2024-10-10 15:00:00
Elon Musk in an archive photo
in a conversation engraved between Adam Burrows, professor of astrophysics at Princetonand Elon Musk, the former is surprised by the use of stainless steel in SpaceX’s Starship. Instead of using “more aerospace” materials like carbon fiber composites or aluminum-lithium alloys, the revolutionary private space industry is turning to older stainless steelthe same one with which the pots are made.
This conversation, reproduced in the red social Xhas gone viral again, with over 25 million views as of this writing.
THE Elon Musk explained about the use of stainless steel for the oxygen tanks of SpaceX’s newest spacecraft is no slouch. A “life” material like steel, which it already was fashion when in the early 20th century it was used as an example of advanced technology in Chrisler Building in New Yorkit might be better than state-of-the-art carbon fiber or the famous aerospace aluminum.
Although the stainless steel used by SpaceX’s Starship is patented and protected, it looks a lot like conventional ones. domestic stainless steels, which we find everywhere.
The Starship rocket ship set
When Elon Musk and space space shuttle: what things were done poorly and caused accidents, but also what made the production of ships and rockets more expensive. The magnifying glass had to be placed, as has happened many times before, on the materials.
The spaceship was designed as a combination of rocket and ship with a cylindrical shape. Its goal is to be a fully reusable transportation system to transport crew and cargo to Earth orbit, the Moon or Mars. It is arguably the world’s most powerful launch vehicle ever developed, capable of carrying up to 150 metric tons fully reusable and 250 metric tons expendable.
The helmet made of polished stainless steel
NASA shuttles have the look and design of airplanes and require external fuel tanks. However, Starship looks like a single rocket. This design allows for better optimization of, for example, the heat shield (which has been the cause of more than one shuttle accident, including the Colombia disaster).
But, without a doubt, one of the most striking things about the Starship is its polished stainless steel hull. How is it possible that stainless steel was chosen? It is a very heavy alloy, unlike carbon fiber or the very light aluminum-lithium alloys, which SpaceX uses for Falcon 9its launch vehicle.
While it is true that carbon fiber composites are very light and strong, they must be manufactured in autoclaves (pressure vessels) on a preform or mold woven with numerous layers (between 60 and 200). Once the material is cured in the autoclave, its surface must be modified and painted to ensure complete sealing, without pores or bubbles, which is difficult.
Considering that the spaceship has a diameter of nine meters, huge autoclaves would be required to manufacture it from fiber composites, as the choice of different modules is even more technologically complex.
However, stainless steel can deform when cold and this ensures the absence of microstructural defects. Furthermore, it can be welded quite easily and can be superficially polished giving a shiny appearance, so it does not need to be painted. Aluminum can compete with steel in terms of ease of production, but it doesn’t weld as easily.
Withstand cryogenic temperatures
The materials for a rocket’s oxygen tank must withstand gases pressurized at cryogenic temperatures – temperatures below -150°C – and cannot leak. This is only guaranteed by stainless steel.
Additionally, carbon fiber and aluminum are brittle at such low temperatures austenitic stainless steel It performs very well from those temperatures to the very high ones generated upon re-entry to Earth, a moment in which the competition (carbon fiber and aluminum) suffers greatly, despite the heat shield. Aluminum runs the risk of melting and the compounds risk degrading. Stainless steel doesn’t even notice.
In terms of weight, it is true that stainless steel quadruples the density of carbon fiber composites and triples that of aluminum-lithium. But, due to its relationship between resistance and weight, the same thing is achieved with stainless steel with smaller thicknesses. This makes the overall weight competitive compared to other materials.
Putting the pros and cons together, it turns out that the old stainless steel is more reliable, watertight, competes in weight and strength, and is also unbeatable at the pressures and temperatures typical of space travel. But, as if that wasn’t enough, producing stainless steel is really something simple and economical.
The price of steel
Producing one kilo of carbon fiber composites costs 118 euros/kg. One kilo of aluminium-lithium alloy, 36 euros/kg. One kilo of 300 series stainless steel (austenitic), approximately €3.6/kg.
But is it a special steel that will take man into space?
Speaking to Adam Burrows, Elon Musk replies that they have started testing the normal steels on the market, the 300 series, as well as the austenitic ones, such as 301 and 304 (the latter is the most used stainless steel). Finally, they had to add a “little twist” (which increases the cost slightly above €3.6/kg). They patented it as 30x steel (also used in the Tesla).
Personally I feel like it’s like the chef’s secret when they add “that special ingredient” that adds a little flavor, but doesn’t fundamentally change the product. Come on, the innovative touch on the material to be able to patent it.
Carbon fiber and aluminium-lithium, especially in the aerospace world, are the bets of an industry that is renewing itself. But stainless steel, the steel that is used in seafront railings, in buildings, in football stadiums or in the mechanical components of industries more vulgar than aerospace, turns out to be good, beautiful and economical even for the spaceships with which we humans we will fly high. above our planet.
In advanced engineering, well-selected ordinary material can perform the best function. The most complex is not always the best.
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