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SpaceX's Starship Mk1 just blew off its bulkhead in a pressurization accident

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Re: SpaceX's Starship Mk1 just blew off its bulkhead in a pressurization accident

#81

Post by perspective1 »

blackguardx wrote: post #67
senectus1 wrote: post #56

Earlier quoted context omitted.

> When their entire business depends on very carefully managing their PR You really think this? My perception is that their PR is fairly blunt and upfront. while they may not tell you everything they dont seem to be trying to "spin" anything

There was a public accusation that a competitor shot one of their rockets with a rifle, causing it to fail. If they had reasonable suspicion of that, they should have kept it to themselves and the FBI/law enforcement. What really happened is that a strut failed due to faulty batch of material that wasn't tested before fabrication. I'm not sure if this was deliberate spin, but it seemed pretty shady to me at the time.

I don't think SpaceX ever made that accusation. At the time (2016) Musk said the cause of failure was unknown. He was asked directly about sabotage on Twitter and replied that they didn't rule that out. As far as I can tell, the first time anyone at SpaceX talked about the rifle hypothesis was Musk simply saying SpaceX looked into it (the implication being it wasn't sabotage).

WaPro: http://archive.is/j8zjc

Re: SpaceX's Starship Mk1 just blew off its bulkhead in a pressurization accident

#82

Post by bdamm »

WalterBright wrote: post #75
zionic wrote: post #14

Earlier quoted context omitted.

Looks like the welds holding the bulkhead on failed. For those who aren't keeping up with this the failure was on the Mk1 prototype. Mk2 has been build nearly in parallel with Mk1 and will take over early flight testing (20km hop). Elon has tweeted that this team will jump to Mk3 instead of trying to repair Mk1.

Airliners rarely use welds because they're very hard to make with consistent high quality and are also very hard to inspect. Instead, they're riveted together.

There are airplanes constructed with chemical bonding as well, such as the Boeing 787 Dreamliner and my personal favorite, the AA-1, released in 1967! Welded airplanes are practically nonexistent, but there are techniques other than riveting. And with the rise in popularity of composite materials, we're likely to see fewer and fewer rivets on airplanes.

Re: SpaceX's Starship Mk1 just blew off its bulkhead in a pressurization accident

#84

Post by larnmar »

lmilcin wrote: post #26
hsnewman wrote: post #6

And that's why they are testing it.

Depends on what kind of test that was supposed to be. If they pumped it until it explodes it would be a kind of test (also called experiment) where it makes sense. If you design something with a margin of safety, then pump it to working pressure and it blows, then it means you made a mistake. If you made a mistake it shows you don't know what is necessary to design a rocket (yet). Seriously, they don't build skyscrap…

Seems like the difference between unit tests and integration tests.

Re: SpaceX's Starship Mk1 just blew off its bulkhead in a pressurization accident

#85

Post by namirez »

taneq wrote: post #80
NamTaf wrote: post #71

Oh dear! It looks like someone accidentally divided by 2 for the cylindrical hoop stresses, forgetting that they're not the same equation as for spherical stresses. :) Less facetiously, a thin-walled cylinder's stress is a function of pressure, radius and thickness with the equation: sigma = P*r/t whereas for a sphere (including the spherical end caps on a cylindrical pressure vessel), it follows the equation: sigma…

That's why you take your maximum design stress and double it, right? /s

I don't know what happened here, but if I remember correctly, in rockets, safety factor is typically smaller than 2 or the design would be too heavy. But I guess the safety factor for pressure testing is 4.

Source: article 6.8.2.2 of this document; https://www.faa.gov/about/office_org/headquarters_offices/as...

Edit: I didn't see the "/s" before writing this comment.

Re: SpaceX's Starship Mk1 just blew off its bulkhead in a pressurization accident

#86

Post by garmaine »

sfifs wrote: post #59
Retric wrote: post #29

Earlier quoted context omitted.

Rockets are designed to have a vastly lower margin of safety. If they never fail in testing that’s a sign you’re over engineering it and sacrificing cargo capacity, which is a bad thing. That said, these failures should be uncommon.

That's basically been the conventional thinking about rocketry historically - scientists and engineers looked at the tyranny of the rocket equation and choose to maximize payload per launch because they were largely funded by government or quasi government "cost plus" types of contracts. The design philosophy of working close to margins comes from this thinking. SpaceX's greatest contribution has been to look at rock…

Doesn't matter. If you take the conservative assumptions that go into manufacturing, say, a car and apply those to a rocket, you'll get something that won't even lift off the ground, much less make orbit.

Any rocket HAS to be very close to the limits of what materials used allow, and not the +50% margin of error you routinely seen in other fields. What you say about SpaceX is true, but only relative to the rocket industry as a whole. E.g. SpaceX uses cheap, available materials and simple designs over exotic composites and complex mechanisms. But they still operate close to the margins, as they have to in order to have any payload capacity at all. In fact, the move to steel probably reduced their mass margins even further.

EDIT: Actually maybe I shouldn't have used a car as an example: https://www.youtube.com/watch?v=pJdrlWR-yFM

Re: SpaceX's Starship Mk1 just blew off its bulkhead in a pressurization accident

#87

Post by kev009 »

Klathmon wrote: post #46
kev009 wrote: post #34

I had an unpopular opinion amongst friends that this thing looked like a total piece of shit, like a movie prop. They were using rented lifts and cranes to assemble it in the field. Clock right twice a day or maybe there's a reason everything about Apollo spacecraft was meticulously assembled.

I have a feeling that they could blow up another dozen of these and still be spending less than doing it the "traditional" way of in cleanrooms and the VFAB building. This was a prototype that they've publicly said was most likely never to reach orbit, they are building this stuff right now to learn, test, and prove that their design works and find improvements that can be made.

Any elementary student of history can tell you how bad an idea this is. Apollo 1 almost ended the program. A backlash in public opinion will crater SpaceX in the market and legislature.

There is no space mission in the near decades worth the loss of human life. Economy in terms of money is no priority if you are to undertake human space flight. Move fast and break things is cute for a global search index or regressing public discourse and attention span; it's astronomically stupid and not acceptable for safety of human life.

If this were a billionaire playboy stroking his ego and putting his own money and life on the line who cares. It's not, he's using my tax dollars and is going to hurt others for negligible gain.

Re: SpaceX's Starship Mk1 just blew off its bulkhead in a pressurization accident

#89

Post by taneq »

londons_explore wrote: post #72

Aren't pressure tests done with water? That way, since water is non-compressible, if it fails, you just get a small hole or buldge somewhere rather than the catastrophic damage seen here. Perhaps they already tested with water and now needed to test with the real fuel/oxygen to get the temperature correct?

Is it strong enough to take a full tank of water? Liquid methane weighs less than half what water weighs.
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