The failure of the computers, which control the International Space Station's positioning, have NASA managers considering another extension of space shuttle Atlantis' voyage to the orbiting outpost, officials said.
Without the computers, the station cannot maintain proper orbit and its crew cannot stay on board in a worstcase scenario.
The Atlantis, on its first mission this year, blasted off last Friday to bring back Sunita after her record six-month space sojourn and was due to return next Tuesday. The mission, originally scheduled for 11 days, had already been extended by two days so that astronauts can undertake a spacewalk to repair a thermal blanket covering on the engine pod that peeled off during launch.
Since the failure of the computers, thrusters on the docked space shuttle have been fired periodically to help maintain the space station's positioning. NASA managers hoped to have the computers back up before Atlantis and its seven crew members undock from the 16-nation space station.
But if the computers are not functioning, NASA may look into extending the space shuttle's stay a day or two. The extension is being considered since the shuttle's altitude-control jets and life support could be used to supplement the station while engineers work on the problem.
Space station programme manager Mike
Suffredini said on Wednesday that he expected the computer problem to be fixed over the next couple of days. The astronauts will look at the thermal tear problem during the third of the fourth spacewalks scheduled for Friday.
In a worst-case scenario, if at least one of the computers was not operating after the shuttle left, the space station's three crew members could return to Earth, he said.
"We always have an option to depart," Suffredini said.
Engineers were studying whether the new solar power unit was the cause of the problem and whether disconnecting it to reboot the computers would resolve it.
On Wednesday, two astronauts went on a spacewalk to complete two tasks. They helped fold up a solar wing and tried to bring to life a rotating joint that will allow a new pair of solar arrays to track the sun.
Back on the ground, NASA managers were focusing on sewing the blanket with stainless steel wire and an instrument that resembles a small needle. The 4-by-6-inch damaged section sits over an engine pod.
The US space agency has however played down concerns over the tear to the thermal blanket.
Engineers do not think the damaged section of the thermal blanket, which protects part of the shuttle from the blazing heat of re-entry, would endanger the spacecraft during landing. But it could cause enough damage to require schedule-busting repairs.
Since shuttle damage resulted in the 2003 Columbia disaster that killed seven astronauts including Indian-born astronaut Kalpana Chawla, NASA has greatly focussed on any problems that could jeopardize a shuttle's re-entry.
