SPACE.com -- Spacewalkers Add New Experiments to Space Station

This story was updated at 2:46 a.m. EST.

Two astronauts floated outside the International Space Station late Monday to install new experiments that will study the harsh orbital environment and help explain recent glitches with Russian Soyuz spacecraft.

Clad in Russian-built spacesuits, station commander Michael Fincke of NASA and flight engineer Yury Lonchakov spent more than five hours working outside the orbiting laboratory to attach the new science equipment. The only hitch popped up late in the spacewalk, when a problematic data relay for a joint Russian-European experiment thwarted repeated attempts to install it.

"Okay, going out into space again," said Fincke, who made his fifth career spacewalk in the excursion. "Excellent! It's good to be here again."

Lonchakov, a cosmonaut with Russia's Federal Space Agency, led the five-hour, 38-minute spacewalk with Fincke while their NASA crewmate Sandra Magnus monitored their progress from inside the space station. The spacewalk began at 7:51 p.m. EST (0051 Dec. 23 GMT), about 40 minutes late, due to a pressure valve glitch.

The spacewalkers swiftly accomplished their primary task to install a so-called Langmuir probe near their airlock hatch of the space station's Russian-built Pirs docking compartment. The tool is designed to measure the surrounding plasma and electromagnetic environment.

Data from the probe is expected to help Russian engineers pin down the cause of explosive bolt malfunctions that sent two of the last three Soyuz spacecraft that ferried station astronauts back to Earth to suffer module separation glitches during their descents. The malfunctions, in October 2007 and April 2008, forced the Soyuz vehicles into off-target landings and subjected their crews to higher gravitational stresses than nominal landings.

Russian engineers believe that electrical arcs or other electromagnetic interference near the space station's Soyuz docking ports may have prompted the explosive bolt failures. A suspect bolt was removed from the last Soyuz to land prior to its Oct. 24 descent this year and it touched down on target as planned.

But Russian engineers hope the new plasma probe outside the station will yield more insights.

"It's definitely a step in that process," said Kirk Shireman, NASA's deputy space station program manager. "There's still a ways to go in the overall understanding and confirmation of the root cause that we have on the Soyuz."

In addition to attaching the plasma probe, Lonchakov and Fincke retrieved a Russian experiment canister of biological samples from the space station's hull. They also installed a Russian plasma physics experiment called Impuls to the exterior of the station's Zvezda service module, at times working uncomfortably closed to a solar array, which they asked flight controllers to move to give them more room.

"I'm very close to the solar array," Fincke said. "It's very important that nothing be broken here."

But it was a second experiment, dubbed EXPOSE-R, which refused to activate properly after the spacewalkers installed it near Impuls. A joint project between the European and Russian space agencies, the experiment is designed to understand how organic materials are affected when exposed directly to space.

Despite repeated efforts to activate it, flight controllers at Russia's Mission Control near Moscow were unable to receive any telemetry from the device via a data relay connector. Flight controllers eventually ordered Fincke and Lonchakov to remove the experiment and return it back inside the International Space Station.

"We had to remove the entire EXPOSE-R because of one connector," said a disappointed Lonchakov. "Yes, that's a shame."

Monday night's spacewalk marked the 19th excursion outside the space station this year and the 119th dedicated to construction and maintenance of the orbiting laboratory since its first element launched in 1998. Fincke ended his fifth spacewalk with 21 hours and 23 minutes of spacewalking time. Lonchakov, meanwhile, ended with five hours and 38 minutes in his spacewalking debut.

"Yury, was it beautiful?" Magnus asked after the spacewalk.

"Yes it was beautiful, although we really had no time to look around," Lonchakov replied.

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