space X test failure. 3

[Alistair_Heaton]

https://youtu.be/wFXQ5SRCy74

Doesn't look like buckling to me. More of a someone opened the wrong tap without opening another one first to equalise the pressure.

 

[thebard3]

It looks like the failure has already started at the beginning of the video. The buckling seems to have started in the intertank area, but I can't find anything online that describes the tanks configuration of the vehicle so that's just speculation.
Also, Elon Musk commented later that it may have been caused bye a 'test configuration mistake'.

https://www.nasaspaceflight.com/2020/04/spacex-starship-sn3-ground-flight-testing/

The forum section has a long thread discussing the lead-up and aftermath of the test. I'll have to peruse it thoroughly and maybe a likely cause will emerge. You have to register to access it.

Brad Waybright

It's all okay as long as it's okay.

 

[Spartan5]

I was able to access the forum here without registration.

https://forum.nasaspaceflight.com/index.php?topic=48895.2200

 

[SWComposites]

Thin shell buckling is notoriously difficult to predict. Very sensitive to initial imperfections. Hopefully they didn’t design it using eigenvalue buckling analysis. Lots of good info on shell buckling here: shellbuckling.com.

 

[Alistair_Heaton]

there is a huge fuel tank under those shells.. And it is the loadbearing structure. There is pics in the forum links.

I have seen a silo with a tank in it do this before because someone started pumping the contents out without injecting N2 in at the top to maintain positive deferential tank pressure to outside.

 

[IRstuff]

Looks more like a variety of vacuum collapse; if there were a cryofuel leak, it could supercool the atmosphere inside the cylinder, causing a pressure differential. Even a small pressure differential would be enough to buckle from the external air pressure.

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert!

https://www.youtube.com/watch?v=BKorP55Aqvg

faq731-376 forum1529 Entire Forum list

http://www.eng-tips.com/forumlist.cfm

 

[Alistair_Heaton]

Does anyone actually know what the test involved doing?

From the video it was clean outside then loads of condensation and ice formed then it rapidly melted again after a period.

Do they just use liquid nitrogen or fill both tanks with fuel and oxidiser?.

 

[Andries]

A great example of thin-shell compressive buckling. The shell really tried to do an Euler buckling as shown by the initial diamond-like buckling mode shapes.

Andries

 

[hokie66]

I think they miscalculated the viscosity of the snake oil in the cylinder.

 

[hydrae]

I have been following the construction of starship as a hobby
they did an initial test with water in both tanks and were testing in cold conditions using liquid Nitrogen

Starship does not have an inter-tank since lox and liquid methane are chilled there is a common bulkhead.
it failed is the lower tank which had lost pressure due to ground equipment (is the assumption)

Scott Manly has a good video with the common speculation
also goes into detail on the welding methods

https://www.youtube.com/watch?v=XJslqGkb9So

Hydrae

 

[Alistair_Heaton]

which tank is highest I am presuming LOX is on the bottom.

 

[Sparweb]

Since I haven't looked at the Starship in detail before, it would not make sense for me to pretend to know much about their design, but I'm really puzzled by something I see ("don't see) in the photos. Here's an example:

So while I can see strong evidence of numerous reinforcing members in the lower tank and possibly even a double-wall, the upper tank looks completely unreinforced. Those perforated straps would have some purpose, and I can see that there a a number of them in there, but with no evidence of inherent stiffness in the straps themselves, and few points of connection to the walls, I can't picture what they're there for. Also, the surfaces inside the upper tank wall are clean of any attached members. Not even a ring stiffener!

Say what you want about this structure withstanding 1G standing vertically in gravity, my question is how this was expected to tolerate >5g under rocket thrust.

A lot was learned from the Atlas rocket program (1960's) which was the first design like this one that used (a) stainless steel balloon tanks and (b) relied on propellant pressure to stand its own weight vertically on the pad.

http://www.sparweb.ca

 

[MJCronin]

This is why we need real engineers and not just "designers"....


MJCronin
Sr. Process Engineer

 

[thebard3]

I know there is a small envelope of performance for rockets to keep the weight at an absolute minimum. Years back a rocket on display at the U.S. Air Force museum (I believe it was an Atlas) collapsed during a power failure. A blower was used to keep the fuel tanks under a small amount of pressure and absent that it was unable to support itself. It was structurally sound when loaded with the many tons of fuel necessary for flight, up until the moment it was jettisoned. I'd be surprised if any testing of SN3 involved filling it with water. I guess the LN2 used for this test is close enough to that of methane and LOX, and was probably included in the design criteria to allow such a test.

Edited- Sorry, SparWeb, I just saw your comment about Atlas, you beat me to it.

Brad Waybright

It's all okay as long as it's okay.

 

[thebard3]

https://www.nasaspaceflight.com/2020/04/spacex-starship-sn3-ground-flight-testing/

I think this is the same link that was posted before but the content has been edited with some explanation of what went wrong.

Brad Waybright

It's all okay as long as it's okay.

 

[waross]

Rockets are hard.

Well it is rocket science.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[moon161]

I had a physics prof who took part in the 50's and could verify that it was, with lots of failures.

 

[monkeydog]

Hokie66

With regards to the snake oil comment - Still
Could not find LMAF emoji

 

[Sparweb]

...Elon Musk has since clarified the issue was the result of incorrect commanding resulting in the loss of pressure, as opposed to any material issue with the Starship build. As a result, SN4 will not require alternations to its structure, with construction work on the next Starship already taking place...

Ah, he blames software, not hardware. Elon has no sense of irony.

http://www.sparweb.ca

 

[Alistair_Heaton]

This is quite interesting...

https://www.spacex.com/sites/spacex/files/starship_users_guide_v1.pdf