The U.S. space shuttle Discovery is to undock from the International Space Station Saturday after a week-and-a-half resupply and maintenance visit. The shuttle crew made a final inspection of the orbiter's exterior to look for damage that might interfere with a safe return to Earth next week.

Mission controllers have given Discovery permission to depart the space station.

On their last full day at the outpost, the shuttle crew used a crane to transfer the big Italian-built cargo carrier it brought to the station back into the shuttle. It was filled with completed science experiments and rubbish. It had carried up tons of new supplies and hardware for the station, more than any previous shuttle flight, and station flight director Rick LaBrode says the crew offloaded it faster than expected. They also performed spacewalks to repair critical station components.

"They did a great job. We worked them, we worked them. We got our money's worth out of them, that's for sure," he said.

One of the shuttle crew's last jobs Friday was to make a final damage inspection of Discovery's left wing, which was exposed to tiny space rocks called micrometeoroids. They used a camera at the end of a boom to scan the wing for possible cracks. Engineers on the ground will analyze the images before Monday's landing.

Deputy shuttle manager John Shannon says micrometeoroids can pose a significant threat to shuttles in orbit. "When we went through all of the risks to the shuttle, it was number two on the list. Historically we had not done much to mitigate that risk. It was just part of the space environment and you lived with it," he said.

But the U.S. space agency NASA is taking no chances in its effort to avoid another shuttle catastrophe like Columbia in 2003. Launch debris punctured a hole in its wing, leading to its disintegration upon re-entry into the atmosphere. If Discovery's wing is seriously damaged by space rocks, the crew can seek safe haven on the space station until another shuttle comes to rescue them.

Earlier in the mission, the astronauts scanned the rest of the orbiter for possible launch debris damage, but found none.

But mission controllers are monitoring another problem -- a leak of some substance from one of three units that supply power to hydraulic systems used during shuttle re-entry and landing. One possibility is a fuel leak. Mission officials say the leak is so slow that it poses no fire threat if it is fuel. If the leak rate increases, they will activate the power unit before re-entry to use up the fuel to avoid any possible trouble. They say two hydraulic power units are enough for a safe landing.