After a series of delays on the morning of Oct. 31, 2014, pilot Peter Siebold and co-pilot Michael Alsbury soared over the Mojave Desert on the fourth rocket-powered test flight of Virgin Galactic’s SpaceShipTwo spaceplane. An anomaly caused the vehicle to break up 13 seconds into the flight and end in catastrophic failure. Alsbury did not survive the crash, and Siebold was severely injured. Nearly nine months later, on July 28, 2015, the National Transportation and Safety Board (NTSB) met to discuss the probable cause behind the fatal crash of the suborbital spaceplane built by Scaled Composites for Virgin Galactic, called SpaceShipTwo.
The NTSB determined the cause of the crash was Scaled Composites’ failure to consider human error and the co-pilot’s early deployment of the feathering mechanism that slows the vehicle during reentry. The plane was traveling at a speed of 0.8 Mach during the boost phase when Alsbury unlocked the feather system, which was not supposed to happen until 1.4 Mach. The loads overcame the feather’s actuators and deployed without being commanded to do so. The Federal Aviation Administration (FAA) oversaw the investigation of the crash; however, as noted by NTSB Chairman Christopher Hart, the FAA’s role in commercial space is different from the administration’s role in aviation. The FAA only certifies the launch, not the vehicle, and focuses mainly on public safety.
A detailed presentation by Lorenda Ward, Investigator-in-Charge, explained that telemetry data showed that the feather had moved even though neither pilot deployed the feather. Video from inside the cockpit showed the co-pilot unlocking the feather early just after .8 Mach. The co-pilot wasn’t supposed to unlock the feather until 1.4 Mach in order to enable the aircraft to transition to the transonic stage of the flight. Aerodynamic and inertial loads on the aircraft were sufficient enough for the wings to extend uncommanded and cause catastrophic failure.
“Range instrumentation radar located on Edwards Air Force Base tracked WhiteKnightTwo with SpaceShipTwo attached and SpaceShip Two itself following its release from WhiteKnightTwo until the impact of SpaceShipTwo’s main oxidizer tank and wings hit the ground,” explained Ward in her presentation.
During the break up, Siebold, the pilot, was thrown from the spaceplane while still strapped in his seat. Upon descent, Siebold released himself from his seat and his parachute deployed automatically. The seat and parachute were found separate from the wreckage.
The following safety issues were found during the investigation:
- A lack of human factors guidance for commercial space operators
- The efficiency and timing of the pre-application process
- Limited interactions between FAA and applicants during the experimental permit evaluation process
- Missed opportunities during the FAA’s evaluation of Scaled Composites hazard analysis and waiver from regulatory requirements
- The limited inspector familiarity with commercial space operators
- Need for improved emergency response planning
- Need for a fully developed database for commercial space operators on mishaps learned
Katherine Wilson, Ph.D. Human Performance, gave a Human Factors and Organizational Issues presentation surrounding the SpaceShipTwo crash. Wilson stated that Powered Flight 4, or PF04, flight training began in January 2014. Scaled Composites required SpaceShipTwo pilots to complete at least three full mission rehearsals, three simulated approaches in WhiteKnightTwo, and three aerobatic training flights in the Extra 300 (an aerobatic aircraft) to prepare for SpaceShipTwo’s fourth powered flight.
Wilson also stated that Scaled Composites performed several pre-flight readiness reviews before the fourth powered test flight. A town hall meeting was held to identify risks and potential issues that could delay the program schedule. No issues were discussed at these meetings for PF04 pilot procedures for the feathering system on SpaceShipTwo.
Delays and Concerns Surrounding the Fourth Powered Flight of SpaceShipTwo
On Jan. 16, 2015, the surviving pilot, Siebold, spoke in an interview at NTSB Headquarters in Washington, D.C. He said he considered PF04 a “high-risk” flight, though Scaled Composites did not have a scale for evaluating flights. Despite the lack of formal differentiation between PF04 and past test flights, Siebold in the interview stated that they were “doing a significant envelope expansion that day. Flying an unproven rocket motor in an unexplored aerodynamic regime … classic test hazard assessments would categorize that as a high-risk flight.” The interview also states that Siebold explained that they were “using a propulsion system that history has shown can be unreliable, or much less reliable than a turbine or reciprocating engine.”
Michael Massuci was the WhiteKnightTwo pilot the day of the crash. In an interview on Nov. 1, 2014, as detailed in the NTSB Interview Summaries regarding Operational Factors, he said he arrived at work at 0330 PT in preparation to tow but an avionics issue caused a delay. Once both vehicles were ready, Massuci followed the Tow Pilot Checklist and WhiteKnightTwo and SpaceShipTwo were towed to the runway. Incorrect nitrous oxide (N2O) temperatures caused another “short” delay prior to take off.
Interviews of those involved in the investigation regarding operational factors, as noted in the interview summaries, also speak about a delay regarding cooler than normal nitrous oxide temperatures.
A malfunctioning Data Acquisition Unit (DAU) 1 also raised concerns the day of the crash. According to an interview with Scaled Composites project engineer Peter Kalogiannis, he removed the faulty DAU 1, tested it, found the failure, and replaced the malfunctioning component. He retested the unit and then reinstalled it.
Mark Bassette, Scaled Design Engineer, also spoke of the faulty DAU unit. He said in his interview that they “had a program history of DAU’s not as reliable as they should be.” Bassette was unable to recall a flight failure of the DAU but said they performed many simulated sessions that included a DAU failure. He also noted that “a DAU failure does not preclude safe operation of the SpaceShip but you lose redundancy and some of the signals.”
As the cooler-than-normal N2O temperatures and faulty DAU delayed the flight, winds and visibility also became an issue. Mark Stucky, a Scaled Composites test pilot, said the window to conduct the operation that day was getting small. When asked if he felt pressured to launch, he said if there was any pressure it was from himself because of the shrinking window.
It is unknown at this time if any of the delays before PF04 of SpaceShipTwo had anything to do with the accident. They were not mentioned in the July 28 NTSB discussion.
The FAA evaluated Scaled Composites’ applications for test flights and later found that the hazard analysis did not meet software and human error requirements for experimental permits. FAA waived these requirements based on the mitigations in the experimental permit application. The FAA failed to follow up and make sure the mitigations were being implemented by Scaled Composites.
“Manned commercial spaceflight is a new frontier, with many unknown risks and hazards,” Chairman Hart said. “In such an environment, safety margins around known hazards must be rigorously established and, where possible, expanded.”
The fatal crash of the SpaceShipTwo spaceplane caused a stir in the space community and brought about concerns regarding the safety of commercial human spaceflight. The NTSB made recommendations to the FAA and Commercial Spaceflight Federation to prevent this from occurring in the future.
Virgin Galactic is currently making progress on the second SpaceShipTwo. The company’s manufacturing organization, The Spaceship Company, hopes to put the second suborbital spacecraft into testing later this year.
Video Credit: NTSB
The author would like to extend a thank you to AmericaSpace’s Michael Galindo for help with the research on this article.