Posted on 11/03/2014 7:48:16 AM PST by Jack Hydrazine
Virgin Galactic’s SpaceShipTwo rocket plane disintegrated in mid-air after two tail stabilizers prematurely extended, federal investigators said Sunday, a discovery that could shift the focus of the probe into Friday’s fatal crash away from the craft’s rocket motor.
But the National Transportation Safety Board’s acting chairman Christopher Hart cautioned against jumping to conclusions.
“What I’m about to say is a statement of fact and not a statement of cause,” Hart said. “We are a long way from finding cause. We still have months and months of investigation to do, and there’s a lot that we don’t know. We have extensive data sources to go through.”
An analysis of telemetry and video recorded aboard the doomed space plane has revealed SpaceShipTwo’s novel braking system deployed earlier than designed.
The rocket plane’s rear-mounted feathering system is supposed to extend before the ship descends back into the atmosphere from space, slowing SpaceShipTwo’s speed and putting the craft into a belly-down position during re-entry.
But SpaceShipTwo’s twin tail booms rotated upward seconds after it fired a hybrid rocket motor following a drop from Virgin Galactic’s WhiteKnightTwo carrier plane 50,000 feet above California’s Mojave Desert.
The NTSB is leading the investigation into Friday’s crash, and Hart said Sunday that ShipShipTwo’s co-pilot moved a lever inside the space plane’s cockpit to unlock the tail feathers, which are normally pointed toward the rear of the vehicle when it flies under rocket power.
The co-pilot on Friday’s flight — 39-year-old Michael Alsbury — died in the accident. Alsbury’s co-workers at Scaled Composites, builder of SpaceShipTwo, have established a memorial fund.
Pilot Peter Siebold, 43, was able to get free of the space plane and parachute to the ground. He was hospitalized with serious injuries.
The rocket’s hybrid rocket motor, consuming a mix of nitrous oxide and a plastic-based solid fuel mix, ignited a few seconds after SpaceShipTwo’s release from the carrier aircraft. Friday’s test flight marked the first time the rocket motor was used on SpaceShipTwo since Virgin Galactic switched from a rubber-based to a plastic-based fuel.
“About nine seconds after the engine ignited, the telemetry data showed us that the feather parameters changed from lock to unlock,” Hart said.
According to Hart, a camera mounted inside SpaceShipTwo’s cockpit showed Alsbury move a handle to unlock the feather system as the rocket plane passed Mach 1 — the speed of sound.
Such action on a SpaceShipTwo flight is not expected until the rocket plane reaches Mach 1.4, Hart told reporters in a press conference Sunday night in Mojave, Calif.
“Normal launch procedures are that after the release, the ignition of the rocket and acceleration, that the feathering devices are not to be moved — the lock/unlock lever is not to be moved into the unlock position — until the acceleration up to Mach 1.4. Instead, as indicated, that occurred (at) approximately Mach 1.0,” Hart said.
The tail booms extended after they were unlocked, even though they were not commanded to do so, Hart said. SpaceShipTwo’s pilots normally must unlock the feathers, then send a separate command to move the tail booms into position for descent.
“This was what we would call an uncommanded feather, which means the feather occurred without the feather lever being moved into the feather position,” Hart said.
“After it was unlocked, the feathers moved into the deployed position, and two seconds later we saw disintegration,” Hart said.
“Shortly after the feathering occurred, the telemtry data terminated and the video data terminated,” Hart said.
The video embedded below shows how SpaceShipTwo’s feathering system works from a camera attached to one of the ship’s tail booms on a previous flight.
The performance of SpaceShipTwo’s rocket motor, which was flying for the first time with a new type of propellant, was normal up until the extension of the rocket plane’s tail feathers, according to Hart.
Investigators combing the five-mile-long debris field have located SpaceShipTwo’s rocket motor and propellant tanks, which were found intact and show no sign of burn-through or breaching, according to Hart. Some of the rocket plane’s wreckage has been moved into hangars for examination.
Six video cameras and six data recorders on-board SpaceShipTwo will also help the investigation, Hart said, along with footage from the space plane’s carrier plane, ground-based imagers, and eyewitness interviews. Investigators also planned to interview Siebold, the surviving pilot.
When asked if Sunday’s revelation would put the focus of the investigation on pilot error, Hart said the NTSB is not ruling anything out.
“We are looking at a number of possibilities, including that possibility,” Hart said.
“I want to emphasize that we have not determined the cause,” Hart said. “I am not stating that this is the cause of this mishap. We have months and months of investigation to determine what the cause was. We’ll be looking at training issues, we’ll be looking at was there pressure to continue testing, we’ll be looking at safety culture. We’ll be looking at the design (and) the procedure. We’ve got many, many issues to look into much more extensively before we can determine the cause.
“There is much that we don’t know, and our investigation is far from over.”
Friday’s test flight was the next step to realize Virgin Galactic’s plans to start operational service with SpaceShipTwo by next spring, ferrying paying passengers to a speed three-and-a-half times the speed of sound at an altitude of more than 100 kilometers, or 62 miles, above Earth — the internationally-recognized boundary of space.
Passengers at that altitude could unstrap from their seats and float around the rocket plane’s six-person cabin for a few minutes before gliding back to the ground for landing on a runway.
Virgin Galactic issued a statement Sunday defending the company’s safety record and urging against speculation on the cause of Friday’s mishap.
“At Virgin Galactic, we are dedicated to opening the space frontier, while keeping safety as our ‘North Star’. This has guided every decision we have made over the past decade, and any suggestion to the contrary is categorically untrue,” the company said.
“We have the privilege to work with some of the best minds in the space industry, who have dedicated their lives to the development of technologies to enable the continued exploration of space,” the company said. “All of us at Virgin Galactic understand the importance of our mission and the significance of creating the first ever commercial spaceline. This is not a mission that anyone takes lightly.”
The company, founded by Virgin Group’s Richard Branson, said it would not comment on the investigation while the NTSB is doing its work.
“Now is not the time for speculation,” the company said. “Now is the time to focus on all those affected by this tragic accident and to work with the experts at the NTSB, to get to the bottom of what happened on that tragic day, and to learn from it so that we can move forward safely with this important mission.”
Interesting... possibly a systemic failure rather than engine.
Sounds like pilot error which must be unusual for a test pilot.
“Normal launch procedures are that after the release, the ignition of the rocket and acceleration, that the feathering devices are not to be moved — the lock/unlock lever is not to be moved into the unlock position — until the acceleration up to Mach 1.4. Instead, as indicated, that occurred (at) approximately Mach 1.0,” Hart said.
Question: At what speed are they supposed to unlock and at what speed deploy. The fact it was unlocked may not indicate pilot error. It may be a systems problem or in fact may be pilot error. We need to know the procedures for the flight.
He unlocked the tail feathers at Mach 1.0 which is a bad idea because it is right in the middle of the transonic region between sub-sonic and supersonic (Mach 0.8 to 1.2) which is very bumpy and unstable.
http://en.wikipedia.org/wiki/Transonic
“Severe instability can occur at transonic speeds. Shock waves move through the air at the speed of sound. When an object such as an aircraft also moves at the speed of sound, these shock waves build up in front of it to form a single, very large shock wave. During transonic flight, the plane must pass through this large shock wave, as well as contend with the instability caused by air moving faster than sound over parts of the wing and slower in other parts.
Transonic speeds can also occur at the tips of rotor blades of helicopters and aircraft. However, as this puts severe, unequal stresses on the rotor blade, it is avoided and may lead to dangerous accidents if it occurs. It is one of the limiting factors to the size of rotors, and also to the forward speeds of helicopters (as this speed is added to the forward-sweeping (leading) side of the rotor, thus possibly causing localized transonics).”
The tail feathers are supposed to be unlocked at Mach 1.4 which is out of the transonic region.
If the feathering system can be deployed at mach 1.4, why would it fail at the lower speed of mach 1.0? Lower altitude and denser air? Or is feathering only possible when the rocket engine is not burning?
Sounds like a combination of pilot error and system failure. Unlocking should not have led to deployment, but it apparently did. Of course, these reports could be subject to revision, but the engine and fuel are no longer the prime suspects.
Sounds like cockpiit video shows the co-pilot unlocking the tail at just over Mach, and not at the prescribed airspeed. Lots of weird stuff happens when you are transonic. An unfortunate loss of machine and more importantly human life.
See post #5.
You answered my question. Another thought is did they have a faulty mach number indicated and think they were at mach 1.4 and then unlocked the braking system.
““This was what we would call an uncommanded feather, which means the feather occurred without the feather lever being moved into the feather position,” Hart said. “
Not a very well engineered product if it can perform such a significant event on its own.
They’ll probably design into the software a lockout for this problem for future spacecraft.
Interesting.
Always worried that one of those “flutter down” wings would malfunction during a reentry. Never thought it would be during a climb.
Damn. This sounds like an operation where it should take a very intentional effort by the crew to override control system safeguards. We’ll see what the investigation turns up.
It might have been the turbulent, transonic shock waves that moved the tail feathers, not necessarily inputs from the pilots or the flight computer.
Wouldn’t that have shown up in wind tunnel testing ?
The atmosphere is much, much thicker at 50,000 feet than at 62.5 miles so deploying the flutter down wings at apogee isn’t that stressful.
Burt Rutan never wind tunnel tested his Space Ship 1 to the dismay of many NASA aerospace engineers. That is because the CFD and virtual wind tunnel software is good enough to do the same as the real thing.
It is going to be difficult from media account exactly how bad unlocking the tail at that speed would be, from media sources. The main reason being that media sources always get things wrong. To find the truth one would need to know the planned flight profile, how that fits in with the events, etc.
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