CAPE CANAVERAL, Florida (AP) – Two astronauts swapped out balky equipment to fix the international space station’s rail transporter and started to test whether a boom is stable enough to be used as a platform to make repairs to the space shuttle.

While initial tests went well for Piers Sellers, Mike Fossum’s turn standing at the end of the boom was delayed because of a glitch.

His tether that connects him to the boom would not retract.

The duo decided to try to “coil it up” and tied it up with a metal twistie-tie, much like getting a garden hose rolled up.

Finally, Fossum got his turn as the two stood on a 100 feet (30 meters) of extension.

“It’s beautiful,” Fossum said. “The thin glow of the moonlit Earth below.”

They astronauts travelled to the space station on the shuttle Discovery, and dropped off German astronaut Thomas Reiter, who is becoming the third person on the station’s crew.

The planned 6 1/2-hour jaunt, which began as the space station passed over Asia 220 miles below, was the first spacewalk for Fossum and the fourth for the British-born Sellers.

“Enjoy the view, gentlemen!” NASA communicator Megan McArthur said from Houston.

Both astronauts did. When Mission Control pointed out to Sellers that he could view Britain over his left shoulder, the British-born spacewalker said, “Wow! Oh, my goodness. It’s a beautiful day in Ireland.”

As he looked down at the Caspian Sea several minutes later, Fossum said, “Ha, ha, ha. This is a good view… I’m in a dream; nobody wake me up.”

In the most daring part of the spacewalk, Sellers contorted to test the dual extension as a long-planned possible work platform for potential emergency repairs to the space shuttle’s heat shield.

In their bulky spacesuits and in the zero gravity, Sellers and then Fossum laid back, reached forward, mimed the motion of taking pictures, and did pirouettes with their feet and swimming motions with their arms.

While there was swaying and oscillating during the work, Sellers was able to accomplish all his pretend tasks in their first series of manoeuvers. Fossum’s turn was delayed by the tether problem.

The tether in question was to the end of the boom and a required part of the spacewalk experiment. They went for a spare tether elsewhere around the shuttle, pushing the astronauts further behind on their already behind schedule spacewalk.

But the ride, which was the whole point of the test, was not bad at all. As he was being moved into position on the extension, Sellers called it “a very slow gentle sway in and out of the bay.”

And when he got his turn, Fossum described the feeling as “smooth, very smooth.”

Last June, Sellers described that he thought it would feel like “standing on a diving board or standing at the top of a telephone pole or hanging down from a ceiling. It’s disorienting.”

Lead spacewalk officer Tomas Gonzalez-Torres described the expected effect as similar to trying to paint a house from the top of a rickety ladder.

Just because it was not as wobbly as expected at first, did not mean Sellers and Fossum were not enjoying themselves. While waiting for Fossum, Sellers did a couple of flips. The two spacewalkers let out frequent “woo-hoos” and Sellers occasionally grunted while making his required acrobatics.

The spacewalkers finished their first task, a bit behind schedule, immobilizing a cable cutter on the station’s mobile transporter, or railroad car, and rerouting a cable through it. A duplicate cable cutter accidentally cut a cable leading to the transporter late last year, and NASA wanted to make sure it doesn’t happen again because the cable is a conduit for power, data and video images.

The transporter moves along the space station and is used for constructing the complex. The severed cable will be replaced during a second spacewalk set for Monday.

The technique was developed to make sure there is never a repeat of the Columbia disaster, which killed seven astronauts in 2003. Foam from the shuttle’s external tank struck Columbia’s wing during launch, creating a breach that allowed fiery gases to penetrate the shuttle during the return flight to Earth.

Fossum and Sellers may get a chance to use the boom for a real repair on their third spacewalk, now scheduled for next Wednesday. NASA managers are evaluating whether a piece of fabric filler protruding from the thermal tiles on Discovery’s belly needs to be removed by the spacewalkers.

Two pieces of gap filler had to be removed from Discovery’s belly during a spacewalk last year because of concerns they would cause problems during re-entry.

In their morning message, flight controllers told the Discovery crew that they wanted to take additional pictures of slightly damaged thermal blankets using a camera on the space station.

NASA managers do not think two of the blankets pose any problems but want to make sure the other two small blankets don’t tear off during re-entry into Earth’s atmosphere. The thermal blankets are used to protect the shuttle against searing heat during ascent and descent.

The flight controllers also had a request for the shuttle crew: Stop pouring unused drinks down the shuttle’s toilet. “An example of how closely Big Brother watches,” they wrote.

The space shuttle crew awoke Saturday to “God of Wonders,” a popular Christian music recording chosen by Fossum’s family.

“I do think it’s particularly appropriate as I prepare to step outside for about 4 1/2-trips around this chunk of creation we call Earth,” Fossum radioed Houston.