I've spent a little bit of time with Eileen ... and she is so together, and so ready, and the crew is so ready, that there's very little advice I could give her," he told

But Hauck said he and Collins have discussed how to pay tribute to Columbia's crew. Although Collins has kept mum about exactly what she and her crewmates will do, Hauck recalled that his crew set aside some time toward the end of the 1988 mission for personal memorials to Challenger.

"Each one of the five of us tailored some remarks," he said, "We each spoke our words."

Changed mission
Originally, Collins and her crew were to fly right after Columbia, in March 2003, ferrying a fresh crew to the space station. Now the mission has changed.

Discovery will still bring tons of supplies to the station. Spacewalkers will replace a balky station gyroscope and install a storage platform on the station's hull. But the mission's biggest job is to test the methods for inspecting the shuttle and fixing cracks in the shuttle's protective outer skin.

For the first time, the shuttle's 50-foot-long robot arm will stretch out a newly designed extension boom that's just as long, using sensors and cameras to check the orbiter's nose and edges of the wings.

The on-orbit inspection, along with the unprecedented imagery of the launch and readings from temperature sensors on the shuttle orbiter and fuel tank, would have detected the kind of damage that felled Columbia, NASA says.

Discovery's crew will try out three techniques for sealing cracks in the shuttle's thermal protection tiles and its reinforced wing panels: a glorified caulking gun, a daub-on adhesive applicator and screw-in plugs. But even the space agency admits that astronauts could not have fixed a Columbia-size hole.

In that event, Discovery's astronauts would have to take shelter on the space station and wait for a rescue mission. Spaulding said the next shuttle in line, Atlantis, could be launched as early as Aug. 13 if needed to retrieve a marooned crew.

Many of the shuttle's upgrades are aimed at avoiding damage in the first place: The external fuel tank and its fittings have been redesigned to minimize the risk of flying foam, and new, improved heaters have been installed on the tank to keep hazardous ice from building up.

Last month, a task force monitoring NASA's return to flight reported that the space agency still hadn't fully addressed the risks from foam and ice, but members of the task force also said that "incomplete" mark shouldn't stand in the way of this week's scheduled launch.

Then and now
Discovery's astronauts have voiced more anticipation than trepidation during the final days before flight.

"It's been two and a half years since a crew stood here before you, and that's way too long," Australian-American spacewalker Andrew Thomas told reporters Saturday night after he and the rest of the crew arrived at Kennedy Space Center. "And it is definitely time that we went back to flight and back to space."

Hauck said that sentiment isn't surprising, based on his own return-to-flight experience. "You find yourself saying, 'Let's get on board this ship and head out to space,'" he said.

Hauck recalled that he breathed a big sigh of relief after Discovery's launch in 1988, but he guessed that Collins and her crew members would have an additional nagging thought in the back of their minds all the way until landing. "You know you've got to come back home, and that's when your friends were killed," he said.

But an awareness of the risks comes with the territory. It is a part of every spaceflight, Hauck said.

"If you don't have some fears and some issues to deal with, then you probably should not be in this," he said.

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