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Shuttle crew in home stretch of station resupply

The Discovery astronauts are in the home stretch of a busy space station resupply mission, wrapping up equipment transfers before undocking Tuesday and landing Thursday.

JOHNSON SPACE CENTER, Houston--Sailing into the home stretch of a busy space station resupply mission, the shuttle Discovery astronauts worked Sunday to wrap up equipment and supply transfers before taking a half day off to relax and enjoy the view.

Overnight, engineers successfully tested a new motor-driven bolt in the berthing mechanism holding the shuttle-delivered Leonardo cargo module in place on the Earth-facing port of the lab's Harmony module.

Astronauts Nicole Stott and Danny Olivas retrieve experiments from the Columbus module during a spacewalk last Tuesday. NASA

The bolt, one of 16 in the complex interface, jammed during earlier tests and flight engineers Timothy Kopra and Robert Thirsk carried out a lengthy replacement procedure Saturday.

"The checkout activity went perfectly fine, the bolt that jammed on us the other day when we tried to drive it out of the interface...we worked it this evening and it worked just fine," station Flight Director Royce Renfrew said early Sunday.

The testing confirmed the astronauts will have no trouble detaching the Leonardo module Monday so it can be stowed in the shuttle Discovery's cargo bay for return to Earth.

It also cleared the way for the arrival later this month of Japan's new HTV cargo ship, scheduled for launch Thursday, the same day Discovery returns to Earth. The HTV cargo craft will be docked at the same port used by Leonardo.

After the bolt was replaced, flight engineers Michael Barratt and Frank De Winne carried out another lengthy procedure to replace a filter in the U.S. oxygen generation system. Based on a performance degradation, engineers suspected the filter was clogged and sure enough, Barratt and De Winne reported it was 70 percent to 80 percent blocked by debris. A replacement was installed.

Astronauts move new equipment into the Japanese Kibo module. The shuttle Discovery delivered more than 7.5 tons of equipment and supplies to the station. NASA

As of Sunday morning, the combined 13-member shuttle-station crew had completed about 85 percent of the required logistics transfers to and from the station.

The Leonardo module was loaded with some 7.5 tons of equipment and supplies, including two science racks, an experiment sample freezer, a crew sleep station, a carbon dioxide removal assembly, a stowage rack, food, clothing, and other gear.

During three spacewalks on Tuesday, Thursday, and Saturday, John "Danny" Olivas, Christer Fuglesang, and Nicole Stott replaced a 1,800-pound ammonia coolant tank, retrieved two space exposure experiments, deployed a cargo mounting mechanism, installed two GPS antennas, and replaced a blown circuit breaker and a rate gyro assembly that helps determine the station's orientation in space.

The only problems of any significance other than the stuck docking system bolt and the clogged filter in the oxygen assembly were two external wiring problems.

During the crew's second spacewalk, Olivas was directed to hook up two power cables to drive heaters in pressurized mating adapter No. 3, a docking port currently mounted on the multi-hatch Unity module's left port. The idea was to open the docking adapter later to temporarily store supplies.

But Olivas was unable to make the required electrical connections because the cables were not in the correct position. As it turns out, the wiring bundles were attached to PMA-3 assuming the module would be oriented, or "clocked," in a specific way, putting the connectors within reach of their counterparts on the Unity module.

When PMA-3 was docked to Unity's nadir, or Earth-facing port, the cables and connectors were in the expected orientation. But when PMA-3 was recently moved to Unity's left-side port, it was clocked 180 degrees from the orientation the installers of the wiring bundle apparently expected.

Robert Thirsk, foreground, and Discovery pilot Kevin Ford operating the space station's robot arm from a work station in the Destiny lab module. NASA

The module was in the correct orientation, officials said, but the cables ended up 90 degrees away from the corresponding connectors.

PMA-3 is scheduled to be moved back to Unity's nadir port in December and in the long term, the wiring issue will have no impact. But in the near term, the stubby module will not be used to store supplies because without heaters, condensation control could prove difficult.

The other wiring problem encountered by Discovery's crew occurred during the third spacewalk Saturday.

Olivas and Fuglesang routed two 60-foot-long cable bundles to deliver power and data to a new module--node 3, or "Tranquility"--scheduled for launch next year. Seven of eight connectors hooked up properly, but one power cable's connector could not be plugged in. Engineers are looking into possible work arounds.