Elon Musk Explains Why the Starship Will Be Stainless Steel - ExtremeTech

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SpaceX is working on the initial prototype of the Starship rocket (formerly BFR) that could eventually carry people to the moon and Mars. However, CEO Elon Musk recently announced a significant design revision that seems counterintuitive at first. Instead of aluminum and carbon fiber, the company has decided to build the Starship out of stainless steel. Now, he’s explaining why.

While the Starship prototype looks like a golden age sci-fi fantasy brought to life, that’s not the ultimate goal. See above for the real prototype on the left and a render of the final product on the right. SpaceX is going with a shiny steel design because it’s easier to build and has the potential to perform much better. The initial resin-strengthened carbon fiber frame had the potential to save a lot of mass, but it was a slow process, and 35 percent of the material was unusable scrap.

Stainless steel is much cheaper than carbon fiber, but it’s heavier. Although, Musk explains the rocket can be lighter with stainless steel than if you built it with other metals. Most steel alloys get brittle at cryogenic temperatures. That’s not the case for stainless steel with high chrome-nickel content. It gets stronger in cold conditions, but it also maintains ductility. That means stainless steel has high fracture toughness, which could prevent small structural imperfections from developing into cracks.

A rendering of what the Starship could look like in space.

Going with stainless steel also allows SpaceX to work on Musk’s dream of a regenerative heat shield. This probably won’t happen right away, but Musk wants to replace the tiles used on current spacecraft with a stainless steel sandwich. A stainless steel surface can remain completely sound at 1,500 degrees Fahrenheit, about five times higher than carbon fiber or aluminum. So, SpaceX could inject water into the space between the two layers where it absorbs heat. The regenerative shield would bleed that water through micro-perforations to cool the windward side of the rocket, which is known as transpiration cooling.

Musk says SpaceX will initially use 301 stainless — that’s similar to the metal used in pots and pans. It doesn’t sound very space age, but SpaceX seems to think it’s the best option. Strong winds knocked the prototype rocket over recently, but nothing important was damaged. The company could conduct its first test flight in the coming weeks. That will just be a sub-orbital “hop,” though. For deep space missions, the Starship will be paired with a booster vehicle called Super Heavy, but SpaceX hasn’t built that yet.

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