Russian cosmonauts Pavel Vinogradov, left, and Roman Romanenko perform a spacewalk outside the International Space Station to gather old science experiments and install new ones, and replace a navigation device.AP Photo/NASA

SPACE STATION A 59-year-old Russian cosmonaut became the world's oldest spacewalker Friday, joining a much younger cosmonaut's son for maintenance work outside the International Space Station.

Pavel Vinogradov, a cosmonaut for two decades, claimed the honor as he emerged from the hatch with Roman Romanenko. But he inadvertently added to the booming population of space junk when he lost his grip on an experiment tray that he was retrieving toward the end of the 6 1/2-hour spacewalk.

The lost aluminum panel -- 18 inches by 12 inches and about 6 1/2 pounds -- contained metal samples. Scientists wanted to see how the samples had fared after a year out in the vacuum of space.

Otherwise, the spacewalk had gone well, with the spacewalkers installing new science equipment and replacing a navigation device needed for the June arrival of a European cargo ship.

Collecting the experiment tray was Vinogradov's last task outside.

The tray drifted toward the solar panels of the main Russian space station compartment, called Zvezda, Russian for Star. Flight controllers did not believe it struck anything, and the object was not thought to pose a safety hazard in the hours and days ahead.

"That's unfortunate," someone radioed in Russian.

Another panel of similar experiments will be collected on a future spacewalk.

This is the first of eight spacewalks to be conducted this year, most of them by Russians. Two will be led by NASA this summer.

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2 Russians take spacewalk outside space station