CAPE CANAVERAL, Fla. Dec 18 (bdnews24.com/Reuters) - A pair of spacewalking astronauts left the International Space Station on Tuesday to begin a planned 6.5-hour outing to inspect damaged parts of the outpost's power system.

Clad in bulky spacesuits, station commander Peggy Whitson and flight engineer Dan Tani floated outside the station's airlock at 5 a m EST/1000GMT to begin the 100th spacewalk devoted to space station assembly and maintenance.

NASA had planned the spacewalk during the shuttle Atlantis mission to the station, but the ship was grounded after two attempts due to problems with fuel sensors that are part of an emergency engine cutoff system.

The shuttle is scheduled to be filled with fuel on Tuesday so engineers can find what is suspected to be a faulty circuit in the wiring connecting the sensors in the fuel tank to electronic control boxes in the shuttle's engine compartment.

If the problem can be found and fixed while the shuttle is at the launch pad, NASA hopes to launch Atlantis on Jan. 10.

During Tuesday's spacewalk, Whitson and Tani are scheduled to make a detailed inspection of a contaminated joint needed to rotate solar panels so they can track the sun for power.

During a spacewalk during NASA's last shuttle mission in October, Tani discovered shards of metal inside the joint. Engineers had been curious why one of the two joints was generating a slight vibration as it rotated. After the spacewalk, the joint was locked in place to prevent additional damage.

A second problem with the solar wings cropped up 10 days ago when a series of circuits tripped in an second joint that allows the wing panels to tilt toward the sun even with the rotary joint locked in place.

Engineers suspect damage from a micrometeorite impact may be to blame.

NASA needs to resolve the station's power issues before Japan's science laboratory arrives next year.

Atlantis is scheduled to deliver Europe's Columbus science module.

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