SpaceShipOne (search) is one flight away from clinching the Ansari X Prize (search), a $10 million award for the first privately developed manned rocket to reach space twice within 14 days.

SpaceShipOne was scheduled to be launched Monday in an attempt to reach an altitude of at least 328,000 feet, or just over 62 miles, for the second time since Sept. 29.

The choice of pilot for the flight remained a secret on the eve of launch, as it did last week.

That flight and a test flight into space on June 21 were flown by Michael Melvill, who has been awarded the nation's first commercial astronaut wings by the Federal Aviation Administration (search).

Melvill is one of four pilots who have undergone special training to fly SpaceShipOne. He had difficulty controlling the ship during the June flight but still reached 62 miles. Last week, he flew a perfect trajectory to an altitude of 337,600 feet, or nearly 64 miles, but the ship began rolling as it neared space.

After a safety analysis, SpaceShipOne designer Burt Rutan posted preliminary information about the rolls on his Web site this weekend to address what he called the "incorrect rumors" that have circulated.

The first roll occurred at a high speed, about Mach 2.7, but aerodynamic loads on the spacecraft were low and decreasing rapidly "so the ship never saw any significant structural stresses," he said.

The spacecraft rolled so often because the rolls started as it was nearing the edge of the atmosphere and Melvill could not dampen the motions with the aerodynamic controls, according to Rutan. Since aerodynamic controls don't work in space, SpaceShipOne is equipped with a reaction control system that uses jets of a compressed gas to control movements.

Melvill used the system to successfully stop the rolling before reaching the peak altitude, Rutan said.

"While we did not plan the rolls, we did get valuable engineering data on how well our RCS system works in space," he said.

The St. Louis-based Ansari X Prize was founded in 1996 to kickstart private-sector development of rocket ships.

Founder Peter Diamandis hoped the multimillion-dollar incentive would have the same effect on space travel as the Orteig Prize had on air travel. Charles Lindbergh claimed that $25,000 prize in 1927 after making his solo trans-Atlantic flight.

Major funding came from the Ansari family of Dallas. More than two dozen teams around the world are trying to win the X Prize, but only SpaceShipOne has reached space.

Funded by Microsoft co-founder Paul Allen, SpaceShipOne was developed in secret at Rutan's Mojave Airport-based Scaled Composites LLC until it was unveiled in April 2003. Allen has not said exactly how much he has put into the project, but has characterized it as more than $20 million.