Space station commander Pavel Vinogradov successfully installed a new hydrogen vent port in the hull of the Zvezda command module Thursday evening that should improve the operation of the Russian segment's Elektron oxygen generator.

The generator uses solar-powered electrolysis to extract oxygen from on-board water supplies. The oxygen is added to the station's air supply while the other product of the electrolysis process - hydrogen - is vented overboard.

The Elektron had been tied into a vent used by a hazardous contaminant monitor that must be shut down periodically, interfering with Elektron operations. By providing another vent, the crew will be able to more efficiently utilize the oxygen generator. If all goes well, the Electron will be reactivated Monday.

The spacewalk began when the crew opened the hatch of the Pirs docking module at 6:48 p.m. EDT.

The spacewalkers fell behind schedule completing a variety of relatively minor tasks on the Russian segment of the station and controllers briefly considered ending the spacewalk and postponing replacement of a camera on the U.S. section of the lab complex.

But Russian controllers decided the Orlan spacesuits could safely go an extra half hour and the originally planned six-hour excursion was extended.

Earlier, Vinogradov reported that an adapter used to secure a foot restraint to a telescoping boom had somehow gotten loose and floated away.

"How fast is it going, a meter per second?" a Russian flight controller asked.

"Less."

"Copy. ... Why did it open, though?"

"It was in the closed position," Vinogradov said of the adapter clamp.

"OK, anyway."

"That's bad."

"Don't be too concerned."

Later, Vinogradov repeated "the latch was closed. We don't understand it."

The spacewalkers completed all of their planned objectives, installing the vent valve; repositioning a cable causing interference with an antenna; retrieving experiment packages; and replacing the U.S. camera.

The crewmates re-entered the Pirs airlock module and closed the hatch at 1:19 a.m. Friday to officially end a six-hour 31-minute spacewalk.

This was the first spacewalk for the Expedition 13 crew and the 65th carried out since space station assembly began in 1998. It was the sixth spacewalk for Vinogradov, a Mir veteran who logged 26 hours and 19 minutes of spacewalk time during five excursions. Williams logged six hours and 44 minutes during a single station spacewalk during shuttle mission STS-101 in 2000.

With tonight's excursion, 41 U.S. astronauts, 13 Russian cosmonauts, one Japanese astronaut and one Frenchman have logged 390 hours and 54 minutes in space station EVA time.

Vinogradov and WIlliams plan to stage a second spacewalk Aug. 3.