11 January 2019 Elon Musk tweeted a photo of a new spacecraft “Starship”. We are talking about the missile module to test suborbital flights. And earlier, at the end of last year, Musk mentioned that SpaceX goes to stainless steel instead of carbon fiber when creating buildings of new missiles. He gave an interview with Popular Mechanics, where he explained the reasons for this choice.
The last time the use of stainless steel in the space rocket took place in the 50-ies in the framework of the project “Atlas”. But nothing came of it – the designers failed to achieve the desired thin-walled structures-strength and reinforcing and heavier missile was afraid. Musk also fearless and ready to apply new types of Nickel-chromium alloys, because the Starship will have an alternative housing design.
On the outside of the Starship, no thermal protection, instead it has a double hull. At takeoff the space between the two walls of steel is empty, and this layer of air protects the rocket from hypothermia. And when they start to land into the cavity water will be supplied through the micropores near the surface, turning into steam and cooling overheated from the friction of the body of the rocket. Water reserves can be replenished – this technology called “regenerative heat shield. Steel can withstand temperatures of up to 1.5 thousand degrees, while the carbon fiber is less than 400.
Another aspect is economic. The price of carbon fiber starts at $135 per 1 kg, when cutting up to 35 % of the material goes to the scrap, which increases the cost to $200 per 1 kg. how many layers in each sq. m. the rocket body need a lot of 60-120. Stainless steel costs SpaceX only $3 for 1 kg. And it is much easier to work with than composite materials, said Musk.
Source — Popular Mechanics