Canada's robotic arm stretches out from a pallet mounted to the side of the space station. Photo: NASA TV/Spaceflight Now

Spacewalkers Chris Hadfield and Scott Parazynski, clearly awed by the view from 243 miles up, successfully assembled and deployed the space station's new $900 million Canadian-built robot arm today after briefly wrestling with a set of balky fasteners.

Shortly after the spacewalkers returned to Endeavour's airlock, space station astronaut Susan Helms, operating the arm for the first time from a computer work station in the Destiny laboratory module, sent commands to begin unfolding the new space crane.

"And Houston, the big arm's in motion," Helms matter-of-factly reported at 2:54 p.m., marking a major milestone in the 104th shuttle mission.

The arm was left in an extended "park" position overnight, both of its identical ends locked to a Spacelab launch pallet temporarily bolted to the Destiny module's hull. On Monday, Helms will power up the arm, unlatch one end and plug it into a power and data socket on Destiny's hull.

Canadian astronaut Chris Hadfield works to activate the space station's new robotic arm. Photo: NASA TV/Spaceflight Now

The other end of the arm later will hand the Spacelab launch cradle back to the shuttle's robot arm - also built by Canada - for return to Earth.

The arm, able to move end-over-end about the station like an inchworm, is required for installation of the station's main airlock in June. Getting it assembled today was a major milestone in the complex system's checkout and activation.

"This is a major component, it's actually in the critical path, required to be fully functional prior to the next shuttle mission when we actually install the airlock," said lead station flight director John Curry. "And today went perfectly, beautifully, from a station arm perspective."

Benoit Marcotte, director of operations for the Canadian Space Agency, said "today is really an awesome day for Canada."

"We've reached two key milestones in our space development," he said. "The first one being a first-ever EVA for a Canadian astronaut and the second one was just accomplished when we saw Canadarm 2 making its first movements on its own power.

The Canadian arm sits folded in its craddle before the start of today's spacewalk. Photo: NASA TV/Spaceflight Now

"So it is important to note on the 22nd of April for us in Canada that we're joining the international space station, contributing the next major element to the station."

Hadfield and Parazynski began the 103 spacewalk in U.S. space history - the 19th devoted to space station construction - at 7:45 a.m. The seven-hour 10-minute excursion officially ended at 2:55 p.m. when the astronauts began repressurizing the shuttle Endeavour's airlock.

While some spacewalkers adopt a strictly-business attitude and seldom comment on the spectacular vista below, Parazynski and Hadfield could not help marveling aloud thoughout the spacewalk, attempting to share the view with flight controllers in Houston.

"Words cannot describe this experience," Hadfield said shortly after the spacewalk began.

"Well, we'll give it a shot," Parazynski quipped. "Just in case people think astronauts aren't poetic."

And Hadfield did just that.

"There's just a beautiful inevitability of the way this moves along, this station," he marveled as the spacecraft approached the coast of Chile at five miles per second. "Like a graceful, enormous building, just unstoppably plowing along up here. It's just beautiful, with the world rolling underneath."

Toward the end of the excursion, Hadfield took a moment to turn off his helmet lights and enjoy the view of the aurora.

"Oh wow! Northern Lights!" Hadfield exclaimed.

"Really? Wow!" Parazynski replied.

"I just shut off my lights while I'm translating across (the station) and way off to orbiter starboard... where are we?"

"We're off the southwest corner of Australia," astronaut John Phillips replied from Endeavour's flight deck.

"Southern lights. Wow. That's beautiful," Hadfield said. "There's lightning down below me and just the whole horizon is lit up green with tendrils going up into space off to the south. That is beautiful. Oh wow..."

The Canadarm 2 was launched on a Spacelab pallet, unpowered and with its two long booms folded in half and doubled over. Parazynski first attached four electrical lines so internal heaters could begin warming up the booms and joints prior to deployment.

The craddle carrying the station's robot arm is moved into position by the shuttle's arm. Photo: NASA TV/Spaceflight Now

While the arm warmed up, Parazynski and Hadfield installed a new UHF radio antenna near the station's PMA-2 shuttle docking port to improve communications between arriving shuttles and station crews. They then returned to the Canadarm 2 and removed eight so-called superbolts locking the arm in place on the Spacelab pallet.

"This is, Scott," Hadfield said at 10:20 a.m. as Parazynski began removing smaller bolts holding the meter-long superbolts in place.

"Yep, I've got it."

"Canadarm 2 is staying in space!"

With Hadfield providing guidance, Parazynski then lifted the arm's folded booms to an angle of about 35 degrees.

"Going for the gold and the world record..." Parazynski joked as he began lifting. It took about 65 pounds of force to move the booms.

"We have motion," Hadfield said. "You've come five degrees, you've come eight, 10 degrees... Looking marvelous..."

"OK, great."

When the folded booms elevated to 35 degrees, Hadfield then climbed on the end of the shuttle's robot arm, grabbed the other end of the booms and unfolded them completely. To lock the extended booms in place, the spacewalkers took turns using a power wrench to turn internal fasteners designed to expand like concrete bolts.

And that's when the day's only trouble cropped up. The fasteners did not initially take hold at the torque settings expected. The spacewalkers then cranked up the torque in stages and repeatedly tightened the fasteners until - finally - they would not budge any more.

In the middle of that, Hadfield reported a drop of soap used to clean his helmet visor apparently had floated into his right eye, causing quite a bit of irritation. He was told to increase the flow of air through his helmet and within a few minutes, he reported the condition was improving.

"My eye's definitely getting better," he said. "My right eye is kind of half closed all the time, but I think it's going to clear."

With the arm booms locked in place, Parazynski and Hadfield began cleaning up, taking a moment to looking into the Destiny module's picture window where Helms could be seen smiling and waving back.

Hadfield and Parazynski pose at the Destiny lab's window for some IMAX footage. Photo: NASA TV/Spaceflight Now

Station astronaut James Voss then filmed the spacewalkers using a large-format IMAX camera before Hadfield and Parazynski headed back to Endeavour's airlock. As they did so, Canadian astronaut Steven MacLean in mission control radioed up a tribute to Hadfield and the Canadian arm, playing a recording of "Oh Canada" over the air-to-ground radio loop.

"And Chris and Scott, we'ree real proud of your work up there getting Canadarm 2 operational," he said when the song ended. "And if you turn around and look down, I believe you're right over Newfoundland."

"We are indeed!" Hadfield exclaimed. "Thank you very much to all the people who helped put the arm up here. Scott and I were just the deliverymen. And it really just opens the door to what all of us can be doing together here internationally, beginning to explore space as a planet."

"Congratulations," Maclean said.

"And I just want to thank you, Steve, for making me an honorary Canadian for today," Parazynski said. "It was real pleasure and an honor and I'm really proud of the work that everyone put into this very complex piece of hardware. It's going to serve the station well for many years to come."