Shuttle mission STS-124

If NASA measured the importance of its shuttle missions by the size of the cargo they carried, then Discovery's trip to the International Space Station would have to be considered its biggest venture yet.

The shuttle, scheduled to lift off Saturday, May 31, at 5:02 p.m. ET, will be carrying the Japanese Pressurized Module (JPM), the tour-bus-sized main component of Japan's Kibo space laboratory.

The 11.2 metre-long module — with a launch weight of 14.8 tonnes — is the biggest piece yet to the orbiting jigsaw puzzle that is the space station. The module comes with its own robotic arm and is just one part of the even larger Kibo lab, which includes the JPM, a storage room delivered earlier in March and a third component expected to be delivered next year that will hold science experiments exposed to the space environment.

Kibo — which means "Hope" — along with the U.S. Destiny lab and the European Space Agency's recently installed Columbus lab, will help form the backbone of the space station's rapidly-expanding area for scientific experimentation.

Attaching the module will be the primary focus for the seven-person crew of the shuttle and the three-man crew on the space station during the shuttle's 14-day mission, leaving little time for other activities, although two astronauts are expected to perform some repair work during one of the mission's three spacewalks.

The shuttle crew's routine inspection of the spaceship for damage to its thermal tiles will occur near the end of the mission rather than before the shuttle docks because the laser-tipped pole used to inspect the ship was left at the station during the last mission to make room for the enormous JPM.

Japan hopes for big things from Kibo

The $1 billion Kibo lab, which Discovery shuttle commander Mark Kelly called in the week before the scheduled launch "the Lexus of the space station modules," is Japan's contribution to the space station.

It's a project that has been two decades in the making, and when complete it will be home to as many as 23 experiments focusing on space medicine, biology, Earth observations, material production, biotechnology and communications research.

On the fourth day of the mission, and the second day after the shuttle arrives at the station, the module will be unloaded from the shuttle's cargo bay using the station's Canadarm 2 and installed on the port side of the station's Harmony module, the short hallway at the front of the space station connecting Destiny, Columbus and Kibo. After two days of setting and activating the module, and installing its robotic arm, the Candarm 2 will again be put to work on the seventh day of the mission, moving Kibo's storage unit — the Japanese Logistics Module — to its permanent home on top of the JPM. The Japanese Logistics Module has been attached to its temporary home on Harmony since it was delivered in March.

The third and final piece of Kibo, the experimental logistics module — a kind of back porch to the main structure where experiments dependent on exposure to the outer space environment will be housed — will not be delivered until 2009.

Unlike the space station's Canadarm 2 and Dextre or the shuttle's Canadarm, Kibo's robotic arm was developed by the National Space Development Agency of Japan and not in conjunction with the Canadian Space Agency.

The 10-metre-long, six-joint arm robotic arm is a lightweight when compared with Canadarm 2, however, and won't be taking over any of the station robot's main duties. While Canadarm 2 can carry a maximum payload mass of 116,000 kilograms, the Japanese robot arm can lift only up to 7,000 kg, making it unsuited to heft anything other than experiments.

A second robot arm designed for smaller tasks will also be delivered next year aboard an unmanned Japanese-built cargo ship called the HTV (H-II Transfer Vehicle).

Arriving astronauts include former Montrealer

Discovery's seven-person crew comprises six Americans and one Japanese astronaut: commander Mark Kelly, pilot Ken Ham, mission specialists Ken Nyberg, Ron Garan, Mike Fossum and Greg Chamitoff from NASA and mission specialist Akihiko Hoshide from Japan's space agency, JAXA.

Nyberg will operate the station and shuttle's robotic arms, Hoshide will be responsible for Kibo-related operations and Garan and Fossum will handle all three of the mission's spacewalks.

The Montreal-born Chamitoff will replace American astronaut Garrett Reisman as a member of the space station's three-person crew.

Although no longer a Canadian citizen, Chamitoff, 45, grew up in Montreal before moving to California at age 10.

He would be the first Canadian-born astronaut to live aboard the space station for longer than a shuttle mission. But he likely won't be the last. Earlier this year, the Canadian Space Agency announced astronaut Robert Thirsk, of New Westminster, B.C., is scheduled to visit the station in May 2009 and stay on board for as long as six months.

Urgent repair added to schedule

While room aboard the space shuttle's cargo hold was limited, NASA was still able to make room in the final week before launch for one 16-kilogram spare part: a toilet pump.

The part was rushed in from Russia on Wednesday night after the toilet motor fan aboard the Russian section of the station stopped working, NASA said the week before launch. Since then, the liquid-waste-gathering part of the toilet has been working intermittently. The breakdown forced the three-person crew to periodically manually flush the urine side, a process that takes 10 minutes and two people.

"Insert that into your daily life and you can see it would be quite inconvenient," Kirk Shireman, NASA's deputy space station program manager, said at a news conference.