Structural failure – not a faulty rocket motor – has quickly emerged as a key focus of the investigation into the 31 October crash of the Scaled Composites SpaceShipTwo that killed a test pilot and launched a new crisis for Virgin Galactic and the nascent suborbital space tourism industry.

SpaceShipTwo’s fourth powered flight only lasted 11s, but as a heavily-instrumented test aircraft it deluged investigators with more than 1,000 test parameters updated multiple times every second. There was also streaming video from the ground, nearby aircraft and inside the cockpit.

With so much information available, one telemetry point stood out almost immediately, says Christopher Hart, acting chairman of the US National Transportation Safety Board. The lever controlling SpaceShipTwo’s distinctive tail feathers moved to the unlock position as it passed through Mach 1.0. Cockpit video confirmed that co-pilot Mike Alsbury prematurely switched the tail feathers to the unlock position.

Neither Alsbury nor test pilot Pete Siebold, however, activated a second lever, which would have commanded the tail feathers to rotate 90° into the descent position, Hart says. But telemetry and video shows the unlocked tail feathers somehow deployed anyway. At around 55,000ft and within about 3s, SpaceShipTwo was ripped apart.

Siebold managed to escape from the fragmented vehicle and – though severely injured – deploy his parachute. Alsbury, however, was found on the ground by local police, still strapped into his seat. The wreckage of SpaceShipTwo was scattered over a 8km arc of the Mojave desert in California.

Hart cautions that the investigation is not over, as the NTSB investigation has reviewed only a small fraction of the huge volume of data collected. But it was clear from the wreckage that the Sierra Nevada-designed hybrid rocket motor did not explode before the vehicle broke apart. The three fuel and gas tanks carried by SpaceShipTwo – carrying nitrous oxide, methane and a plastic solid fuel – were found intact on the ground, Hart says.

Virgin Galactic crash

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Early speculation had focused on whether a decision by Virgin Galactic to switch from a rubber to a plastic fuel for the hybrid motor had caused the accident, but the propulsion system appears to have functioned as designed. Whether the plastic fuel was energetic enough to propel SpaceShipTwo above the Von Karman Line at an altitude of 100km – the widely accepted border of space – is another question left unanswered.

How the tail feathers deployed prematurely will be a more relevant question for the crash investigation. SpaceShipTwo’s tail feathers are meant to bend upward at the apogee of a suborbital parabolic flight path, to automatically configure the aircraft in a safe descent attitude. As the aircraft re-enters the atmosphere and control surfaces regain aerodynamic authority, the tail feathers are lowered to guide the aircraft on a 15min glide back to the airport.

Burt Rutan, the designer of SpaceShipOne, included the tail feathers in the design as a safety measure. In his early career, Rutan was a flight test engineer at Edwards AFB, California, and he remembered the day whenX-15 test pilot Michael Adamsdied after losing control of the aircraft upon re-entry. The tail feather design on SpaceShipOne and SpaceShipTwo was intended to make the re-entry “carefree” for the pilot.

The NTSB investigation of the crash will be broad. Hart says the investigation team will consider a wide array of factors, including the safety culture at Scaled Composites and Virgin Galactic.

It promises to be the toughest inquiry yet faced by a space tourism industry that has so far sent only a handful of tourists into space using Russia’s Soyuz launch system. Virgin Galactic at one point planned to begin regular space launches by 2007, but has struggled to overcome a string of setbacks, including a nitrous oxide explosion seven years ago that killed three Scaled Composites workers. Despite the delays, Virgin Galactic’s backlog of deposit holders for the $250,000 ticket to space has swelled to more than 700.

For Virgin Galactic founder Richard Branson, the results of the investigation will determine the next move for his 10-year-old space tourism venture. “Once we find out what went wrong, if we can overcome it, we’ll make absolutely certain the dream lives on,” Branson told reporters on 2 November before meeting privately with 400 employees in Mojave, California.

Branson pledged to invest $100 million to launch Virgin Galactic in 2004, just as SpaceShipOne claimed the Ansari X-Prize by completing two flights to space within 10 days. In 2009, Branson secured a $280 million investment by Aabar, an Abu Dhabi-based investment firm. Aabar committed to invest another $110 million two years later, raising the overall financing committed to the project to $490 million. Meanwhile, Aabar also committed to invest $100 million for Virgin Galactic to develop a small satellite launch capability based in Abu Dhabi. The taxpayers of New Mexico also committed $200 million to build Spaceport America near Truth or Consequences, New Mexico.

“Aabar Investments is aware of the test flight accident,” the investment firm says in a statement posted on its website. “Our thoughts and prayers are with the pilots' families, and everybody at Virgin Galactic and Scaled Composites.”

Virgin Galactic programme timeline

2002 Microsoft co-founder Paul Allen’s bid to win the $10 million Ansari X-Prize for the first private operator to reach space in a reusable craft attracts attention from Virgin Group boss Richard Branson, who goes on to sponsor the effort

2004 Allen’s team wins the X-Prize in air-launched rocketplane SpaceShipOne, built – along with its carrier aircraft – by Burt Rutan’s Scaled Composites

2005 At EAA AirVenture Oshkosh, Branson and Rutan announce the formation of a joint venture, The Spaceship Company, to develop the SpaceShipOne concept into a passenger-carrying spaceplane that would come to be known as SpaceShipTwo (SS2)

2007 Three Scaled Composites workers are killed and three injured in an explosion during a fuel flow test at Mojave Air and Space Port in California on 26 July. The accident puts on hold Scaled’s design work on SS2, and Virgin Galactic’s then-chief operating officer Alex Tai underscores the company’s focus on safety, telling a Royal Aeronautical Society audience: "Safety is our North Star” – a phrase that would be used seven years later by Richard Branson following SS2’s fatal crash in October 2014

2008 In July, Branson unveils SS2’s twin-fuselage carrier aircraft – or “mothership” – WhiteKnightTwo (WK2) and predicts first space tourism flights “in 18 months”. Just before year-end, WK2 makes its maiden flight

2009 June sees groundbreaking at Spaceport America near Las Cruces, New Mexico; the state and local counties raise $212 million through bond issues to finance construction of facilities, including a Norman Foster-designed terminal and 3,660m (12,000ft) runway. With Virgin Galactic as anchor tenant of the spaceport, the region hopes to become the focal point of the nascent commercial space industry – in May 2013, SpaceX leases facilities to test its reusable rockets, and in October 2014 the spaceport hosts its 21st launch, of a sounding rocket by UP Aerospace

In December, Branson unveils SpaceShipTwo

2010 In March, SS2 makes its first captive flight, under the wing of WK2, and, in October, the as-yet-unpowered spaceplane makes its first free flight, gliding after release from WK2 with pilots Peter Siebold and Mike Alsbury at the controls. Virgin Galactic talks about making its first flights to space in late 2011

2011 In May, SS2 makes its first unpowered flight in the “feathered” configuration, in which the wings are turned up into the airflow; in a flight to space, feathering would slow the craft during re-entry before SS2’s glide back to the runway in normal configuration – the feathering technique is likened to a badminton shuttle, whose aerodynamic drag ensures a stable, nose-first trajectory. At this point, 425 tickets have been sold, costing $250,000 each

In September SS2 suffers a tail stall during a glide test; the crew recover and land without incident, but SS2 is grounded for nine months for modifications

2012 SS2 returns to flight in June, and 515 tickets have been sold; in September, Virgin Galactic declares the unpowered, subsonic flight test programme to be essentially “finished”

Branson appears at July’s Farnborough air show to announce “LauncherOne”, a liquid-fuel rocket to be air-launched from WK2 and capable of putting 250kg payloads of 1m diameter into low Earth orbit. Later, in October, Virgin Galactic buys Scaled’s 30% share in The Spaceship Company to take full ownership of the SS2 builder

2013 Virgin Galactic in January begins paying rent on a 20-year lease on the “Gateway to Space” building at Spaceport America; the New Mexico Spaceport Authority is charging the company $1 million per year for facilities, plus $2,500 per month for land, according to the Las Cruces Sun News

On 29 April, SS2 makes its first powered flight; a second sortie under rocket power follows on 5 September. In December, Virgin Galactic says it is sticking to its plan to put its first fare-paying passengers into suborbital space in 2014 and expects to have a US Federal Aviation Administration operating licence in the first quarter of the year

2014 On 10 January, in SS2’s third powered flight, a 20s rocket burn after release take the spaceplane to Mach 1.4 and 71,000ft – its highest altitude to date. At the controls are Virgin Galactic chief pilot Dave Mackay and Mark Stucky, his counterpart at Scaled Composites. Branson says: “2014 will be the year when we will finally put our beautiful spaceship in her natural environment of space"

In May, Virgin Galactic selects a new polyamide-based rocket fuel for the remaining SS2 test flights and commercial operations. In September, there have been no further test flights, but Branson appears on David Letterman’s US late-night talk show to say a 2014 flight to space is possible, and he declares firmly that commercial flights to space from New Mexico would begin “in February or March” 2015

On 31 October, SS2 experiences a fatal crash, breaking up after its release from WK2 and the firing of its rocket motor. Co-pilot Michael Alsbury is killed, and pilot Peter Siebold is seriously injured.

Source: Flight International