NASA officials gave the green light to the lift-off for 11:40 am (1540 GMT) Friday after managers held a meeting to weigh their options and review engineering analysis.

"We'll try to launch Friday," said Dean Acosta, spokesman for the National Aeronautics and Space Administration.

The mission is to be Atlantis's first construction mission to the International Space Station (ISS) in nearly four years.

The Atlantis had been set for launch Wednesday but the blast off was delayed twice because one of the three fuel cells providing electricity to the shuttle had malfunctioned.

But after an extensive review, NASA managers opted to proceed and said the problematic fuel cell presented no serious risk.

"I believe it's acceptable to fly, I am comfortable with this," said mission manager Wayne Hale.

He acknowledged some NASA officials argued for postponing the flight as the troubled fuel cell could force the mission to be cut short.

"We had vigorous discussions and the decision was not quite unanimous," he said.

The electrical problem, discovered Wednesday morning in one of the fuel cells that deliver electricity for all on-board systems, was probably caused by a worn cable, said Steve Poulos, shuttle orbiter projects office manager.

But he said that all tests conducted and possible scenarios anticipated showed the fuel cell presented only a "minimum risk."

NASA was anxious to proceed because if Atlantis does not launch on Friday its 11-day mission could be delayed until late October, as it would interfere with a scheduled September 18 mission to the ISS by a Russian Soyuz spacecraft.

If Friday's launch has to be scrubbed, Hale said it may be possible to try again on Saturday after discussions with his Russian counterparts.

Atlantis had been scheduled to blast off on August 27, but was delayed by the effects of Tropical Storm Ernesto that pounded Florida with heavy rain and winds, then by technical problems.

The agency plans to undertake 16 shuttle missions to complete the complex assembly of the half-finished space station by 2010, when the three-shuttle fleet is set to retire.

Atlantis is to take a new 16-tonne segment with two huge solar panels that will double the station's ability to produce power from sunlight and ultimately provide a quarter of the completed ISS's power.

After the Space Shuttle Discovery returned safely in July from a mission aimed at improving safety, NASA declared it was ready to resume construction of the ISS, which is central to US ambitions to fly humans to Mars.

Three lengthy spacewalks are planned to install the solar arrays, which are 73 meters (240 feet) long when unfurled.

Officials said it will be the most complex work ever undertaken at the nearly eight-year-old space station and that the next few missions will only get harder.

During their 11-day mission, the six shuttle astronauts will also use a robotic arm to scan the orbiter's heat shield for potential damage from debris falling off the external fuel tank during liftoff.

The safety check has become routine since the Space Shuttle Columbia was struck by foam that peeled off from its fuel tank during liftoff, eventually causing the shuttle to disintegrate as it returned to Earth in February 2003, killing all seven astronauts on board.

The concern over debris has prompted NASA to favor daytime launches, which allow engineers to take pictures of the liftoff to detect any foam loss. The requirement limits the available launch dates.

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