Virgin Galactic’s SpaceShipTwo telemetry data has offered a vital clue to investigators searching for the cause of the fatal 31 October crash while the wreckage appears to rule out an engine or fuel tank malfunction.
Nine seconds after the Scaled Composites spacecraft separated from mothership WhiteKnightTwo, co-pilot Mike Alsbury unlocked the tail feather deployment mechanism as SpaceShipTwo passed through Mach 1.0, says US National Transportation Safety Board chairman Christopher Hart, citing review of telemetry data and cockpit video.
Like the X-Prize-winning SpaceShipOne design, SpaceShipTwo deploys two aft-mounted feathers as the vehicle approaches the top of its climb into suborbital space. The deployed feathers are intended to enable a “carefree re-entry” attitude, automatically configuring the vehicle in a safe position during the most dangerous phase of the flight .SpaceShipOne founder Burt Rutan says he came up with the idea to reduce the workload on the pilot, after being present at Edwards AFB, California, in 1967 when X-15 pilot Michael Adams died during a botched re-entry from suborbital space.
On the fourth powered flight test of SpaceShipTwo, however, the tail features deployed well within the Earth’s atmosphere at a crucial stage of the vehicle’s ascent.
Alsbury was not supposed to unlock the tail feathers until the aircraft was in thinner air and passing through M1.4, but his action alone should not have been fatal.
The tail feathers are designed to deploy after two commands, Hart says. First, the co-pilot or pilot must unlock the tail feather, as Alsbury did. Secondly, Hart says, the crew must pull on the feather deployment lever to move the control surfaces into a different position.
Although no evidence reviewed so far indicates that either pilot moved the second lever, the tail feathers deployed anyway, Hart says.
Two seconds later, the composite-skinned SpaceShipTwo began to break-up at supersonic speed, he says.
The break-up scattered a debris field over 8.23km (5mi) long on the floor of the Mojave desert, which included fully intact oxidiser and fuel tanks. The tanks had not been breeched despite the break-up, Hart says.
Although the tail feather data appears to point to a probable cause for the accident, Hart is cautious. He describes the information as a statement of fact rather than a statement of cause.
“There is much more that we don’t know and our investigation is far from over,” he says.
The surviving pilot, Pete Siebold, escaped the aircraft after the in-flight break-up and deployed his parachute. He landed with severe injuries and remains under medical care in a local hospital.
The information about the intact oxidiser tanks will likely silence a chorus of criticism that arose in the hours since the fatal crash, which focused on a move by Virgin Galactic earlier this year to revise the fuel formulation of the hybrid engine called RocketMotorTwo, which is designed by Sierra Nevada.
But the in-flight break-up and the uncommanded deployment of the dual tail feathers will also raise questions about the design and safety of SpaceShipTwo. The tail feathers were intended to increase the safety of the design, yet could be implicated in the fatal accident.