CRS-7 Investigation Update | Hacker News Reader

CRS-7 Investigation Update

spacex.com

29 pointslutorm18 comments

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.

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.

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.

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

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

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

What do you want? Self-flagellation? 20 hail mary's for repentance of their sins? They're being incredibly open and transparent in their investigation, Musk even went out of his way to make a comment about how they've become less vigilant in their approach to reliability than they should be. We should hope that all corporations were as forthright in their investigations of major fuckups. Just look at the average case out there in industry. You have people who are forced into resigning as scapegoats, you have attempts to shift the blame away from institutional or policy problems, and then you frequently have "fixes" which are nothing more than bandaids with no significant sweeping changes to address the underlying root cause of the problem (in this case, SpaceX's reliance on the stated specs of parts from a supplier).

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.

They were using a large number of small struts, a few hundred per rocket. The problem with redundancy through quantity is that occasionally one of those many redundant parts will fail in an interesting way, like happened here, and cause that one in a million cascade. The trick is finding just the right amount of redundancy for the task at hand. Sometimes that's a few strong pieces, sometimes it's a lot of little pieces.

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.

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.

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.

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.

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.

i see what you did there

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...

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.

How so? 2017 is plenty far out to work out the bugs in Falcon 9, and this failure won't impact Dragon 2 development at all.

What's ambitious is when they say they plan to complete their original 2015 launch manifest in 2015. That made me sit up and take notice.

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