SpaceX’s planned Starship rocket is supposed to one day shuttle people to Mars, but it’s also got something in common with your typical kitchen appliance: CEO Elon Musk recently revealed that the aerospace company plans to craft Starship out of stainless steel instead of the traditionally used aluminum and carbon fiber.
The decision is not aesthetic, he explained in a recent interview with Popular Mechanics about Starship’s specs. The material is also a lot cheaper. To ensure it’s up to the rigors of space flight, Musk said he envisions it being used as the foundation for a kind of self-healing heat shield that would coat Starship almost entirely. He described the concept as a “stainless-steel sandwich” that can “bleed water…fuel” through tiny holes on its surface to keep it cool as it enters the Martian atmosphere at breakneck speeds.
“What I want to do is have the first-ever regenerative heat shield,” he said. “A double-walled stainless shell—like a stainless-steel sandwich…with two layers [to] flow either fuel or water in between the sandwich layer, and then you have micro-perforations on the outside… to cool the windward side of the rocket.”
How It Could Work
The concept is known as transpiration cooling, which is fancy engineering jargon for passing a liquid through a porous surface to lower the surface’s overall temperature. Musk says in theory that either water or super-chilled liquid oxygen would pass through a Swiss cheese-like heat shield, absorb a part of the component’s energy, and prevent serious heat damage.
In previous statements, Musk has also said he envisions Starship’s landing maneuver and it’s absolutely bonkers. SpaceX’s specifications state that it’ll enter the martian atmosphere at 7.5 kilometers per second (16,777 mph) and begin to slow down aerodynamically, as if it where a skydiver. Because of that high speed, some wear and tear will be inevitable, but this proposed bleeding heat shield could work to offset the damage.
“The way it operates is more like a skydiver than an aircraft. The whole time it is entering, it is just trying to brake. It is just trying to stop,” explained Musk during a September press conference. “This will look really epic in person, guaranteed to be exciting.”
Stainless Steel Working Double Time
The virtues of stainless steel are actually two-fold, Musk says. Not only could stainless steel contain heat damage, but Musk also says it’ll serve as an ideal skeleton.
“One side will be double-walled and that serves a double purpose, which is to stiffen the structure of the vehicle,” he said. “You have a heat shield that serves double duty as structure.”
SpaceX's final, stainless steel Starship Hopper
While it’s still the same grade as what’s sometimes found in your pots and pans, the 300-series stainless steel that Musk said would make up Starship has a melting point of up to 2,786 Fahrenheit, compared to aluminum’s 1,221 degrees Fahrenheit melting point. And while carbon fiber doesn’t melt, it can begin to degrade if exposed to heat upwards of 400 degrees, according to the CEO.
SpaceX has already completed a “Hopper” prototype of Starship in its Boca Chica test facility in Texas. Seems like the final result will look a lot more like this retro-sci-fi inspired model than previously expected.
