Elon Musk has indicated that one of the reasons for switching to stainless steel for the SpaceX Super Heavy Starship was to use $3 per kilogram of steel instead of $200 per kilogram for carbon composite.
Above is a rendering of the stainless steel SpaceX rocket by Kimi Talvitie. He rendered the SpaceX Super Heavy Starship with shiny metallic steel.
Previously the BFS was to have a drymass of 85 tons.
The Super Heavy booster dry mass was not revealed but the booster is about twice as heavy as the Starship upper stage.
Most of the rocket was going to be aluminum alloys.
SpaceX did reveal the carbon fiber fuel tanks.
The overall dry mass of the rocket is probably in the range of 250 to 300 tons. If 20% was going to be carbon composite, then this would have been 50 to 60 tons of carbon materials.
This would have cost $10 million to $12 million if the rocket was 20% carbon composites. If the rocket was 40% carbon composites then there was $20 to $24 million in carbon materials used for the SpaceX Super Heavy Starship. The steel would end up being $150,000 in the 20% case to $300,000 for the 40% case.
SpaceX should save $10 to $24 million to build each rocket from using stainless steel.
Elon Musk has also discussed large time-savings using stainless steel. This will save lot of labor costs and development costs.
If the development time can be cut from 3 or 4 years to 1 or 2 years, then this will save SpaceX billions of dollars.
There are some videos that discuss the transpiration cooling of the SpaceX Super Heavy Starship.
The 777 Jet Uses About 11% Composites
The Airbus A380, one of the largest passenger airliner in the world, contains 10 times the amount of aluminum used in the Airbus A320. And Boeing’s 787 Dreamliner, which is often described as a composite aircraft, contains 20% aluminum (by weight) which includes aluminum 7085, a relatively new aluminum alloy.
Boeing’s Composite Fuel Tank
Boeing developed a carbon composite fuel tank for a rocket and they were trying to save 30% of the weight of a metal fuel tank.