With the ship about nine miles above Earth, pilot Peter Siebold said the craft broke apart around him and he was ejected into the thin, subfreezing air still strapped to his seat. As he was falling, Siebold unbuckled himself “at some point" before the parachute opened, according to a recounting of events released on Thursday by the US National Transportation Safety Board.
Siebold, who spoke to NTSB investigators on 7 November about the test flight of Richard Branson’s SpaceShipTwo, said he wasn’t aware that co-pilot Michael Alsbury had unlocked a braking system earlier than procedures allowed. The NTSB said that system, known as a feather, opened seconds before SpaceShipTwo disintegrated over the California desert. Alsbury was killed.
Siebold’s survival was “extremely remarkable" after being heaved into that inhospitable environment, said Jeff Sventek, an aerospace physiologist who is executive director of the Alexandria, Virginia-based Aerospace Medical Association.
“I can’t imagine the forces he must have experienced being thrown out of the aircraft," Sventek, who spent 31 years in the US Air Force, said in an interview.
SpaceShipTwo’s feather system lets the craft fly stable with its belly into the wind, similar to how a leaf falls. The feather accomplishes this by rotating the entire tail section upward. The air rushing past the tail forces the ship’s nose upward and keeps it stable.
It is designed to slow the craft during re-entry. In normal flight, when the feather is closed, the space plane slices nose- first into the wind.
The feather isn’t supposed to be moved until the ship reaches the near-vacuum conditions of its highest point. NTSB is reviewing the feather system’s design and how it was documented, though investigators haven’t drawn any definitive conclusions about the cause of the accident.
Pilots are instructed to unlock the system at Mach 1.4, about 920 miles (1,480 kilometers) an hour at that altitude. Once the feather system is unlocked, it can be tested to ensure it will work later in the flight, the NTSB’s acting chairman, Christopher Hart, said in an earlier interview.
Instead, the co-pilot moved the lock switch as the craft reached Mach 1, about 660 miles an hour. Buffeting from air rushing over the ship caused it to begin moving into place, according to the NTSB.
A second switch to activate the feather mechanism wasn’t moved by either pilot, according to the NTSB.
While the initial facts suggest that a pilot mistake may have been part of the sequence, that doesn’t necessarily indicate the NTSB will focus on pilot error. In other investigations, the safety board has examined training, aircraft design and other factors leading to pilots’ actions.
Siebold’s comments to investigators are the first account of how he survived. He wasn’t wearing a spacesuit when SpaceShipTwo came apart in the thin air at about 50,000 feet (15,200 meters), almost twice as high as the world’s highest mountain peak, Mount Everest.
The temperature at that altitude is about minus 70 degrees Fahrenheit (minus 57 degrees Celsius) and he would have spilled into the air traveling at more than 600 mph.
The wind at that speed would have battered his body, Sventek said.
Air Force pilots typically must wear pressurized space suits at those altitudes and higher to ensure survival in case of a loss of pressure, Sventek said. Siebold wasn’t in such a suit, Eric Weiss, an NTSB spokesman, said in an interview.
Without oxygen, the pilot would have become unconscious within seconds, according to the Federal Aviation Administration.
Exposure to those extreme conditions doesn’t cause permanent damage if it’s only for a brief time, according to research on humans and animals.
In 1965, a National Aeronautics and Space Administration (Nasa) test accidentally subjected a person to a near vacuum when his pressure suit began leaking in an atmospheric chamber, according to an account on a Nasa website. The person remained conscious for about 14 seconds and woke up as the chamber reached an altitude of 15,000 feet.
The subject’s last memory before passing out was the realization that the water on his tongue was boiling, according to Nasa. Water boils at lower temperatures as pressure decreases.
Siebold’s account of the motion of SpaceShipTwo before its breakup is consistent with other data sources reviewed in the probe, NTSB said.
The agency has completed its on-scene investigation and has stored pieces of the wreckage in case they need to be inspected again, it said.
Investigators are reviewing video from the spacecraft and the ground, telemetry data from the craft and other data sources recovered after the crash. Bloomberg