After a three-month delay, NASA entered the final day of a launch countdown for space shuttle Atlantis Thursday with no major technical problems looming and a forecast for promising weather.

Forecasters predicted an 80 percent chance that the weather would allow NASA to launch its first space shuttle mission of the year at 7:38 p.m. Friday.

Engineers were not working on any technical problems, said Steve Payne, NASA test director.

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A freak storm set back the mission in late February, when golf-ball-size hail knocked thousands of pockmarks in the insulating foam of Atlantis' external tank as it stood on the launch pad.

Atlantis was moved from the launch pad back to the Vehicle Assembly Building and the original launch date in mid-March was postponed.

NASA managers chose to repair the tank rather than swap it out for another, and scores of engineers and technicians worked over two months to remove, sand down and reapply foam to the tank.

"We had a great deal of effort for this repair work," said Roy Worthy, external tank/solid rocket booster NASA vehicle manager. "We have complete confidence in our repair technique. ... We're ready to fly."

Some of the engineers and technicians worked 16-hour days devising the repairs, including mechanical engineer Glenn Lapeyronnie, who created from scratch in 10 days a 7½-foot tool to trim foam around the nose cone, where the tank had the most damage.

"I've seen some intense moments, but this has probably been the most intense," said Lapeyronnie, who works for Lockheed Martin, NASA's primary contractor on the tank.

While NASA managers praised the technicians for their work on the tank, they kept a wary eye on another set of workers who may strike as early as this weekend.

Almost 570 machinists and aerospace workers at the Kennedy Space Center last week rejected a contract offer from United Space Alliance, NASA's primary contractor for the space shuttle.

Few of the workers who might strike have any direct role in the final preparations for space shuttle launches, and NASA officials have said there are other employees who could fill the roles of striking workers if necessary.

During the 11-day mission, Atlantis and its seven astronauts will deliver a new segment and a pair of energy-producing solar panels to the international space station.

Astronaut Clay Anderson will replace astronaut Sunita Williams as the U.S. representative at the orbiting outpost.

NASA hopes to fly at least 13 more construction missions to the space station before the space shuttle fleet is grounded in 2010.

The space agency also wants to fly a single mission to repair the Hubble Space Telescope, which officials said Thursday would be in September 2008.