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this post was submitted on 15 Feb 2024
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Because steel is cheap and "good enough" for whatever Starship's application is. Titanium would be lighter but far, far, more expensive. And the cost of the titanium would probably out weight the extra fuel costs.
Which is why most rockets today use aluminum for their fuel tanks, not steel.
And you’ve just accidentally stumbled into the Rocket Equation! My favorite.
So you want to make a rocket with enough energy to get to orbit. Okay so my engine puts out X amount of thrust at sea level. I’ll need Y fuel to get to orbit. But because the fuel weighs something, now I need 2 engines to lift the weight of the fuel and tanks. But because I have 2 engines, now my craft weighs more and I need more fuel to feed both engines. This cycle repeats until you can either balance them, or decide to say fuck it and move over to building bridges.
One way you can balance the rocket equation is by making the dry, or empty, weight of your vehicle lighter. Now you can lift more fuel on the engines you have and get higher and faster.
So again, why the hell are they using one of the most dense building materials to make up most of the rocket. Sure manufacturing is cheaper and easier, but that only counts if the thing can actually reach orbit and be useful.