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SpaceShip Two’s Tail “Feather” Brake Malfunctioned 2 Seconds Before Breakup
The design was supposed to require the pilots to first move a lever to unlock the mechanism and instruct it to perform the rotation. Unfortunately, SpaceFlight Now reported from [spaceflightnow.com] the NTSB press conference, things didn't go remotely as planned:
“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,” Hart said.
The tail booms extended after they were unlocked, even though they were not commanded to do so, Hart said. SpaceShipTwo’s pilots normally must unlock the feathers, then send a separate command to move the tail booms into position for descent. “This was what we could call an uncommanded feather, which means the feather occurred without the feather lever being moved into the feather position…and two seconds later we saw disintegration…the telemetry data terminated and the video data terminated,” Hart said.
On the upside, “because it was a test flight, it was heavily documented, in ways that we don't usually see with normal accidents,” including three cameras watching from WhiteKnight Two plus SpaceShip Two’s own six video cameras & six data recorders. It has already been discovered that the rocket motor & propellant tanks landed intact with no signs of burn-through or breaching, indicating they were most likely not involved in the failure.
Space.com reports that [space.com] doctors have advised the NTSB against talking to surviving pilot Michael Alsbury for now, and in the meantime, the NTSB can’t yet rule out pilot error as a major cause:
“We are looking at a number of possibilities, including that possibility,” Hart said. “I want to emphasize that we have not determined the cause. … I am not stating that this is the cause of this mishap. We have months and months of investigation to determine what the cause was. We’ll be looking at training issues, we’ll be looking at ‘was there pressure to continue testing’, we’ll be looking at safety culture. We’ll be looking at the design (and) the procedure. We’ve got many, many issues to look into much more extensively before we can determine the cause.”
