Washington  - The Endeavour mission's motto - "A Porch in Space" - sets the tone for the first spacewalk Saturday at 1558 GMT, when two astronauts start preparations to attach a four-ton outdoor shelf to Japan's Kibo laboratory module.

The six-and-a-half hour job is the first of five spacewalks that are among the most complex in the 11-year history of the International Space Station (ISS).

For one, at various times, all three of the available robotic arms will be put to use, sometimes all on the same day.

For another, Japanese flight controllers on the ground are to be involved for the first time operating their own mechanism, US space agency NASA said.

"Before, even when we had pieces of hardware that were built by someone else, we have, here in the US control centre, still maintained a lot of the technical leadership," said lead station flight director Holly Ridings in a NASA statement.

"In this case, (the Japanese) truly have technical leadership for some of the things that must work to make the mission a success. It's unique."

The porch, delivered to the station in Endeavour's cargo bay, will be used to expose scientific experiments to the extremities of space through X-ray cameras and studies of cosmic dust.

The shuttle Endeavour docked Friday at the space station, providing a record crowd of 13 astronauts - the largest ever in the space station history and yet another sign that the station is nearly completed.

The expanded team reflected the final build-out of ISS capacity in May, when it doubled to six astronauts. Endeavour is carrying seven astronauts, including the replacement for Japan's astronaut Koichi Wakata, US astronaut Timothy Kopra. Wakata will return to Earth with the shuttle crew.

It is also a banner mission because all five international partners - Russia, Canada, Japan, the European Space Agency and the United States - have astronauts at the station.

US astronauts Dave Wolf and Tim Kopra will carry out Saturday's jobs, removing insulation from the current Kibo module where the porch is to be attached, and, with the help of the robotic arm, transporting the porch from the Endeavour cargo bay for installation at the station.

During subsequent spacewalks slated for every other day in the 16- day mission, the X-ray cameras and other equipment will be secured on the exposed porch.

In addition, other maintenance work is slated for the station.

Endeavour suffered some damages during launch on Wednesday when insulation broke free from the external fuel tank and hit three heat- resistant tiles on the shuttle's underside.

But the damage was dismissed as superficial by the associate administrator for space operations, William H Gerstenmaier. As has become routine since the 2003 Columbia disaster, Endeavour pirouetted in a back flip before docking at the space station for a high- resolution image from station cameras of the tiles on its underbelly.

The space shuttles will be closed down next year, leaving only Russia's Soyuz as transport to the station.

NASA is building a new spacecraft Orion to return to the moon by 2015 and prepare launches into space from there to nearby planets like Mars. (dpa)