Stainless Steel: Reaching for the Stars
The long-awaited big reveal of Starship, the interplanetary space vessel designed and built by Elon Musk's company SpaceX, has finally taken place. Earlier this month, Musk revealed a big change to the design: originally intended to be built from carbon fibre, Starship has in fact been constructed using stainless steel. So what motivated this significant alteration?
A major factor influencing SpaceX's decision to use stainless steel instead of carbon fibre was cost. The initial cost of carbon fibre is around £110 per kilogram though, as 35% of the material cannot be reused, the actual cost works out to nearer £160 per kilogram: this compares to around £4.00 / $5.20 per kilogram for stainless steel 1.4404 / 316 when purchased in such large quantities.
Another reason for the switch is the difference in melting points between carbon fibre and stainless steel. At a steady operating temperature, carbon fibre is limited to around 150 degrees Celsius: it can be pushed briefly to temperatures approaching 200 degrees Celsius but this causes weakening of the material. Stainless steel, on the other hand, can easily withstand temperatures of up to 80 degrees Celsius with no reduction in performance.
Among many other innovative features, Starship has a heat-shield system that employs transpiration cooling, something that has never been proposed before. Two layers of stainless steel are attached together with a gap between, through which either fuel or water can flow. Minute perforations in the outer layer allow fluids to bleed through, cooling vital systems.
Once again, stainless steel has proved itself as one of the strongest, most versatile materials on the planet and, if the Starship project is a success, could soon be proving its worth on other planets in our solar system.