Space Shuttle Launch Just Hours Away

NASA is going forward with its Wednesday launch of space shuttle Discovery, the space agency announced Tuesday. It will be the first shuttle launch since Columbia blew apart on re-entry over the skies of Texas on February 1, 2003, killing all seven astronauts onboard.

Launch is scheduled for Wednesday for 3:51 p.m. ET from Florida's Kennedy Space Center.

"We're tracking no significant issues in our preparations as the hardware continues to perform nominally," said NASA Test Director Jeff Spaulding at Tuesday's countdown status briefing.

Storm systems have threatened to delay the launch, but NASA officials said conditions still indicate only a 40 percent chance for a launch delay due to weather, according to Shuttle Weather Officer Kathy Winters.

"We're going to see some showers and possibly even a thunderstorm develop during the countdown. We might actually have to go red during the countdown. But then as the sea breeze progresses to the west with the easterly flow, we should actually see an improvement in the weather at the launch pad," Winters said.

NASA has committed to daytime launches for the next two shuttle missions to ensure ideal lighting conditions for the cameras that will scrutinize the shuttle's ascent into orbit.

The shuttle Columbia accident was caused by foam insulation which broke off during launch from the shuttle's external fuel tank, striking and cracking a panel on the orbiter's wing. When the shuttle re-entered the Earth's atmosphere 16 days later, searing hot gases seeped into the wing and incinerated the spacecraft.

NASA immediately grounded its three remaining shuttles and pledged to find the problems, fix the shuttle and return to flight.

In the 2 1/2 years since the accident, NASA has undergone a wrenching overhaul of the shuttle program.

The shuttle has a new fuel tank designed to prevent foam chunks like the size that downed Columbia from breaking off and hitting the spacecraft.

NASA engineers have also designed an orbital boom sensor system, which is a second robotic arm that is tipped with cameras and other instruments and mounted in the shuttle's payload bay.

Once in orbit, shuttle astronauts will use the boom to inspect the panels on the orbiter's wings and nose cone for any damage that might have occurred during launch.

But repairing damage to the protection system -- should any be found -- could prove difficult.

Engineers have been developing and testing plugs and crack-repair procedures for the reinforced carbon-carbon panels, as well as tile-repair techniques, for use in the event of damage. Two such methods will undergo limited testing in orbit by Discovery astronauts, but mission managers acknowledge that their techniques will likely need to be modified before they can be certified.

Most NASA engineers agree that astronauts would never be able to repair a hole the size of the one that doomed Columbia.

"The past two and half years have resulted in significant improvements that have greatly reduced the risk of flying the shuttle. But we should never lose sight of the fact that space flight is risky," said NASA Administrator Michael Griffin.

Discovery will also deliver much-needed supplies to the international space station.

Two and half years have passed since the space shuttle, with its school bus-sized payload bay, visited the station. Discovery will deliver a replacement gyroscope, an external storage platform and an Italian cargo carrier called Raffaello. The storage platform is needed for upcoming flights when it will be used to assembly the rest of the station.

For most of its scheduled 13-day mission, the crew will devote its time to inspecting and testing repairs for the shuttle's delicate silicon tiles and reinforced carbon-carbon panels around the nose and wings. Damage to the panels on the left wing led to Columbia's destruction.

"This has been a long journey for all of us. It's been a long story in many of our lives, but we're all committed to seeing that we have a happy ending. And with that, our hardware is ready to fly, " said STS-114 Payload Manager Scott Higginbotham.