Shuttle set to resume space station construction

CAPE CANAVERAL, Florida (Reuters) - NASA is set to launch another component of the International Space Station into orbit on Friday, three months behind schedule but in compliance with more rigorous safety standards imposed after the space shuttle Columbia disaster in 2003.

A double piece of the station's structural backbone is in the cargo bay of shuttle Atlantis, which is scheduled for liftoff at 7:38 p.m. EDT (2338 GMT) from the Kennedy Space Center in central Florida.

Meteorologists on Wednesday predicted a 70-percent chance that the weather would be suitable for launch.

"It's been quite a long road for us, longer than usual," Robbie Ashley, the NASA manager who oversaw preparation of the truss segments at the Florida spaceport, told reporters.

Delivery and installation of the trusses, which include a pair of solar panels to boost electric power on the station, was delayed more than three years by the Columbia accident, which killed seven astronauts and prompted the U.S. space agency to ground its shuttles for repairs and test flights.

NASA has just three years to finish launching the remaining station modules and trusses before the shuttles are retired in 2010. The shuttles are the only space vehicles capable of delivering the larger components of the $100 billion space station, a project of 16 nations.

Much of the assembly work on the station has shifted to the crews living on the orbital outpost, which hovers about 220 miles above Earth.

On Wednesday, two Russian cosmonauts conducted a spacewalk to install a dozen debris-protection panels on the outside of the crew's living quarters. The Russian-built module did not meet U.S. standards for protection from orbital debris and micrometeoroids.

Station commander Fyodor Yurchikhin and flight engineer Oleg Kotov, who conducted similar work during a spacewalk last week, also hooked up an Ethernet cable so the Russian parts of the station can be controlled from the U.S. laboratory and set up a science experiment.

CREW SWAP

The station crew, which also includes NASA astronaut Sunita Williams, is packing up equipment that will need to be flown back to Earth aboard the shuttle. If Atlantis is launched on Friday it will arrive at the station on Sunday for a week-long servicing call.

Williams, who flew to the station with the last shuttle crew in December, will be returning home aboard Atlantis. Her replacement, Clayton Anderson, was added to the Atlantis crew during the three-month delay for fuel tank repairs.

The tank was pummeled by hail on February 26 as the shuttle was being prepared at the launch pad for an aborted mid-March liftoff.

The top of the tank was so battered that NASA was forced to respray insulating foam in that area. The tank's foam has been the top concern since the Columbia accident, which was triggered by a piece of foam debris that fell off the fuel tank during launch and struck the ship's wing. The impact damaged Columbia's heat shield, causing the shuttle to disintegrate over Texas during re-entry into the atmosphere.

NASA designed special tests to make sure Atlantis' tank repairs would not break free during the climb to orbit. "All of our testing indicates that will not happen," said shuttle program manager Wayne Hale.

While launch weather is expected to be good, NASA said it was concerned about afternoon thunderstorms predicted throughout the rest of the week.

The forecast for Wednesday night included a slight chance of hail.

"We're going to get what we're going to get and we'll deal with it," said launch director Mike Leinbach. "We would have to be so unlucky to get more hail on this tank."