Mission specialists Lisa Nowak and Stephanie Wilson began their first full day inside the ISS by guiding the station's robotic arm to pull the Italian-made container from Discovery's payload and berth it to the ISS.

Discovery's seven astronauts docked to the orbiting outpost Thursday, two days after blasting off from Florida on just the second shuttle flight since the Columbia accident that killed seven astronauts in February 2003.

Nowak and Wilson attached the cylindrical-shaped Multi-Purpose Logistics Module, dubbed "Leonardo," to the ISS. The astronauts will transfer equipment and supplies to the ISS over the next few days.

In addition to food and clothes, the container holds a lab freezer to store scientific samples, a large incubator to study plant growth in space, and an oxygen generator system that will allow the ISS to accommodate six crew members.

The Discovery astronauts also brought two spacesuits for two spacewalks, with the first one scheduled on Saturday. NASA hopes to extend the mission by a day to conduct a third excursion.

One of Discovery's passengers, European Space Agency astronaut Thomas Reiter of Germany, will remain in the space station for a six-month mission after his colleagues leave in nine to 10 days.

Reiter's arrival brings the ISS back to a three-person crew for the first time since the Columbia tragedy.

NASA is in race against time because it wants to complete the ISS before the 25-year-old shuttle fleet is retired in 2010.

NASA chief Michael Griffin wants to conduct more than four flights a year by 2010 to complete the space station, making this Discovery mission critical since it will show whether the US space agency has made space flight safer since Columbia.

Another major accident would likely spell an immediate end to the shuttle fleet, which includes Endeavour, Atlantis and Discovery.

While the astronauts transferred cargo into the ISS, NASA reviewed hundreds of pictures of Discovery's heat shield to find any cracks that could threaten its return to Earth.

Before docking to the ISS, Discovery Commander Steven Lindsey steered the shuttle into a back flip about 180 meters (600 feet) below the space station to allow the ISS crew to take photos of the heat shield protecting the spacecraft's underbelly.

NASA said Thursday the vessel looked "clean" so far but that the shuttle crew will have to wait for the weekend to get the green light to return to Earth at the end of the mission.

"It is so clean. The vehicle is doing so well," mission management team chairman John Shannon told reporters Thursday at the Johnson Space Center in Houston, Texas.

NASA has said the astronauts could take refuge inside the ISS while waiting for a rescue mission if the shuttle suffered irreparable damage.

Columbia disintegrated during its return to Earth on February 1, 2003, after its heat shield was pierced on liftoff by debris from its external fuel tank.

NASA has since strived to reduce the amount and size of foam insulation that sheds from the tank during liftoff.

More modifications were made after foam shed from the tank during the first post-tragedy flight last July. The debris missed the Discovery shuttle at the time, but NASA grounded the fleet until now.

NASA officials have touted the tank's performance in the launch Tuesday after it shed small debris too late during ascension to be of any concern.

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