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Space shuttle Discovery is preparing to launch on a mission to deliver new supplies and science equipment to the International Space Station.

The Discovery crew is set to launch early Tuesday to deliver nearly 8,000 kilograms of equipment to the International Space Station. NASA engineers cleared the shuttle to fly on Sunday, after deciding there were no technical concerns to delay launch from Kennedy Space Center in Florida.

Shuttle weather officer Kathy Winters said the skies should be clear for the evening launch, but storms could delay the delicate process of filling the shuttle's external fuel tanks.

"Overall the weather is looking good for launch, we just gonna get there. So the tanking weather is what we have been watching very closely. By the time we get to launch there is just a 20 percent chance of KSC [Kennedy Space Center] weather prohibiting launch," she said.

Storms and lighting pose a threat to the shuttle while it is on the launch pad, especially during the rainy summer months. The concerns are greater when loading fuel, because engineers are pumping volatile liquid hydrogen into the shuttle's tanks.

Mission management chair Mike Moses said the launch area at Kennedy space center took a direct lightning strike last Saturday.

"We did affect some of the camera systems, the ground servicing equipment, and some leak detectors. So we definitely did damage from that lightning event. Those systems have all been replaced and everything is fine. But that shows that lightning is a very serious thing," he said.

Moses added that one problem that engineers continue to watch is foam insulation falling off the shuttle's external fuel tanks during launch. The issue of falling foam has plagued several recent shuttle flights, and is blamed for causing damage that led to the break-up of shuttle Columbia in 2003.

Moses said the foam loss does pose a small risk of damaging shuttle Discovery when it takes off early Tuesday.

Shuttle Discovery set to launch Tuesday

"But we felt that risk was acceptable enough and the processes to control that risk are robust enough that we are ok to fly. We need to keep improving that tank so it doesn't happen again," he added.

The Discovery crew is expected to spend 13 days in orbit, and astronauts will conduct three space walks after the orbiter's rendezvous with the space station. The team will deliver a new freezer and other equipment for future experiments in space, as well as a new treadmill named after U.S. comedian Stephen Colbert.

tank: to place, store, or process in a tank 把……貯放在箱（或罐等容器）內

launch pad: the base or platform from which a rocket or space vehicle is launched 發射臺

foam insulation: foam used in insulating 泡沫絕緣材料

orbiter: man-made equipment that orbits around the earth or the moon 人造衛星

rendezvous: a meeting at a prearranged time and place 約會

treadmill: an exercise device consisting of a continuous moving belt on which a person can walk or jog while remaining in one place 跑步機