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SpaceX Starship is made of Stainless Steel

Elon Musk explained that SpaceX chose stainless steel over carbon fibre for the construction of its Starship rocket for several reasons, despite carbon fiber’s high strength and light weight:

  1. Porosity and Flammability: Carbon fibre’s porous nature and its susceptibility to flammability posed significant challenges, especially when dealing with the pressurized cryogenic methane and hot oxygen gases used in the Starship. This required a lining that compromised carbon fiber’s mass efficiency.
  2. Manufacturing Challenges: The Starship’s large nine-meter diameter necessitated precise application of multiple layers of carbon fiber, with any imperfections such as bubbles or leftover separator sheets potentially jeopardizing the entire structure.
  3. Cost and Weldability of Alternatives: While SpaceX had previously used an aluminium-lithium alloy in its Falcon 9 rockets, it was too expensive and difficult to weld.
  4. Advantages of Stainless Steel: Stainless steel, particularly the 300 series, exhibited remarkable cryogenic properties. At liquid oxygen temperatures, its strength increased without becoming more brittle, an important factor as both fuel and oxygen are cryogenically chilled. Stainless steel was also easier to weld and significantly more affordable, costing roughly $4 per kilogram compared to aluminium-lithium’s $40 per kilogram.
  5. Heat Shielding: Stainless steel’s ability to withstand high temperatures (over 1000 degrees Celsius) reduced the need for extensive heat shielding during reentry, as opposed to carbon fiber, which loses strength beyond 200 degrees Celsius. This resilience allows for a lighter heat shield.
  6. Elimination of Paint: Using stainless steel also negated the need for paint, which adds significant weight to the structure, especially considering the Starship’s substantial diameter.
  7. Development of a Proprietary Alloy: SpaceX started with stainless steel 301 but moved to 304 and ultimately developed its proprietary alloy, 30X, which surpassed the performance of both 301 and 304.

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