Sky News looks at the details that have emerged since the Virgin Galactic spaceship crashed in California's Mojave Desert on Friday, killing one of the two pilots on board.
:: Feathering Function
Experts say the critical "feathering" function, which involves the tail boom rotating and the wings being placed in an upward position to slow the spacecraft for re-entry into Earth's atmosphere, was performed too early.
According to investigators from America's National Transportation Safety Board (NTSB), the feathering system was deployed when SpaceShipTwo was flying at a speed of around Mach 1.0 (the speed of sound), instead of the faster speed of Mach 1.4.
But the NTSB said is too soon to speculate on whether this caused the crash and that the investigation is still in its earliest stages.
:: Warnings
A rocket-propulsion expert with the Netherlands-based International Association for the Advancement of Space Safety has claimed multiple warnings about the spacecraft's motor were issued to Virgin since 2007 when three engineers died during a ground-based rocket test.
Carolynne Campbell's warnings related to nitrous oxide, reportedly used as a fuel component in the craft along with a new substance derived from nylon plastic grains.
Ms Campbell said she outlined her concerns to Virgin Galactic in a subsequent telephone conversation, but her warning again went unheeded.
"Based on the work we've done, including me writing a paper on the handling of nitrous oxide, we were concerned about what was going on at Virgin Galactic," Ms Campbell said.
"I sent copies of the paper to various people at Virgin Galactic in 2009, and they were ignored."
:: No Explosion
Witnesses to Friday's crash say there were no obvious signs of an explosion before SpaceShipTwo broke apart and hurtled to earth.
Despite crashing from an altitude of 45,000ft (13,700m) the spacecraft's fuel tanks and engine were recovered intact.
This almost certainly suggests the disaster was not caused by the fuel tanks exploding and that the engines were operating normally up until the moment the feathering function was executed.
"The engine burn was normal up until the extension of the feathers," the head of NTSB, Christopher Hart, said.
:: Safety
After the crash, Virgin boss Richard Branson said that safety was Virgin's paramount concern.
"Safety has always been our number one priority," he said, adding the company would not "push on blindly" with its space programme until the causes of the accident had been determined.
"I find it slightly irresponsible that people who know nothing about what they're saying can be saying things before the NTSB makes their comments," he told reporters.
Virgin Galactic's chief executive George Whitesides also cautioned against early speculation of the causes of the crash.
"In the space community you will be able to find people who have favourite technologies of different types," he said.
"One group will say their type of technology is better than another," he told the Financial Times.
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