The test showed an open circuit, which was causing the fuel sensors to erratically sense hydrogen fuel levels. NASA is not sure yet how long it will take to fix the connector and, thus, how long before the mission can get off the ground.

If the fix can be made on the launch pad, they have a much better chance of launching in January than if they have to drive everything back to the hanger for more complex repairs.

January 10, 2008 still stands as the earliest that the mission will take off.

Expedition 16 commander Peggy Whitson and flight engineer Daniel Tani took the 100th space walk at the International Space Station on Tuesday to look for two problems involving the station’s power system.

They found that a bad motor was the cause of a solar wing-tilting mechanism that shut down unexpectedly on December 8th as circuit breakers kept popping off.

The tilting mechanism allows a set of solar panels to always face the Sun for maximum energy generation. A new motor will be onboard Atlantis (STS-122) when it goes up next year.

The ISS astronauts, however, still could not find out the problem with a damaged 10-foot (3-meter) wide solar rotary joint (officially called the Solar Alpha Rotary Joint (SARJ)) that rotates a starboard (right) solar array.

The joint took up most of the seven-hour spacewalk for the two astronauts. They inspected the joint, removed covers, and looked at the mechanism from all angles with a specially made mirror device.

They found more gritty substances all over the large gear, which Tani had first discovered on a previous spacewalk. They retrieved some samples for further study back on the ground. The bearing, gears, and motors all looked fine upon inspection. No damage was found at the base of the joint. One bearing out of twelve was removed so that NASA engineers could look it over down on Earth.

The inspections seem to be centering on a race ring that looks patchy. The SARJ contains two large parallel race rings. One of the rings rotates while the other one just holds the twelve trundle bearing assemblies. If they eventually use a backup race ring, it will take several spacewalks to set it up properly. The spacewalk, if needed, will not be performed before the last half of 2008.

Additional information on the station's power system problems is found at the Spaceflight Now article “NASA studying options to fix solar array problems”.

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