Astronaut Ed Lu leaves the shuttle's airlock at the start of the 50th shuttle spacewalk. Photo: NASA TV/Spaceflight Now

Working up to 11 stories above the shuttle Atlantis's cargo bay, two high-flying spacewalkers hooked up power and data cables between the international space station and its newest module early today to accomplish one of the primary goals of the mission.

If all goes well, Atlantis's seven-man crew will float into the space station late this evening to begin outfitting and activating the new Zvezda command module before arrival of the lab's first full-time crew in early November.

"We've got a lot of work to do, clearly, once we ingress the modules," said Milt Heflin, a senior NASA manager at the Johnson Space Center in Houston

"It's a cabin we have that we're trying to get some furniture into to get it ready to move into," he said. "So it's just a tremendous amount of work and coordination that's required between now and the end of the flight to get it done."

Before calling it a day, shuttle commander Terrence Wilcutt and pilot Scott Altman fired Atlantis's steering jets 36 times over a one-hour period to boost the station's altitude by about 3.5 statute miles. Two more reboost maneuvers are planned later in the flight.

Astronaut Ed Lu loads cosmonaut Yuri Malenchenko's backpack with equipment and tools needed for the spacewalk. Photo: NASA TV/Spaceflight Now

NASA mission management team, meanwhile, met early today in Houston to consider extending Atlantis's flight by one day to give the crew more time to complete all of the planned mission objectives.

It appears likely, based on the shuttle's available supplies and the crew's conservation efforts, an extension will be granted at some point. But as of 9:30 a.m., an official decision had not yet been made.

Today's problem-free spacewalk was the first of nearly two dozen such outings planned over the next few years to build the international space station.

"This was the 50th shuttle-based spacewalk, the 89th spacewalk by U.S. astronauts and the sixth spacewalk performed on the international space station," said Mike Hess, a spacewalk planner at the Johnson Space Center in Houston.

"We have a surge of spacewalks that are about to occur over the next year and a half or so, we have about 20 spacewalks planned and we're going to really start getting into the assembly of space station in very short order here," he added. "I feel like this spacewalk set the tone for what's about to come."

Lu and Malenchenko ride the robot arm out of the cargo bay and up the station stack. Photo: NASA TV/Spaceflight Now

Floating in Atlantis's airlock, astronaut Edward Lu and cosmonaut Yuri Malenchenko began the excursion at 12:47 a.m. when they switched their spacesuits to internal power. They floated into the shuttle's cargo bay 12 minutes later.

After attaching tools and bulky cable spools to their backpacks, Lu and Malenchenko hitched a ride on the shuttle's 50-foot-long robot arm to a drop-off point on the Russian-built, NASA-financed Zarya propulsion module.

From there, the spacewalkers made their way, hand over hand, up the "stack," stopping along the way to free up a jammed docking target that failed to fully deploy after the Zvezda module reached orbit July 12.

While the target is no longer needed, flight controllers worried its spring-loaded mast might suddenly jump free some day, possibly posing a hazard to future spacewalkers. So Lu floated up to the boom and gave it a push.

"Deploying this target was very simple," Hess said. "Ed Lu approached it, described what he saw, Moscow gave the go-ahead to move in closer and he moved in and pushed on it. Once he pushed on it, it popped into the deployed position and locked in place and we were able to continue our EVA."

Lu and Malenchenko then continued their ascent "up" the station, stopping at a point some 110 feet above Atlantis - twice as far from the safety of the shuttle's airlock as U.S. spacewalkers have ever ventured.

Lu and Malenchenko work to install a magnetometer boom on the Zvezda module. Photo: NASA TV/Spaceflight Now

Lu then mounted an orientation-sensing magnetometer on a boom and bolted it in place.

Computers aboard the Zvezda module normally use data from star trackers to determine the station's orientation in space. But the star trackers field of view can occasionally be blocked by solar arrays or other station structures.

So Zvezda is equipped with a magnetometer that can use Earth's magnetic field to establish an attitude reference. At launch, the magnetometer head was stowed against Zvezda's hull. To work properly, it needed to be mounted on a boom, away from the metal skin of the station.

After completing the magnetometer work, Lu and Malenchenko began working their way back down the station to begin the hardest part of their work: Connecting nine power and data cables between Zvezda and the Russian Zarya module. See a diagram of the wiring task.

"The first set of cables they laid were power system cables, there were four of those, and the connections really went without incident," Hess said. "The next set of cables that they set up were the television, communications and data handling cables, again the connections and routing of those cables went very smoothly."

The two spacewalkers work to install cables between Zarya and Zvezda. Photo: NASA TV/Spaceflight Now

The spacewalkers had a bit of trouble with the last cable, a fragile fiber optic line that will carry telemetry from Russian spacesuits. In the end, however, "they were able to work through the routing of that cable relatively easily," Hess said.

The spacewalk ended 16 minutes early at 7:01 a.m. after a duration of six hours and 14 minutes. U.S. and Russian spacewalkers have now logged 42 hours and 15 minutes in space station assembly over the past three years.

Overall, shuttle astronauts have now carried out 50 spacewalks in 99 missions, logging a total of 310 hours and 51 minutes.

"I've been working spacewalks for about 11 years now and this was one of the most challenging ones to put together from a planning perspective, primarily because we had to use two different water tanks in two different countries to choreograph this spacewalk," Hess said.

"We did a lot of our training in Russia, 16 water tank runs in Russia and a number of water tank runs here in the U.S. We were never able to complete training for this spacewalk in one facility. And when it was all said and done, we finished up 16 minutes early today."