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Comment by 35787 | Hacker News Reader

Eventually the shell will be a single large roll of steel that is unrolled, bent into a tube with a seam going hotdog that is welded. It will be very strong, lighter than the current patchwork, and extremely beautiful. More similar to the renderings. Can’t wait.

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Definitely not hotdog (assuming that's from stem to stern). Musk wasn't totally clear when describing it, but he said mk3 would be in three months. The circumference of starship is 28.26 meters. For a single weld the entire length of the ship, the roll itself would need to be that wide.

The largest rolling mills in the world are ~4 meters wide[1]. They require backup rollers[2], ie rollers that push down the rollers that push down the rollers that push down the metal. Bending deflection increases with width^2. A 28 meter wide rolling mill does not exist AFAIK and cannot be built in three months.

[1]: https://www.aleris.com/company/rolled-products/

[2]: http://www.yourarticlelibrary.com/metallurgy/types-of-rollin...

Wow what an incredibly substantive comment. I remember pretty clearly he said that there would be a single seam weld. Maybe I’m remembering wrong. Or maybe they’ll seam weld multiple rolls into a really wide roll and the only weld required to turn the final roll into the shell is that final hotdog weld.

I think the idea's to go like a Pringles can, with a spiraling single seam.

this is the correct answer. They can simply use the 4 meter wide steel no problem.

If getting out of your yoga pants is like opening a can of biscuits, then making a starship is like putting your yoga pants back on...

They can't do that because they need to thickness to taper off up the sides of the vehicle.

maybe, but that's also pretty unlikely. For reference here's where musk talks about it: https://youtu.be/sOpMrVnjYeY?t=3156

No real indication he means a spiral.

There are a lot of problems with a spiral. Thin sheets of steel, even hot rolled, are very affected by the rolling process. There's also the weld line going up in a spiral. That will cause uneven heat diffusion and expansion, which is a recipe for disaster given that the skin will be cold enough to liquify helium on one side and boiling hot on the other. Then red hot during reentry. Straight lines don't have the same problems.

I think when Elon said "there will be a single seam weld" (which I also remember), he meant this in comparison to the current welds.

It's been 12 hours and I only skimmed the video, so I might be misremembering what he said. My understanding was this: Mk1 is welded from plates so at each layer of the stack you have n-1 welds holding the n plates together. My understanding of his comment was that the steel coils will wrap around the major axis of the rocket but instead of each layer containing n-1 welds to join n plates, there will just be one weld in each layer to join the beginning and end of that coil. That would still leave you with welds joining the different layers of coils but only one "seam" weld along the rocket's major axis.

I feel like he was talking about a single weld on each ring section.

The "single piece" method he is talking about is that the individual _rings_ will be made of a single piece with a single weld, and the rings are then stacked. You can see it already in the Starship under construction in Florida. (Look at the unstacked rings.)

https://twitter.com/FarryFaz/status/1170535411678101504/phot...

https://pbs.twimg.com/media/ED6Tva7XYAESQJJ?format=jpg&name=...

How do you picture them rolling a piece of steel 50 meters wide? As far as I know, the widest rolling mills in existence are 5 meters wide.

Think of it like a paper towel tube. It's a spiral.

Single helical weld.

They said they would do butt welds, not spiral.

Spiral tube are a bad choice for a rocket. Because rolled steel has the grains largely aligned with the direction of rolling, it is stiffer and has less thermal expansion in one axis than the other. Large forces and temperature changes therefore cause a twisting motion, which can put weird strains on the internal components.

Pillsbury rolls come to mind. The tube is under pressure from the leavening agent, and you apply torsion on the tub until the can ruptures along the spiral seam.

That would not go over well with the occupants.

I recall the rolls scaring the shit out of a fair number of people and those were with the promise of warm, flaky goodness, not hot, fiery death.

This of course matters if the seam is weaker than the rest of the metal.

I've been assured time and again that you can make welds that are stronger than the rest of the metal, but my lizard brain thinks they're all liars.

Just curious - what industry are you in that you know off of the top of your head the max size of rolled steel?

Nearly anyone who buys sheets of rolled steel eventually finds they can't buy a sheet bigger than a certain size...

Same exists for most goods - try to buy a dustsheet to cover your room, and you can't buy one wider than 5 meters without a seam

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