NTSB Investigative Update on Crash of Virgin Galactic SpaceShipTwo
November 12
The National Transportation Safety Board issued an investigative update today into the crash of SpaceShip Two on Oct. 31, 2014, in Mojave, Calif.
The on-scene portion of the investigation into the crash of Virgin Galactic SpaceShipTwo, a test flight conducted by Scaled Composites, has concluded and all NTSB investigators have returned to Washington, DC.
The SpaceShipTwo wreckage has been recovered and is being stored in a secure location for follow-on examination.
The NTSB operations and human performance investigators interviewed the surviving pilot on Friday. According to the pilot, he was unaware that the feather system had been unlocked early by the copilot. His description of the vehicle motion was consistent with other data sources in the investigation. He stated that he was extracted from the vehicle as a result of the break-up sequence and unbuckled from his seat at some point before the parachute deployed automatically.
Recorded information from telemetry, non-volatile memory, and videos are being processed and validated to assist the investigative groups.
An investigative group to further evaluate the vehicle and ground based videos will convene next week at the NTSB Recorders Laboratory in Washington, D.C.
The systems group continues to review available data for the vehicle's systems (flight controls, displays, environmental control, etc.). The group is also reviewing design data for the feather system components and the systems safety documentation.
The vehicle performance group continues to examine the aerodynamic and inertial forces that acted on the vehicle during the launch.
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The difference between catastrophe and survival might have been a matter of mere seconds, said Princeton University's Robert Stengel, who has studied the aerodynamics of SpaceShipTwo's predecessor.
Stengel has not been involved in the development of SpaceShipTwo, but he does use SpaceShipOne's aerodynamics as a teaching tool for his course in flight dynamics. The experimental SpaceShipOne craft successfully flew into space three times during 2004.
The wing-feathering mechanism is not designed to be deployed during the plane's rocket-powered ascent. Unfortunately, that's what happened on Friday: The National Transportation Safety Board said video and telemetry showed that co-pilot Mike Alsbury unlocked the mechanism earlier than scheduled, when the craft was traveling at just above the speed of sound. Seconds later, the mechanism was deployed, even though neither one of the pilots pulled the lever to deploy it.
"The feathering occurred at the worst possible flight condition: Mach 1 and maximum dynamic pressure," Stengel told NBC News in an email. "The craft was never structurally designed to withstand such a condition. Had the feathering occurred 10 or 20 seconds later, there probably would not have been a problem."
That may seem counterintuitive, because the rocket engine would have continued firing to accelerate SpaceShipTwo to Mach 1.4. But in a follow-up phone interview, Stengel pointed out that even a few more seconds would have allowed SpaceShipTwo to go higher, where the atmosphere is thinner.
"The air density is going down at a humongous rate," he said.
Because of the thinner atmospheric density, folding the wings that high up at Mach 1.4 would have produced less aerodynamic stress than folding them at a lower altitude at Mach 1, Stengel said.
