NASA plans to send the astronauts, members of the shuttle Discovery crew who arrived at the station last week, outside the orbiting laboratory on Friday to repair a solar wing that ripped when it was deployed on Tuesday.

ISS program manager Mike Suffredini told reporters he was concerned that the solar array was in a position that could worsen the tear and eventually make the power-generating panel inoperable.

"It became clear to me that this needed to be our top priority as a program," Suffredini said.

"I need this array," he said. "First of all, this array is in a position (where) we believe a potential exists for further damage. ... And if we damage this array enough we can potentially not have it available for the length of the program."

The orbiting laboratory currently has three pairs of solar arrays that are needed to provide energy to European and Japanese laboratories due to be taken to the station in shuttle missions in December and early 2008, respectively.

"We made the determination that the priority for the remainder of the (shuttle) dock period (at the ISS) is to try to recover this array," Suffredini said.

The station's three-member crew would not be able to perform the repair work after Discovery undocks, he said.

The astronauts were originally scheduled to perform the Discovery mission's fourth space walk on Thursday to inspect a rotary joint problem in one of the station's other solar arrays.

But the space walk will now focus on repairing the solar wing.

NASA engineers are working furiously back at the Johnson Space Center in Houston, Texas, to figure out how to repair the torn wing, Suffredini said.

NASA will try to schedule a fifth space walk on Sunday if the astronauts have not finished the repair work on Friday, he said.

A fifth space walk would force NASA to delay Discovery's return to Earth with seven astronauts by another day.

The shuttle, whose mission was already extended by one day for landing on November 7, would instead return to Earth on November 8 if an extra space walk is needed to fix the wing. Discovery launched on October 23.

Even after the astronauts fix the torn solar panel, the ISS crew will have work to do before the station can be ready for the arrival of Europe's Columbus laboratory in December.

The ISS crew will have to inspect or maybe even fix the rotary joint on the other array. They will also have to move the Harmony module -- an Italian-made chamber brought by Discovery -- to its final location, which is where the shuttle is currently docked.

Columbus and Japan's Kibo lab will be attached to Harmony.

"We want to preserve the December 6 launch (of Columbus) and I think we can make it," Suffredini said, adding that otherwise the mission would have to be delayed to January.

NASA plans to finish building the 100-billion-dollar space station, which is considered key to US ambitions to send a manned mission to Mars, by 2010.

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