Lightweight debris from last week's in-flight breakup of Virgin Galactic's SpaceShipTwo rocket plane has been found as far away as 30 to 35 miles from the main crash site, the head of the National Transportation Safety Board said Monday night.
The dispersal of debris testifies to the thoroughness of the plane's disintegration, after an anomaly that occurred on Friday during a flight test high above California's Mojave Desert. SpaceShipTwo's wing-feathering system — a mechanism that's designed to slow the craft down during its descent — has emerged as a focus of the NTSB's investigation.
Experts on human performance have been added to the NTSB team to help determine why the mechanism was unlocked prematurely.
The plane's co-pilot, Michael Alsbury, was killed in Friday's crash. The pilot, Pete Siebold, survived the breakup and parachuted to the ground, although he's being hospitalized for serious injuries. Hart said that investigators have not yet interviewed Siebold, but will do so on a schedule worked out in consultation with his medical team and family members.
Both pilots worked for Scaled Composites, the Mojave-based company that was developing and testing SpaceShipTwo for Virgin Galactic. Virgin Galactic had hoped to begin flying passengers to the edge of outer space as early as next year. More than 700 passengers have paid as much as $250,000 each for a ride.
Final news briefing
Monday night marked the NTSB's final scheduled news briefing during the on-site investigation in and near Mojave, California, but Hart said additional evidence would be gathered over the next few days. It will take several months longer to sift through the data and issue a report identifying the cause and making recommendations for future operations, he said.
"We would anticipate taking as much as 12 months to complete the analysis," Hart told reporters at the Mojave Air and Space Port.
Hart laid out a detailed time line for the final minutes of SpaceShipTwo's flight, which originated at the Mojave airport, about 95 miles (150 kilometers) north of Los Angeles. The rocket-powered craft was taken up to almost 50,000 feet by its WhiteKnightTwo carrier airplane, and then released for an air launch at 10:07:19 a.m. PT, he said.
The rocket motor was lit up at 10:07:21. Eight seconds later, the craft was traveling at Mach 0.94 — that is, 0.94 times the speed of sound. Two seconds later, at 10:07:31, the speed was Mach 1.02. Video and telemetry shows that one of the pilots pulled a lever to unlock the wing-feathering system. Hart said Friday's flight plan called for that lever to be pulled at a later time, when the speed reached Mach 1.4.
Sometime during the three seconds that followed the unlocking, the wings went into their "feathered" position, even though a second lever that was supposed to deploy the system was not pulled, Hart said. The video and telemetry signals were lost at 10:07:34, presumably because the plane was breaking up.
Unanticipated stress
The feathering system is designed to rotate the back sections of the rocket plane's wings during the plane's descent, into an angle that would increase atmospheric drag and slow the supersonic craft in a controlled manner. The process is called "feathering" because it's similar to the self-righting, floating effect produced by the feathers on an old-fashioned badminton shuttlecock.
The system is not designed to be deployed during the rocket-powered ascent. At that point in the flight, the drag created by the angled wings would put unanticipated stress on the carbon-composite craft.
Hart said the NTSB assembled additional experts on Monday to look at the human factors behind the crash — for example, how the flight crew interacted with the displays and controls in the cockpit.
During the news conference, Hart said he wasn't sure which pilot unlocked the wing-feathering system, but in a series of follow-up tweets, the NTSB confirmed that it was Alsbury.
This report was revised to emphasize the fact that entire sections of SpaceShipTwo's wings were feathered, and not just the craft's tail booms. NBCUniversal established a multi-platform partnership with Virgin Galactic to track the development of SpaceShipTwo.