In a recorded conversation between Adam Burrows, a professor of astrophysics at Princeton, and Elon Musk, the former is surprised by the use of stainless steel in SpaceX’s Starship. Instead of using “more aerospace” materials such as carbon fiber composites or aluminum-lithium alloys, the private space industry revolution is turning to good old stainless steel, the same kind that pots are made from.
This conversation, reproduced on social network X, has gone viral again, with more than 25 million views as of this writing.
Elon Musk’s explanation for using stainless steel for the oxygen tanks of SpaceX’s new spacecraft is not a mistake. A “lifetime” material such as steel that is already completely fashion When it was used as an example of advanced technology in the Crisler Building in New York in the early 20th century, it was arguably better than cutting-edge carbon fiber or famous aerospace aluminum.
Although the stainless steel used in SpaceX’s craft is patented and protected, it is very similar to the regular household stainless steel we see everywhere.
Starship Rocket Ship Set
When Elon Musk and space. The magnifying glass had to be placed, as happened many times, on the materials.
The starship was designed as a combination of a rocket and a cylindrical ship. Its goal is to become a fully reusable transport system for delivering crew and cargo to orbit around the Earth, the Moon or Mars. It is likely the world’s most powerful launch vehicle ever built, capable of carrying up to 150 fully reusable metric tons and 250 expendable metric tons.
Shiny stainless steel helmet
NASA’s shuttles look and are designed like airplanes and require external fuel tanks. However, Starship looks like a single rocket. This design makes it possible to better optimize, for example, the heat shield (which was the cause of more than one shuttle accident, including the Columbia disaster).
SpaceX
But without a doubt, one of the Starship’s most striking features is its shiny stainless steel hull. How is it possible that stainless steel was chosen? It is a very heavy alloy, unlike the carbon fiber or extremely light aluminum-lithium alloys that SpaceX uses for its Falcon 9 launch vehicle.
While it is true that carbon fiber composites are very light and strong, they must be produced in autoclaves (pressure vessels) on a preform or mold woven from many layers (60 to 200). After curing the material in an autoclave, its surface must be modified and painted to ensure a complete seal without pores or bubbles, which is difficult.
Given that the starship has a diameter of nine meters, its manufacture from fiber composites will require huge autoclaves, since the option of different modules is even more complex from a technological point of view.
However, stainless steel can be deformed when cold, and this ensures that there are no microstructural defects. In addition, it can be easily welded and surface polished to give it a shiny appearance, so it does not need to be painted. Aluminum can rival steel in ease of manufacture, but it is not as easy to weld.
Withstand cryogenic temperatures
The rocket’s oxygen tank materials must withstand exposure to pressurized gases at cryogenic temperatures—temperatures below -150°C—and must not leak. This is guaranteed only by stainless steel.
Additionally, carbon fiber and aluminum are brittle at such low temperatures, while austenitic stainless steel performs very well both from these temperatures and to the very high temperatures encountered upon return to Earth, while competition (carbon fiber , carbon and aluminum) suffers a lot, despite the heat shield. Aluminum is at risk of melting and decomposition of compounds. 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 composites. But because of the relationship between resistance and weight, the same thing is achieved with thinner stainless steel. This makes the overall weight competitive with other materials.
When you add up all the pros and cons, old stainless steel is more durable, waterproof, competitive in weight and durability, and invincible at the pressures and temperatures typical of space travel. But what’s worse is that stainless steel production is actually something simple and cheap.
Steel price
The production of a kilogram of carbon fiber composites costs 118 euros/kg. One kilogram of aluminum-lithium alloy, 36 euros/kg. One kilogram of 300 series stainless steel (austenitic), about 3.6 euros/kg.
But is this the special steel that will take people into space?
In a conversation with Adam Burrows, Elon Musk responds that they have begun testing regular, market-grade 300-series steels, as well as austenitic ones such as 301 and 304 (the latter being the most used stainless steel). Finally, they had to add a “small detail” (which raised the cost slightly above 3.6 euros/kg). They patented it as 30x steel (also used in Tesla).
Personally, I have a feeling that it’s kind of a chef’s secret where they add “that special ingredient” that adds flavor but doesn’t significantly change the product. Come on, an innovative approach to the material in order to be able to patent it.
Carbon fiber and aluminum-lithium, especially in aerospace, are the bets of a reinventing industry. But stainless steel, the kind of steel used in walkway railings, buildings, football stadiums or mechanical components in industries more vulgar than aerospace, turns out to be good, beautiful and cheap for the spaceships we humans will fly on. high. over our planet.
In advanced engineering, a well-chosen common material can perform the best function. The hardest thing is not always the best.