Investigators examining the wreckage of the Virgin Galactic spacecraft which crashed in the Mojave Desert say it could take a year to determine the cause of the accident.
National Transportation Safety Board (NTSB) officials are expected to spend the next week at the crash site in California.
They will then carry out interviews and further evidence gathering before beginning an analysis of what caused Friday's crash, which killed one pilot and injured another.
NTSB acting chairman Christopher Hart said the full investigation may take up to 12 months, adding that Virgin Galactic can continue to operate while the probe is under way.
"The on-scene part (of the investigation) I would estimate probably four to seven days, and then we go off-scene and continue the factual collection," he said.
"The total time... will be probably about 12 months or so, but again, as I say, this does not stop the operator from operating."
Mr Hart said investigators will use evidence from several cameras located on the craft to determine why it broke apart over the desert.
"Because it was a test flight it was heavily documented in ways that we don't usually see with normal accidents," he said.
Mr Hart has been briefing the media:
Sir Richard Branson has admitted the fatal Virgin Galactic crash is a "massive setback for commercial space travel", but says he hopes the programme will be back on track in six months.
The Virgin Group founder said: "It is a horrible day for Virgin Galactic, for commercial space travel - it's a massive setback.
"But we've got to pick ourselves up and see whether the problem is fixable, and hopefully move the programme forward. I'm hopeful we'll be able to overcome the problems."
Pilot Michael Alsbury, 39, was killed in the crash. Mr Alsbury, from Tehachapi, California, worked as a project engineer and test pilot.
The flight was his ninth onboard SpaceShipTwo.
His co-pilot, Peter Siebold, 43, was badly injured after parachuting to the ground.
Scaled Composites has confirmed that Mr Siebold has begun to communicate with his family at the Antelope Valley Hospital, where he is being treated.
The tragedy occurred after SpaceShipTwo fired up its rocket following a high-altitude drop from its WhiteKnightTwo mothership.
Mr Alsbury's death is the project's fourth fatality after three people were killed in a 2007 explosion while working for Scaled Composites, the company that teamed up with Virgin Galactic to build SpaceShipTwo.
Virgin Galactic had been aiming to become the first commercial "spaceline", by beginning tourist flights to the edge of space next year.
