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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

#31

Post by contravariant »

roywiggins wrote: post #13
cracker_jacks wrote: post #9

Is the Starship Mk1 more structurally sound than it looks? From a first glance and having no knowledge of its design, it looks like an empty soda can that would deform at the slightest disturbance. And the way it crumpled in the video doesn't seem far off from what I would expect.

Rockets are actually pretty easy to poke holes in. They're meant to keep stuff in, not out. A dropped torque wrench blew up a Titan. https://en.m.wikipedia.org/wiki/1980_Damascus_Titan_missile_...

It's somewhat impressive that the actual nuclear warhead didn't so much as leak. Which is what's supposed to happen but still you don't usually design something to withstand a botched missile launch capable of 'catapulting' a 740 ton door.

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

#32

Post by JshWright »

elihu wrote: post #27
TheSpiceIsLife wrote: post #16

I don’t know the specifics of this particular setup, but aren’t pressure vessels usually tested hydrostatically. Water, for example, can be pressurised without actually compressing, and therefore doesn’t undergo rapid expansion when a failure occurs. There may be reason that precluded pressure testing with a fluid tough.

Maybe weight? Filling something that big with water would be very heavy; maybe it's not strong enough in all the right places to support that much mass.

Water is lighter than liquid oxygen (which is what this tank would be holding in "production"). For the purposes of this test, they were likely using liquid nitrogen, which has ~80% the mass of water.

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

#33

Post by m0zg »

AWildC182 wrote: post #19
TheSpiceIsLife wrote: post #16

I don’t know the specifics of this particular setup, but aren’t pressure vessels usually tested hydrostatically. Water, for example, can be pressurised without actually compressing, and therefore doesn’t undergo rapid expansion when a failure occurs. There may be reason that precluded pressure testing with a fluid tough.

Compared to the fuels that the vessel is designed to carry, water might as well be liquid lead. It would easily crush the structure before you got enough in there to do hydro testing. Edit: correction, looks like they're using methane/LOX. Methane is 422g/L and LOX is 1141g/L (compared to water at 1000g/L). If it was the LOX tank then they could have probably hydro tested it. Not so much with the CH4 which is probabl…

How do you "hydro" test it at cryogenic temperatures, where physical properties of the vessel material are markedly different?

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

#34

Post by kev009 »

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.

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

#35

Post by JshWright »

cracker_jacks wrote: post #9

Is the Starship Mk1 more structurally sound than it looks? From a first glance and having no knowledge of its design, it looks like an empty soda can that would deform at the slightest disturbance. And the way it crumpled in the video doesn't seem far off from what I would expect.

You're not wrong that Starship has very thin walls, but they're actually quite thick compared to some rockets. There are rockets in use today that have to be pressurized to avoid collapsing under their own weight.

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

#36

Post by JshWright »

MattRix wrote: post #10
cracker_jacks wrote: post #9

Is the Starship Mk1 more structurally sound than it looks? From a first glance and having no knowledge of its design, it looks like an empty soda can that would deform at the slightest disturbance. And the way it crumpled in the video doesn't seem far off from what I would expect.

Yes, your impressions are wrong.

Not really... a soda can is a pretty good analogy, actually.

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

#37

Post by CydeWeys »

Retric wrote: post #29
lmilcin wrote: post #26

Earlier quoted context omitted.

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…

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.

Starship needs to be reusable dozens of times, with no refit between launches (only refueling). Fuel is cheap; the vehicle needs to survive. It also needs to be reliable enough to carry people. They're not using razor-thin safety margins on it.

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

#38

Post by manicdee »

cracker_jacks wrote: post #9

Is the Starship Mk1 more structurally sound than it looks? From a first glance and having no knowledge of its design, it looks like an empty soda can that would deform at the slightest disturbance. And the way it crumpled in the video doesn't seem far off from what I would expect.

Yes, rockets are basically soda cans full of propellant with rocket engines on the bottom and the payload usually on the top.

They are entirely constrained by thrust versus mass, so the designers make the structure as light/thin as possible while still being able to handle the acceleration forces when fuelled and pressurised.

If the weight of the rocket itself is too high it will not be able to lift any payload. If it is too light it falls apart in flight (or in one spectacular case, crumples in on itself when pressurisation fails).

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

#39

Post by war1025 »

mlyle wrote: post #22
roywiggins wrote: post #13

Earlier quoted context omitted.

Rockets are actually pretty easy to poke holes in. They're meant to keep stuff in, not out. A dropped torque wrench blew up a Titan. https://en.m.wikipedia.org/wiki/1980_Damascus_Titan_missile_...

An 8lb socket dropped 80 feet. That's going to put a heck of a dent in almost anything.

Assuming I remember my high school physics correctly, the socket would be moving ~50mph on impact. Definitely a recipe for a bad day.

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

#40

Post by cyrux004 »

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 wish more smart people like you worked there.
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