Fuel gauge problem traced to connector

CAPE CANAVERAL - 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.

NASA is up against a 2010 presidential deadline for completing the space station and retiring the shuttles.

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 Dec. 8 and shut down. Testing by Whitson and Tani indicated that the motor most likely was at fault.

NASA space station program manager Mike Suffredini said a spare motor already on board will be installed during Atlantis' visit, a difficult space-walking job.

Repairs to the damaged solar rotary joint, on the other hand, will be a huge effort requiring as many as four space walks 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 has 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 space walk inspecting the clogged rotary joint. 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.

"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.

As for Atlantis' woes, two of the four fuel gauges at the bottom of the external tank failed during Tuesday's test, and another did not work right. The space agency has been struggling with sporadic fuel gauge problems for two years. The gauges prevent the shuttle's main engines from running on an empty tank, which could be catastrophic.

[Last modified December 19, 2007, 01:34:01]