The National Transportation Safety Board (NTSB) has provided details into the probable cause of the SpaceShipTwo failure during last year’s test flight. The investigation found co-pilot error and procedural issues relating to the SS2’s feather system were to blame. With the investigation now closed, Virgin Galactic are building a new spacecraft with modifications to mitigate a repeat issue.
Hailed as the gateway to space tourism, the suborbital vehicle was developed from the historic advancements made by the world’s first manned private spacecraft SpaceShipOne (SS1).
SS2 is the design of renowned aircraft designer Burt Rutan and his company, Scaled Composites – the latter in charge of the ill-fated test flight in October 2014.
Initially, the plan, under the leadership of Virgin head Sir Richard Branson, was to launch passengers by 2008. The start date continued to slip by years, but the company claimed interest failed to diminish, with claims of several hundred customers paying a hefty deposit for rides on SS2.
The customers will only enjoy a few minutes of micro-G, but will get to spend several days of training, prior to boarding a SS2 from the newly built Spaceport America in New Mexico.
Testing towards that start date had proceeded without a major flight incident, prior to the October test.
The test flight began with SS2 being lofted to around 47,000 feet altitude over the Mojave desert by the WhiteKnight2 (WK2) carrier aircraft. SS2 was nominally released from WK2.
Once the two vehicles were clear of each other, the pilots triggered ignition of the rocket motor, causing the main oxidizer valve to open and igniters to fire within the fuel case.
This was the program’s 55th overall and fourth powered test flight (PF-04) of SpaceShipTwo.
Just seconds into the powered flight, the NTSB concluded that co-pilot Michael Alsbury prematurely unlocked the feathering system. The system is supposed to be unlocked while SpaceShipTwo is traveling at around Mach 1.4.
“Data shows that the feather moved, even though we know that neither pilot had deployed the feather,” noted the NTSB’s Lorenda Ward. “However, the cockpit video showed that the co-pilot unlocked the feather.”
This pilot error was a large focus of the investigation and it remains a mystery as to why a highly trained pilot would make such an error.
It was cited that there was a large amount of “pressure” on pilots to ensure the feather system was activated during a busy period of the flight milestones, due to fear of the potentially disastrous results of re-entry without deployment.
A lack of flight experience with the stresses of a real flight, versus simulator training, was also mentioned.
It was also claimed that the training procedures and checklists failed to emphasise the potential of a flight failure via a premature unlocking of the system.
“Since the feather was unlocked, aerodynamic and inertial loads imposed on the assembly overcame the actuators and the feather extended un-commanded, causing the catastrophic structural failure,” added Ms. Ward.
With the vehicle breaking up, the pilot Peter Siebold was miraculously thrown free of SS2 before his parachute automatically deployed.
Virgin Galactic released an amazing photo of Mr. Siebold under chute moments after the accident. He was seriously injured during the accident.
The co-pilot remained with the vehicle and was killed.
While videos of the test flight were shown, the webcasted hearing did not show footage of the actual breakup – for obvious reasons – although the investigators had witnessed extended videos, including from the cockpit, allowing them to formulate their conclusions.
Most of the NTSB findings were based around technical and procedural matters, but importantly found no issues with the spacecraft itself.
One investigator’s intimation – claiming the accident was caused by “pilot error on a flawed system” – mainly related to the single-fault – or single-point – tolerant issue of prematurely unlocking the feather system and such an actions ability to result in vehicle break-up.
This was later stressed via the finding that: “The recovered vehicle components showed no evidence of any structural system or rocket motor failures before the in-flight breakup.”
While the accident will be forever painful for all involved, Virgin Galactic can now continue to progress towards the final construction of the replacement vehicle (SS2-002), which they are building in-house.
“While it is good to have passed this milestone and be able to focus on the future, we are acutely aware that it does not alter the fact that this was at heart a human tragedy. Our thoughts go out again today to the family, friends and colleagues of Mike,” noted Sir Richard Branson.
“The NTSB board also looked closely at whether the Scaled Composite’s accident meant Virgin Galactic should change its own procedures for future test flights and commercial operations, or indeed the design of future vehicles.
“We cooperated fully with the investigation, and the NTSB has made no recommendations for the company. Over the past months, our engineers have already designed a mechanism to prevent the feather from being unlocked at the wrong time.”
Moving forward, Virgin Galactic will evaluate a new test schedule, but will now be in full control of completing the test program ahead of commercial flights.
“Scaled Composites was responsible for all aspects of the flight test program at the time of the accident. Subsequently, Virgin Galactic has assumed full responsibility for the completion of SpaceShipTwo flight test program and the commercial operations which will follow,” added the company in a document released later on Tuesday.
The company has also set out a set of requirements for all of its active pilots, while updating its procedures and checklists.
“We remain as humbled as ever by the difficulty of our work and the challenges of space. To date, only 549 people have gone to space and we are as passionate and resolved as ever to increase that number,” added CEO George T. Whitesides. “The goal of people around the world to access space is as unwavering as the commitment of our team and brave pilots like Mike.
“We are encouraged by the progress to date with our second spaceship, and we look to the future with hope and determination.”
While NTSB chairman Christopher Hart noted the investigation would echo throughout the commercial space sector, hopefully preventing a similar accident recurring, Sir Richard Branson is hopeful his company can now move on and fulfill its ambitions.
“With the investigation completed, Virgin Galactic can now focus fully on the future with a clean bill of health and a strengthened resolve to achieve its goals.”
(Images via Virgin Galactic and the NTSB – New Spaceport America photo via L2).