Astronauts complete ISS assembly

Mike Fincke and Greg Chamitoff doubled the reach of the USD100 billion station's robotic crane by transferring shuttle Endeavour's 15-meter inspection boom to the station during their fourth and final spacewalk on Friday.

"Space station assembly is complete," shuttle commander Mark Kelly told Mission Control in Houston after the final spacewalk.

"We're floating here on the shoulders of giants," said Chamitoff. "This space station is the pinnacle of human achievement and international cooperation."

The spacewalk was the 159th and the last which astronauts undertook before turning over Endeavour and sister ships Discovery and Atlantis to museums.

The ISS crew will continue maintenance spacewalks which began with the robotic attachment of the US Unity node with the Russian Zarya base block in 1998.

The 16-nation station has now turned into a more than 455,000 kilograms of hardware orbiting 220 miles above Earth.

The interior of the station has grown to the size of a Boeing 747 jet and the wingspan of its power-generating solar wings would nearly cover the surface of a US football field, Reuters reported.

"I am sad to see the three space shuttles be rolled into a museum here shortly," Kelly said. "I think it's a necessary step so we can go on and do some more exciting things."

Russia is soon expected to be the only country to conduct missions for the International Space Station as the US is planning to retire its reusable space shuttles.

NASA is also investing in commercial companies looking forward to private industry providing launch services for astronauts by about 2015.

The six-man Endeavour delivered the station's USD 2 billion Alpha Magnetic Spectrometer particle detector and spare parts. The shuttle will leave the station late on Sunday and is expected to land at the Kennedy Space Center on June 1, 2011.

Shuttle Atlantis is set to launch on July 8 as NASA's 135th and final flight.