Next at space station: Mission Most Complex

During the past several space-station construction missions, the phrase "most complex" has virtually become a cliché.

Yet, in the history of human spaceflight, no single building or patching job in space has ever been as complicated as the one confronting the crews of the shuttle Discovery and the International Space Station (ISS) during the next eight days. Nor are there likely to be any challengers over the shuttle program's remaining two years.

If all goes well, in a record five space-walks, the crews will have installed an Italian-built module on the station and rendered it fit for human occupancy. They will have used the shuttle's and station's robotic arms as an orbiting bucket brigade, gingerly passing an 18.5-ton set of solar panels from its current temporary location to a permanent spot at one end of the station's backbone, or truss. The distance covered: roughly half the length of a football field. And spacewalkers will have disconnected and reconnected various exterior power and cooling lines.

Once the tasks are finished – and the space-station crew conducts two additional spacewalks between now and December – the station will finally be fit to receive the first major laboratory built by the station's non-US partners: Europe's Columbus laboratory, slated for launch aboard Atlantis on Dec. 6.

The module being installed in the next week, dubbed Harmony by the United States and Esperia by the Italians, "is a gateway to the international partners' laboratories," says Derek Hassmann, NASA's lead flight director for the space station.

Little wonder, then, why the partners are eager to see it installed. "This is the start of a very exciting period for Europeans," notes Alan Thirkettle, space-station program manager for the European Space Agency (ESA). Yet he adds, "We can't get too excited. We're big enough and ugly enough to know we can be disappointed in this game. But we're getting there."

In the past, astronauts performed these tasks one at a time over several missions, observes William Gerstenmaier, NASA's associate administrator for space operations. "But we've never lumped them all together in one flight," he says.

The first of two main assembly tasks focuses on installing Harmony. The station crew will use the ISS's robotic arm to install the nearly 16-ton cylinder in a temporary location. Once the shuttle leaves, the ISS crew will take the docking adapter the shuttle uses, move it from its current spot at the end of the US Destiny lab, attach it to the outboard end of Harmony, and then return the whole assembly to the end of Destiny.

There, it will serve as a docking station for shuttles as well as Columbus's attach point. Eventually, the Japanese laboratory, scheduled for launch next year, will mate with Harmony as well.

The module, however, is more than a mere connecting point for hardware, notes Mr. Thirkettle. It also serves as the crossroads for cooling and power connections. And it eventually will have sleep stations for two more crew members.

For the Europeans, a successful installation means that they has gone a long way toward squaring accounts with NASA for launching and installing Columbus, according to Thirkettle. "There is no free ride," he notes. Harmony and one more interconnecting "node" represent payment-in-kind for adding Columbus to the station.

Moreover, early next year, the Europeans hope to launch the first of five disposable automated transfer vehicles to ferry freight and fuel to the station. After a six-month stay at the station and loaded with waste, they will leave to burn up on reentry.

The second major assembly task in the coming week aims to move an enormous solar array – panels retracted – from its current temporary location about halfway along the station's truss to one end. The entire operation occurs over three days to give spacewalking astronauts a breather between the various steps.

With such an ambitious schedule, crew preparation is vital. Crew members participating in spacewalks, for instance, have spent seven hours in the training tank for each hour they plan to spend outside the shuttle and station. "We have a tremendous series of challenges ahead of us," notes Mr. Gerstenmaier. "There's not a lot of flexibility" in the timeline "to shift things around."