Astronauts float through new station airlock

Walz and Bursch, upper left, hovering near the Quest Airlock

(CNN) -- Two residents of the international space station stepped outside their orbital home on Wednesday, testing a new airlock, performing numerous maintenance jobs and soaking up space radiation for an experiment.

NASA flight engineers Carl Walz and Dan Bursch wrapped up their foray into space abour six hours after it began, closing the hatch on the Quest Airlock at 12:25 p.m. EST.

The expedition was the first use of Quest without the assistance of a visiting space shuttle and set the stage for four upcoming spacewalks from the U.S.-built portal.

Those walks will be to attach the first of several large truss segments to the station during a shuttle mission currently scheduled for early April.

Other spacewalks have been conducted through the Russian airlock, which is attached to the Russian portion of the modular outpost.

Walz and Bursch, both of whom performed spacewalks last month, took orders from Russian commander Yuri Onufrienko, who choreographed the walk from his perch inside the space station.

When they left the station through Quest, they marveled at what they saw from 250 miles high.

"The view is spectacular," Walz said.

"Yee-haw!" exclaimed Bursch.

The Americans performed a bevy of tasks while on the outside, removing four thermal blankets from the Z-1 truss, the base structure for the U.S. solar array on the space station, and picking up tools to take back inside the station so the next spacewalking team will be able to use them.

The two also tested electrical circuitry, tightened loose latches and took high frontier insurance pictures of dings and dents on station radiators, likely caused by a tiny meteor or orbita debris fragment.

On the experimental front, Walz and Bursch wore devices to monitor space radiation dosages encountered by the eyes, internal organs and skin. The test will help scientists better understand the effects of intense space radiation and design better spacesuits.

Walz works on the T-1 truss

Halfway into the work detail, the spacewalkers paused to reflect on a historic day in space exactly four decades ago, when John Glenn became the first American in orbit.

"One of the biggest differences from 40 years ago, the space race was a competition," said Bursch, speaking of the rivalry between the United States and the Soviet Union at the time.

"But now the space race has turned into cooperation," he said, noting that the space station currently had a Russian commander and American crew, which would have been unthinkable years ago.

Walz, Bursch and Onufrienko, who comprise the Expedition Four crew, are in their third month of a planned five-month stay on the station.

The next shuttle flight is scheduled for February 28. That mission, on space shuttle Columbia, will be a Hubble Space Telescope repair mission and will not visit the international space station.

-- CNN's Richard Stenger contributed to this report