Washington - Two astronauts from the Discovery space shuttle on Sunday completed their mission's third and final spacewalk devoted to construction on the International Space Station.

Astronauts Mike Fossum and Ron Garan spent six hours and 33 minutes on tasks including installing a new nitrogen tank on the ISS 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 that scientists could examine it on Earth.

Two earlier spacewalks during the 14-day Discovery mission were devoted to installing and preparing the Kibo laboratory on the ISS. 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.

Sunday's spacewalk was the 112th spacewalk devoted to station assembly and maintenance on the ISS since construction began in 1998.

Discovery is scheduled to land Saturday at the Kennedy Space Centre in Florida. (dpa)