LOS ANGELES – Federal investigators say they have determined that a space tourism rocket broke apart in flight over California’s Mojave Desert after a device to slow the experimental spaceship’s descent deployed too soon.

National Transportation Safety Board Acting Chairman Christopher Hart said that while no cause for Friday’s crash of Virgin Galactic’s SpaceShipTwo has been determined, investigators found the “feathering” system – which rotates the tail to create drag – 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.”

“What we know is that after it was unlocked, the feathers moved into the deploy position and two seconds later we saw disintegration,” Hart said.

The finding moves away from initial speculation that an explosion brought down the craft, but still doesn’t fully explain why the disaster occurred.

The investigation is months from being completed and pilot error, mechanical failure, the design and whether there was pressure to continue testing are among many things being looked at, Hart said.

“We are not edging toward anything, we’re not ruling anything out,” Hart said. “We are looking at all these issues to determine the root cause of this accident.”

The co-pilot Michael Alsbury, 39, was killed. Peter Siebold, 43, who piloted the mission, parachuted to the ground and is receiving treatments at a hospital for serious injuries.

Hart said investigators have not interviewed the pilot because of his medical condition.

Virgin Galactic – owned by billionaire Richard Branson’s Virgin Group and Aabar Investments PJS of Abu Dhabi – plans to fly passengers to altitudes more than 62 miles above Earth. The company sells seats on each prospective journey for $250,000.

Branson told Sky News on Monday that the company will “move forward” despite the crash. He said there would be a “whole massive series of test flights” before he and his family – and then the company’s customers – would fly into space.

“We need to be absolutely certain our spaceship has been thoroughly tested – and that it will be – and once it’s thoroughly tested and we can go to space, we will go to space,” he said.

He said, “We must push on. There are incredible things that can happen through mankind being able to explore space properly.”

Branson dismissed British newspaper reports about a midair explosion as insulting and untrue.

Branson had hoped to begin commercial flights next year.

Hart said a review of footage from a camera mounted to the ceiling of the cockpit shows the co-pilot moving the feathering lever to the unlock position.

The feathering is a feature unique to the craft to help it slow as it re-enters the atmosphere. After being unlocked, a lever must be pulled to rotate the tail section toward a nearly vertical position to act as a rudder. After decelerating, the pilots reconfigure the tail section to its normal position so the craft can glide to Earth.

Hart said the feathers activated at Mach 1.0, the speed of sound or 760 mph. They shouldn’t have deployed until the craft had at least reached a speed of Mach 1.4, or more than 1,000 mph.

SpaceShipTwo tore apart Friday about 11 seconds after it detached from the underside of its jet-powered mother ship and fired its rocket engine for the test flight. Initial speculation was that an explosion occurred but Hart said the fuel and oxidizer tanks and rocket engine were found and showed no sign of being burned or breached.

Virgin Galactic CEO George Whitesides issued a statement Sunday to tamp down conjecture about the cause of the crash.

“Now is not the time for speculation,” he said. “Now is the time to focus on all those affected by this tragic accident and to work with the experts at the NTSB, to get to the bottom of what happened on that tragic day, and to learn from it so that we can move forward safely with this important mission.”

SpaceShipTwo has been under development for years and, like all space projects, has suffered setbacks. In 2007, an explosion killed three people on the ground and critically injured three others during a ground test in the development of a rocket engine.