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Space Station Tinkering Works

Space station commander Gennady Padalka and flight engineer Michael Fincke completed a five-hour 21-minute spacewalk, successfully installing a new coolant system component and three antennas that an unmanned European cargo craft will use for future dockings.

There were no problems of any significance during the fourth and final spacewalk for Fincke and Expedition 9 commander Padalka, who will be replaced next month by a fresh crew, reports CBS News Space Consultant Bill Harwood.

While the station's control moment gyroscopes once again had to contend with an unexplained torque that acted to pull the complex out of its proper orientation, Russian rocket thrusters were re-enabled in plenty of time to prevent problems.

Padalka and Fincks had left the orbiting outpost unmanned on Friday, as the international space station's two astronauts popped open the hatch on the Russian side of the orbiting outpost slightly ahead of schedule and got down to work.

The goal was to replace a coolant system pump control panel on the Russian Zarya module and to install three S-band antennas on the aft end of the Zvezda command module for use next year by the unmanned European cargo vehicle, reports Harwood. The astronauts also installed new safety tether guides and photographed a space-exposure experiment panel.

"Be careful," Mission Control repeatedly warned the spacewalkers, telling them something like snow might float out when the old pump panel comes out. "Go slowly."

Because no one was left inside the 225-mile-high complex, flight controllers in both Moscow and Houston kept close watch over the two men and all their systems.

NASA prefers having a crew member inside during spacewalks but has had to settle for one less person on board for more than a year because of the grounding of the shuttle fleet. This was the fifth spacewalk with an empty outpost.

The space station has been relying on Russia's much smaller spacecraft for deliveries ever since Columbia broke apart over Texas during re-entry on Feb. 1, 2003.

During Friday's outing, flight controllers hoped to better understand the mysterious force that tilted the space station 80 degrees off-center during the men's last spacewalk, one month ago.

Reports Harwood, engineers believe the mystery torque could be the result of air venting from the Russian airlock, from sublimators on the Russian spacesuits or the normal activity of astronauts working at the aft end of Zvezda, far from the CMGs and the station's center of mass.

The concern is that if the station drifts too far out of "attitude," its solar arrays will not be able to generate enough electricity. During the most recent spacewalk, flight controllers powered down non-critical systems and, due to an oversight, the S-band radio system used by the spacewalkers when not in contact with Russian ground stations.

CBS News Space Consultant William Harwood has covered America's space program full time for nearly 20 years, focusing on space shuttle operations, planetary exploration and astronomy. Based at the Kennedy Space Center in Florida, Harwood provides up-to-the-minute space reports for CBS News and regularly contributes to Spaceflight Now and The Washington Post.