Nasa tracks large debris close to ISS

       Nasa yesterday tracked a large piece of space debris set to pass close to the International Space Station (ISS) as astronauts prepared for the second of three spacewalks.
       Astronauts Danny Olivas and Christer Fuglesang planned to camp out in the Quest airlock in order to acclimatize their bodies for their outing in space more than 12 hours later.
       Mission Control was keeping a close watch on the remains of the three-yearold Ariane 5, a European space rocket,that was moving in an oval-shaped orbit.
       The piece, around 19sq m in size,was expected to pass almost 3km from the ISS today.
       Nasa Flight Director Office chief John McCullough said it did not appear that the ISS would have to move to avoid the space junk.
       A final decision was to be made during the last hour of yesterday's spacewalk,but Mission Control was developing a contingency plan to potentially "reboost"the station-shuttle complex that currently holds 13 astronauts. The linked spacecraft are currently orbiting 354km above the Earth.
       During their spacewalk, Mr Olivas and Sweden's Mr Fuglesang were to install a new liquid ammonia tank used to keep the ISS cool.
       On Wednesday, Mr Olivas and fellow astronaut Nicole Stott performed the first spacewalk of the space shuttle Discovery 's nine-day mission at the ISS,removing an old tank from the outpost's truss. The tank will return to Earth with Discovery .The duo also fetched US and European experiment 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 programme this year. The last is scheduled for November.
       The two crews continued unloading equipment from the Leonardo MultiPurpose Logistics Module, a huge pressurised chamber carrying 7.5 tonnes of supplies, including new station crew quarters, a freezer, two research racks and a treadmill named after popular US talkshow comedian Stephen Colbert.
       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.
       Discovery , which blasted off from Cape Canaveral, Florida, on Friday is due to return to Earth on Sept 10.
       The mission is the 128th for the space shuttle programme, and the 30th mission to the ISS.
       Once the Discovery mission is complete, just six more shuttle flights remain before Nasa's three shuttles are retired in September next year.