HOUSTON (Reuters) - The U.S. space shuttle Discovery backed away from the International Space Station on Wednesday, leaving behind a Japanese research laboratory, a new crewmember and high hopes for the outpost’s completion by 2010.

Pilot Ken Ham pulsed Discovery’s steering jets to slip away from the station’s Harmony docking port at 7:42 a.m. EDT(1142 GMT) as the two space ships sailed 210 miles above the south Pacific Ocean east of Australia.

The shuttle arrived at the station on June 2 to deliver Japan’s primary contribution to the $100 billion complex, the 37-foot-long (11-metre-long) Kibo laboratory.

"We hope we left them a better, more capable station than when we arrived," Discovery commander Mark Kelly radioed to flight controllers as the shuttle prepared for undocking.

From aboard the station, Greg Chamitoff, who replaced returning flight engineer Garrett Reisman, replied, "It was amazing how much got done here. We wish you guys a terrific flight back and awesome landing."

Discovery is due to land at the Kennedy Space Center in Florida on Saturday after completing the third of five shuttle missions NASA has planned for this year.

NASA’s next flight is scheduled for October when shuttle Atlantis lifts off for a final servicing call to the Hubble Space Telescope.

NASA has 10 missions remaining before the shuttle fleet is retired in 2010 and work begins on a new ship that can travel to the moon as well as the space station.

FIXING THE STATION

In addition to delivering Kibo, the Discovery crew brought parts to fix the station’s sole toilet, the first bagels in space and supplies for station commander Sergei Volkov, flight engineer Oleg Kononenko and Chamitoff.

Chamitoff’s family owns a bagel shop in Montreal and he brought the bagels as a treat for his crewmates.

During a final round of interviews on Tuesday before taking fellow Jew Reisman’s place on the space station, Chamitoff said, "This is a handover between one Jewish astronaut and another so we’re pretty excited about that."

Shuttle astronauts Michael Fossum and Ronald Garan conducted three spacewalks during the mission to install and outfit Kibo, inspect joints that rotate the station’s solar power wings and recharge its cooling system.

One of the solar wing joints has been contaminated with metal shavings and will need to be cleaned up before it will be used full time to track the sun for power.

Fossum found a thin coat of debris on the other joint and collected samples for engineers to analyze back on Earth.

NASA wants to get the station in tip-top shape before the shuttle program comes to an end. Russian Soyuz capsules will be used to ferry crewmembers to and from the outpost and a variety of vehicles from Russia, Europe and eventually Japan will haul cargo.

No other ships besides the shuttle, however, can return equipment and heavy payloads to Earth.

The Discovery crew has one main job left before it is cleared for landing — an inspection of the ship’s wings and nose cap to make sure there was no damage from debris impacts during its May 31 launch.

Typically the inspection, which has become a routine part of all flights since the shuttle Columbia disintegrated during re-entry into the atmosphere in 2003, is conducted the day after liftoff.

But the Kibo lab was too large for Discovery to also carry in its payload bay the 50-foot-long (15-metre-long) sensor-laden boom used for the inspection. During the first spacewalk, the astronauts retrieved a boom left behind for Discovery by the crew of the last shuttle mission.