"Go out there and finish up the job, and have a good time," Voss told Richards and Thomas before the two exited the shuttle's airlock.

"OK, Jim. Thanks. We copied all that, and they are ready to go," replied Helms, who was directing the spacewalk from Discovery's flight deck.

Added Voss: "We are watching, and looking at you guys. Take a look at us through the window when you come by."

Working inside the station's $1.4 billion U.S. Destiny laboratory, which sports an Earth-facing window on the world, Voss was busy unpacking an Italian-built moving van that was mounted to the station early Monday.

The Leonardo cargo carrier was hauled to the complex with five tons of supplies and equipment that Voss, Helms and incoming Russian outpost commander Yuri Usachev will need during a four-month tour of duty at the station.

Important electrical power converters and space-to-ground communications gear were off-loaded from the cylindrical module Monday, giving the 10 astronauts and cosmonauts at the shuttle-station complex a leg up on five days of transfer operations.

Richards and Thomas, meanwhile, faced a full day of spacewalking work, the most important of which is to take place on the underside of the bus-sized Destiny lab.

Voss and Helms mounted a metal tray laced with electrical wiring harnesses there during Sunday's 8-hour, 56-minute sortie, but the two didn't have time to connect the cables to the lab.

The deferred work is considered critical to operating the station's 57-foot (17-meter) robot arm, which is to be launched to the outpost aboard shuttle Endeavour in mid-April.

"Until you mate those connections, you have no power or command and control of the arm," NASA space station lead flight director Rick LaBrode told SPACE.com during a news conference early Monday.

Further station construction work cannot be done until the Canadian crane is set up by spacewalking astronauts and then activated by Usachev and his so-called Expedition Two crewmates.

Inch-worming from work site to work site outside the growing outpost, the sophisticated station crane will be able to crawl to places the shuttle's fixed robot arm cannot reach.

That capability will be vital as NASA and its 15 international partners add new labs, solar power wings and support trusses to the outpost, which eventually will span an area nearly as large as two football fields.

During the planned 6.5-hour spacewalk, Richards and Thomas also aim to place an external stowage platform and spare cooling system equipment outside the newly arrived Destiny lab, which was delivered to the outpost last month.

The spacewalkers also intend to scale the 17-story station in a bid to fix a metal latching bar that failed to snap firmly into place when a U.S. electric power tower was erected at the station last December.

The $600 million tower serves as the base for the station's massive U.S. solar wings, which stretch to 240 feet (73 meters) from tip to tip, generating enough electricity to run 15 average American homes with air conditioning.

The high-voltage arrays are so powerful that under certain circumstances, they can create an electric arc that would shoot out from the station's metal structure into the surrounding environment, potentially creating a shock hazard for spacewalking construction workers.

Ground controllers routinely shunt the arrays prior to any spacewalk to negate a dangerous situation.

A device meant to measure electrical potential outside the station, however, has been operating intermittently for the past several weeks, so Richards and Thomas also plan to check it out while they're working atop the power tower.

NASA's 102nd spacewalk will set the stage for the delivery late Tuesday of the station's first science research package: A refrigerator-sized rack of biomedical experiment apparatus.

The so-called Human Research Facility is to be unloaded from the Leonardo moving van about 9:42 p.m. EST Tuesday (02:42 GMT Wednesday) and then set up inside the Destiny lab.

The final part of a highly choreographed crew "handover" at the station also is on tap.

Current station skipper Bill Shepherd will be moving over to shuttle Discovery about 10 p.m. EST Tuesday (03:00 GMT Wednesday) while Helms takes up residence aboard the station.

The changing of the guard began last Saturday as Usachev and Expedition One crewmember Yuri Gidzenko traded places aboard the shuttle-station complex. Voss replaced Russian cosmonaut Sergei Krikalev aboard the outpost early Monday.

The Expedition Two crew, however, will not take official command of the outpost until hatches between the shuttle and the station swing shut a few hours before Discovery's scheduled departure on Saturday.

The hatch closure will mark the end of a 4.5-month station "shakedown cruise" for Shepherd, Gidzenko and Krikalev. The trio will taxi back to Earth aboard Discovery on March 20, capping a 140-day stay in space.