Astronauts prepare for spacewalk to rewire station

LOS ANGELES, Dec 14 (Reuters) Astronauts aboard the International Space Station prepared for a crucial spacewalk today to reroute the outpost's power system as NASA engineers worked on plans for a possible fourth spacewalk to fix a stuck solar panel.

The Discovery crew, which arrived at the station on Monday for a week-long stay, needs to rewire the station's electrical system to use power produced by new solar arrays installed on the station in September.

The rewiring will pave the way for laboratories built by Europe countries and Japan to be attached to the space station beginning next year.

The shift to the new arrays will increase power for the station bring by roughly 50 percent, Kirk Shireman, deputy program manager for the International Space Station, said at a briefing yesterday.

''It's a big step to put us in a configuration ... to allow us to go to a six-person crew and accomplish the mission that (the space station) was designed to accomplish,'' Shireman said.

Spacewalkers Robert Curbeam and Christer Fuglesang, who completed the first of three planned spacewalks on Tuesday, camped out in the station's airlock last night in preparation for a six-hour foray starting at about 2 p.m. CST (2000 GMT).

Today, the NASA ground crew will power down half of the station to allow the spacewalkers to unplug power cables from a temporary power supply and attach them to the permanent system.

NASA wanted to rewire the station in 2003, but the destruction of the space shuttle Columbia that year halted all shuttle flights for more than two years.

NASA engineers were not sure if the electrical equipment, which has been subjected to extremes of space thermal cycles for longer than expected, would work once it was connected.

If it fails, Curbeam and Fuglesang will have to quickly fix the problem before they run out of time on the spacewalk.

It will be a tense time with little or no backup power if problems arise.

The astronauts also are set to activate part of the station's thermal control system and to relocate a work platform for storing tools and spacewalking hardware.

If all goes well, Curbeam and astronaut Sunita Williams will rewire the other half of the station during a third spacewalk scheduled for Saturday.

NASA engineers asked the astronauts yesterday about the possibility of doing a fourth spacewalk after efforts to retract a 33 metre solar panel failed, leaving it half deployed.

''You don't want to execute a space walk until you know it's a good thing to do,'' said John Curry, shuttle lead flight director.

The extra spacewalk, probably by Curbeam and Fuglesang, will be scrapped if the ground team and astronauts cannot agree on a plan to manually retract the solar panel by the 10th day of the flight, Curry said.

The panel will not cause problems for the current mission but must be stowed inside a storage box at the base of the array before upcoming missions in 2007, Curry said.

Station assembly resumed in September, with a new deadline to complete the outpost before the shuttle fleet is retired in 2010.

NASA needs at least 13 more missions to finish building the complex.

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