By Irene Klotz
Cape Canaveral, Florida
Space shuttle Atlantis is poised to launch from the Kennedy Space Center in Florida, US, at 1938 (2338 GMT).
The weather is looking good for Friday's launch opportunity
It will fly to the International Space Station to continue construction work.
The mission will lay the groundwork - and the power lines - for Europe's Columbus module to join the orbiting platform later this year.
The major elements for installation include a new pair of giant solar wing panels and a rotary joint so they can track the Sun for power.
"It's the foundation for the power supply that will now allow us to truly become an integrated International Space Station with the European and the Japanese labs," said Nasa astronaut James Reilly, the lead spacewalker for Atlantis' seven-man crew.
The US space agency (Nasa) had hoped to be launching its second flight of the year by now, not its first; but an unusual storm passed over the Central Florida launch site in late February and dropped large hailstones on the shuttle.
Atlantis was at the launch pad being prepared for a mid-March flight.
Technicians found more than 4,200 dings and gouges from hail strikes in the external fuel tank's foam insulation. The insulation is needed to prevent ice from forming when cryogenic propellants are pumped into the inner tanks for launch. Ice, like the foam itself, can pose a debris hazard during launch.
Europe's ATV will take supplies to the space station
Atlantis' tank was repaired, but Nasa had to give up three months' time in a tight and inflexible schedule to finish space station construction before the shuttle fleet is retired in three years.
The agency has some major milestones coming up, including the launch of the European Space Agency's Columbus module in December and three flights to attach Japan's Kibo laboratory complex to the station.
"They need electricity for those new modules and that's part of our job," said Atlantis' flight engineer Steven Swanson, one of the crew's four rookie fliers.
Despite the delays, managers are confident they will be able to complete the station before the shuttles' 2010 retirement date.
Nasa plans to fly 15 more missions to the station to deliver large components, spare parts and other supplies. In addition, one final servicing call to the Hubble Space Telescope is planned for September 2008.
Before completion, the station is expected to be able to support six resident crewmembers - twice as many as what is possible now.
Nasa also is preparing for the debut flight of a European cargo ship that is scheduled to begin flying to the station later this year.
The Automated Transfer Vehicle launches on an Ariane 5 rocket from Kourou, French Guiana. The first flight is expected later this year.
In addition to Reilly and Swanson, Atlantis' crew includes commander Frederick Sturckow, pilot Lee Archambault, Pat Forrester, John "Danny" Olivas and Clayton Anderson. Sturckow has two previous spaceflights and Forrester has one.
Clayton will not be coming home with the Atlantis astronauts.
His job is to replace Nasa astronaut Sunita Williams who has been aboard the space station since December. She will return with the Atlantis astronauts. Anderson's ride home is with the crew that delivers Columbus.