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Why SpaceX Starship motivated for Stainless Steel heat shield? What's scientific reason behind it?

Why SpaceX Starship motivated for Stainless Steel heat shield? What's scientific reason behind it?

WHY ELON MUSK TURNED TO STAINLESS STEEL FOR SPACEX'S STARSHIP MARS ROCKET?

Why Spacex Starship motivated for Stainless Steel heat shield? What's scientific reason behind it?


SpaceX is working on the initial prototype of the Starship rocket (formerly BFR) that could eventually carry people to the moon and Mars. However, CEO Elon Musk recently announced a significant design revision that seems counterintuitive at first. Instead of aluminum and carbon fiber, the company has decided to build the Starship out of stainless steel.

SpaceX CEO Elon Musk shared considerable insight into the thought processes, that ultimately led him to - in his own words -“convince” his team, that the spacex company’s BFR rocket, which now Starship and Super Heavy, should pivot from an advanced composite structure to a relatively common form of stainless steel.
In this video, Engineering Today will try to explain, Why Elon Musk Turned to Stainless Steel for SpaceX's Starship Mars Rocket? WHAT DOES SCIENCE SAY about Stainless Steel SpaceX Starship future?
Lets gets started.
WHAT MOTIVATED THE SWITCH?

While the Starship prototype looks like a golden age sci-fi fantasy brought to life, that’s not the ultimate goal. SpaceX is going with a shiny steel design

Musk explained what motivated the switch for stainless steel.

Musk explains the rocket can be lighter with stainless steel. That’s not the case for stainless steel with high chrome-nickel content. That means stainless steel has high fracture toughness, which could prevent small structural imperfections from developing into cracks.

Going with stainless steel also allows SpaceX to work on Musk’s dream of a regenerative heat shield. This probably won’t happen right away, but Musk wants to replace the tiles used on current spacecraft with a stainless steel sandwich. A stainless steel surface can remain completely sound at 1,500 degrees Fahrenheit, about five times higher than carbon fiber or aluminum. So, SpaceX could inject water into the space

Musk says SpaceX will initially use 301 stainless — that’s similar to the metal used in pots and pans. It doesn’t sound very space age, but SpaceX seems to think it’s the best option.

Aside from steel’s relative ease of manipulation and affordability, Musk delved into the technical solution he arrived at for an advanced, ultra-reusable heat shield for Starship
Musk is by no means wrong, when he says that a stainless steel sandwich-hulled spaceship regeneratively cooled by microscopic holes, and liquid water or propellant “has never been proposed before”.

metallic thermal protection systems (TPS) are already fairly exotic, and unproven in the realm of modern aerospace.

While Musk’s solution could dramatically simplify, what is needed for Starship’s high-performance heat shield, a stainless steel sandwich on half of Starship offers another huge benefit: the spacecraft can still gain many of the mass ratio benefits of stainless steel balloon tanks.

At the end of the day, Musk very well might be correct when he states that a stainless steel Starship can ultimately be more mass-efficient, “lighter” than a Starship built out of advanced carbon composites, a characteristic he rightly describes as “counterintuitive”
Starship’s water-cooled shield.

Assuming that the windward side of Starship’s regeneratively cooled heat shield,

thermal protection (TPS).
water during potential Starship reentries. Assuming that Starship will need to rely heavily on aerobraking to maintain efficient interplanetary operations.

Given that SpaceX intends (at least as of September 2018) for Starship to be able to land more than 100 tons on the surface of Mars, 15t of water would cut drastically into payload margins, and is thus likely an unfeasibly large mass reserve or any given interplanetary mission.
Conclutions

The assumptions needed for this calculations do mean that 30 tons is an absolute worst case scenario for a regeneratively cooled Starship reentry, given that SpaceX may only have to vigorously cool a small fraction of its windward surface needed by allowing Starship’s steel skin to heat quite a lot, while still staying well below its melting point, likely around 800°C, 1500°F or higher.

This also fails to account for the fact, that a regeneratively-cooled stainless steel heat shield, would effectively let SpaceX do away with what would otherwise be a massive and heavy ablative heat shield and mounting mechanism. Perhaps the benefits of stainless steel might ultimately mean that, carrying around 10-30 tons of coolant is actually performance-neutral or a minimal burden, when all costs and benefits are properly accounted for.

Musk clearly believes with almost zero doubt that a stainless steel Starship and booster Super Heavy is the way forward for the company’s BFR program, For now, all we can do is watch as the first Starship prototype

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