HOUSTON - Space shuttle Discovery was prepared to pull away from the International Space Station on Saturday, marking the end of a nine-day visit that positioned NASA to resume assembly of the outpost as early as next month.

NASA's flight team, meanwhile, weighed options for handing a tiny fuel leak in one of the shuttle's power units that are needed for landing.

Piers Sellers (top, L) covers his head as his crewmates laugh after he was described as the spacewalker who lost the spatula during a crew news conference from aboard the International Space Station in this view from NASA TV July 14, 2006. The members of the crew are front row (L-R) Pilot Mark Kelly, ISS Commander Pavel Vinogradov, Jeff Williams, and back row, Sellers, Stephanie Wilson, Lisa Nowak and Mike Fossum. [Reuters]

"The mission has just gone outstanding," said flight director Rick LaBrode. "We're ready to proceed with assembly operations."

NASA's next shuttle mission is scheduled for launch around August 28.

The Discovery astronauts spent a long and somewhat frustrating final day at the space station on Friday, conducting a painstaking scan of one of their ship's wings to check for damage from micrometeoroids. NASA added the survey as part of the safety upgrades imposed after the Columbia disaster.

The shuttle now flies with a laser imager and digital cameras mounted on the end of a 50-foot (15-metre) extension to the shuttle robot arm. The sensors are used to check for damage to the shuttle's heat shield from launch debris, which is what doomed Columbia and its seven-member crew.

Discovery has been cleared for landing, but NASA decided to take advantage of the equipment to make a final survey of the heat shield to check for damage that could have occurred while the shuttle was in orbit.

The crew had problems with the robot arm and the scan was delayed. At one point, flight directors offered to let the crew skip part of the survey, but Discovery commander Steve Lindsey decided to trim the crew's sleep time instead.

The other wing and the shuttle's nosecap were scheduled to be surveyed on Saturday after the spacecraft undocks from the station, which is planned for 6:08 a.m. EDT (1008 GMT).

Landing at the Kennedy Space Center in Florida is set for 9:14 a.m. EDT (1314 GMT) on Monday.

Also on Friday, engineers prepared a revised landing plan in case the shuttle has to touch down with just two of its three power units operational. The devices are used to control the body flaps, rudder and speed brakes for landing. One unit has a tiny leak and may be shut down, though managers said there would be no additional risk to the shuttle or crew.