- Parabolic Arc
- June 2, 2023
A Niche in Time: One Chute
by Douglas Messier
Pete Siebold and Mike Alsbury heard the sound of hooks disengaging and felt a sharp jolt as SpaceShipTwo was released from its WhiteKnightTwo mother ship. Relieved of a giant weight, WhiteKnightTwo shot upward as the spacecraft plunged toward the desert floor.
“Fire,” Siebold said as the shadow of one of WhiteKnightTwo’s wings passed across the cabin.
“Arm,” Alsbury responded. “Fire.”
The pilots were pushed back into their seats as SpaceShipTwo’s nylon-nitrous oxide hybrid engine ignited behind them, sending the ship soaring skyward on a pillar of flames.
“Good light,” Siebold said, his voice straining against the rapid acceleration. He had both hands on the control stick as he made lateral corrections to SpaceShipTwo’s left and right rolls.
“Yeehaw,” Siebold exclaimed.
“Point eight [mach],” Alsbury announced.
The call was to alert Siebold to prepare for the pitch bobble SpaceShipTwo would experience as it approached Mach 1. The ship’s wings and tails don’t shock up at the same time; as a result, SpaceShipTwo would pitch nose up and then nose down in quick succession. Siebold would need to trim the vehicle to maintain control of the ship.
Alsbury placed his left hand on the Feather Locks Handles and leaned forward, preparing for a key task he would soon have to perform. SpaceShipTwo’s unique feather system consisted of movable tail booms that reconfigured the spacecraft into the shape of a shuttlecock to provide a gentle reentry into the Earth’s atmosphere.
Alsbury’s job was to release the locks that held the tail booms in place during powered ascent to make sure they did unlock properly. If they didn’t, Alsbury and Siebold would have to quickly abort the flight to save the ship and their own lives. SpaceShipTwo could likely not survive a reentry in a feather down configuration.
“Unlocking,” Albury said, pulling the Feather Locks Handles all the way down. The Feather Not Locked light illuminated on the instrument panel.
Task accomplished – but too early. Alsbury was supposed to unlock the feather when the ship hit Mach 1.4, not as it was going transonic. At Mach 1.4, the movable tail booms would remain in place. At Mach 0.8, aerodynamic forces would cause the feather to deploy with catastrophic results. SpaceShipTwo had three seconds to fly.
The tail booms began to move as the ship began a slight but noticeable roll to the right as it approached the speed of sound.
“Pitch up,” Siebold said, his body straining against the ship’s movement.
“Pitch up,” Alsbury repeated.
Siebold suspected something was wrong. The pitch up was much higher and more violent than he expected. He and Alsbury grunted heavily as the g forces increased.
Behind the pilots, SpaceShipTwo was beginning to break up as the tail booms reconfigured the ship for reentry with the ship soaring skyward and its engine still burning. Cracks appeared on the outboard root fairings. Silvery Kapton foil that covered the inside of the tail booms stripped away as the upper feather flap skin and root fairings failed. A skin panel from the bottom of the vehicle then peeled away.
SpaceShipTwo’s right boom began to rotate inboard toward the center line of the vehicle. Then a crack appeared from the feather’s hinge line into the fuselage near SpaceShipTwo’s tail cone as the aft fuselage began to separate.
SpaceshipTwo started to pitching up wildly, subjecting Siebold and Alsbury to g forces much higher than the 5 to 6 g’s for which they had trained. They could do nothing to save the ship as their heads moved toward their laps.
SpaceShipTwo’s giant tank of nitrous oxide began to vent a large white cloud into the air as the ship began to pitch over violently on its back.
Siebold heard a loud bang followed by the sound of “paper fluttering in the wind” as the cabin depressurized. At the rear of SpaceShipTwo the engine’s case throat nozzle assembly and twin tail booms then separated, falling away from the disintegrating ship.
Alsbury was killed as the ship broke up. Thrown free of the cockpit, Siebold passed out in the thin air, regained consciousness long enough to separate himself from his seat, and then passed out again until he was jolted awake when his parachute deployed automatically at 14,000 feet. He suffered serious injuries but survived.
Richard Branson looked wan and shaken as he stood before the television cameras at the Mojave Air and Space Port almost 24 hours after the crash of SpaceShipTwo. He had flown all the previous day in his private jet from his home in the British Virgin Islands to personally take charge of the worst crisis to engulf his fledgling suborbital space tourism company, Virgin Galactic.
“Is it fair to say that the dream lives on?” a reporter asked.
“It’s fair to say that all 400 engineers who work here, and I think most people in the world, would love to see the dream living on,” Branson said. “As I say that we owe it to our test pilots to find out exactly what went wrong, and once we’ve found out what went wrong, if we can overcome it, we’ll make absolutely certain that the dream lives on.”
Branson a handful of additional questions before heading off to meet with those 400 engineers. Many had watched the fatal accident from the flight line, others had watched horrified as it unfold on the monitors at mission control. They were still in shock and probably wondering how much longer they would still have jobs. Branson’s carefully couched answer probably wasn’t very reassuring.
If Sir Richard had decided to throw in the towel, few people would have blamed him. SpaceShipTwo had consumed 10 years and hundreds of millions of dollars without getting even remotely close to space. Now the program’s only spaceship, which had taken years to build, lay in thousands of pieces across 35 miles of the Mojave Desert. Nobody yet knew how much time and money would be required to get another one into the air.
More seriously, Branson’s space effort had claimed yet another life. Alsbury wasn’t the first to die in the SpaceShipTwo program, he was the fourth. How many more lives would Branson be willing to risk to fulfill his dream of flying into space?
A Dream, Delayed
It had all started so optimistically a decade earlier. Branson had been in Mojave on Oct. 4, 2004, when Burt Rutan’s SpaceShipOne won the $10 million Ansari X Prize for making two crewed flights into suborbital space within two weeks.
The prize, dreamed up by Peter Diamandis, was intended to kick start a new age of spaceflight by proving that a private company could send humans to space without any government support. Space would no longer be limited to a small group of highly-training astronauts; instead, it would be open to anyone rich enough to afford a ticket from a growing list of providers.
Microsoft co-founder Paul Allen had spent $28 million to back Rutan’s entry in the competition. But, he wasn’t interested in commercializing SpaceShipOne. So, Branson licensed the technology and commissioned Rutan to build a much larger vehicle for Virgin Galactic that would carry paying passengers on suborbital joyrides.
SpaceShipTwo would be twice the size of its predecessor with room for two pilots and six passengers who would float freely around the cabin gazing down on Earth from more than 100 km up. Branson set ticket prices at $200,000 and confidently predicted that flights would begin as early as 2007. The plan was to fly 500 people within the first year, doubling the number of individuals who had flown to space since Yuri Gagarin became the first in 1961.
It wasn’t long before Branson’s dream of spaceflight turned into a nightmare. By late July 2007, the program was lagging far behind the billionaire’s optimistic projections, within neither WhiteKnightTwo nor SpaceShipTwo even close to flying. And then the schedule fell even further behind as tragedy struck.
On a typically hot mid-summer day in Mojave, three Scaled engineers were killed and three others hospitalized when a nitrous oxide tank suddenly exploded. They had been conducting a cold flow test – sending nitrous oxide through a new valve without fuel present – when the tank exploded without warning. Not believing that nitrous oxide could explode on its own, the test conductors had not cleared the stand. Ten people were standing around it when the tank blew.
The reaction to the accident was much different from what it was seven years later when SpaceShipTwo crashed. Branson didn’t drop everything he was doing and rush to Mojave to take charge and express his condolences before the world’s media. Virgin Galactic issued the briefest of press releases that referred to the explosion as an industrial accident and did not include the names of the dead and injured.
Diamandis insisted had the tragedy was an industrial accident that had nothing to do with the safety of the spacecraft. It was a ridiculous claim given that the oxidizer they thought couldn’t explode on its own had just done so, and it might do so again if the wrong conditions occurred. But, that became the narrative of the accident. Virgin Galactic continued to advertise the hybrid engine as safe and benign as Scaled resumed working on the two vehicles.
Rutan and Branson rolled out WhiteKnightTwo one year after the accident. It flew for the first time five months later just before Christmas. SpaceShipTwo was rolled out amid much fanfare on Dec. 7, 2009. Ten months later, WhiteKnightTwo carried SpaceShipTwo aloft for the first of 30 glide flights.
While SpaceShipTwo glided through the Mojave skies, engineers on the ground continued to struggle with its hybrid engine. The motor had worked well enough for the much smaller SpaceShipOne. But, scaling the engine up for its larger successor resulted in vibrations and oscillations that threatened to tear the ship apart. The pilots dared not fire it in flight for longer than 30 seconds.
SpaceShipTwo’s first powered occurred on April 29, 2013, more than 8.5 years after Branson announced the development of the vehicle. The ship burned its engine for 16 seconds and broke the sound barrier before gliding to a safe landing. Two more powered flights followed in September 2013 and January 2014, with burns limited to 20 seconds apiece due to the engine limitations. The highest the space plane got was 71,000 feet (21.6 km), well short of the 328,084-foot (100 km) boundary of space.
By the time of the fourth powered flight, engineers had worked out the problems with the engine. Siebold and Alsbury had been aiming for an engine burn of 38 seconds and an altitude of 135,000 to 138,000 feet (41.1 to 42 km). A couple of more flights with longer engine burns would have followed to complete the flight test program if SpaceShipTwo had not crashed.
At that point, Virgin Galactic would have taken possession of SpaceShipTwo from Scaled Composites and moved the vehicle down to Spaceport America in New Mexico to begin commercial operations. Branson planned to be on the first operational flight, which had been scheduled for no later than March 2015.
But, now those plans lay in ruins across a broad stretch of the Mojave Desert. And Branson had to decide whether how many more lives and how much more of his fortune to risk on his dream of flying to space.
Reasons Not to Fly
So, how did Branson’s predicament after the loss of SpaceShipTwo compare with the situations faced after the other two fatal accidents we’ve examine in this series, the Hindenburg in 1937 and the space shuttle Columbia in 2003? In many ways, Branson’s space tourism venture was in far worse shape than these other two programs.
After the Columbia disaster, NASA had three space shuttles remaining in its fleet, providing it with enormous capability. The space agency also had a lot of experience, having launched shuttles 113 times with two failures over 22 years. NASA could also trace its human spaceflight history back 42 years to 1961. During that time, it had twice before recovered from fatal accidents (Apollo 1 and Challenger) that had killed 10 astronauts. In short, the agency was well equipped to fix the problem that had brought down Columbia and resume flights.
The Zeppelin Company was in a much more precarious situation in 1937. The Hindenburg disaster destroyed half of its Zeppelin fleet. The Graf Zeppelin was immediately retired because it couldn’t be easily converted to use helium. So, the company was left with nothing to fly until it could complete one of the Hindenburg’s two sister ships and convince the United States to export helium for the program.
The Hindenburg was the first catastrophic loss of one of the company’s passenger vehicles in the 37 years since Count Ferdinand von Zeppelin had flown his first rigid airship. So, officials were confident they could safely resume transatlantic service if they obtain helium from the American government. The U.S. refusal to export the gas effectively ended the German rigid airship program.
In the long run, German Zeppelins were probably headed for extinction given the rapid improvements in airplanes of the time. Their extinction resulted from a lack of a safer gas to fly with, not from any lack of confidence or expertise on the part of the people who flew them.
By contrast, Virgin Galactic had little flight experience to draw upon and no real record of success in suborbital spaceflight. It had flown SpaceShipTwo only four times under power, with the fourth flight ending catastrophically. The vehicle had never gotten anywhere close to space. And after the accident, it had no other completed ships to fly. it would be a while one under construction in the company’s hangar would be completed.
Its predecessor, SpaceShipOne, had flown only six times under power, including three flights into space, before it was retired. However, SpaceShipOne was a much smaller ship with a significantly different design. Its flight test program had been short, and it had never carried a single passenger aloft. The experience gained from the earlier program had been invaluable, but SpaceShipTwo was a new vehicle that had still not proven itself in space.
It was also a first-generation suborbital space tourism vehicle. Unlike the Boeing and Airbus airplanes flown by Branson’s Virgin airlines, SpaceShipTwo had not the benefitted of the experience gained from generations of previous suborbital vehicles with millions of hours flown. Flying it would be a lot riskier than boarding a Boeing 777 for a transatlantic flight.
The Federal Aviation Administration (FAA) would not certify the spacecraft as the agency does for commercial airliners. In fact, the FAA was even prohibited from writing mandatory safety regulations to protect passengers and their pilots unless there was an accident or close call. That provision, which had been set to expire in 2015, was extended despite the loss of SpaceShipTwo.
At the time of the accident, Virgin Galactic had about 700 customers signed up to fly on SpaceShipTwo. Officials now say the number is around 650. Assuming full ships with six passengers aboard, Virgin Galactic would need 109 flights just to fly out its current manifest. The figure doesn’t include flight tests and missions filled with microgravity experiments. That’s a lot of launches to make without expecting at least one catastrophic failure, possibly involving prominent wealthy passengers.
Finally, there were costs to consider. It seemed very unlikely that Virgin Galactic would ever make any real money from flying passengers to space. Hundreds of millions of dollars had been poured into the program already; even more would be required to continue it.
And SpaceShipTwo would be an expensive vehicle to operate. Despite its appearance, it was not fully reusable. The hybrid rocket motor needed to be replaced after each flight. Even with tickets costly $250,000, it would probably be difficult to make a profit.
Ultimately, Branson pushed aside all these concerns and decided to continue with the program. He confidently (and erroneously) predicted that a second SpaceShipTwo then under construction would be completed within five or six months. Sources on the ground in Mojave were more accurate when they said it could take about two years.
Branson has given a number of reasons over the past three years for continuing the program. They appear to fall into three broad areas.
The Employees Wanted to Continue. Branson said that after meeting with employees in Mojave after the crash, he came away with the clear message that they wanted to finish what they started. And they believed that they could do so safely.
This explanation has always been a bit problematic. During his 22-hour visit to the High Desert, Branson was meeting with people in a deep state of shock who were not necessarily thinking very clearly and were worried about their jobs. Not necessarily the best basis upon which to make such a momentous decision.
At Least it Wasn’t the Engine. Branson appeared greatly relieved that the ship wasn’t brought down by the hybrid engine that everyone had been so worried about. Instead, it was a pilot error that had nothing to do with the overall safety of the ship.
This is not entirely correct. Alsbury indeed made a mistake, but the feather had been badly designed from a safety standpoint. Scaled Composites officials had assumed that a well-trained pilot would never make such a mistake, so there was little in place to prevent it.
The system had to be redesigned to prevent a premature unlocking of the feather system during ascent. It also needs to be tested in flight to make sure that in addressing one problem, engineers hadn’t created another risk that prove fatal.
SpaceShipTwo is also using the same engine with the volatile nitrous oxide as the oxidizer. Rocket engines have a tendency to explode suddenly without warning.
NGUNS (Never Give Up, Never Surrender): Branson really, really wants to fly into space and open up that domain to thousands of other people who would not otherwise get the change.
In the end, the dream remained alive. Whether that will prove to be a good or a bad decision remains to be seen.
Introduction: Human Flight Through the Ages
Part 1: Behemoths of the Sky
Part 2: “One of the worst catastrophes in the world”
Part 3: “Lock the doors”
Part 4: One Chute
Part 5: First Flight
5 responses to “A Niche in Time: One Chute”
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Excellent narrative – that engine could be dangerous in future flights.
I’m pretty sure SpaceX will be giving away free rides to Alpha Centauri before they toss a single customer into sub-orbit.
Doug, what did you make of the debate during the 2015-07-28 NTSB meeting regarding their official “probable cause” of the accident?
Recall that 90 minutes into the meeting, after discussing other aspects of the report, staff recommended that the probable cause be reported as, “the copilot’s premature unlocking of the SpaceShipTwo (SS2) feather system as a result of time pressure and vibration and loads that he had not recently experienced, which led to the uncommanded extension of the feather during the transonic region and resulted in the aerodynamic overload and in-flight breakup of the SS2 vehicle. Contributing to the accident was Scaled Composite’s failure to consider the possibility that the effects of a single human error could cause the feather to extend uncommitted and fully inform pilots about the risk of unlocking the system early.”
That sounded reasonable to me, but Chairman Christopher Hart suggest that it should instead read, “Scaled Composites’ failure to protect against the possibility that a single human error in an environment involving time pressure, vibration, and unusual G loads could result in premature unlocking of the feather in SpaceShipTwo at a time when such action could result in uncommanded feather extension and cause aerodynamic overload and in-flight breakup of the vehicle.”
Board Member Robert Sumwalt objected, arguing that this omitted the triggering event (the copilot’s action), without which the accident would not have happened. At that point the board recessed for a private discussion, and when they resumed half an hour later they adopted a compromise: “The National Transportation Safety Board determines that the probable cause of this accident was Scaled Composites’ failure to consider and protect against the possibility that a single human error could result in a catastrophic hazard to the SpaceShipTwo vehicle. This failure set the stage for the copilot’s premature unlocking of the feather system as a result of time pressure and vibration and loads that he had not recently experienced, which led to uncommanded feather extension and the subsequent aerodynamic overload and in-flight breakup of the vehicle.”
Note that while it states that SC’s design failure set the stage for the copilot’s action, that action was still not explicitly stated as being part of the probable cause. I’ve heard criticism that the NTSB in the past has been too quick to blame some accidents on pilot error, but in this case they seemed to be bending over backwards to avoid stating that there was any pilot error.
Transcript with YouTube video link are at: http://shitelonsays.com/tra…
Probable cause discussion starts at 1:30:04
I think some of this has to do with the FAA AST’s actions. The office approved the experimental permit in 2012. The hazard analysis Scaled did was reviewed by a FAA official without a great deal of experience. Other safety experts with experience in the shuttle program said the hazard analysis didn’t meet requirements. Instead of making Scaled redo it, FAA AST renewed the permit in 2013 and granted a waiver on pilot and software errors. Then there was a pilot error that destroyed the ship.
There was nothing in place to prevent premature deployment. No challenge-response. The shuttle safety guys knew that astronauts make mistakes all the time. The shuttle was designed so that no single action could bring it down during ascent.