This story was updated at 5:10 p.m. EDT.
CAPE CANAVERAL - Discovery is moving in the wrong direction but for the right reasons, workers said as the shuttle began rolling back to the launch pad at Kennedy Space Center this morning.
The gigantic crawler-transporter first nudged forward at 6:44 a.m. under cloudy skies, delayed from a 2 a.m. start while paperwork was completed. Then it moved steadily along the river-rock-lined crawlerway at nearly 1 mph.
The shuttle paused near the Vehicle Assembly Building early this afternoon with an overheated bearing in the crawler-transporter. Workers repacked the bearing in grease and let it cool, NASA spokesman Bruce Buckingham said. It was under way again before 3 p.m. and entered the Vehicle Assembly Building about 4:30 p.m.
"It's another slow step in the right direction, and it's another indication that we're not going to fly until it's safe to do so," said crawler supervisor Ray Trapp of Port St. John as he watched the ship move slowly off the pad.
Brian Jones and a couple of co-workers were there to take pictures of the ship, for "the excitement of going back to flying again," he said.
The rollback, which will allow NASA to substitute the shuttle's external fuel tank, was essential for safety reasons, he said.
"I think it's a good thing," said Jones, an elevator worker for contractor United Space Alliance who lives in Mims. "It has to be right before it goes."
The new fuel tank will have a heater designed to prevent ice from building up as supercold propellants are loaded. Ice and insulating foam can fly off the tank during launch and strike the orbiter.
Such a strike fatally damaged Columbia during its January 2003 launch, leading to a breach that allowed hot gases to penetrate the orbiter when it tried to re-enter the atmosphere.
Discovery, moving at nearly 1 mph, should reach the Vehicle Assembly Building in mid-afternoon.
It is expected to roll back to the pad with the new tank and solid rocket boosters my mid-June, aiming for a July 13 launch.
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