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Forum:	Commercial Space - Military Space
Topic:	[Discuss] SpaceX Starship and Super Heavy

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Your Reply: HTML is ON UBB Code is ON Smilies Legend	[QUOTE]Originally posted by Robert Pearlman: [B]Elon Musk describes the choice of stainless steel over carbon fiber in [URL=https://www.popularmechanics.com/space/rockets/a25953663/elon-musk-spacex-bfr-stainless-steel/]this interview[/URL] with Popular Mechanics. <BLOCKQUOTE>[i]The thing that's counterintuitive about the stainless steel is, it's obviously cheap, it's obviously fast — but it's not obviously the lightest. But it is actually the lightest. If you look at the properties of a high-quality stainless steel, the thing that isn't obvious is that at cryogenic temperatures, the strength is boosted by 50 percent. Most steels, as you get to cryogenic temperatures, they become very brittle. You've seen the trick with liquid nitrogen on typical carbon steel: You spray liquid nitrogen, you can hit it with a hammer, it shatters like glass. That's true of most steels, but not of stainless steel that has a high chrome-nickel content. That actually increases in strength, and ductility is still very high. So you have, like, 12 to 18 percent ductility at, say, minus 330 degrees Fahrenheit. Very ductile, very tough. No fracture issues.[/i]</BLOCKQUOTE> Musk also talks about his plans for a first-of-its-kind heat shield. <BLOCKQUOTE>[i]On the windward side, what I want to do is have the first-ever regenerative heat shield. A double-walled stainless shell — like a stainless-steel sandwich, essentially, with two layers. You just need, essentially, two layers that are joined with stringers. You flow either fuel or water in between the sandwich layer, and then you have micro-perforations on the outside — very tiny perforations — and you essentially bleed water, or you could bleed fuel, through the micro-perforations on the outside. You wouldn't see them unless you got up close. But you use transpiration cooling to cool the windward side of the rocket. So the whole thing will still look fully chrome, like this cocktail shaker in front of us. But one side will be double-walled and that serves a double purpose, which is to stiffen the structure of the vehicle so it does not suffer from the fate of the Atlas. You have a heat shield that serves double duty as structure. Yeah. To the best of my knowledge this has never been proposed before.[/i]</BLOCKQUOTE>[/B][/QUOTE]
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