CAPE CANAVERAL, Fla. » A commercial craft carrying a ton of supplies for the International Space Station ran into thruster trouble shortly after liftoff today. Flight controllers managed to gain control, but were forced to delay its arrival at the orbiting lab.

The earliest the Dragon capsule could show up is Sunday, a full day late, said top officials for NASA and the private company SpaceX.

"We’re definitely not going to rush it," said SpaceX’s billionaire founder Elon Musk. "We want to make sure first and foremost that things are safe before proceeding."

The Dragon, owned and operated by SpaceX, holds considerable science experiments for the International Space Station — including a hydroponic lab experiment from a team of eight Oahu Girl Scouts — as well as food and spare parts.

Musk said six hours into the flight that all four sets of thrusters finally were working properly. "All systems green," he reported via Twitter. The problem might have been caused by a stuck valve or line blockage. The thrusters are small rockets used for maneuvering the capsule.

It is the first serious trouble to strike a Dragon in orbit. None of the three previous flights had any signs of thruster issues, Musk told reporters by phone from company headquarters in Hawthorne, Calif.

He said it appeared to be a glitch versus a major concern.

NASA space station program manager Mike Suffredini said at least three groups of thrusters on the Dragon need to work before the capsule can come close to the complex. That’s a safety rule that will not be waived, Suffredini said.

Engineers for both SpaceX and NASA plan an exhaustive study before allowing the rendezvous to take place. The Dragon could hang around at least a month before linking up with the station, Musk said. It’s supposed to spend more than three weeks there.

A crucial maneuver needed to be made quickly, however, to raise the orbit and keep the capsule from plunging down through the atmosphere. Musk promised in a tweet that was forthcoming.

SpaceX has a $1.6 billion contract with NASA to make a dozen deliveries to restock the space station. This is the third trip by a Dragon capsule to the station; the first Dragon flight, in 2010, was a solo test.

Musk acknowledged it was scary for a while.

"Yes, absolutely, it was a little frightening there," he told reporters.

He stressed that the company’s Falcon 9 rocket performed "really well" and that the thruster problem was isolated to the Dragon.

On the previous flight in October, one of nine first-stage engines on the Falcon shut down too soon. A communication satellite hitching a ride was lost.

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