
NTSB: SpaceShipTwo broke apart when “feathering” activated early - lisper
http://arstechnica.com/science/2014/11/ntsb-spaceshiptwo-broke-apart-when-feathering-activated-early/
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clickbyclick
As terrible as it is to write this, (while still really early and I'm far from
a NTSB expert), but if you had to pin a failure event on human or design,
you'd be better to have it rest on human cause.

Resolution could then be practiced or automated out of existence, versus
structural design that could take years to resolve.

RIP Michael Alsbury.

~~~
lisper
I don't see any way this could be anything other than a design problem. The
engine can't be throttled, so there are no circumstances under which you'd
want to feather during the burn. So there should have been, at the very least,
an interlock to make it impossible. Either there was no such interlock, or it
failed. One way or the other, I can't see how the root cause could end up
being pilot error.

~~~
hga
There are tradeoffs here. Added complexity ... if the interlock fails to
unlock when it's supposed to, you have a fatal "anomaly" on reentry.

What's going to determine its state? Could that get confused in emergency
situations where feathering is an option worth trying?

In the end, if you're going to have real pilots, it's going to be very _very_
hard not to allow them to make mistakes which will destroy the craft.

~~~
toomuchtodo
> In the end, if you're going to have real pilots, it's going to be very very
> hard not to allow them to make mistakes which will destroy the craft.

Perhaps the solution is to not have pilots, and live with the loss of craft
when its piloted autonomously and software hits an edge case.

There is precedent for aircraft that can't be flown without computer
assistance/control:
[http://en.wikipedia.org/wiki/Northrop_Grumman_B-2_Spirit](http://en.wikipedia.org/wiki/Northrop_Grumman_B-2_Spirit)

~~~
hga
Indeed.

A better example might be the the Mercury Project, which made 17 unmanned test
flights before attempting to put a man into suborbital tests, and a few more
before into orbit.

As for "can't be flowing without computer assistance", I think the F-16 was
the first production plane of ours, in the '70s
([https://en.wikipedia.org/wiki/General_Dynamics_F-16_Fighting...](https://en.wikipedia.org/wiki/General_Dynamics_F-16_Fighting_Falcon#Negative_stability_and_fly-
by-wire)). Airbus's A320 the first airliner in the early '80s, albeit with
some mechanical backup (in a fighter you have the option of ejecting):
[https://en.wikipedia.org/wiki/Fly-by-wire](https://en.wikipedia.org/wiki/Fly-
by-wire)

There's also the relaxed stability concept
([https://en.wikipedia.org/wiki/Relaxed_stability](https://en.wikipedia.org/wiki/Relaxed_stability)),
which I assume is what you were referring to with the reference to the B-2,
and per that Wikipedia article the MD-11 airliner employs it (although back
when it was flying passengers if I'd had _any_ option at all I'd have avoided
flying in one, for many reasons I and others don't consider it to be a safe
plane. And its parent DC-10 was the least safe wide body airliner in its days;
as some people said before, and probably still now that Airbus is on the
scene, "If it ain't Boeing, I ain't going").

As I noted in another posting, the new fuel used in this flight meant new
patterns of vibration, some of which can only be found/tested in free flight.
Sometimes you can get away with that, e.g. the Space Shuttle was never
unmanned, then again the first flights had only two crew and they had SR-71
survival systems (ejection seats and intense environmental suits).

