Two spacewalkers replaced an old door on the International Space Station early Wednesday during a rare — and brief — internal service call that primed the outpost for the arrival of a new Russian-built room later this year.

Russian cosmonaut Gennady Padalka and American astronaut Michael Barratt spent just 12 minutes working in close quarters to remove the roof-mounted hatch cover in the forward transfer compartment of the station's Zvezda service module.

They replaced the door with a docking cone that will allow Russia's new Mini-Research Module 2 to latch onto the station in November.

"I think this is it," said Padalka, who commands the station's six-man Expedition 20 crew. "Michael, you did such a great job replacing that cover."

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It was a tight fit for the two spacewalkers. Zvezda's small spherical transfer compartment is only five feet (1.5 meters) across at its widest point, giving little room for Padalka and Barratt to move in their bulky Russian spacesuits.

"Michael, do you have enough space there?" asked Padalka after they two men squirmed into position.

"Yeah, I have more than enough," Barratt replied.

An inside job

Wednesday's spacewalk began at 2:55 a.m. EDT (0655 GMT) and finished 12 minutes later, though Padalka and Barratt had a more than six-hour supply of air in case the door swap went awry.

At no point did the two spacewalkers exit the space station or detach the spacesuit umbilical cables linking them to the outpost.

Not since 2001 have spacewalkers worked inside the space station in a vacuum, NASA officials said.

That earlier spacewalk was performed on June 8, 2001 — nearly eight years to the day of Wednesday's work — by the station's then-Expedition 2 crew to prime Zvezda to receive its Earth-facing Pirs docking compartment. It lasted 19 minutes.

NASA and Russia's Federal Space Agency consider any activity in which astronauts and cosmonauts work in a vacuum as a spacewalk.

Russian spacewalks are timed by the duration between a hatch opening and closing, while NASA spacewalks are measured by the period between the switch to a spacesuit's internal battery power and airlock repressurization.

Russian cosmonauts also performed three internal spacewalks in 1997 to inspect and repair a damaged module on Russia's Space Station Mir.

The internal spacewalk by Padalka and Barratt was the second excursion dedicated to preparing the space station for its new Russian room.

The two spacewalkers ventured outside the station on June 5 to install docking antennas that will help the Mini-Research Module 2 attach to its final berth when it arrives this fall.

Russia's new station room

With the new docking cone installed, the space station's Zvezda module is now a step closer to welcoming Mini-Research Module 2, a new room slated to launch toward the outpost atop an unmanned rocket.

The module will add a new docking port to the space station, which currently has four available berths, three on the Russian segment and one at the front of the outpost on NASA's Harmony connecting node.

The space station needs more docking ports to support its larger, six-person crew, which took up residence earlier this month.

In addition to Padalka and Barratt, another Russian cosmonaut and astronauts from Japan, Belgium and Canada currently live aboard the space station.

Two Russian Soyuz vehicles are currently parked at the station as lifeboats and a taxi home for the six spaceflyers aboard. An unmanned Progress cargo ship is docked at the remaining Russian port.

The Mini-Research Module 2 will also serve as an airlock for Russian spacewalks and will have exterior attach points for future experiments, NASA officials said.

Russia's Federal Space Agency built two Mini-Research Modules for the station at the same time and always planned to launch the first one completed to the outpost atop an unmanned booster, NASA officials told SPACE.com.

Mini-Research Module 2 was completed slightly ahead of its counterpart and jumped to the head of the line, they added.

NASA and Russia plan to launch the Mini-Research Module 1 to the station in May 2010 aboard the U.S. space shuttle Atlantis.

Shuttle mission ahead

Wednesday's spacewalk was the 125th excursion dedicated to station construction and maintenance.

It was the eighth spacewalk for Padalka, who finished with 27 hours and 15 minutes of spacewalking time. It was the second career spacewalk for Barratt, who ended with just over five hours of orbital work.

The six men aboard the space station have an extended rest period ahead as they prepare for the arrival next week of NASA's shuttle Endeavour and seven more astronauts.

Endeavour is slated to launch Saturday morning from Florida to deliver a porch-like experiment platform for the station's Japanese Kibo lab, as well as new solar array batteries and spare parts. Five spacewalks are planned for the 16-day shuttle mission.

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