CAPE CANAVERAL, Fla.—A pair of spacewalking astronauts prepped a giant billion-dollar Japanese lab Tuesday for its long-awaited anchoring to the international space station.

Spacewalkers Michael Fossum and Ronald Garan Jr. quickly took care of all the preliminaries, removing covers and disconnecting cables on the bus-size lab, named Kibo, Japanese for hope. They left it to their colleagues inside to do the heavy lifting, by way of the space station’s robot arm.

The honor of operating the arm for the installation fell to Japanese astronaut Akihiko Hoshide, who accompanied Kibo to orbit aboard space shuttle Discovery.

Kibo—a behemoth stretching 37 feet and weighing more than 32,000 pounds—was set to become the biggest lab at the space station by nine feet.

It’s also more sophisticated. Kibo sports a hatch to the outside and a robot arm for sliding out science experiments.

A smaller arm will arrive next spring, along with an outdoor porch for holding the experiment packages.

The first part of Kibo—essentially a storage shed—was delivered by the last shuttle crew in March. The astronauts aboard the linked shuttle and station will attach the shed to the lab on Friday.

Japanese Space Agency officials estimate more than $2 billion went into all the pieces, which had to be split up to fit into NASA’s shuttles. The project has been in the works for more than 20 years.

The lab work was just part of Tuesday’s spacewalk, the first of three planned for Discovery’s nine-day space station visit. Coincidentally, it fell on the 43rd anniversary of America’s first spacewalk, by Gemini 4’s Edward White.

White spent 21 minutes outside his capsule on June 3, 1965. Fossum and Garan were looking at 6 1/2 hours outdoors.

The spacewalkers got off to a late start because of a bad cable in Fossum’s communications cap, but soon made up for lost time, helping to remove a 50-foot shuttle inspection boom from the space station. The laser-tipped pole was left there by the last shuttle crew, for use by Discovery’s astronauts to survey the shuttle’s thermal skin before returning to Earth.

Kibo took up so much of Discovery’s payload bay that there wasn’t room for the boom.

Fossum also took a stab at cleaning a solar wing rotating joint that is clogged with metal shavings, while Garan worked to put in a new bearing. The joint has been used only sparingly since last fall, hampering energy production.

NASA still does not know where the grit came from or how best to deal with the problem.

It was the fourth spacewalk for Fossum, a colonel in the Air Force Reserves who is making his second shuttle flight, and the first for Garan, an Air Force pilot.

As the spacewalk got under way, Fossum offered this advice: “Enjoy the view, but don’t look down.”