NASA identifies cause of recent shuttle fuel glitch

0 Comments | Oakland Tribune, Dec 19, 2007 | by Marcia Dunn

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 Tuesdays tank test, NASA had been aiming for a Jan. 10 liftoff of Atlantis with a European space station lab.

Were going to follow this trail where it leads us and were going to solve this problem, and then well go fly ... whether its 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 stations power system. But they unearthed few clues involving an even bigger problem with a fouled rotating joint for the solar wings.

As NASA pumped liquid hydrogen fuel into Atlantis tank at the pad, astronauts Peggy Whitson and Daniel Tani inspected the space stations 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.

NASAs 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 major effort requiring as many as four spacewalks and likely will not be attempted until next fall, Suffredini said. It will take that long to figure out whats wrong and train a crew on repairs, he said.

The joint is supposed to rotate 360 degrees to keep the solar wings facing the sun. Its been used sparingly over the past three months, ever since it began vibrating and showing 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. They found more of the metallic grit that was first detected by Tani during a spacewalk in October, and collected more samples.

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 didnt 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.

Suffredini said that if both dilemmas persist, the space station may not be able to generate enough power to support the Japanese lab thats supposed to arrive in three sections beginning in February. Theres a fighting chance to keep the first Japanese delivery mission on track, but beyond that, it would be extremely difficult to continue assembly, he said.

As for Atlantis woes, two of the four fuel gauges at the bottom of the external tank failed during Tuesdays test, and another did not work right.

Special test equipment indicated open circuits in the connector that passes through the wall of the fuel tank, linking wiring between the gauges in the tank and Atlantis. It was too soon to know whether the shuttle would need to be returned to its hangar for repairs, Hale said.

The space agency has been struggling with sporadic fuel gauge problems for two years, ever since flights resumed following the Columbia tragedy. The gauges prevent the shuttles main engines from running on an empty tank, which could be catastrophic.

Hale said its unclear whether the same type of connector caused the previous problems. There could be a manufacturing defect or flawed design, or the part may have been installed improperly, he noted. The connector is less than 10 years old, pretty new by shuttle standards.

We are not going to be driven by schedule on this one, Hale said at a late afternoon news conference. We need to get to the bottom of this, fix it and make sure its fixed once and for all.

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