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Two spacewalking astronauts bolted a new beam on to the International Space Station on Saturday as Nasa wrestled with a balky computer and worried about a gash in the heat shield of space shuttle Endeavour.
Installation of the 3m two-tonne, aluminum extension was the main task of Endeavour's flight to the station and another step toward planned completion of the $100 billion ($135 billion) international project by 2010.
In the midst of Saturday's six-hour spacewalk by astronauts Rick Mastracchio and Dave Williams, Nasa said the primary US command-and-control computer on the station had suddenly shut down.
Two backup computers immediately kicked in to take over its tasks, so there was "no issue whatsoever with the health of the station systems or the health of the crew on board," Nasa spokesman Kyle Herring said.
But he said Nasa engineers did not know why the computer failed. There was no word on whether it could be fixed or posed any sort of long-term problem.
Failure of the US computer follows problems with computers in the Russian segment of the space station during a shuttle visit earlier this summer.
The Russian problem was traced to a corroded electronics box, which is now being replaced.
Photographs taken by the station crew as the shuttle arrived at the station on Friday revealed a small but possibly deep gash in a heat-resistant tile on the ship's belly.
Mission management team chairman John Shannon said the gouge may have been caused by ice that formed on the shuttle fuel tank - filled with very cold fuel - then flew off and struck the ship during Wednesday's launch from Florida.
Endeavour astronauts will take a close look at the damage on Sunday with remote sensors on a robotic arm. Nasa will then decide if a repair by spacewalking astronauts is required.
The shuttle is covered with ceramic heat-resistant tiles and carbon panels to protect the ship's aluminum skin from melting during the plunge back through the atmosphere for landing. Temperatures around the damage site can reach up to about 2000 degrees Fahrenheit (1,093 degrees Celsius).
Nasa has been cautious about heat-shield damage since shuttle Columbia disintegrated while returning to Earth in 2003, killing all seven astronauts on board.
The accident was blamed on a break in the heat shield caused by fuel tank insulation foam that flew off during launch and struck the wing.
The damage went undetected, so Nasa now incorporates three damage inspections into each flight, including one from photographs taken of the shuttle's underside as it approaches the space station.
Endeavour is currently scheduled to return to Earth on Aug. 19, but Nasa has said it may extend the mission by three days. The shuttle crew includes teacher-turned-astronaut Barbara Morgan, the backup to fellow teacher Christa McAuliffe, who died in the 1986 after-launch explosion of shuttle Challenger.
(Additional reporting by Irene Klotz)
- REUTERS
