Spacecraft brake may have torn it apart in seconds at sound’s speed4 min read . Updated: 04 Nov 2014, 09:38 PM IST
The system on SpaceShipTwo's tail moved into position after a pilot unlocked the brake before he was supposed to, says US NTSB
Washington: The air rushing past Virgin Galactic Ltd. SpaceShipTwo’s braking system may have torn the spacecraft apart seconds after launch as the ship traveled at the speed of sound.
The system on SpaceShipTwo’s tail, designed to slow the craft’s reentry into Earth’s atmosphere, moved into position after a pilot unlocked the brake before he was supposed to, according to the US National Transportation Safety Board.
“There would be a sudden, massive increase in drag on the aircraft," Alexander Smits, a professor of mechanical and aerospace engineering at Princeton University in New Jersey, said in an interview. “That obviously could lead to structural failure."
The 31 October accident raises questions about pilot performance and the ship’s design, though investigators cautioned that it will take as long as a year to find the cause. A project of billionaire Richard Branson, Virgin Galactic had targeted a 2015 debut for commercial space tourism.
“We are all determined to understand the cause of the accident and to learn all we can," the company said in e-mailed statement on Tuesday.
The brake system, known as a “feather," began to deploy about 10 seconds after SpaceShipTwo’s engine fired and the craft exceeded the speed of sound, acting NTSB chairman Christopher Hart said on Monday at a briefing in Mojave, California.
Hart said the flight lasted only 15 seconds after the spacecraft was dropped from the mothership that carried it to about 45,000 feet (13,700 meters).
While pilots are supposed to leave that braking system locked until the craft reaches a speed of Mach 1.4 in thinner air, it was unlocked earlier when the plane reached Mach 1, or the speed of sound, Hart said in an earlier interview. The sequence of events was verified by telemetry data as well as video from a camera in the cockpit, he said.
While Smits and Noel Clemens, an aerospace engineering professor at the University of Texas in Austin, said a full analysis of the aerodynamic forces would need to be conducted before establishing it triggered the breakup, they agreed deployment of the system in heavier air would add stress to the spacecraft.
“Just my intuition, that’s going to be quite a jolt," Clemens said in an interview.
Test co-pilot Michael Alsbury was killed when SpaceShipTwo broke apart above the California desert. Peter Siebold, director of flight operations at Scaled Composites LLC, which built the craft, parachuted to the ground and was hospitalized, according to a statement by the company.
The feather isn’t supposed to be activated until the spacecraft reaches its highest altitude. Pilots unlock it at lower altitudes to ensure it is functioning properly, Hart said.
A second switch must be moved to activate the braking system and it wasn’t touched by the pilots, he said at a 2 November briefing. Without the lock to hold it in place, air pressure rushing over the tail caused it to activate, the NTSB said.
Alsbury moved the handle into the unlock position, according to the NTSB. Siebold, who remains hospitalized, hasn’t been interviewed yet.
Twin booms on the tail of the spacecraft are made to rotate upward — like the feathers on a badminton shuttlecock — when the pilots want to slow and stabilize the ship as it comes down to Earth.
Debris from the ship has been found as far as 35 miles (56 kilometers) from the main wreckage, he said.
The rocket fired normally and SpaceShipTwo’s fuel tanks and its engine show no signs of failure, according to Hart.
If a failure of the feathering device is identified as a cause of the breakup, that is easier to fix than some other issues, such as a balky rocket motor, said John McGraw, a former deputy safety director at the Federal Aviation Administration, in an interview.
There are numerous precedents in aircraft design for preventing pilots from accidentally deploying systems at times when they may compromise the plane, McGraw said.
“Those are relatively straightforward and could be easily put in, in my opinion, in a follow-on design," he said.
SpaceShipTwo was designed to make the first stage of its flight to the fringes of space while slung beneath a carrier plane, the WhiteKnightTwo. Virgin used WhiteKnightTwo to take the spacecraft to almost 50,000 feet (15,000 meters). From there, the rocket-powered craft was to climb to 360,000 feet, or 68 miles, letting passengers experience weightlessness and dark skies, and view the curvature of the Earth.
Branson said last month that almost 800 would-be passengers have signed up for a $250,000 ride on the spacecraft.
Scaled Composites, which manufactured the carrier plane and employed both test pilots, is a unit of Northrop Grumman Corp.
Virgin Galactic — backed by Abu Dhabi-based Aabar Investments PJS — says it’s still on track to become the world’s first commercial spaceline, having accepted more than $80 million in deposits from a clientele that includes some of the world’s highest net-worth individuals. Bloomberg