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Jae C. Hong, File, Associated Press
FILE - In this May 29, 2014 file photo, Elon Musk, CEO and CTO of SpaceX, introduces the SpaceX Dragon V2 spaceship at the SpaceX headquarters in Hawthorne, Calif. Minutes after a planned launch from Cape Canaveral on Tuesday morning, Jan. 6, 2014, the first stage of the unmanned Falcon rocket will aim for a vertical test landing on a barge in the Atlantic. The California company has attempted such landings on the open sea, but never on a platform like this.

CAPE CANAVERAL, Fla. — A SpaceX rocket stands poised at Cape Canaveral, Florida, for a pre-dawn flight to the International Space Station.

The unmanned Dragon capsule contains more than 5,000 pounds of supplies and experiments ordered up by NASA. That's the primary objective for SpaceX. But the California-based company will attempt an even more extraordinary feat once the Dragon is on its way: flying the booster rocket to a platform in the Atlantic. No one has ever pulled off such a touchdown.

SpaceX's billionaire founder Elon Musk figures there's a 50-50 chance, at best, that the first-stage booster will land on the platform that's stationed a couple hundred miles off the northeastern Florida coast. He says recovering and reusing rockets could speed up launches and drive down costs.

Launch is set for 6:20 a.m.