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So when will it fly?

Chip East / Reuters

 SpaceShipTwo designer Burt Rutan meets the press.

One big question was left hanging over today's fresh revelations about Virgin Galactic's SpaceShipTwo design: Exactly when will the company begin commercial passenger service?

The answer seems hazier today than it was a year ago - primarily because of last July's fatal accident during early tests of the SpaceShipTwo rocket plane's propulsion system.

"We don't know yet exactly what caused it," the craft's designer, Burt Rutan, told me.

Yes, California safety officials issued their citations - and levied more than $25,000 in fines - just a few days ago. But those citations had to do more with what the officials saw as inadequate training for handling nitrous oxide at Scaled Composites, the company behind SpaceShipTwo as well as its predecessor, SpaceShipOne.

Scaled's executive vice president, Doug Shane, said last week that the company was cooperating with state officials to resolve the workplace issues. Today, Rutan emphasized that last July's accident did not involve an engine firing - but a "cold flow" test that had repeatedly been done before without incident.

"We were doing something that we thought was extremely safe," said Rutan, Scaled's founder and chief executive officer.

During SpaceShipOne's successful run for the $10 million Ansari X Prize, Rutan had praised the craft's hybrid rocket system - which used solid rubber-based fuel and pressurized nitrous oxide - as the safest alternative. Last year's accident threw that into question, and sparked rumblings that the propulsion system's design might have to be reviewed.

Today, Rutan said the design of SpaceShipTwo's rocket engine was still up in the air.

"We are having delays in development of the rocket engine," he acknowledged. "We just don't know how long those delays will be yet."

He was confident, however, that any problems will be worked out - in consultation not only with the state but also with experts from elsewhere in the rocket industry.

Rutan has always been reluctant to talk about his future development schedule, to avoid tipping off competitors as well as to head off questions about development delays. But he's not reluctant to declare that air-launch systems like WhiteKnightTwo and SpaceShipTwo are the wave of the future.

Rutan said his agreement with Virgin Galactic calls for building five SpaceShipTwo planes, with an option for seven more. Over the first 12 years or so, Rutan said he envisions building 40 to 45 SpaceShipTwos, and 15 WhiteKnightTwo motherships. That could bring 100,000 passengers to the edge of space, adding new volumes to the current list of less than 200 astronauts.

Of course, Virgin Galactic would love to see the service start sooner rather than later - either in Mojave, Calif., where Rutan's team is currently working, or at the yet-to-be-built Spaceport America in New Mexico. But Virgin Galactic officials say it will be Rutan rather than Richard Branson, the company's billionaire founder, who will set the development schedule. That means an end, at least for the time being, to the predictions about 2009, 2010 or 2011.

"We're not in a race with anyone," Virgin Galactic's president, Will Whitehorn, said this afternoon. "We're in a race for safety, for our own sake and the sake of our customers."

Check out our slide show about SpaceShipTwo and WhiteKnightTwo, and get the full background from our special report on commercial spaceflight, titled "The New Space Race."