Astronauts step out to rewire space station

Hoston, Dec 15: A pair of spacewalking astronauts left an airlock on the International Space Station to begin rewiring the outpost's power grid.

The work, which will be continued during another spacewalk tomorrow, is essential to NASA's promise to install laboratory modules built by Europe and Japan onto the space station beginning next year.

The spacewalk, the second of shuttle Discovery's 12-day mission, is scheduled to last about six hours, although it may be cut short if radiation levels near Earth begin to rise as a result of a solar flare on Wednesday.

The shuttle and station crews have spent the past two nights sleeping in protected areas of their spaceships in case X-ray and heavy particle emissions from the sun began passing through the metal hulls.

Veteran US astronaut Robert Curbeam and Sweden's first-time flier Christer Fuglesang floated out of the station's airlock shortly before 3 pm EST (0130 IST). The station crew had spent the morning shutting down equipment in preparation for a safety blackout.

NASA turned off two of the station's four main power circuits, which are being rerouted during the spacewalk. Live lines could pose a shock hazard for Curbeam and Fuglesang.

The power-down knocked off half the lights in the station's Destiny laboratory module, cut communications between the US and Russian sides of the station and left critical gear without a backup power supply.

Audio-Only Spacewalk

Because the area where the spacewalkers will work is right above the shuttle's main Ku-band antenna, which is used to relay television images, the system was turned off to avoid exposing the astronauts to potentially harmful beams. As a result, the spacewalk was expected to be an audio-only event.

Curbeam and Fuglesang plan to unplug electrical connectors and re-attach the cables to reroute power coming from a new set of solar arrays installed in September.

About halfway through the outing, ground controllers will attempt to start a cooling pump that has never been turned on in space. If the system fails, the astronauts would have to backtrack to the old power grid while engineers assessed the situation.

NASA also is reckoning with a balky solar wing panel that failed to fully retract during a tedious six-hour task on Wednesday. The panel is part of the station's original, though temporary, power system that is being replaced during the spacewalk.

The 110-foot panel retracted enough to allow room for the new arrays to rotate and track the sun for power, but it must be fully closed before it can be relocated later next year.

Managers decided to abandon efforts on Wednesday to fix the panel, which repeatedly jammed as it was being lowered, like pleats in a window shade, into a storage box.

NASA may decide to add a fourth spacewalk to Discovery's planned 12-day mission so astronauts can manually fold up the wing. The shuttle's homecoming, scheduled for Dec. 21, likely would be delayed if the extra work is ordered.

Reuters

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