From: Reuters
Published December 18, 2007 06:49 PM

NASA makes headway with shuttle, station problems

By Irene Klotz

CAPE CANAVERAL, Florida (Reuters) - Spacewalking astronauts and technicians on the ground conducted a day of trouble-shooting that shed light on a spate of problems that have stalled construction of the International Space Station, NASA managers said Tuesday.

The space shuttle Atlantis, which is due to carry Europe's Columbus science laboratory to the station, was sidelined by problems with sensors in its fuel tank that are part of an emergency engine cutoff system.

On Tuesday, NASA filled the shuttle's fuel tank with 500,000 gallons of liquid hydrogen and liquid oxygen to try to pinpoint the location of a suspected wiring or circuit problem that was causing erratic readings from the sensors, which are located in the ship's fuel tank.

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The problems caused NASA to cancel launch attempts on December 6 and December 9.

With monitors placed along 100 feet of wiring between the sensors and the shuttle's engine compartment, engineers traced the problem to a three-part connector in the tank's hull.

"We know exactly what we need to work on," shuttle program manager Wayne Hale told reporters after the test.

If repairs can be made at the launch pad, NASA believes it can launch the shuttle as early as January 10, though Hale said he is in no rush.

"I would like to fly as soon as practical but more than that I would like to fix this problem," Hale said. "We need to get to the bottom of this once and for all."

Meanwhile, astronauts aboard the space station inspected two troubled mechanisms that allow the station's solar wings to track the sun for power.

Clad in bulky spacesuits, station commander Peggy Whitson and flight engineer Dan Tani floated outside the station for seven hours on the 100th spacewalk devoted to space station assembly and maintenance.

BUSY DAY FOR SPACEWALKERS

The astronauts' first stop was a device used to tilt a set of solar panels so they face the sun. Engineers suspected a micrometeoroid strike may have damaged the equipment since three circuits failed suddenly and simultaneously on December 8.

Whitson and Tani, both making their fifth spacewalks, found a slightly discolored cable, but no signs of physical damage.

"No smoking gun yet," said spacewalk commentator Rob Navias from NASA's Mission Control Center in Houston.

The pair moved on to the massive rotary joint that spins the wings like a paddle wheel. The joint has been locked in place since an initial inspection in October revealed metal shards in the joint.

Whitson and Tani spent most of their outing pulling off covers to look at the 10-foot (3-metre)-wide joint from different angles. Whitson had one word to describe the mess inside: "Ugly."

The astronauts snared samples of the metal filings on tape to be brought back to Earth for analysis. They also took out one of the mechanism's 12 support bearings for additional inspections.

NASA needs to repair the joint and bring the station to full power before the main part of Japan's laboratory complex arrives next year. Even with the power shortfalls, NASA expects the station to be able to support Europe's Columbus laboratory.

The U.S. space agency plans 10 more construction missions and two resupply flights to the space station before the shuttle's September 2010 retirement date. The agency also plans a servicing call to the Hubble Space Telescope next year.

The $100 billion outpost is a little more than 60 percent complete.

(Editing by Jane Sutton and Todd Eastham)

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