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We Know What Happened in the SpaceShipTwo Crash, Just Not Why

Investigators have a pretty good idea what happened in the Virgin Galactic crash but not why, exactly. That difference is very important.

by Ryan Faith
Nov 3 2014, 10:25pm

Photo via AP/Ringo H.W. Chiu

The crash of Virgin Galactic's SpaceShipTwo, a suborbital tourist spacecraft, on Friday turned a grim week for the space community into a downright ugly one. Just days after Tuesday's explosion of a cargo mission to the International Space Station, the crash of the VSS Enterprise (the SpaceShipTwo test vehicle) reminded us that even getting to the edge of space can be a formidable task.

The test flight, the first with a new propellant, was an important step on the way to starting paid rides (reportedly within a year). But just seconds after the VSS Enterprise was dropped apart and turned its engines on, it experienced an "in-flight anomaly" and broke apart, ultimately killing co-pilot, Mark Alsbury and seriously injuring pilot Peter Siebold.

In the hours after the crash a great deal of speculation centered on the performance of the propellant in its first flight test. A new fuel was being introduced because the previous one produced too much vibration at full throttle, threatening to shake the ship apart. The substitute propellant was supposed to provide a cleaner burn, correcting the vibration problem and providing a bit more power.

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Some initial public observations supported this theory. The accident occurred shortly after SpaceShipTwo separated from its mothership, which is when the engine is usually ignited. Furthermore, the change was being managed entirely by Virgin Galactic and the maker of SpaceShipTwo, the Spaceship Company, companies that have rather less experience with rocket engines, instead of the original engine manufacturer, the Sierra Nevada Corporation.

Speculation was further fueled by rumors about pressures being put on Virgin Galactic by a major investor. Supposedly, Abu Dhabi-based Aabar Investments had demanded that Virgin carry out a full-power test flight by the end of 2014 and if Virgin wasn't able to deliver they would risk losing funding. Virgin Galactic had strenuously denied these rumors before the accident.

Nonetheless, these rumors gained further credence from claims by author Joel Glenn Brenner, who has been closely following the development of SpaceShipTwo. In an interview on CNN shortly after the accident, she alleged that the management of Virgin Galactic had been too ambitious, pushing testing and development beyond the dictates of engineering and safety.

The investigation of the SpaceShipTwo crash is being led by the federal National Transportation Safety Board (NTSB), a group that is routinely involved in transportation accident investigations, including space disasters. Because space tourism is regulated under the auspices of the Federal Aviation Administration, rather than NASA or a government agency, for the first time the NTSB is taking the lead on the space-related investigation, rather than a supporting role.

Fortunately for the accident investigators, this was a test flight, so the vehicle was very well instrumented, documented, and observed, greatly simplifying the task of figuring out what happened. Indeed, during a press conference on Sunday, Christopher Hart, acting chairman of the NTSB, explained what tore the ship apart.

SpaceShipTwo uses a novel "feathering" design to help it shed speed during its descent from 68 miles (110 km). During feathering, the back half of the vehicle flips up at a 90-degree angle to the fuselage of the aircraft. This converts the entire wing area into a break. Normally, this configuration isn't used unless the ship is going at Mach 1.4 and higher. But that soon after ignition, the vehicle is moving at or slightly above the speed of sound.

Normally, feathering involves two commands from the cockpit. First, someone unlocks the feathering configuration. Then a second command is sent to actually execute the transition. It's basically like a car door: first you unlock the door, then you pull on the handle to open it.

Based on telemetry and in-cockpit video, investigators were able to see the pilot unlock the feathering configuration. However, the video shows that the pilots did not initiate the transition, but telemetry data shows that the ship started to shift into feathered mode. In other words, just after the door was unlocked it just flew open on its own.

So just a couple days after the crash, the acting NTSB chairman was able to explain what happened. He also repeatedly said that we don't know what happened and that it will take a long time to figure out what happened.

More technically, Hart described that the "uncommanded" change in flight configuration as a "finding of fact" not a "finding of cause". In other words, those in the know have a pretty good idea what happened but not why, exactly. That difference is important.

In the immediate aftermath of the crash, Sir Richard Branson, Virgin Galactic's owner, said that they would not push on blindly with the program, but: "If it is a clear-cut cause and one that can be fixed, then I hope it will be back on track in about four to six months' time." This might suggest that they have an idea about what may have caused the accident.

But for the NTSB, their investigation must go deeper, perhaps a year or more. There's a certain part of an accident investigation when the people there start channeling an especially inquisitive and precocious child. Every answer is always met with the question "Why?" Why did the tail of the craft shift up without command? Why was the unlock command given just after release from the mothership? Was investor pressure forcing too ambitious a test schedule? Was management ignoring steps to ensure proper safety? So on and so forth.

This is because often the NTSB prefers to go beyond stopping this accident from happening again, but preventing this general category of accident from happening again. So it's not just enough to know what went wrong, but what series of events led to the problem and how each item in that series can be prevented in future.

On one hand, this kind of process can be a good tool for chasing down all the engineering and technical elements. Even so, some of the problems are ultimately unsolvable because they get down to organizational behavior and the inherent shortcomings of humans and their institutions. Recommendations that boil down to "don't ever make mistakes" are recommendations that will be violated sooner or later.

Since it's not possible to make spaceflight (or much of anything else) 100 percent safe, it's inevitable that, sooner or later, there will be another accident. As tragic and as much negative attention as this accident has generated, it's hard to imagine that a hypothetical crash involving other prospective SpaceShipTwo passengers from Stephen Hawking to Justin Bieber wouldn't vastly magnify the chatter and speculation over the inherent risks of spaceflight. 

A lot of managing any public fatal accident is knowing how to respond personally and collectively. The death of 39-year-old test pilot Mark Alsbury is an awful loss to friends and family. But as with astronaut deaths from the Apollo 1 fire through to the Space Shuttles Challenger and Columbia, VSS Enterprise and its crew are also showing us the way forward in understanding, accepting, and managing the risks of daring to defy the "surly bonds of Earth."

Follow Ryan Faith on Twitter: @Operation_Ryan