The Dragon, owned and operated by SpaceX, holds considerable science experiments for the space station as well as food and spare parts. Musk said six hours into the flight that all four sets of thrusters finally were working. The problem may have been caused by a stuck valve or a line blockage. An hour later, the Dragon was raised with the thrusters to a safe altitude. "Dragon back on track," he said in a tweet. It was the first serious trouble to strike a Dragon in orbit. None of the four previous unmanned flights had any thruster issues, Musk told reporters by phone from company headquarters in Hawthorne, Calif. It's supposed to spend more than three weeks there, in large part to accommodate science samples that will be on the return trip. SpaceX is in charge of the flight until it gets near the space station. Then NASA calls the shots. "If we can convince ourselves the data's good, I suspect we can find an opportunity on Sunday, but again, we have to go look at it," Suffredini said. The fresh apples aboard Dragon - straight from the family orchard of a SpaceX employee - will be applesauce or worse the longer the delay. There's other fresh fruit as well for the six station astronauts. "Yes, absolutely, it was a little frightening there," said Musk, whose fortune came from co-creating PayPay. He stressed that the company's Falcon 9 rocket performed "really perfectly" 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 rocket shut down too soon. SpaceX hopes the resupply venture will lead to transporting astronauts to the space station in the Dragon capsule in just a couple years. If thrusters stalled like this on a manned mission, Musk said, the outcome wouldn't necessarily be grim. The capsule is designed to return to Earth with just two good sets of thrusters and, in "a super worst case situation," conceivably just one although it would be "a bit of a wobbly trip." The space station was orbiting 250 miles above the Atlantic, just off the New England coast, when the Falcon soared. Astronauts will use a hefty robot arm to draw the Dragon in and dock it to the station. Also on board with the fruit: 640 seeds of a flowering weed used for research, mouse stems cells, protein crystals, astronaut meals and clothing, trash bags, air-purifying devices, computer parts and other gear. The goal is to have SpaceX, or Space Exploration Technologies Corp., and other private firms take over the job of ferrying astronauts to and from the space station. Russia does that now - for a steep price. Russia, Japan and Europe regularly make station deliveries as well. But only the Dragon is designed to bring back substantial amounts of research and used goods. The other supply ships burn up upon re-entry. The newest Dragon is scheduled to spend more than three weeks at the space station before being cut loose by the crew. Then the trouble struck, and the coverage ended. "It's looking like we're going to be back on track here," Musk later assured everyone. NASA: http://www.nasa.gov/mission_pages/station/structure/launch/index.html