The International Space Station is in full view over the Earth's rim after undocking from the Space Shuttle Discovery in this image from NASA TV June 11, 2008.

WASHINGTON, June 11 (Xinhua) -- The U.S. space shuttle Discovery undocked from the International Space Station at 7:42 a.m. EDT (1142 GMT) on Wednesday, beginning its trip back to Earth, NASA TV announced.

The two spacecraft were flying about 340 kilometers above the South Pacific, east of Australia, when they separated.

"Physical separation confirmed ... Everything is OK," NASA TV commentator announced.

Shuttle pilot Kenneth Ham is now flying Discovery around the station before beginning the final separation from the outpost at about 9:25 a.m. (1325 GMT). Astronauts traditionally take this opportunity to capture pictures and inspect the station.

About an hour before the undocking, Discovery commander Mark Kelly said his goodbyes to the three-member crew of the station.

"We wish them the best with their expedition and we hope we left them a better, more capable space station than when we arrived," Kelly said, offering a Japanese goodbye in honor of delivering Japan's Kibo lab, "Sayonara."

Discovery, launched on May 31, arrived at the orbital outpost on June 2. It delivered Kibo's main part -- the 1-billion-U.S. dollar pressurized module, and a new toilet pump for the balky toilet on the station. The astronauts replaced the pump in the toilet system which began working properly again after a testing process.

Two astronauts of the Discovery crew carried out three space walks. They successfully installed the new module, which is a massive orbital room the size of a tour bus and now the biggest of the nine rooms on the station.

The astronauts relocated Kibo's attic-like storage module, which was delivered in March by the space shuttle Endeavour, from a temporary place to the permanent location on the top of the new module.

Spacewalkers also did some maintenance work for the station. They replaced a nitrogen tank, repaired the power supply for one television camera, and inspected the Solar Alpha Rotary Joint on both sides of the station.

In addition, Discovery delivered Expedition 17 flight engineer Gregory Chamitoff, who replaced astronaut Garrett Reisman on the station. Reisman is returning to Earth aboard Discovery.

"Overall, the mission's been a great success," Discovery Commander Mark Kelly told reporters from space on Monday. "I certainly have a great crew and they're well trained, but there's also a little luck involved."

If all goes well, Discovery, with seven astronauts aboard, is scheduled to land at Kennedy Space Center in Florida on Saturday.

This is the second of three shuttle flights to launch components to complete Kibo. In the third flight planned for March2009, Japan will launch Kibo's porch-like external platform for exterior experiments.