Space Shuttle Discovery Returns to Launch Pad

After more than 10 hours and a series of brief delays, the space shuttle Discovery rolls up the ramp toward Launch Pad 39B at NASA's Kennedy Space Center in Cape Canaveral, Florida on June 15, 2005. CREDIT: NASA/KSC.

The space shuttle Discovery is once again atop its Florida launch pad, after receiving a fresh external tank in preparations for NASA's first orbiter flight since the Columbia disaster.

It took Discovery and its Mobile Launch Platform more than 10 hours to reach Launch Pad 39B Wednesday at NASA's Kennedy Space Center in Cape Canaveral.

"It's a good one to have under our belts again," NASA spokesperson Bruce Buckingham said of the successful rollout.

Wednesday's rollout began at 1:58 a.m. EDT (0558 GMT) as Discovery's massive crawler carrier inched its way out of the 52-story Vehicle Assembly Building (VAB) and onto the 4.2-mile (6.7-kilometer) track to the launch pad.

The space shuttle was initially slated to begin rollout operations at about 12:01 a.m. EDT (0401 GMT), but difficulties switching power systems from the VAB to the transporter carrier, as well as minor clearance issues and the need to remove some access platforms, led to the delay, NASA officials said.

USA crawler drivers halted the massive shuttle transporter periodically to allow overheating bearings a chance to cool down before continuing toward the launch pad.

"We had a few stops on the way, but it's there," said Tracy Yates, a spokesperson for shuttle contractor United Space Alliance (USA).

At 12:17 p.m. EDT (1617 GMT), Discovery's Mobile Launch Platform settled onto the launch pad, Buckingham added.

Set to launch no earlier than July 13, Discovery first reached its launch pad on April 7, but returned to NASA's massive Vehicle Assembly Building to switch to a new external tank - originally slated to fuel the Atlantis orbiter during STS-121 - equipped with a heater to cut down ice buildup.

Shuttle managers believed that ice debris from Discovery's original external tank could endanger the orbiter if it shook loose during launch and struck a vulnerable area. That tank will also be equipped with an additional heater to prevent ice buildup.

Minimizing the amount of ice and foam debris from shuttle external tanks at launch has been a prime concern for NASA since the Columbia orbiter was struck by a suitcase-sized chunk of tank insulation foam during launch in 2003. That debris gouged a hole in Columbia's protective thermal skin, and later allowed hot gases to enter the orbiter's wing during reentry on Feb. 1, 2003. The orbiter broke apart while flying over Texas, killing its seven-astronaut crew.

Discovery's STS-114 mission will test a series of orbiter and external tank modifications to increase shuttle flight safety, as well as resupply the International Space Station.

It will be followed by a second test flight, Atlantis' STS-121 mission, later this year, NASA officials said.

• Fixing NASA: Complete Coverage of Space Shuttle Return to Flight