Scaled Composites' SpaceShipOne completed its first qualification flight to win the Ansari X Prize Sept. 29, reaching suborbital space despite an unexpected roll that caused pilot Mike Melvill to shut the vehicle's rocket engine off 11 seconds early.

SpaceShipOne and its White Knight carrier aircraft took off from the Civilian Aerospace Test Center at Mojave Airport at 7:12 a.m. Pacific time. After being carried to 47,000 feet, SpaceShipOne detached and fired its SpaceDev-built hybrid rocket engine.

During ascent, the spacecraft experienced an unexpected series of rolls. Although flight controllers recommended he shut the engine off earlier, Melvill chose to keep it engaged long enough to ensure that he reached the required X Prize altitude of 330,000 feet. After engine cutoff, Melvill used SpaceShipOne's reaction control systems to stop the roll. The spacecraft then glided safely to land back at Mojave at 8:33 a.m.

SpaceShipOne experienced a similar roll phenomenon during its previous space flight in June, although engineers thought they had since solved the problem, according to Kevin Mickey, vice president for program management at Scaled Composites. The roll is believed to be caused by wind shear.

The Mojave Aerospace Ventures LLC team, including Microsoft cofounder Paul Allen and Scaled Composites, will win the $10 million prize if it can conduct another flight with SpaceShipOne within two weeks. The second flight tentatively is scheduled for Oct. 4.

"We will be analyzing why we got the roll near the end," Scaled Composites founder and SpaceShipOne designer Burt Rutan said shortly after the flight. "Will it delay whether we fly on Monday or not? I don't know that. We have to look at the data, but if that doesn't delay us, the ship can easily be turned around for a Sunday or Monday flight."