NASA gave a final green light to continue the countdown to the launch of the shuttle Discovery Tuesday toward the International Space Station, carrying a crew of seven including a Swede.
Mission officials said at a press briefing Sunday they saw no likely technical hurdles to takeoff August 25 at 0136 am (0536 GMT) from Kennedy Space Center in Cape Canaveral, Florida.
The weather also was looking up with about 80 percent chance of launch-friendly meteorological conditions compared to the 70 percent favorable forecast on Friday, said meteorologist Kathy Winters.
Still there was still a risk of thunderstorms and lightning within an eight-kilometer (five-mile) range of the launchpad where the shuttle's external fuel tank is supposed to start being filled with nearly two million liters of liquid hydrogen and oxygen shortly after 2000 GMT Monday, she added.
"Obviously, the weather is going to be one of our challenges" for filling the fuel tank, said Mike Moses, director of the Mission Management Team.
If the fill-up were delayed more than three hours, the launch would be postponed Tuesday and delayed by 24 hours, he said.
But Kathy Winters noted that the storm possibilities looked to be their worst in the first hour of the scheduled tank filling.
Nonetheless, launch director Pete Nickolenko said there were four launch attempts available within five days from August 25-30, and that he was "96 percent certain" of being able to launch in that window.
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.
The Discovery crew, led by astronaut Rick Sturckow, 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 new 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 billion dollars -- largely financed by the United States.
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