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A major, new problem popped up on the International Space Station on Wednesday as space shuttle astronauts finished installing a new solar-power unit - the failure of key computers that could in an extreme scenario force the crew off the station, officials said.
"That's not something I'm really concerned about,' ISS programme manager Mike Suffredini said of having to leave the station at least temporarily with no crew aboard. But "that's the worst-case scenario,' he told a late night news briefing.
The failure occurred in computers on the Russian segment of the 16-nation space station, computers that control navigation and key life-support systems on the huge orbital base. Without them, the station cannot maintain proper orbit and the crew cannot stay on board.
The station relies mostly on big gyroscopes to maintain its proper orientation but also uses control jets and navigation systems run by the troubled computers to help.
Similar station computer failures have occurred before, NASA officials said, but never affecting all three lines of Russian computers to the point that they could not reboot themselves, as happened Wednesday. The US segment has its own computers but they depend on the Russian ones, officials said.
Suffredini said he expects to be able to fix the problem and that there are numerous alternatives short of taking the crew off the station. "I'm not thinking this (is) something we will not recover from,' he said.
Engineers were studying whether the new solar power unit is the cause of the problem and whether disconnecting it to reboot the computers would resolve it.
Space managers were also considering extending the visit of space shuttle Atlantis to use its attitude-control jets and life support to supplement the station's while engineers work on the problem.
Any additional shuttle stay would have to be short, with Atlantis capable of staying no more than about 15 days total, said John Shannon, deputy shuttle programme manager and chairman of the mission management team.
The computer problem overshadowed plans to attempt repair of Atlantis' damaged heat shield during a spacewalk Friday, using staples to try to pin down a loose thermal blanket.
The preferred method will be surgically stapling and pinning back in place the piece of heat-shield blanket that pulled loose from an engine pod as the shuttle launched on Friday for a construction mission to the space station.
The US space agency has been meticulous about monitoring and maintaining the condition of shuttle heat shields since Columbia disintegrated during its return to Earth in 2003, killing all seven astronauts aboard.
The blanket problem is small, a 10cm by 15 cm gap near the rear of the shuttle, and is not considered a serious threat, but managers don't want risk even minor shuttle damage during the fiery reentry.
NASA needs all three remaining shuttles in good shape to complete 12 more space station construction missions by 2010, when the shuttles are scheduled to be retired.
Plans call for one astronaut to do the repair work while standing on the shuttle's robot arm.
What originally was planned as an 11-day mission to boost power at the station already had been extended two days to assure the shuttle repairs can be done prior to landing.
Astronauts Patrick Forrester and Steven Swanson performed a second spacewalk Wednesday, spending about seven hours completing all but one final step in preparation for the new solar power array, which will rotate and track the sun.
NASA wants to boost the station's power supplies so long-delayed laboratories built by Europe and Japan, US partners in the station, can be attached.
- REUTERS
