Cape Canaveral, Fla. NASA on Tuesday traced fuel gauge failures in shuttle Atlantis' tank to a bad connector, and a top manager said he did not know how long it would take to replace the part or when the spaceship might fly.
The erratic shuttle fuel gauges - part of a critical safety system - forced back-to-back launch delays this month. Until Tuesday's tanking test, NASA had been aiming for a Jan. 10 liftoff of Atlantis with a European space station lab.
"We're going to follow this trail where it leads us and we're going to solve this problem, and then we'll go fly ... whether it's Jan. 10 or Feb. 10 or March 10," shuttle program manager Wayne Hale said.
In orbit, meanwhile, spacewalking astronauts helped pinpoint the source of a flawed mechanism in the international space station's power system. But they unearthed few clues involving an even bigger problem with a fouled rotating joint for the solar wings.
Astronauts Peggy Whitson and Daniel Tani inspected the space station's two crippled power components. The unrelated problems are curtailing power generation and threaten to delay future shuttle flights.
Their first stop was a solar wing-tilting mechanism that experienced circuit breaker trips on Dec. 8 and shut down. Engineers initially suspected a piece of space junk may have damaged it, but Whitson and Tani found no signs of impact. They temporarily disconnected cables for a test that exonerated certain parts, leaving the motor most likely at fault.
NASA's space station program manager, Mike Suffredini, said a spare motor already on board will be installed during Atlantis' visit, a difficult spacewalking job.
Repairs to the damaged solar rotary joint, on the other hand, will be a massive effort requiring as many as four spacewalks and likely will not be attempted until next fall, Suffredini said. That's how long it will take to figure out what's wrong and train a crew on the repairs, he said.
The joint is supposed to automatically rotate 360 degrees to keep the solar wings facing the sun. It's been used sparingly over the past three months, ever since it began vibrating and exhibiting electrical current spikes.
Whitson and Tani spent most of their seven-hour spacewalk inspecting the clogged rotary joint, removing covers and peeking deep inside with a dentist-style mirror on a rod.
All the gears, motors and bearings looked fine, although some were dirtier than others. The spacewalkers removed one bearing for return to Earth on the next shuttle flight, for engineering analysis.
NASA had hoped to learn what was grinding against the rotating ring.
"We didn't find anything that stood out," Suffredini said. The space agency will try to limp along with the joint in its current state until repairs are made, he added.