But stormy weather may force another delay.

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(Florida Today) SpaceX is counting down to a 3:25 p.m. liftoff today of an International Space Station resupply mission from Cape Canaveral Air Force Station.

But stormy weather may force another delay.

"The big question mark is the weather," said Mike Suffredini, NASA's ISS program manager, during a press conference this morning. "There's a pretty good chance we'll potentially find a hole in the weather and get off the pad."

Officially, there's a 40 percent chance of favorable weather for the instantaneous window at Launch Complex 40.

If there's no launch today, the next attempt would be at 3:02 p.m. Saturday, when the forecast improves to 60 percent "go."

Suffredini said SpaceX may also have launch opportunities next Tuesday and Friday. Previously NASA had said if there were no launch this week, the SpaceX mission would slip to June and Orbital Sciences would proceed with a cargo launch from Virginia in early May.

Fueling of SpaceX's 208-foot Falcon 9 rocket is scheduled to start about four hours before launch.

Atop the rocket is a Dragon capsule packed with nearly 5,000 pounds of food, supplies and science experiments.

This is the mission's second launch attempt, after a scrub Monday. SpaceX replaced a helium valve that was not maintaining proper pressure in the rocket's pneumatic stage separation system.

"That's all been repaired," said Suffredini. "We put fresh science on board (the Dragon), buttoned it up and rolled out last night. The veicle is currently at the pad, and we're counting down to the launch at 3:25 this afternoon."

Launch attempt today

» Rocket: SpaceX Falcon 9

» Mission: SpaceX Dragon flying cargo to ISS (third Commercial Resupply Services mission)

» Launch time: 3:25 p.m.

» Launch window: Instantaneous

» Launch complex: 40 at Cape Canaveral Air Force Station

» Weather: 40 percent "go"

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