The crash of Virgin Galactic's SpaceshipTwo last year was caused by a catastrophic structural failure triggered when the co-pilot unlocked the craft's braking system too early, investigators say.
National Transportation Safety Board investigators say the resulting aerodynamic forces caused the brakes to actually be applied without any further action by the crew.
And no safeguards were built into the system to overcome the error.
The spaceship broke apart over the Mojave Desert during a test flight 10 months ago. The accident killed the co-pilot and seriously injured the pilot.
NTSB officials said early in the investigation the co-pilot prematurely unlocked equipment designed to slow the descent of the spacecraft during initial re-entry.
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Simply unlocking the spacecraft's brakes shouldn't have applied them but it happened anyway.
In determining the probable cause of the accident, investigators focused on the lack of systems in place to mitigate or overcome human error.
Scaled Composites developed the craft for Virgin Galactic.
NTSB member Robert Sumwalt said on Tuesday the company "put all its eggs in the basket" on the crew doing everything correctly.
"My point is that a single-point human failure has to be anticipated," Sumwalt said.
"The system has to be designed to compensate for the error."
Chairman Christopher Hart said the NTSB learned "with a high degree of certainty the events that resulted in the breakup."
"Many of the safety issues that we will hear about today arose not from the novelty of a space launch test flight but from human factors that were already known elsewhere in transportation," Hart said.
Virgin Galactic has been proceeding with its plans for space flight and is now building another craft.
Company officials have said in recent months their commitment to commercial spacecraft has not wavered despite the crash and they expect the company to resume test flights later this year.
Eventually, the company envisions flights with six passengers climbing more than 100km above Earth.
