The Falcon 9 SpaceX rocket lifts off from launch complex 40 at the Cape Canaveral Air Force Station in Cape Canaveral, Fla., Friday, March 1, 2013. The rocket is transporting the Dragon capsule to the International Space Station containing more than a ton of food, tools, computer hardware and science experiments. (AP Photo/John Raoux)

A commercial vessel carrying a ton of supplies for the International Space Station ran into thruster trouble shortly after liftoff Friday, and flight controllers scrambled to fix the problem.

SpaceX founder Elon Musk said three of the four sets of thrusters on the company's unmanned Dragon capsule did not immediately kick in, delaying the release of the solar panels.

Dragon's twin solar wings swung open two hours later than planned as SpaceX worked to bring up the idled thrusters and keep the capsule on track for a planned Saturday arrival at the space station. The company said in a statement that a fuel valve was at fault, and that two sets of thrusters were needed before the Dragon could begin the series of maneuvers needed to get to the space station.

The Dragon is equipped with 18 thrusters, divided into four sets, and can maneuver adequately even with some unavailable.

The problem cropped up following Dragon's separation from the rocket upper stage, nine minutes into the flight. The liftoff was right on time and appeared to go flawlessly; the previous Falcon launch in October suffered a single engine failure that resulted in the loss of a communications satellite that was hitching a ride on the rocket.

This is the first major trouble to strike a Dragon in orbit. Two similar capsules, launched last year, had no problem getting to the orbiting lab.

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