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SpaceX called off the planned launch of a Falcon 9 rocket Saturday less than 15 seconds before liftoff to investigate the “slightly odd” behavior of the vehicle’s upper stage engine steering system, company chief Elon Musk said.

SpaceX scrubbed a Falcon 9 launch attempt Thursday, citing an issue associated with the planned recovery of the rocket’s first stage or payload fairing in the Atlantic Ocean. Officials later said the mission would be grounded to await improved weather in downrange recovery area in the Atlantic Ocean.

Stormy weather near NASA’s Kennedy Space Center kept SpaceX’s Falcon 9 rocket on the ground Thursday, delaying liftoff of a commercial supply ship with equipment and experiments for the International Space Station until Saturday.