SpaceX has changed the design of the SpaceX Super Heavy Starship to stainless steel. However, the design changes are more complicated than just using stainless steel instead of carbon fiber or aluminum. SpaceX will not need advanced Pica-x ceramic heat shields in most of the rocket.
Elon Musk indicates that active cooling with super-cold fuel only has to reduce the temperature during re-entry by 300 degrees. The 310S stainless steel that SpaceX will use can repeatedly withstand ~1450 Kelvin.
SpaceX and Elon Musk have to make the materials, design and technology work. If they succeed using stainless steel they will massively cut the development time. Stainless steel is much easier and faster to work with than dozens of layers of carbon fiber. Success with this material and designs would provide SpaceX with another acceleration in development speed compared to their competition.
Elon Musk and SpaceX still have many skeptics. SpaceX now has the best track record for developing and launching new rockets with the multiple Falcon 9 version and the Falcon Heavy. I will assume that SpaceX has the data, the simulations, and physical testing to justify the design choices that are being made.
SpaceX and Elon Musk are far from perfect. They just allowed the Starhopper to be damaged in 50 mph winds which will cost weeks in repairs. However, United Launch Alliance (ULA) and Blue Origin have not launched new rockets to orbit in the last fourteen years. ULA has launched many older rockets. Blue Origin has had sub-orbital launches.
When going to ~1750 Kelvin, specific heat is more important than latent heat of vaporization, which is why cryogenic fuel is a slightly better choice than water
— Elon Musk (@elonmusk) January 22, 2019
310S stainless is better for high temp outer skin, as it can take ~1450 Kelvin, so active cooling with cryogenic fuel only has to mitigate 300 degrees of delta temp
— Elon Musk (@elonmusk) January 23, 2019
80% of the SpaceX Starship will not reach a temperature that will need a heat shield. Only 20% of the ship will need the active cooling system that SpaceX is building.
~1750K is peak heating expected on about 20% of Starship for LEO entry, ~1600K on 20%. Rest drops below 1450K, so no heat shield needed. Radiative cooling at T^4 takes care of 60% of the ship. Another reason for steel.
— Elon Musk (@elonmusk) January 23, 2019
Brian Wang is a Futurist Thought Leader and a popular Science blogger with 1 million readers per month. His blog Nextbigfuture.com is ranked #1 Science News Blog. It covers many disruptive technology and trends including Space, Robotics, Artificial Intelligence, Medicine, Anti-aging Biotechnology, and Nanotechnology.
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Thanks. Very helpful.