Spaceshiptwo Has Exploded

[CraigD]

On its 3rd powered test flight, the 1st with a new polymer solid fuel motor, Virgin Atlantic's SpaceShipTwo rocket plane, the 8-person successor to 2-passenger SpaceShipOne that won the Ansari X Prize in 2003, has blown up, killing one and badly injuring the other test pilot.

 

One of may news stories: http://www.express.co.uk/news/world/529988/Virgin-Galactic-spaceship-two-CRASHES-test-flight

 

I'm sad for the loss of this beautiful machine and the dead pilot, and hope the surviving one lives. Riding rockets is a daring, dangerous business.

[Deepwater6]

I agree Craig, it's been a terrible week for space flight all around. The loss of Orbital Science's resupply ship was bad, although thankfully no loss of life. For those of us hoping this country's private sector can get mankind's transitions into space moving faster it's been quite a setback.

 

Whenever I see events like this and especially the resupply rocket the other night I think of the first astronauts. The early ones like the Mercury and Apollo programs. Those who observed the experimental aches and pains that engineers went through and still climbed on top of those sticks of dynamite. They saw rocket after rocket collapse and explode or spin out of control and still wanted to get in the seat.

 

I heard a DJ on the radio on my way home from work today say that "none of those rich people and stars are going to want to go on these trips now". I hope that's not the case and whatever the issue is can be safely and quickly resolved. The cause needs all the positive PR we can afford it. As well as it being a hobby of mine I think it imperative we make every effort to get the human race off this planet as soon as possible.

 

http://www.space.com/

[CraigD]

While Cygnus CRS Orb-3's failure was a commercial loss and PR setback, it’s technical failure is most likely due to mistakes made reconditioning the 40+ year-old AJ26-62/NK-33 first stage motors of its Antares rocket. Also, all of its components were non-reusable, and it was unmanned, so the loss is really only of the satellites it was meant to launch, and the ISS supplies it was to deliver.

 

VSS Enterprise, on the other hand, was one of only 2 completely reusable SpaceShipTwo rocket planes that have been built of a planned 5. Its RocketMotorTwo hybrid solid fuel motor is of a kind flown only in SpaceShipOne & Two line of rocket planes, and is designed to be much safer than conventional turbo-pump fuel supplied rocket motors while not sacrificing too much performance to reach space (though not yet orbit Earth). As of 2014, its solid fuel was changed from HTPB, a common solid rocket fuel, to a polyamide plastic that should be higher performance and more even-burning. The new motor and fuel has been ground-fired successfully 4 times. Today was its first flight test.

 

Though I hope and expect that Virgin Galactic will continue the SpaceShipTwo program, I can’t help but think that, for a rocket motor that’s intrinsically lower-performance than a conventional liquid fuel motor, but designed to be much safer, this catastrophic failure is catastrophic to the technology’s hope of not just putting a completely reusable spacecraft into space (which SpaceShipOne did in 2003) but putting one in orbit. Perhaps it would be best if Virgin Galactic and their family of private spaceflight businesses abandoned hybrid rocket motors and focused instead on a high-safety liquid fuel motor, such as a pressure-fed design, or a novel pump design, such as the helicopter to orbit scheme first championed by Gary Hudson of the now-defunct Rotary Rocket Company, or variations, in which liquid fuel and oxidizer is pumped by a large, relatively low-speed centrifugal pump that’s a large external component of the motor.

[Deepwater6]

As the article states there will be other private and subsidized companies that will go through these set backs. The British companies Skylon program is some time out yet, but it is right out of a sci-fi movie. It's a single stage space plane capable of some 200 flights hopefully. It would use a combined cycle air breathing propulsion system. It's design would have the plane take off with hydrogen then switch over to liquid oxygen when it achieves the proper altitude. It then uses the (LOX) for its trip into space. But like I said its a long way off. It needs a lot more R-n-D and a lot more money, but if it comes to fruition it would be wild.

 

 

http://www.bbc.com/news/science-environment-29858964

[CraigD]

Though the details aren’t complete, the main cause of VSS Enterprise crash appears to have been found.

 

It wasn’t an explosion of its rocket motor as earlier guessed, but an apparent pilot error leading to the craft deploying its rotating tail and flaps into its reentry configuration a few seconds into its powered flight, at a speed of about Mach 1.0. With its motor at or near full thrust in this configuration, I imagine the ship would have tried to spin like a pinwheel, which tore it apart.

 

This LA Times story is the clearest I’ve read so far, explaining that a recovered video recording of one of the pilots incorrect pulled a lever that unlocks, but shouldn’t deploy the ship’s “tailfeathers” tail and flap system (a 2nd lever, which was not pulled, deploys them).

 

I gather (I’ve not seen a detailed plan for the test flight) what should have happened is the rocket plane accelerate to a speed close to that or reentry, rocket shutdown, then the tailfeathers deploy into the reentry position, allowing a simulation of the reentry, then return to normal flight position for a glider descent and landing.

 

This should be good news for the SpaceShipTwo project, as it moves blame from the motor and airframe design, to pilot error, which surely, in light of this deadly accident, will never be repeated.

[Buffy]

...a recovered video recording of one of the pilots incorrect pulled a lever that unlocks, but shouldn’t deploy the ship’s “tailfeathers” tail and flap system (a 2nd lever, which was not pulled, deploys them).

 

This should be good news for the SpaceShipTwo project, as it moves blame from the motor and airframe design, to pilot error, which surely, in light of this deadly accident, will never be repeated.

 

I have a problem with the "pilot error" excuse. Sounds to me like a User Interface Design Flaw: yah, the co-pilot should have pulled the other switch, but the existence of switches that can cause catastrophic failures is why such switches are often designed to have covers, or confirm sequences, or are completely locked out during inappropriate mission phases (e.g. ejector seats designed not to fire while on the ground).

 

 

I emphasize that virtually every engineering calculation is ultimately a failure calculation, because without a failure criterion against which to measure the calculated result, it is a meaningless number, :phones:

Buffy

[Deepwater6]

Interesting article Craig, has anyone heard how high the craft was when the trouble started?

[CraigD]

A frustrating difference between engineering info on Virgin Galactic’s spacecraft and NASA’s is that VG’s information isn’t public, so it’s difficult (and being by default trade secret, possibly illegal) to get in much detail.

 

From the various news stories and NTSB statements, I gather that 2 levers must be pulled to surely have a SpaceShipTwo’s “tailfeathers” tail and trailing wing edge flip up into its reenty configuration. Neither should be pulled when the motor is throttled up. The cabin videos show that only one of the levers was pulled. It appears this was enough for the tailfeathers to flip up, causing it to be torn apart by the strong aerodynamic forces at about Mach 1.0.

 

I have a problem with the "pilot error" excuse. Sounds to me like a User Interface Design Flaw: yah, the co-pilot should have pulled the other switch, but the existence of switches that can cause catastrophic failures is why such switches are often designed to have covers, or confirm sequences, or are completely locked out during inappropriate mission phases (e.g. ejector seats designed not to fire while on the ground).

I get the impression the tailfeathers levers are not easy-to-move switches, but connect to mechanical linkages and take a fair amount of force to move.

 

Covers and locks can reduce the chance of catastrophy, but can also increase it, if they interfere with or cause the controls to fail, so I’m reluctant to second-guess SpaceShipTwo’s designers.

 

Still, an interlock to prevent the tailfeathers from being flipped up when the motor throttle is open strikes me as a pretty foolproof feature that would have prevented the VSS Enterprise crash.

 

Aircraft of all sorts are inherently at risk due to pilot error, for which sometimes the best approach is to keep the design as simple as possible, and for the pilot to just not make a killer error.

 

From articles like this post-crash Wired one, I think this is the approach Scaled Composites took with SpaceShipOne and is taking with SpaceShipTwo.

 

SS2s have no flight control computers – though the pilots train in a simulator. Landing one of these high-speed, low-glide ratio gliders takes an elite-skilled pilot. They’re unforgiving – as the VSS Enterprise crash shows, errors that would be recoverable in more ordinary aircraft are not in a SS2.

[CraigD]

Interesting article Craig, has anyone heard how high the craft was when the trouble started?

About 50,000 feet.

[Buffy]

Here's an interesting fact about the above discussion of the switch in a great article in PopSci:

 

At Mach 1, the aircraft would have been lower and in much denser air than at Mach 1.4. Releasing the feathers at higher speed would have been safe because the air would be much thinner. The press conference didn't reveal what the flight plan was to be—how long the engine burn was to last, and at what stage pilots would begin and conclude the feathering. Another important detail is that Alsbury merely unlocked the feathers; neither he nor Siebold actually attempted to move them. The feather movement was "uncommanded," in aviation parlance.

 

The premature unlocking of the feathering mechanism might have contributed to the tragic turn of events, since the thick air at that speed could have forced the feather to move. But Hart stressed that this is not a statement of cause, just fact. 

 

-- Source: What's Next for Virgin Galactic, Eric Adams, Popular Science, 11/3/2014

 

There's more on this, and you should read the whole thing.

 

 

No one wants to learn by mistakes, but we cannot learn enough from successes to go beyond the state of the art, :phones:

Buffy

[Deepwater6]

http://www.space.com/27651-space-tourism-virgin-galactic-spaceship-crash.html

 

Has anyone heard or read any update on the specifics of the accident?

 

The attached article describes how some feel that too many wheels are in motion to slow space tourism. Hope so.

[CraigD]

This 7 Nov 2013 Guardian article looks like an accurate and detailed report of what happened, which appears to me now to be well known.

 

A synopsis:

A “full” SS2 flight runs its rocket motor for about 60 seconds.

 

Previous powered flight tests have run it for about 20 s. The 31 Oct mission was to run the engine for more than 20 s.

 

After engine shutdown, for test and full flights, SS2 is to coast to its maximum altitude.

 

Shortly after reaching max altitude, the wing booms (“tailfeathers” in earlier discussions) were to be flipped up, turning SS2 into its belly-first configuration. After falling back to around 50,000 feet altitude, they would be retracted, returning SS3 into its glider configuration.

 

The two levers: One unlocks two hooks that hold down the tail booms. Another controls hydraulic pistons that extend or retract them

 

10:07:21 AM PDT: SS2’s motor starts

10:07:30: Mike Alsbury pushes the unlock lever. He appears to immediately recognize his mistake, and tries to shut down the engine.

10:07:34: The booms begin to deploy, and “all data is lost”, which I take to mean that the cockpit camera and other telemetry and recording stops sending and/or recording due to the same violent forces that broke up the ship.

 

The writers of the Guardian article appears to believe that the tail booms were unlocked prior to motor shutdown in past flights, but at higher speeds of about Mach 1.2, vs the near Mach 1 of the 31 Oct flight, so the hydraulic cylinders were able to hold the booms down.

 

There are still lots of missing information and guesswork in this article, but it’s the best I’ve seen so far.

[Deepwater6]

http://www.cnn.com/video/data/2.0/video/us/2014/11/06/erin-pkg-simon-virgin-galactic-spaceshiptwo-crash.cnn-ap.html

Incredible how the pilot survived this crash. At that altitude, without a pressure suit, and at that speed. Is it possible he blacked out and then regained consciousness? Lots of unknowns about how he did it in this video, buts its just amazing he did it at all.

[CraigD]

It’s interesting that, like many news outlets, blogs, and forums, the CNN story describes the pilot seats in SpaceShipTwo as “ejection seats”. Except in the sense that when the ship disintegrated around the pilots, they were ejected still strapped into their seats, they’re not – they have no system to intentionally shoot them out of the ship. To escape from an intact SS2, a pilot would need to get to and open the cabin door, open it, and jump out.

 

My guess as to why Peter Siebold survived (with surprisingly minor injuries) and Michael Alsbury didn’t, is that Alsbury was knocked unconscious or killed when he was ejected from the disintegrating ship, so couldn’t unstrap himself from his seat and open his parachute. Siebold is reported to have open his chute at about 17,000 feet.

 

Siebold’s has a place in history as the first person to survive a spacecraft crash, using a parachute or any other means.

 

Though pilots of the ca 1960 X-15 spaceplane wore parachutes, none survived a midair breakup.

 

The X-15 is similar in many ways to SpaceShipOne and SpaceShipTwo. Both are launched at about 14 km altitude from a larger “mother” airplane (A B-52 in the case of the F-15, the specially designed WhiteKnightOne for SpaceShipOne). The X-15 reached an altitude of 107.8 km in 1963. SpaceshipOne reached 112.014 km in 2004.

 

One X-15 pilot, Michael J Adams, was killed in a midair breakup an X-15, in 1967. Unlike SpaceShipOne and Two, the X-15 had no special aerodynamics to stabilize it during is descent, but instead had small reaction control jets. Adams failed to keep his X-15 straight using these jets, entering a spin at over Mach 5 and 70 km altitude. He recovered from the spin at about 36 km, but was unable to recover from a 45deg Mach 4.7 dive, breaking up at about Mach 3.9 and 20 km.

 

The X-15 was a more difficult plane to fly than the SpaceShipNs.