Virgin Galatic Spaceship Two down in the Mojave.

[khorton]

Reports so far indicate that feather unlock was selected outside of design parameters.
Looks like it might have been an oops moment. And sophisticated systems just should not allow oops moments.

The problem is that you must be 100% sure you can feather the tail for reentry, or you will die. If there are too many safety interlocks that can prevent the tail from feathering, you run the risk of those interlocks failing to unlock the tail when you need it later.

The best design is probably a simple, reliable mechanical lock, and redundant feather actuators, so you can feather the tail after any single failure in the unfeather system. A mechanical unlock system relies on the crew leaving it locked until it is safe to be unlocked (i.e. after the end of the rocket motor burn and the EAS is less than XXX).

[thcrozier]

Mojave

Thinking about going out there and hearing the latest local speculation at the bar

[tdracer]

Dynamic pressure is greatest at transonic flight (Max Q), then reduces as the aircraft goes supersonic and accelerates past Mach 1.2.

Actually dynamic pressure continues to increase as the speed increases, while dynamic pressure decreases with increasing altitude (less density). The speed at which Max Q occurs is a function of the Mach/altitude profile that is being flown.
That being said, the center of pressure relationships move around in the transonic range, which can result in unwanted movement of the control surfaces when traveling transonic.

[ExSp33db1rd]

Giving the crew the ability to UNLOCK in an emergency and outside of the normal envelope is, surely, different from giving them the ability to UNLOCK by mistake and / or inadvertently.

Of course I know nothing about what happened in this case, but - "there's nowt so queer as folk" ( Yorkshire saying) and I know of an aircraft accident where the crew selected reverse thrust in the air on short finals, secure in the knowledge that the engines wouldn't go into reverse until the undercarriage 'squat' switch was activated when the wheels touched the ground. Guess what happened ? Many died.

There's nowt so queer as folk, and anything operated by humans is subject to human error, whereas with automatic /computer systems nothing can go wrong, go wrong, go wrong.

At this stage it doesn't really matter what went wrong, so long as those who need to know eventually find out.

[SAMPUBLIUS]

NTSB video explanation

BBC News - Virgin Galactic crash: Descent system 'deployed early'

...Christopher Hart, NTSB: "A couple of seconds after the move from lock to unlock, all the data stopped"


Did 'feathering device' cause crash? Watch
Unique 'feathering' system
US official explains early findings Watch

A safety device on the Virgin Galactic spacecraft that crashed on Friday, killing a test pilot, had been deployed early, US investigators have said.

[Mad (Flt) Scientist]

To add to ExSp33db1rd's point, it's also practically impossible to design to eliminate human error, because humans must execute the design. The most you can do is move the potential for error around. And if we ever did somehiow have a design which wasn't done by humans, we'd just have substituted AI-error for human error in all likelihood.

Indeed, overdesigning systems "to be safe" is rarely very successful either. Sometimes you have to trust to the training and skill of someone suitably qualified. (And I'm not saying they were not; even the best pilot in the world can however make a mistake. See, "error, human")

[thcrozier]

What actually unlocks?

Hart's comments in SAMPUBLIUS' link above suggest that the locking mechanism might have the secondary function of strengthening the structure.

Hart's bio: https://www.ntsb.gov/about/bio_hart.html

[gums]

Feather control mechanics

Anyone have a description of the feather activation and control?

Do they "streamline" according to aero loads? Think some shock absorbers and no powered actuactors other than letting them go "free"?

Are they controlled by hydraulic or electric or pneumatic?

Sheesh, imagine the suckers allowed to be moved by aero loads even if the hydraulic/electric actuators normally used at low "q" and 200,000 feet are not a player.

So far, NTSB says the data stopped 2 seconds after..... But is this just the video? Can't imagine the flight data recorders stopped.

[etudiant]

Would an experimental type such as this even have a separate FDR?
Presumably the aircraft is wired pretty extensively just for the flight testing.

[thcrozier]

If I had to guess, I'd say it was loaded with them.

[MrDK]

@gums
So far, NTSB says the data stopped 2 seconds after..... But is this just the video? Can't imagine the flight data recorders stopped.

That sure makes the case for keeping video out of the cockpit ... experimental as well as commercial.

IMHO, I cannot for the life of me understand why video (for the purpose of incident investigation) is not on all commercial aircrafts.
In lack of better, ANY video system is better than none.

[peekay4]

IMHO, I cannot for the life of me understand why video (for the purpose of incident investigation) is not on all commercial aircrafts.
In lack of better, ANY video system is better than none.

Pilot privacy, fear of enforcement action (FAA & law enforcement), and possibility of damaging evidence in civil lawsuits in case of a mishaps.

Little remembered now, but before voice recorders were mandated in cockpits, there was a huge backlash from pilot unions. Concessions were made and early CVRs were limited to 30 minutes (now expanded to 2 hours), no recordings can be made public (only transcripts), only NTSB investigators may access the recordings, and pilots can erase recordings once back on the ground.

The NTSB, UK AAIB, French BEA, etc., have all called for cockpit video or image recorders to be made mandatory for commercial flights, but given very strong union opposition I doubt it will happen anytime soon.

[WhatsaLizad?]

"IMHO, I cannot for the life of me understand why video (for the purpose of incident investigation) is not on all commercial aircrafts.
In lack of better, ANY video system is better than none."

I vote for video recording in my cockpit only if every meeting of Airline Managers and Senior Managers/CEO's are recorded as well and any decisons made regarding expenses for training, policies and procedures and the lack thereof, and the statements during such meetings are transcribed and signed by the attendees afterwards. Same goes for the US FAA when meetings deal with the costs of regulatory changes and enforcement. The statements of airline CEO's should mesh in nicely with the legions of YouTube junkies just salivating at the thought of a pilot getting smeared on the aft cockpit GoPro lens just before the recording ceases due to impact.

Let me know when that board room recording happens.

[Derfred]

IMHO, I cannot for the life of me understand why video (for the purpose of incident investigation) is not on all commercial aircrafts.

How do you get all the jurisdictions around the world to respect the "(for the purpose of incident investigation)" bit. That's the problem.

[deptrai]

Anyone have a description of the feather activation and control?

here: http://www.pprune.org/tech-log/55054...ml#post8726231

The 2nd column of the 3rd page (numbered 56) of http://www.boulder.swri.edu/suborbit...Spacecraft.pdf
states that:

Two main pneumatic 625-psi actuators with a 9.5-in bore and 31-in stroke, change the position of the feather ...

[pchapman]

Just for reference, to wrap one's head around how a vehicle like SS2 might work, here's info on Space Ship ONE. I don't know what systems and methods may have changed when scaling up to Space Ship Two -- with so much more mass to deal with. Info is from "Space Ship One - An Illustrated History", a ~2011 book by Dan Linehan.


Drop at 47,000'
Speed ??
C of G is aft with full fuel
3-4 G accel with rocket
Pull up to avoid overspeeding, Vne about 260 kts EAS.

[As an example, 250 kts EAS at 45,000' is almost exactly Mach 1.0]

Use electric trims after 8-9 seconds of burn due to high stick pressures (slow control by trims only)
Back to control stick once in very low density atmosphere
Maximum it achieved at engine shutdown was Mach 3.1 at 213,000 ft after 84 sec burn.
[That gives only 22 kts EAS - using a calculator on aerospaceweb. Many online calculators don't model the desired altitudes]

Apogee at about 3 min after engine start, 328,000 ft plus at best.
3.5 min weightless
Reaction Control System (pneumatic) at high altitude

Feathering done shortly before apogee. (Do it early in case of issues to deal with)

Feathering has redundant locks.
Feathering takes 13-14 seconds [A video for a prior SS2 flight shows much more rapid movement]
Feathering is by pneumatics, dual redundant interconnected systems.
Feather when under 10 knots EAS. [Low!]

Fastest speed reached (going down) was Mach 3.25, below 160 kts EAS.
5.5 G max on reentry (above 5 for 10 sec)
Max air temp ~ 1200F but with low density, heating rate is low.
(Heat resistant coating on nose and wings needed for boost phase only, not reentry but provides added margin).

Terminal velocity when feathered, if at low altitude, would be about 60 kts with its low wing loading of 12 ft/lb^2.

Un-feather once subsonic and below 1.2g on reentry.


As for SS2 planning to feather at M1.4, what kind of EAS might we be talking about?
If achieved at 100,000 ft, it would be 97 kts EAS.
If achieved at 200,000 ft, it would be 12 kts EAS.
The altitude certainly matters...

Edit:
Another bit of background as to prior achievements, and speeds and altitudes: The January 2014 flight achieved the following in an online article:

The SS2 rocket engine fired for 20 seconds, pushing the suborbital spacecraft to an altitude of 71,000 ft (18 km) and a top speed over Mach 1.4, both of which were new records for SS2. The Reaction Control System, feather re-entry system, and a thermal protection coating were successfully tested during the flight.

Not sure what that implies for feathering -- under 71k and Mach 1.4 would have a high EAS. If the numbers are right, one would expect feathering at a much lower Mach number.

[robdean]

Article which includes prescribed crew interaction regarding feather procedure plus Pete Siebold's primary injury apparently being to his shoulder

Two pilots who were close friends, now tied together by one fatal flight - The Washington Post

[deptrai]

Media, after first spreading unsubstantiated rumours about explosions, now seem to be speculating about pilot error. Methinks this is one of many possibilities, and it can not be ruled out, yet its a premature to jump to conclusions. The NTSB will be more responsible.

Unsurprisingly, it seems someone already pointed out the feathering system as a potential complication in this 4 year old article (it's somewhat "colorful"): "the feathered reentry system is another mechanical system that must absolutely work well for a safe return of the craft, but like all kind of mechanical system can have some malfunctions"

::: Why the suborbital space tourism is TOO DANGEROUS :::

Some previously brought up the question of certification in this thread. I really do wonder according to what ruleset this is going to be certified for commercial passenger transport, and what the risk analysis will look like, but there doesn't seem to be too much information about that? Nevertheless, its commendable that scaled and vg didnt aggressively push their initital schedule.

[Satellite_Driver]

Ah, that article is by Gaetano Marano, who pops up on space discussion boards all over the place regularly spouting his theories of how spaceflight ought to be done, apparently quite unconstrained by any knowledge of physics, engineering, propellant chemistry or any of the other relevant technical fields...

[deptrai]

The graphical design of his website and liberal use of various colors made me suspect he might not be the most credible source. Sadly, he may not have been completely wrong.