Shaped like a giant beer keg, the airlock serves as both an orbital portal for spacewalkers and an extra parking place for Russian Soyuz crew transport vehicles and Progress cargo carriers.

It is berthed to a port at the forward end of the station's Russian-built "Zvezda," or "Star," crew quarters, which is linked to a Russian space tug dubbed "Zarya," or "sunrise."

Two spacewalking cosmonauts set up a "Strela," or "Arrow," cargo boom outside the Pirs airlock last November. That telescoping crane can be extended to the rear end of the Zvezda crew module.

Mounted to the opposite side of Pirs, the Strela boom installed by Onufrienko and Walz is positioned so that it can be reeled out to the end of the Zarya space tug, which is hooked up to the U.S. side of the station.

Both booms are capable of hoisting cargoes that weigh as much as three tons. They can be operated either separately or simultaneously to move cargoes or spacewalkers around the outer hull of the Russian half of the outpost.

In addition, the cranes are expected to play a key role in the assembly of a Russian electrical power tower and its associated solar arrays after their arrival at the outpost around 2005.

The boom installed by Onufrienko and Walz was ferried up to the station in parts during U.S. shuttle missions in May 1999 and May 2000.

Two U.S. spacewalkers assembled the parts during the latter flight and stowed the Strela outside a pressurized mating adapter that links the U.S. and Russian sides of the station.

Operating the Strela boom already set up on Pirs, Onufrienko latched onto the second crane and pulled it away from its storage spot with a spacewalking assist from Walz, who had set up a specially designed clearance bracket on the outside of the Zarya module.

The idea was to route the first Strela boom through the bracket to make sure that neither of the lifting devices came into contact with a solar array jutting out from the side of the Russian space tug.

Specialists in Russia's Mission Control Center still urged caution as Onufrienko moved the second crane within 1.6 feet (a half-meter) of the power-producing wing.

"Be sure you don't touch the array," a mission controller said. "Go up first and to the right and then move around the solar array."

Onufrienko had done similar work in the past. A veteran of six previous spacewalks, he paired two Strela booms outside the Mir space station in March 1996.

The crane installation Monday also came off without major problems.

A continual high-pitched beeping that came from the spacewalkers' suits was a nuisance early on, but Russian ground specialists were able to quell the noise after about 30 minutes.

Once the Strela work was done, the two installed a ham radio antenna on the rear end of the Zvezda module, and Walz also tested a spacesuit glove sporting enhanced thermal installation.

With the station flying on the bitter cold dark side of Earth, Walz grabbed a metal handrail and held on for about 20 minutes. Both spacewalkers were shivering at the time and Walz reported that the enhanced glove was warmer than an older model.

"(There's) no discomfort," he said. "But the left one is a little colder than the right one."

The spacewalk was the first of two planned at the station this month.

Onufrienko and station flight engineer Daniel Bursch plan to install three more ham radio antennas on the Zvezda module during a Jan. 25 spacewalk.

Metal deflectors are to be set up near Zvezda steering thrusters during that outing to prevent toxic rocket exhaust from damaging the outer hull of the bus-sized crew compartment.

Contamination monitors will be installed in that same area, and the two spacewalkers will retrieve an external materials science experiment.

Launched Dec. 5 aboard shuttle Endeavour, Onufrienko and his crewmates are in the midst of a planned five-a-half-month aboard the international outpost. The trio remains scheduled to return to Earth in mid-May.