SpaceShipTwo's descent device deployed prematurely

MOJAVE, Calif. -- Investigators say Virgin Galactic's experimental spaceship broke apart in flight over the Mojave Desert after a device to slow the craft's descent prematurely deployed.

National Transportation Safety Board acting chairman Christophe Hart said Sunday that while no cause for Friday's crash has been determined, investigators found the "feathering" system was activated before the craft reached the appropriate speed.

The system requires a two-step process to deploy. The co-pilot unlocked the system but Hart said the second step occurred "without being commanded."

PHOTOS: Virgin Galactic SpaceShipTwo accident

There was early speculation that an explosion had occurred, but Hart said the SpaceShipTwo's fuel tanks and engines showed no signs of being compromised.

Co-pilot Michael Tyner Alsbury, 39, of Tehachapi was killed. Peter Siebold, 43, sustained moderate to minor injuries after parachuting to safety. He was airlifted to Antelope Valley Hospital where he remains hospitalized.

VIDEO: Crash site of Virgin Galactic's SpaceShipTwo

Both men worked for Scaled Composites, the company developing the spaceship for Virgin Galactic.

"The Scaled Composites family lost a respected and devoted colleague yesterday, Michael Alsbury, who was the co-pilot for the test flight of SpaceShipTwo," the company said in a statement Saturday. "Peter Siebold, the Director of Flight Operations at Scaled Composites, was piloting SpaceShipTwo. He is alert and talking with his family and doctors. We remain focused on supporting the families of the two pilots and all of our employees, as well as the agencies investigating the accident. We ask at this time that everyone please respect the privacy of the families."

The owner of Virgin Galactic, Richard Branson, had hoped to begin flights next year, but he said over the weekend that the project will not resume until the cause of the crash is determined, and the problem is fixed.

According to the NTSB, it could take 12 months before the final report is released.

Virgin Galactic had already sold some 700 tickets for the future flights for $250,000 a ticket, but according to the company, those tickets can now be refunded.