SpaceX launch set for Friday, weather permitting

SpaceX is shooting for another launch attempt Friday to deliver supplies to the International Space Station.

NASA confirmed the launch date Wednesday, two days after a last-minute rocket leak delayed the mission. Stormy weather, however, is forecast for Friday. Saturday is the backup launch date.

Mission Control has rescheduled urgent spacewalking repairs because of the new launch time. Two U.S. astronauts, Rick Mastracchio and Steven Swanson, had been aiming for a Tuesday spacewalk to replace a backup computer that failed late last week.

The prime computer has been working fine, but NASA wants to get a new backup installed outside the station as soon as possible. These computers control the pointing of the radiators and solar wings, among other things.

The spacewalk will be either Easter Sunday or next Wednesday, depending on when — or if — the cargo ship flies.

The Dragon contains more than 2 tons of supplies, including material that would prove useful for the repair, but is not essential.

Former space station astronaut Christopher Cassidy, who's helping from Houston, said the spacewalk job should be "pretty straightforward" and involve the manual turning of just three bolts on the computer box.

"We anticipate it to go quickly, but as with anything in space ... you never know what's going to be thrown at you," said Cassidy, who served on the space station last year.

A bad valve resulted in Monday's helium leak in the unmanned Falcon rocket,SpaceX reported Wednesday. The valve is in the system used to separate the rocket's first stage.

Although a backup valve was working properly and could have supported the flight, SpaceX followed its own policy of canceling a launch in the event of equipment problems such as this.

The faulty valve is being replaced, the private company said in a statement, and inspections are underway to see if anything else might be wrong.

NASA is eager to get these supplies to the orbiting lab as soon as possible. The flight has been on hold since mid-March for various reasons. Much of the cargo is considered critical, including food, a new spacesuit and replacement parts for existing spacesuits.

The SpaceX Dragon and Orbital Sciences Corp.'s Cygnus cargo ship, which launches from Virginia, are NASA's prime means of shipment. Russia, Japan and Europe also make periodic deliveries.

NASA's space shuttles carried most of the resupply load until their retirement in 2011; that's when the space agency turned to private industry to fill the gap. NASA is hoping private companies will do the same for launching astronauts in another few years. SpaceX is among the U.S. companies vying for that job. Until then, Americans will be forced to continue riding Russian rockets to and from the space station at steep cost.

If SpaceX isn't flying by Saturday, then Orbital Sciences will move to the front of the launch line, with a shipment in early May, officials said. That would pushSpaceX into June.

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