NASA managers tonight cleared the shuttle Endeavour for launch Friday evening on a delayed space station assembly mission, deciding the ship's damaged robot arm is more than strong enough to withstand the rigors of flight.

With forecasters calling for good weather in Florida, launch of the 112th shuttle mission is targeted for sometime between 7 p.m. and 11 p.m. EST Friday. The exact launch time will be revealed Thursday evening.

With no other technical problems at pad 39A, NASA managers are continuing to assess the weather at two emergency landing sites in Spain where an inopportune main engine failure during the climb to orbit could force the crew to make a quick return to Earth. Initial forecasts this week called for bad weather, but the outlook may have improved since then. A weather update is expected Thursday morning.

The decision to press ahead with launch Friday came after a week of tests and engineering detective work to assess the integrity of Endeavour's 50-foot-long robot arm. The arm was dinged by a payload bay access platform last week during work to repair a leaking oxygen flex hose that grounded the ship Nov. 10 on the eve of its initial launch try.

The arm damage consisted of torn outer insulation and a small area of delamination in the crane's carbon-composite structure near its shoulder joint. The concern was that vibrations and other "loads" during launch could induce additional separation, possibly compromising the structural integrity of the arm.

Shuttle program manager Ronald Dittemore told reporters this evening that testing in Canada where the arm was built showed the fragile space crane still has more than enough strength to withstand the vibration and bending loads it will experience during Endeavour's climb to space. As such, no problems are expected when commander James Wetherbee uses the arm to lift a 14.5-ton solar array truss segment from the shuttle's cargo bay.

"We had a very good meeting and the bottom line is the RMS is cleared for flight, the O2 line issue has been resolved and we have no constraints to pressing on with the launch count and the planned flight on Friday," Dittemore said.

A key factor in the decision was the ability of arm-builder MacDonald Dettwiler Robotics to duplicate the damage in an arm segment at the plant in Toronto. That segment was then subjected to worst-case launch loads and engineers found no additional delamination.

"We had extensive analysis, a large international team effort, a large engineering community that participated and the testing that was conducted in Canada, in Toronto, was extremely successful," Dittemore said.

"We were able to duplicate the damage that we had seen on the launch pad, duplicated it in the lab, tested it under flight-specific conditions - 3-sigma load conditions - and were able to prove to our satisfaction that the arm is fully functional, withstanding the worst-case loads, which are the ascent loads. And so the team, the supplier, the manufacturer and all the space shuttle team ageed the arm is safe to fly."

Dittemore said engineers also put the oxygen line issue to bed after examining similar flex hoses from other shuttles. There was a bit of initial concern that the fatigue-related crack in the line that derailed Endeavour might represent a fleet-wide concern. But as it turned out, that was not the case.

"We also reviewed the O2 line again," he said. "There was some open work, I had asked them to remove a couple of other lines from other vehicles just to take a look at them. All the other lines that we have removed have been inspected and have been found clean, no damage at all, and so we feel confident the hoses we have replaced on 105 (Endeavour) did the job and we're safe to fly there also.

"So all in all, it has been a tremendous effort over the past week to get to this point. The teams have done a marvelous job."

Endeavour's crew flew to the Kennedy Space Center today in stages. Commander James Wetherbee, speaking at the shuttle landing strip, thanked the engineering community for working around the clock to resolve the technical questions.

"We appreciate that and we thank them for all the work," Wetherbee said. "They're working pretty hard all over the continent, I guess. So anyway, it's nice to be back and this time we'll try to leave going that way (he said, pointing up) instead of that way (pointing west toward Houston)."