Astronauts of the US space shuttle Discovery will venture again into outer space Saturday on a third and final spacewalk of their mission designed to help complete the International Space Station.
The walk, which will be conducted by mission specialists Danny Olivas and Christer Fuglesang, is scheduled to begin at 4:49 pm (2049 GMT), the National Aeronautics and Space Administration (NASA) announced.
After reviewing procedures, Olivas and Fuglesang are spending the night in the Quest airlock to prepare themselves for work in outer space.
On Friday, Fuglesang, of Sweden, and Olivas installed a liquid ammonia tank to keep the space station cool and completed several other tasks, including bolting portable foot restraints on the orbiter's truss.
The pair returned to the decompression chamber after six hours and 39 minutes in space, NASA said, after bolting the 1,760-pound (800-kilogram) tank into place and linking up electrical and fluid lines.
It was the second of three spacewalks for the space shuttle Discovery's mission at the ISS.
The veteran spacewalkers also moved a spent ammonia tank, which was removed Wednesday, into the shuttle's cargo bay to be taken back to Earth.
The ammonia helps move excess heat from inside the ISS to the radiators outside the station.
Earlier, a large piece of space debris drifted toward the ISS, but NASA said it would not affect the mission's spacewalks.
"We got sufficient data to tell us that the debris was no longer a threat to the space station," ISS Flight Director Heather Rarick told reporters during a post-spacewalk briefing.
She said the combined crew of 13 astronauts aboard the ISS and the shuttle were completing the transfer of supplies from Discovery to the orbiter.
The shuttle had brought 7.5 tons of supplies, including new station crew quarters, a freezer, two research racks and a treadmill named after popular US talkshow comedian Stephen Colbert, to the station.
The freezer will store samples of blood, urine and other materials that will eventually be brought back to Earth for study on the effects of zero-gravity.
Mission Control was keeping a close watch on the remains of the three-year-old Ariane 5, a European space rocket, that were moving in an oval-shaped orbit.
The piece, which is some 200 square feet (19 square meters) in size, was expected to pass almost two miles (three kilometers) from the outpost on Friday, NASA said.
Officials have developed a contingency plan to potentially "reboost" the station-shuttle complex if the space junk posed a threat.
The linked spacecraft are currently orbiting 220 miles (354 kilometers) above the Earth.
The duo also fetched US and European equipment from the orbiting station's Columbus laboratory that will be brought back to scientists on Earth.
Discovery's mission is the fourth of five planned for the shuttle program this year. The last is scheduled for November.
The shuttle will remain docked at the ISS for a total of nine days ending Tuesday and is due to return to Earth on September 10.
Once the mission is complete, just six more shuttle flights remain before NASA's three shuttles are retired in September 2010.
(c) 2009 AFP
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