Following the tragic accident on Friday which saw Virgin Galactic's SpaceShipTwo fail catastrophically, engineers are now scrabbling to understand the cause. In a new briefing, the National Transportation Safety Board has explained that the craft deployed its braking system prematurely.
The NTSB's acting chairman, Christopher Hart, has explained that SpaceShipTwo's tail stabilizers were extended earlier than they should have been. While the board is keen to point out that this isn't necessarily the cause of the accident, it does shift focus away from initial speculation that the craft's rocket motor is to blame. Hart explained:
"What I'm about to say is a statement of fact and not a statement of cause. We are a long way from finding cause. We still have months and months of investigation to do, and there's a lot that we don't know. We have extensive data sources to go through."
Analysis of telemetry and video from the craft reveals that the rear-mounted feathering system—which tilts the two distinctive wings up, to slow the plane and bring its belly up during re-entry—rotated just seconds after its rocket fired. The NTSB has stated that ShipShipTwo's co-pilot—who died in the accident—moved a lever in the cockpit to unlock the tail feathers. Hart explains further:
"Normal launch procedures are that after the release, the ignition of the rocket and acceleration, that the feathering devices are not to be moved — the lock/unlock lever is not to be moved into the unlock position — until the acceleration up to Mach 1.4. Instead, as indicated, that occurred (at) approximately Mach 1.0."
However, in usual operation, simply unlocking the feathers shouldn't do anything; a separate command is usually required to tilt them. On Friday, that didn't happen—the feather extended immediately without prompt. More from Hart:
"This was what we would call an uncommanded feather, which means the feather occurred without the feather lever being moved into the feather position. After it was unlocked, the feathers moved into the deployed position, and two seconds later we saw disintegration."
While initial speculation suggested the rocker motor—which was using a new kind of fuel—may have been at fault, Hart explained that it was operating normally until the tail feathers extended. Debris retrieved from the ground also reveals that SpaceShipTwo's rocket motor and propellant tanks were found in tact—with no signs of burn-through or breaching.
Asked whether the news pointed to pilot error, Hart responded his team was "looking at a number of possibilities, including that possibility." It's certainly very early in terms of crash investigation, and Hart expects "months and months of investigation to determine what the cause was." [Space Flight Now]