The US space shuttle Discovery, and its crew of seven astronauts -- including one Swede -- are preparing this weekend to launch on a mission to the International Space Station (ISS).
The shuttle is scheduled to take off Tuesday at 01:36 am (0536 GMT) from the Kennedy Space Center at Cape Canaveral, Florida.
The shuttle is to deliver equipment for a new bedroom, a treadmill, a freezer, food and other supplies. It will also be dropping off the newest member of the ISS team -- US astronaut Nicole Stott.
Stott will be taking over from engineer and fellow American Tim Kopra, who has been aboard the ISS since July and is returning to Earth with the Discovery.
On Friday, NASA weather forecasters said they were expecting a 70 percent chance of favorable launch conditions Tuesday -- the official countdown began Friday evening at 11:00 pm (0300GMT).
"Our systems are in good shape, the launch countdown preps are proceedings without much event and we have no new issues to report," said Test Director Steve Payne. "The flight crew, vehicle and the launch team are ready to go."
The only outstanding issue for the Discovery was a broken electricity switch aboard the shuttle, but NASA said it would be replaced over the weekend.
The Discovery crew, led by astronaut Rick Sturckow, arrived at the Kennedy Space Center from Houston on Wednesday evening.
They will be delivering 6.8 tonnes of cargo transported in a pressurized module called Leonardo that was built by the Italian space agency.
Two astronauts from the team are scheduled to conduct three spacewalks of six and a half hours each during the 13-day mission, which is the fourth of five planned for the shuttle this year. The last is scheduled for November.
One of the key goals of the space walks is the replacement of an old liquid ammonia tank, which will be substituted with a new 800 kilogram replacement brought from Earth aboard the Discovery. The substance is used as a coolant.
The astronauts will also be retrieving experiment equipment from the outside of the ISS and returning it to Earth for processing.
The Discovery team is delivering a freezer and a treadmill. The freezer will store samples of blood, urine and other materials that will eventually be taken back to Earth for study on the effects of zero-gravity.
The COLBERT treadmill, named after popular US comedy talkshow host Stephen Colbert, will be the second aboard the ISS. Exercise is key for astronauts spending long periods of time in space, where zero-gravity can result in muscle atrophy.
The mission will be the 128th for the space shuttle program, 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 2010.
The International Space Station is a project jointly run by 16 countries at a cost of 100 million dollars -- largely financed by the United States.
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