Photo of the feather position immediately before in-flight breakup.

​​Feather position immediately before in-flight breakup. Source: Scaled Composites​

In-Flight Breakup During Test Flight, Scaled Composites SpaceShipTwo

Investigation Details

What Happened

​On October 31, 2014, at 1007:32 Pacific daylight time, the SpaceShipTwo (SS2) reusable suborbital rocket, N339SS, operated by Scaled Composites LLC (Scaled), broke up into multiple pieces during a rocket-powered test flight and impacted terrain over a 5-mile area near Koehn Dry Lake, California. The pilot received serious injuries, and the copilot received fatal injuries. SS2 was destroyed, and no one on the ground was injured as a result of the falling debris. SS2 had been released from its launch vehicle, WhiteKnightTwo (WK2), N348MS, about 13 seconds before the structural breakup. Scaled was operating SS2 under an experimental permit issued by the Federal Aviation Administration’s (FAA) Office of Commercial Space Transportation (AST) according to the provisions of 14 Code of Federal Regulations (CFR) Part 437.

Scaled had developed WK2 and was developing SS2 for Virgin Galactic, which planned to use the vehicles to conduct future commercial space suborbital operations. SS2 was equipped with a feather system that rotated a feather flap assembly with twin tailbooms upward from the vehicle’s normal configuration (0º) to 60º to stabilize SS2’s attitude and increase drag during reentry into the earth’s atmosphere. The feather system included actuators to extend and retract the feather and locks to keep the feather in the retracted position when not in use.

After release from WK2 at an altitude of about 46,400 ft, SS2 entered the boost phase of flight. During this phase, SS2’s rocket motor propels the vehicle from a gliding flight attitude to an almost-vertical attitude, and the vehicle accelerates from subsonic speeds, through the transonic region (0.9 to 1.1 Mach), to supersonic speeds. The flight test data card used during the accident flight indicated that the copilot was to unlock the feather during the boost phase when SS2 reached a speed of 1.4 Mach. (The feather was to be unlocked at this point in the flight to mitigate the hazard resulting from a reentry with the feather down due to a lock failure.) However, a forward-facing cockpit camera and flight data showed that the copilot unlocked the feather just after SS2 passed through a speed of 0.8 Mach. Afterward, the aerodynamic and inertial loads imposed on the feather flap assembly were sufficient to overcome the feather actuators, which were not designed to hold the feather in the retracted position during the transonic region. As a result, the feather extended uncommanded, causing the catastrophic structural failure.

What We Found

The ​​​probable cause of this accident was Scaled Composites’ failure to consider and protect against the possibility that a single human error could result in a catastrophic hazard to the SpaceShipTwo vehicle. This failure set the stage for the copilot’s premature unlocking of the feather system as a result of time pressure and vibration and loads that he had not recently experienced, which led to uncommanded feather extension and the subsequent aerodynamic overload and in-flight breakup of the vehicle.

. Safety issues include the lack of human factors guidance for commercial space operators, the efficacy and timing of the preapplication consultation process, limited interactions between the FAA/AST and applicants during the experimental permit evaluation process, missed opportunities during the FAA/AST’s evaluations of hazard analyses and waivers from regulatory requirements, limited inspector familiarity with commercial space operators, an incomplete commercial space flight database for mishap lessons learned, and the need for improved emergency response planning.

What We Recommended

As a result of this investigation, we made safety recommendations to the FAA ​​and the Commercial Spaceflight Federation.​