SpaceX is making its second try this week to launch supplies to the International Space Station.
If the unmanned Falcon rocket blasts off before dawn Saturday, the California company led by billionaire Elon Musk will attempt to land the rocket at sea. No one has ever attempted to fly a booster rocket back to an ocean platform before. Musk says recovering and reusing rockets is essential for bringing down costs and speeding up operations.
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Excellent weather is forecast for the 4:47 a.m. liftoff.
The Dragon capsule atop the rocket holds more than 5,000 pounds of food, experiments and other cargo for NASA.
Tuesday's countdown was halted at the last minute by a faulty rocket-steering system. SpaceX replaced a suspect motor. The supply run originally was set for mid-December.