CAPE CANAVERAL, Fla. (AP) – The first half of Monday’s spacewalk was a breeze as two Discovery astronauts removed a faulty part on the international space station, but a series of minor problems combined to temporarily gum up the rest of their work on what were supposed to be routine repairs.

At one point, a key device that keeps spacewalkers from floating away free nearly came loose.

Astronauts Piers Sellers and Michael Fossum started their 6 1/2-hour spacewalk by removing a severed cable reel from a crucial rail car on the space station with a simple pull. The cable provides power, video and data to the car.

“We’re getting a workout,” Fossum said.

But then Sellers had problems placing the removed cable reel into the shuttle’s payload bay. Next, a gun-device that anchors spacewalkers nearly came loose; Sellers and Fossum were able to repair in about half an hour. Finally, Fossum had trouble installing the new cable reel, even with Sellers helping.

After much wrangling, the astronauts completed their tasks and started the lengthy process of cleaning up just under six hours into their spacewalk.

The spacewalk’s more mundane tasks included installing a spare external pump compartment on the station’s cooling system. The astronauts attached the pump compartment to the space station’s robotic arm, and it was moved to where it will be installed on the station.

The spacewalk came a day after the astronauts received the good news that everything appeared safe for them to return to Earth aboard Discovery.

Sellers came out of the hatch first, followed by Fossum, as the space station and Discovery passed about 220 miles above Spain.

“Everyone can hear you scream,” said Fossum, in a twist on the tag line from the movie “Alien.”

Sellers retorted: “About the time I get outside, I’ll put on my alien costume.”

At first, Monday’s spacewalk lacked the drama of the astronauts’ trip on Saturday, when they stood on the end of a 50-foot extension connected to the 50-foot shuttle robotic arm. They were testing the sometimes-oscillating assembly as a platform for making repairs to the space shuttle.

The spacewalk, at the middle of space shuttle Discovery’s 13-day mission, was expected to last under seven hours. The last spacewalk of the mission is scheduled for Wednesday.

Replacing the cable on the rail car, or mobile transporter, is crucial for the continuation of construction of the space station. The cable was accidentally severed in December by a cable cutter. During Saturday’s spacewalk, the astronauts immobilized a cable cutter on a duplicate cable leading to the transporter. The rail car could be put back into use as early as September when space shuttle Atlantis visits the space station with construction parts.

Before the spacewalk began, robotics operators in Houston and Quebec remotely moved the transporter 27 feet so that it was easier to access by the astronauts.

In what may be an awkward maneuver, Sellers had to hold the old 330-pound cable reel in one hand and the new one in the other. That worked well, but then the delaying glitches started to pop up.

Fossum had said Sunday that the most challenging part of Monday’s assignments “is going to be just the choreography, going back and forth in the payload bay. It’s quite a ballet.”

Discovery’s four other astronauts helped with the spacewalk by operating the station’s robotic arm and giving directions from inside the orbiting space lab. The international space station’s three crew members on Monday planned to pack up materials and trash that need to be taken back to Earth.

The shuttle’s astronauts got welcome news Sunday when NASA managers cleared Discovery’s thermal protective skin as safe for a return to Earth on July 17. Hundreds of images of Discovery were taken during liftoff, during the orbital flight to the space station and before docking with the complex to make sure the shuttle doesn’t have any damage like the kind that doomed Columbia’s seven astronauts in 2003.

Foam falling from Columbia’s external tank struck the shuttle’s wings during liftoff and allowed fiery gases to penetrate the vehicle during re-entry. During last week’s launch, Discovery’s tank performed well and no pieces of the insulating foam fell off the tank in excess of what was allowed, flight controllers told the astronauts.

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