Feathering malfunction, not hyped motor, suspected in SpaceShipTwo crash

On October 31, a manned suborbital test flight broke up mid-air and crashed into the California desert, a 50,000-foot dive that left it smashed. The pilot was killed and the copilot was critically injured. The vehicle was SpaceShipTwo (SS2), owned by British businessman Richard Branson’sVirgin Galactic enterprise, which wants to debut commercial spaceflight in 2015. With SS2’s crash, that’s not going to happen before 2016. The investigation of its crash alone is due to take a year.

In a press conference on November 3 (IST), the National Transportation Safety Board (NTSB), an autonomous federal agency in the United States tasked with investigating civilian aviation accidents, revealed more information about the SS2’s behavior before it tumbled to the ground. The agency didn’t blame any specific incidents or actions, and only addressed some anomalous events that could have contributed to the tragedy. Specifically, the hyped ‘feathering’ mechanism appeared to have been executed abnormally.

On the SS2, a portion of the vehicle’s wings are capable of folding upward and becoming almost perpendicular to the fuselage (see image below; more here). This is called feathering: it controls the pitch, roll and yaw motions of the vehicle, and is used to achieve aerodynamic stability during reentry. It is feasible only for reentry achieved at speeds much lower than the orbital velocity, around 25,000 km/hr. This is why the now-retired NASA Space Shuttle couldn’t use feathering to stabilize itself.

SpaceShipTwo schematic.
SpaceShipTwo schematic.

Feathering increases the aerodynamic drag generated by the vehicle while ensuring the surface isn’t heated up. This eliminates the need for heat shields.

According to the NTSB, on October 31, the engine first fired for nine seconds. Then, a pilot prematurely unlocked the feathering (at Mach 1 instead of at Mach 1.4). However, he didn’t push the lever that moves the feathers to their perpendicular position – but the feathers moved anyway. This caused SS2 to brake suddenly and induce significant structural loads in its frame leading to the mid-air disintegration.

Before the presser, there was speculation that SS2’s motor, the predictably named RocketMotorTwo, might have been responsible for the accident. It is derived from an older variant built by the Sierra Nevada Corporation first tested in April 2013. On the day of the crash, SS2 was debuting a new version of the motor that was using a polyamide plastic fuel. The NTSB said that, after ascertaining they’d found all the parts of the crashed vehicle, they couldn’t find any burn marks that might’ve implicated RocketMotorTwo.

According to an article in Financial Times on November 2,

A second spacecraft under construction for the last three years in New Mexico is “65 per cent complete”, Mr [George] Whitesides [CEO, Virgin Galactic] said, adding that it could be ready to fly next year, once the cause of last week’s accident has been resolved. “The second spaceship is getting close to readiness,” he said.

All eyes on the investigation now…

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