The failure earlier was structural (defective bracket) not system per se. The
failure chain after the bracket broke led to a tank breaking but there aren't
many parts on a rocket you can survivably break loose during flight.
Sent from my iPhone
On Nov 2, 2016, at 7:57 AM, Craig Fink <webegood@xxxxxxxxx> wrote:
On Sat, Oct 29, 2016 at 2:15 PM, David Weinshenker <daze39@xxxxxxxxxxxxx>
wrote:
I suspect the thermal gradient across the tank wall didn't behave
according to their original expectations. Maybe they put in too
much heat while the helium tank was only partially submerged in
LOX, and either cooked the top of it or created a sharp temperature
gradient that made a damaging local stress concentration.
http://www.floridatoday.com/story/tech/science/space/2016/07/29/nasa-orders-second-spacex-crew-mission-iss/87672158/
Phil McAlister, head of commercial spaceflight at NASA headquarters, last
week told the NASA Advisory Council that the companies' schedules are
“optimistic but achievable.”
McAlister also said that NASA continues to assess SpaceX's new method for
fueling upgraded Falcon 9 rockets just a half-hour before launch. That
timeline would put astronauts on top of the rocket while fuel is loaded, a
potentially hazardous operation
....
“We are getting more comfortable with it, but we are not yet ready to say
we’re good,” McAlister said of SpaceX's procedure. “We’re still working
through that.”
Back in August NASA was getting comfortable with the late fueling but was
still working through it with SpaceX. I can imagine that one of NASA's
concerns would be the amount of time the astronauts had to sit in their seat
ready for an instant abort. SpaceX may have been addressing this concern with
shortening the loading time as much as possible, changing operational
procedures to load as much in parallel and load faster. All speculation, but
one wonders if NASA may have been a contributing factor.
The 2015 loss of the ISS Dragon in flight was due to the same subsystem
during flight. SpaceX recovered from this flight incident by doing
essentially nothing to the He subsystem hardware, blaming it on the failure
of a part that didn't meet specifications, changing vendors and a little more
testing.
In 2016 same subsystem fails again during loading, SpaceX characterizes it as
a completely separate event from the 2015 incident. The apparent fix is again
to essentially do nothing to the He subsystem hardware, blaming it on
operational procedures. Fix the procedures and move on.
It does make me wonder if the two incidents might actually be related.
--
Craig Fink
WeBeGood@xxxxxxxxx
