Linked to the shuttle and looming above them was the 13-story international station, which now comprises three permanent wings and a Russian supply ship.

"Woo-hoo!" rookie spacewalker McArthur said as he drifted into open space. "Its huge."

"Its gorgeous," added Chiao. "Just wonderful."

Chiao and McArthur set out to wire up a nine-ton metal truss that was mounted atop the station Saturday despite a short circuit that temporarily knocked out a computerized television system critical to the installation work.

Now sitting atop a space station docking module dubbed "Unity," the truss houses four dome-shaped gyroscopes designed to reduce the amount fuel needed to keep the outpost properly positioned in orbit.

Also packed within it is a dish-shaped antenna that will enable resident crews at the station to beam television signals and voice communications to earthbound ground controllers.

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Plan for today

During the planned 6.5-hour spacewalk, the astronauts will attempt to route electrical cables between the truss and the Unity module, which is a pressurized passageway to the stations new Russian-made crew quarters.

Discovery astronaut Leroy Chiao works outside the International Space Station during the first spacewalk.

Also on the spacewalking to-do list: Attaching the dish-shaped antenna to the end of a 12-foot (3.6-meter) boom and then swinging it into place outside of the station.

A smaller, less capable communications antenna also is to be set up during the day, and the astronauts plan to stow a toolbox for future spacewalking construction crews.

The assembly chores call for Japanese astronaut Koichi Wakata to hoist the spacewalkers to various work sites outside the towering station with the shuttles 50-foot (13-meter) robot arm. That lift began about a half-hour after the start of the spacewalk.

"Lets go for a ride," McArthur said as Wakata started raising him up to a point some three stories above Discovery. "Hey, that space shuttle is a long way down."

McArthur said before the flight that he expected the perch at the end of Canadian-built construction boom to offer up some spectacular panoramic views of the planet and deep space.

"Ive been thinking about being just being lifted to the middle of nowhere. I bet its going to be an interesting -- a very interesting experience," McArthur, a veteran of two previous shuttle flights, said in a recent interview with SPACE.com.

"Everything Ive seen from space has been really awe-inspiring. It doesnt matter whether youre looking out at the stars, or you get to see the moon, or you look down on Earth," he added.

"The entire physical experience of being in space -- from feeling weightlessness, to the sounds, to the sights -- it all vastly exceeds what you imagine."

The girder-like truss segment was mounted atop the Unity module Saturday despite a short circuit that temporarily disabled a computerized television system considered crucial to the construction job.

The so-called "space vision system" serves as a set of "electronic eyes," giving astronauts camera views of station work sites that otherwise are blocked by the 69-ton outpost.

The astronauts, however, were able to plug a spare vision system into an alternate power source, enabling Wakata -- who is considered a master robot arm operator -- to carry out the most complex station assembly job to date.

"Well, I have to tell you, Wakatasan is `Da Man," NASA lead flight director Chuck Shaw told Japanese reporters assembled at Johnson Space Center to cover the mission. "He was flawless. He made it look very, very easy."

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Electrical unknowns

Still unexplained, the electrical short was the second significant snag to crop up on the mission. The shuttles high-speed communications antenna failed Thursday, triggering a near-total TV blackout for the remainder of the flight.

Mission Discovery

Look here for the latest news from NASA's STS-92.

Consequently, only sequential still video snapshots of the spacewalking construction work can be beamed back to the ground.

"It seems to be a plot to frustrate the press," Shaw joked.

Launched last Wednesday from Kennedy Space Center, Discoverys six-man, one-woman crew also plans to mount a new shuttle docking port at the station. Wakata will carry that job out Monday with an assist from spacewalkers Jeff Wisoff and Michael Lopez-Alegria.

Two bulky electrical voltage converters are to be installed on the cube-shaped truss by Chiao and McArthur Tuesday during a third spacewalk.

The voltage converters are designed to route electricity to the station from giant solar arrays that are to be placed atop the truss during NASAs next outpost construction mission, which is scheduled for launch on shuttle Endeavour Nov. 30.

Wisoff and Lopez Alegria will conduct the fourth and final foray Wednesday, testing jet backpacks designed to enable spacewalkers to fly back to the station if their braided steel safety tethers snap, casting them adrift in space.

The crew also will spend a day inside the station, delivering supplies for the outposts first full-time tenants, who are due to take up residence at the station in early November.

As it stands now, Discovery and its crew are scheduled to depart the station next Friday, heading out on a two-day trip back to Earth.

NASAs 100th shuttle flight is slated to wrap up with a 2:10 p.m. EDT (1810 GMT) Oct. 22 landing here at KSC.