Five hours after starting space shuttle Atlantis on a slow crawl toward its hangar, NASA reversed course Tuesday and sent it back to the launch pad, saying the forecast for Tropical Storm Ernesto had improved.

The change could give NASA a small window — a day or two — to attempt a launch next week. The space agency is trying to keep to a tight schedule of flights to complete construction of the international space station.

"We're going to give it a fighting chance," said launch integration manager LeRoy Cain.

Atlantis was almost halfway into the 12-hour journey back to the Vehicle Assembly Building aboard a giant, caterpillar-track platform Tuesday afternoon when NASA officials changed their mind and sent the shuttle back to the pad, something that never has been done before.

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At the launch pad, the shuttle will be partially protected from gusts by a 130-foot-high rotating metal structure. Technicians planned to hook up essential connections between Atlantis and the launch pad late Tuesday before leaving the space center ahead of the storm.

"We made a call that surprised some folks," said launch director Mike Leinbach. "We feel good about the decision. ... This is the best way to go."

Ernesto's peak winds were expected to be less than 79 mph, the threshold at which it is mandatory to move the shuttle indoors. Earlier, the National Hurricane Center had forecast a higher chance of such winds.

Tuesday morning, when the decision was made to start moving Atlantis back indoors, the forecast showed gusts of up to 75 mph approaching the Kennedy Space Center on Wednesday, but by noontime the forecast had top winds reaching only 63 mph at most, Leinbach said.

It takes about a week of preparations for liftoff once the shuttle returns to the launch pad. That means NASA has only a day or two if it is to launch Atlantis by Sept. 7.

If Atlantis does not take off by then, NASA may have to wait for weeks, because a Russian spacecraft is scheduled to travel to the space station next month with two new crew members, and the orbiting outpost would be too crowded for a visit by the shuttle.

NASA is negotiating with the Russians over the launch dates of both the shuttle and the Soyuz spacecraft.

To give itself more launch opportunities in September, NASA is considering waiving a post-Columbia rule that says the space shuttle must be launched in clear daylight so that its external fuel tank can be photographed for broken-off pieces of foam like the one that doomed the shuttle in 2003.

"What I've asked the team to do is examine those reasons to see if they're still applicable," space shuttle program manager Wayne Hale said.

The chairman of the board that investigated the Columbia accident said Tuesday that he didn't believe NASA was rushing into a launch by trying for next week.

"I don't see anything happening in which I see the old bugaboo of schedule taking precedence over safety yet," Adm. Hal Gehman told The Associated Press.

Atlantis' six astronauts flew back to Houston on Tuesday. The shuttle had originally been set to blast off last Sunday, but a lightning bolt struck the launch pad and the liftoff was postponed while engineers checked for damage.

The flight would mark the resumption of construction on the international space station, which has been on hold since the Columbia disaster 3 1/2 years ago.

Atlantis' main mission is to add a key 17 1/2-ton truss to the space station, including two solar wings that will produce power. The shuttle's six astronauts planned to make three spacewalks during the 11-day mission.

Fourteen more shuttle flights are planned through 2010.

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