SpaceShipTwo Feathering System Prematurely Deployed before Fatal Breakup
Virgin Galactic's SpaceShipTwo disintegrated shortly after the vehicle's tail stabilizers prematurely deployed, according to the National Transportation Safety Board. Friday's crash killed co-pilot Michael Asbury and injured pilot Peter Siebold. The exact cause of the accident is still unknown, and acting NTSB Chair Christopher A. Hart cautioned against drawing conclusions from the initial findings.
"I would like to emphasize that what I'm about to say is a statement of fact, and not a statement of cause," Hart said, speaking at a late Nov. 2 press conference. There, he used two models of SpaceShipTwo to show how the vehicle "feathers" during reentry. Under normal operations, SpaceShipTwo is flown to a pre-determined altitude and released by its carrier aircraft, WhiteKnightTwo. For Friday's test, this happened at about 50,000 feet.
Shortly after SpaceShipTwo is released, it ignites its rocket engine and pitches upward, flying into a high arc designed to eventually reach the boundary of space. After the spaceship reaches apogee—the highest point of its flight—the vehicle's twin tails rotate upward, stabilizing and slowing SpaceShipTwo as it reenters the atmosphere.
It is not clear what the intended sequence of events was for Friday's test flight, but Hart said that the feathering system deployed prematurely. In order to feather the vehicle, two levers must be moved inside the cockpit. One unlocks the system, and the second deploys the stabilizers.
"About nine seconds after the engine ignited, the telemetry data showed us that the feather parameters changed from lock to unlock," Hart said. The telemetry data was confirmed by a camera inside the cockpit that showed co-pilot Asbury moving the handle. Normally, the feathers are not unlocked until the vehicle reaches Mach 1.4, Hart said. On Friday, Asbury unlocked the feathers around Mach 1.0.
However, neither pilot commanded the feathers to deploy. Shortly after the system was unlocked, the tail stabilizers began moving into their feather positions. Moments later, telemetry and video data stopped. The engine burn was normal up to the extension of the feathers, Hart said. This information runs contrary to speculation that the accident may have been caused by the engine, which was using a new fuel mixture during the flight. Scaled Composites, SpaceShipTwo's contractor, said the engine had been tested on the ground "many times," according to company president Kevin Mickey.
Hart said pieces of SpaceShipTwo, which are spread over a wide swatch of the Mojave Desert, are being moved into a hangar. "Among other things, [the investigators] found the fuel tanks, the oxidizer tanks, and the engine. All were intact and showed no signs of burn-through, and no signs of being breached," he said.
Because Friday's accident was a test flight, NTSB officials have a wealth of telemetry and video data to sift through. "There's much more that we don't know," Hart said, "and our investigation is far from over."