CAPE CANAVERAL, Florida - The space shuttle Endeavour's astronauts packed their gear and prepared to leave the International Space Station on Sunday, wrapping up a 12-day visit to complete the construction of the US side of the orbital outpost.

The crew cleaned up from their four spacewalks and reinstalled the station's upgraded air purification system, the last maintenance task on a long to-do list that included servicing the station's cooling and power systems and extending the reach of its robotic crane.

The shuttle's landing is scheduled for early Wednesday in Florida at the Kennedy Space Center.

The space shuttle Atlantis and a crew of four are scheduled to close out the 30-year-old shuttle program with a final cargo run to the station in July.

"We're really pleased to be able to help round out the program with the successful work that we've had up here," Endeavour's lead spacewalker Drew Feustel said during an in-flight interview.

"There's one more flight after us and they'll finish out the space shuttle program. We really believe that we're ending on a very strong and positive note and looking forward to future opportunities," he said.

The United States is retiring its three space shuttles due to high operating costs and to free up funds to develop new spaceships that can carry astronauts beyond the station's 342-kilometer-high orbit.

"Once the space shuttle retires, we're going to lose a lot of capability of moving large payloads out in space, but then that opens the doors for new things that are going to come across the horizon," said Endeavour's pilot, Greg Johnson.

The primary goal of Endeavour's flight, the 134th for NASA's space shuttle program, was to deliver and install the Alpha Magnetic Spectrometer particle detector, designed to study dark matter, antimatter and other high-energy phenomena that cannot be detected by telescopes.

That job was accomplished shortly after Endeavour's May 18 arrival at the $100 billion space station, a joint project between 16 nations that began in 1998.

In July, Atlantis will be delivering a year's worth of supplies to the station. After Atlantis' mission, NASA will be turning over US cargo runs to two companies, Space Exploration Technologies and Orbital Sciences Corp, and is hoping commercial flights will be available to ferry station crew members within four or five years.

Reuters

(China Daily 05/30/2011 page10)