Washington - The Discovery space shuttle closed its hatch with the International Space Station Tuesday and was poised to begin returning home. Discovery is due to undock from the space station at 1142 GMT Wednesday and undergo a safety inspection before heading back to Earth with a landing scheduled for Saturday at the Kennedy Space Centre in Florida.
Two astronauts from the Discovery space shuttle completed their mission's third and final spacewalk devoted to construction on the station Sunday.
Mike Fossum and Ron Garan spent six hours and 33 minutes on tasks including installing a new nitrogen tank on the station and carrying out further work to install a robot arm on the Japanese module Kibo.
They also reinstalled a fixed television camera on one of the station's trusses and took samples of dust from a solar panel joint so scientists could examine it.
Two earlier spacewalks during the 14-day Discovery mission were devoted to installing and preparing the Kibo laboratory on the station. About 100 scientific experiments are already planned for the 12-metre by 5-metre Kibo, including efforts to examine the effects of weightlessness and help develop allergy medications.
Kibo is to be completed in a third mission later this year.
