The preliminary findings of the National Transportation Safety Board were disclosed by its acting chairman, Christopher Hart, but he said it was too soon to know whether the untimely unlocking of the tail mechanism caused Friday's (local time) accident.
The suborbital rocket plane dubbed SpaceShipTwo was undergoing its first powered test flight since January over California's Mojave Desert when it crashed shortly after the craft separated from the special jet aircraft that had carried it aloft for its high-altitude launch.
One pilot was killed, and the other survived with serious injuries after ejecting from the spacecraft and parachuting to the ground.
SpaceShipTwo, developed by the fledgling space tourism company of billionaire entrepreneur Richard Branson, was designed to carry wealthy passengers on short rides into space, with Virgin Galactic planning to begin offering its first flights to paying customers next spring.
The crash came three days after the unmanned rocket of another private space company, Orbital Sciences Corp, exploded during liftoff from a commercial launch pad in Virginia on a mission to deliver cargo to the International Space Station under contract with NASA.
On Monday, Branson vowed to determine the cause of Friday's crash and correct the problem. "We need to know exactly what happened to make absolutely certain it will never happen again," he told CBS's "This Morning" program.
NTSB's Hart told a news conference on Sunday investigators had determined that the spacecraft's 'feathering' tail system, designed to help slow its descent into the atmosphere from space, was supposed to have been released for deployment as the craft was traveling about 1.4 times the speed of sound.
Instead, the feather began rotating when the rocket-powered vehicle was traveling at Mach 1, the speed of sound.
Hart said the feathering tail system, which folds the vehicle in half aerodynamically to create more atmospheric drag, appeared from video footage to have been unlocked early by the co-pilot. About two seconds later, the space plane's tail section began to rotate.
"I'm not stating that this is the cause of the mishap. We have months and months of investigation to determine what the cause was," Hart said.
Asked if pilot error was a possible factor, Hart said: "We are looking at all of these issues to determine what was the root cause of this mishap ... We are looking at a number of possibilities, including that possibility."
Branson early NTSB findings indicated to him that premature tail deployment could be a possibility.
"They're indicating that that may well be the cause, but we need them to examine it further and let us know," he told NBC's "Today" show.
NO EXPLOSION
SpaceShipTwo was released normally from the carrier jet WhiteKnightTwo at an altitude of about 45,000 feet. The rocket motor, fueled for the first time in flight with a new plastic-based propellant formula, then ignited as planned, Hart said.
SpaceShipTwo's propellant tanks and engine were recovered intact, indicating there was no explosion. "The engine burn was normal up until the extension of the feathers," Hart told reporters.
About 800 people have paid or put down deposits for a ride into space at $250,000 a seat and Branson plans to be on the first commercial flight with his son.
Branson said Monday his company's venture is "absolutely" worth the risks.
"It's a grand program, which has had a horrible setback, but I don't think anybody .... would want us to abandon it at this stage," he told NBC.
Virgin Galactic is a U.S. offshoot of the London-based Virgin Group founded by Branson, whose empire ranges from airlines to music stores and mobile phones.
