Investigators examining debris from the exploded Virgin Galactic rocket said a mechanism designed to slow down the craft before atmospheric re-entry had likely caused the accident.
Contrary to previous assumptions of some space industry experts that the rocket’s hybrid engine with onboard nitrous oxide may have exploded, the US National Transportation Safety Board (NTSB) said the propellant tanks and engine were found intact, suggesting there had been no explosion.
They said that SpaceShipTwo's rotating tail boom, a key safety feature for re-entering the atmosphere, deployed and started rotating while the spaceship was travelling at a supersonic speed, possibly causing the space plane to break up in the air.
"The debris field indicates an in-flight breakup," Christopher Hart, acting chairman of the NTSB, told Reuters.
"We'll know that for certaint when we look at all the sources we have," he said, adding it was still too early to determine the exact cause of the tragic crash that killed a 38-year-old test pilot and left his co-pilot badly injured.
The accident during a test flight above California’s Mojave Desert will considerably derail Sir Richard Branson’s plans to start ferrying paying tourists to space in the near future for £150,000 a seat. Prior to the accident, the already heavily delayed venture was, according to Branson, on the right track to start commercial operations as early as 2015.
However, the tragic accident has sparked a backlash of criticism from multiple space industry experts who claimed Virgin Galactic’s design and safety practices have long been of grave concern.
British rocket scientist Carollyne Campbell said she had warned Virgin Galactic in a letter several years ago about the risks related to the use of nitrous oxide as an oxidiser.
“Nitrous oxide can explode on its own. Unlike oxygen [used to power conventional rockets], it’s an explosive. And rockets blow up because that’s their nature,” she said.
The doomed flight was the first test of a new nylon-based fuel, which was supposed to give SpaceShipTwo more thrust. Previously the rocket was powered by a rubber-based mix ignited by the nitrous oxide, similarly to the nylon-based variety.
Virgin Galactic previously stated its innovative propulsion design ensures that their rockets produce considerably less carbon and toxic emissions than other types of propulsion.
The Friday fatality, however, was not the first in Virgin Galactic’s research and development process. In 2007, three engineers were killed in an explosion of a nitrous-oxide tank during an engine test on the ground.
Virgin Galactic remained secretive about what happened during the disaster. "They operated in secrecy, which is difficult to understand,” Tommaso Sgobba, president of the International Association for the Advancement of Space Safety (IAASS) and former head of safety at the European Space Agency, told the Daily Mail last year.
“They don’t use modern techniques in putting safety into the design. They use outdated methods like testing and seeing what happens. It’s old and dangerous technology. And he (Branson) was told that.”
However, the NTSB investigation results suggest that, in the case of Friday's accident, the engine was running nominally after SpaceShipTwo separated from its carrier aircraft WhiteKnightTwo at the altitude of about 45,000ft.
"The engine burn was normal up until the extension of the feathers," NTSB’s Christopher Hart told reporters.
As the spacecraft was travelling at about 1.4 times the speed of sound, the feathering system, designed to slow down the vehicle before it re-enters atmosphere on its return from space, began rotating either due to a pilot error or a technical glitch.
Investigators examined video from the vehicle’s cockpit and found evidence that the pilot pre-activated the mechanism intentionally. However, it was not clear what triggered the actual deployment two seconds later.
The feathering system, which folds the vehicle in half to create more atmospheric drag, was unlocked early by the co-pilot according to video from the spaceship's cockpit. About two seconds later the spaceplane's tail section began to fold.
Virgin Galactic crash infographic