One of the most ambitious building projects ever undertaken will begin in the predawn darkness, when six astronauts and a large aluminum cylinder rocket into space aboard the shuttle Endeavour Dec. 3.
During the 13-day mission, the astronauts will mate the cylinder to a Russian "space tug" already in orbit. The 25,600 pound cylinder, known as Unity, will become the high-tech crossroads that will link future segments of the International Space Station (ISS).
When finished, the orbiting outpost will house a crew of seven astronauts, who will tend a broad range of scientific experiments, from human adaptation to weightlessness to X-ray astronomy. The process, involving 16 countries, is expected to open a new era of international cooperation in human spaceflight.
"This is going to be a significant step in human history," says Frank Culbertson, the space station's deputy program manager for operations.
The project is turning the Kennedy Space Center in Florida into the Home Depot of outer space. Randy Brinkley, the ISS program manager in Houston, says 400,000 pounds of flight hardware, some 80 percent of the US contribution, are undergoing various stages of testing and flight preparation in Florida.
Earlier this month, Boeing delivered the US laboratory module, which also will serve as the station's nerve center. Tomorrow, the head of Italy's space agency is scheduled to hand NASA the keys to Leonardo, a reusable module that fits in the shuttle's cargo bay and carries supplies to the station.
FROM the standpoint of station assembly, Endeavour's objectives are the simplest of any construction flight, says Bob Castle, the mission's lead flight director. In terms of maneuvering the shuttle, "it's as complex as any mission the shuttle has flown," he says.
Indeed, there's something for every orbital taste: a rendezvous, three six-hour space walks, and the first time that astronauts will have used the shuttle arm to manipulate a massive payload that is out of the operator's line of sight.
The mission is a "dream flight for a robotic-arm operator," says US Army Lt. Col. Nancy Currie, who will have that job on this flight. Using the shuttle's arm, she will have to gently coax the 12.5 ton Unity out of the payload bay with mere inches of clearance on either side.
Once the node is installed on the shuttle's docking system, it will block any view from the operator's window.
Once the shuttle is close enough to the Russian tug Zarya, Colonel Currie will have to rely on cameras in the cargo bay, and on the arm itself, to guide her as she grabs Zarya and positions it just above Unity. A nudge from shuttle thrusters will mate the two modules, which form an 85-foot-high stack.
"This is not so much crane operations as fine manipulations," Currie says.
Once the two units are joined, astronauts Jerry Ross and James Newman begin the first of three spacewalks, aimed at connecting communication and data cables that run on the outside of the modules, attaching communications antennas to the exteriors, and - if time permits - testing small rocket packs that will help astronauts return to the station if they lose hold during a spacewalk.
The crew, including Russian cosmonaut Sergi Krikalev, will be the first humans to set foot in the new station. They will install computer, guidance, and communications equipment.
While the crew is breaking in the new modules in orbit, controllers on the ground will be breaking in a new mission control center dedicated to station operations. Separate from the shuttle mission control, the new facility will be staffed 24 hours a day for the duration of the station's construction and operation.
As NASA moves from the shuttle to the space station era, "this is a significant change in the way we're doing business," Mr. Culbertson says.