News Virgin Galactic SpaceShipTwo accident during powered test flight

[garyw]

Interesting little snippet from a bigger article

The NTSB hasn't disclosed whether or not he was conscious and on his own oxygen system, or rendered unconscious by the rapid depressurization at high altitude. Presumably, he was unconscious and injured, and his parachute deployed automatically at 10,000 feet. Siebold landed on the ground, where first responders found him shortly thereafter and then flew him to the hospital. (It's worth noting Siebold is the first person to successfully bail out of a firing rocketship. Investigators and aerospace engineers will undoubtedly study the specifics of his survival in the days to come.)

http://www.popsci.com/article/technology/whats-next-virgin-galactic?src=SOC&dom=tw

Would unlocking the feathering system that early in the flight actually be OK procedure wise, rather like arming the thrust reversers on an airliner prior to touchdown?

Depends, if unlocking it truly means unlocking it then I'd have to say no, otherwise it could rotate freely in the airstream and cause a tumble and breakup (which maybe is what happened).
From the sound of the rest of the article, an unlocked feathering system means that the tail booms are only electronically locked rather than physically locked (hand waving guess work from the wording)

On an Airbus it is impossible to arm the thrust reversers until the weight on wheels sensors are active.

 

[kamaz]

“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

This is interesting. To me, this can mean one of three things:

(1) The actuator was underpowered (to save mass), and the lock was relied on to prevent unwanted deployment earlier in flight. As a result, external forces have overpowered the actuator. This would mean pilot error, but also that the design is not foolproof.

(2) The actuator was strong enough, but it was overpowered/damaged due to engine behavior.

(3) A hardware or software fault has caused the actuator to move prematurely after the lock has been released.

 

[garyw]

Another one to add to the list

(4) The feathering mechanism moved due to the shockwave of passing through Mach-1 which lead to an uncommanded deployment due to the lever being moved to unlocked sooner than it should have been

 

[ISProgram]

I don't think a engine hard start has been confirmed yet. That ground observation of the engine doing multiple uncommanded ignitions before disintegration had been withdrawn. The guy later said he couldn't confirm what he saw.

Apologies, I seem to have forgotten who it was.

 

[boogabooga]

Perhaps the engine did cut-out, and for some reason that is why the co-pilot armed the feather, only or the engine to relight and shred the aircraft.

Speculation, but just pointing out the engine cut-off is not mutually exclusive to the armed feather.

 

[RisingFury]

#SpaceShipTwo PLEASE avoid any rush to judgment relating to pilot error. BOTH levers had to be moved to deploy booms. The second wasn't.

Source:
https://twitter.com/spacecom


Might just be "some guy on the internets saying so", so I don't usually like Twitter as a source. What do you think?


EDIT:

Also found this, same source:

Video in the cockpit shows that co-pilot Mike Alsbury moved one of the two levers needed to deploy the feathering system at Mach 1.

 

[ISProgram]

It's true. Alsbury was the one who unlocked the feathering mechanism, but another command is required to actually initiate the feathering configuration change. The actual feather deploy, as what happened in the anomaly, was entirely uncommanded from what we currently know. 2 seconds after that, the vehicle disintegrated.

There ARE two levers to deploy the feathers. Only the unlock lever was hit. Pilot error is possible, but not confirmed, at this point.

 

[Keatah]

Perhaps the engine did cut-out, and for some reason that is why the co-pilot armed the feather, only or the engine to relight and shred the aircraft.

Speculation, but just pointing out the engine cut-off is not mutually exclusive to the armed feather.

Yes. But why would you need to feather this early in the flight? Engine fail or not, wouldn't you just continue to glide?

 

[RisingFury]

So at this point we still have no idea what brought down SS2?

 

[C3PO]

So at this point we still have no idea what brought down SS2?

http://www.bbc.com/news/world-us-canada-29876154

The root cause is still unknown, but so far it looks like the booms went to 'shuttlecock mode' uncommanded. Any conclusions will have to wait until further investigations have been made.

 

[Andy44]

I can't imagine that having the engine running in feathered configuration would be a good thing, no matter which aerodynamic regime you're operating in...

 

[dbeachy1]

What I don't understand is why would SOP call for arming the booms for feathering during ascent at all, even at Mach 1.4 (vs. Mach 1.0)? Aren't the booms supposed to be feathered just after MECO?

 

[ISProgram]

What I don't understand is why would SOP call for arming the booms for feathering during ascent at all, even at Mach 1.4 (vs. Mach 1.0)? Aren't the booms supposed to be feathered just after MECO?

Presumably, the time Mach 1.4 is reached, SS2 has already gained altitude, where the air is subsequently thinner, and it is past the maximum aerodynamic loads on the ascent, so switching to a feather configuration is safe.

AFAIK, the booms are feathered at apogee, after a coast from MECO.

 

[pattersonlee]

If you watch the 3rd powered test video on Youtube, you see it all happens really fast from drop to fire to enginer cutoff. But then they coast for probably 10 seconds before feathering happens as they begin decent.

I also don't follow why you would arm the feathers during burn? Perhaps that Mach 1.4 reference implies actually coast phase?

Would they perhaps arm the feathers during burn in case the engine stops firing or has to be aborted during burn such that the feathers are already armed in the event they need to ditch the flight early?

 

[Thunder Chicken]

What I don't understand is why would SOP call for arming the booms for feathering during ascent at all, even at Mach 1.4 (vs. Mach 1.0)? Aren't the booms supposed to be feathered just after MECO?

The news quotes citing the Mach 1.4 business sounded like SS2 had to speed up to Mach 1.4 before feathering was magically safe. I didn't see the NTSB presentation but it sounds like the explanation got a little butchered.

The feathering is normally supposed to occur after apogee, at very high altitude. The aerodynamic loads at Mach 1.4 at 50,000 ft are much greater than when the SS2 achieves Mach 1.4 at much higher altitudes (100ks of feet) at re-entry. Why the booms were unlocked during powered flight (and whether that contributed to the accident) is a burning question right now.

The Mach number merely tells you how fast you are going relative to sound, which is dependent mostly on air temperature, not density. However, the aerodynamic loads on a vehicle are directly proportional to air density. Mach 1.4 coming down from 360,000 ft, aerodynamic loads are small because air density is low. Mach 1.4 at 50,000 ft, you are flying through Jello. Mis-configured vehicles can and will fly apart at those speeds and pressures.

Recent examples - Felix Baumgartner and Alan Eustace both exceeded Mach 1 at 100,000 ft wearing just pressure suits. However, there are (sadly) many examples of lower altitude ejections where crewmembers were killed by the aerodynamic loads at similar Mach numbers. Air is pretty thick stuff down here near sea level.

 

[Quick_Nick]

The fourth and final NTSB media briefing is in under two hours.
Edit: Starting now.

---------- Post added at 10:02 PM ---------- Previous post was at 08:23 PM ----------

https://twitter.com/NTSB/status/529482537291497472

---------- Post added at 10:21 PM ---------- Previous post was at 10:02 PM ----------

Timeline (seconds after 10:07)
19 release from White Knight
21 engine start
29 Mach 0.94
Feather unlocks during this time
31 Mach 1.02
Feather deploys during this time (details unclear from briefing)
34 End telemetry

Small parts are being found as far as 30-35 miles away from the larger parts.

The full investigation may take as much as 12 months, though may be expedited by the wealth of data on hand.

The pilot has not yet been interviewed because interviews are not yet recommended by the medical staff.

The 'flight card' specifically states do not unlock the feathers until Mach 1.4

It is not yet known if the pilots' indicators were accurate. Minor detail: It's a glass cockpit.

The pilot in the right seat unlocked the feathers. Details about the unlocking will be asked of the surviving pilot eventually. IMPORTANT: The NTSB chairman made a mistake in the previous briefing when he said that it was the copilot who unlocked the feathers. It is not clear if the person in the right seat is the pilot or copilot and whether that is the person who survived or the one who did not.

Edit: That "important" bit has been reverted by NTSB. In other words, the right seat was indeed the copilot, who unlocked the feathering mechanism and also died in the accident.

 

[Hielor]

(It's worth noting Siebold is the first person to successfully bail out of a firing rocketship. Investigators and aerospace engineers will undoubtedly study the specifics of his survival in the days to come.)

I've been thinking about this particular point a lot today. Does it count as a "successful bail out" when the ship simply disintegrates around you?

All that engineering work that went into Apollo-style LES towers that (thankfully) never needed to be used, and the first successful ejection required no real planning at all other than equipping the pilots with parachutes that automatically open.

"A parachute? But how am I supposed to get out of the ship and use it?" - pilot
"100% of the previous times that astronauts have needed a parachute, they didn't have to worry about exiting on their own..." - engineer

Sorry...just a bit of morbid humor...

 

[Urwumpe]

All that engineering work that went into Apollo-style LES towers that (thankfully) never needed to be used

*cough*Soyuz*cough*

 

[Artlav]

All that engineering work that went into Apollo-style LES towers that (thankfully) never needed to be used

It saved lives once.
Only thing they had to worry about in the capsule is to switch off the CVR for modesty's sake.

 

[C3PO]

It saved lives once.

I thought Soyuz 18a also used the escape system, but it was after it was jettisoned. That separation was made using the Soyuz main engine.