

CRS-7 Investigation Update - lutorm
http://www.spacex.com/news/2015/07/20/crs-7-investigation-update

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OrwellianChild
Just popping in to say that it is refreshing to see how open and transparent
SpaceX attempts to be with this kind of development... It illustrates the
competence with which the company is addressing the rocket failure in terms of
diagnosis, rectification, and impacts on their future launch timeline. I'd
expect this from an internal memo to affected employees or a private message
to SpaceX's clients, but we the public get it too and for free. No expose.
Just disclosure.

~~~
pvg
What do you mean? The write-up is hardly dispassionate or neutral -
"Everything about our technology is great and kept working despite the fact
our rocket blew up. We collect so much telemetry! Our engineers work so very
hard! An nigh-unbreakable strut somehow broke and our rocket blew up. We will
no longer use this nigh-unbreakable strut."

It's great they're publicly releasing their preliminary findings, but they're
also practically patting themselves on the back while doing it. It reads more
smarmy than refreshing.

~~~
megrimlock
A suggestion. Your comment reads as though you wrote your own press release to
then take issue with. Mis-quoting them with hyperbole for emphasis is less
persuasive than directly addressing what they actually wrote.

~~~
pvg
Your suggestion reads as though you read your own version of my comment to
then be condescending to.

~~~
ecnahc515
Your replies are really not adding to this discussion. The sarcasm isn't
particularly necessary.

~~~
pvg
There was neither sarcasm nor discussion so I struggle with the meaning (or
necessity!) of your reply.

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DenisM
_The strut that we believe failed was designed and material certified to
handle 10,000 lbs of force, but failed at 2,000 lbs, a five-fold difference._
[...] _these struts have been used on all previous Falcon 9 flights and are
certified to withstand well beyond the expected loads during flight_ [...]

Huh. So the strut was way over-engineered for the load and still failed,
likely due to a hidden mechanical flaw. Would that make more sense to use a
large number of smaller struts then, such that a failure of one or two would
be less problematic? You can even test the design for it - make sure the
rocket is still working when certain number of struts fail. The assembly cost
would certainly rise, but the current design seems to be not sufficiently
redundant.

~~~
CamperBob2
My guess is that anything much bigger than a 4-40 hex nut that comes loose
inside a LOX tank is enough to ruin everybody's day.

~~~
TheOtherHobbes
Overengineering by a factor of 5 seems decently conservative.

If you add triple-redundancy to all the mechanical elements you build a rocket
that probably can't fly - which is certainly very safe, but maybe not so very
useful.

I'd guess the problem has more to do with insufficient testing than
insufficient design. It's likely the initial batch was easily up to spec, then
there was little or no testing of further batches.

Easy mistake, IMO. If you think about the number of critical components, re-
testing everything before every flight would be a huge and very expensive job.

I wonder if SpaceX are going to do less business with the strut supplier in
future.

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userbinator
Does anyone else find this style of verbiage a bit too wordy? "the helium
system integrity was breached" and "was no longer able to maintain its
structural integrity" is overdoing it, IMHO.

I think there is a more succinct and straightforward, if not completely
accurate, summary of events: A strut broke and smashed into the helium system,
and released helium pressure blew the tank apart.

~~~
Mithaldu
Good question!

If you're talking to average people, yes, your way of wording it would be more
efficient.

However in certain domains accuracy is key, so one tries to communicate with
as much detail as possible. In order to achieve this without being hyper-
verbose, one uses an established set of vocabulary, whose subtle and detailed
meaning is well-understood and common in that industry. That may make it sound
strange to outsiders, but minimizes the risk for misunderstandings and lack of
clarity amongst peers.

~~~
69_years_and
So reading between the lines - the bracket holding the helium tank (inside the
oxygen tank) broke, the helium tank ripped away from it's plumbing (pressure
lines and valve(s)) and the high pressure gas contained in it escaped into the
oxygen tank causing it to burst.

The SpaceX description is a little vague about the plumbing, I'd like to know
more about that - is it an on off vale that opens and closes under command of
the flight computer to maintain pressure, or is it a modulated valve that is
controlled by a PID loop or the like.

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zekevermillion
It's amazing what they've accomplished so far, and I hate to criticize
anything this awesome from the comfort of my armchair. But it does seem rather
ambitious to keep the 2017 date for manned flight...

~~~
Sanddancer
If the analysis continues to point to this flawed component being the cause,
then 2017 isn't overly ambitious at all. They've already planned to stop using
those components, and all the telemetry shows that every other piece of the
rocket continued to work fine. Notably, stage one continued to fire, and the
capsule remained intact until it went over the horizon and out of radio
contact. While it would have been beneficial to have better failure recovery
on these cargo-only capsules, the future capsules have already been built to
handle an event like this, and one of the steps in certifying it is to
simulate an abort a lot like the one that happened here. So it's not really
all that ambitious, once all the stuff scheduled to happen happens.

