In article ,
says...

On 2019-10-15 06:51, Jeff Findley wrote:

Musk has said several times that the higher temperature stainless steel
structure allows for a thinner and lighter heat shield. And aluminum or
carbon composite structure would require far more insulation on the heat
shield to protect it from reentry heat. So in the end, your Starship
might be heavier if you make it out of carbon fiber.

The way I see it, we are still very much at prototype stage, and steel
is cheaper and faster to get built, it makes much sense for the
portotype stage.


At the time Musk announced he was switching to steel, the argument was
that the weight gain from steel would be offset by weight loss due to
lighter/no heat shield.

The problem is that since heat shield had not been decided/final yet,
that math couldn't have happened.

Bull****. The amount of insulation and/or cooling could be calculated
for the different materials. Regardless of what heat shield would be
used, it would still be *lighter* for stainless steel than the other
materials due to the much *higher* temperature tolerance of stainless
steel.

They've moved to transirational cooling and now to tiles. They've
changed the shape of the rocket. The design is advancing, evolving.

Yes, but that does not negate the fact that choosing a different
structural material with a *higher* temperature tolerance allows for a
*lighter* cooling/insulating solution.

And since the design is changing, it makes much sense to test things in
easy steel. No point building design specific tooling/mandrels for
ccarbon rocket when the design is still changing.

True.

So I am still not convinced that the long term "productized" sharship
will be steel.

You keep being you, but you're wrong on this. Stainless steel allows
for far cheaper and *faster* production of Starships and Super Boosters.
And given SpaceX's application for even *more* Starlink satellites,
they're going to need a lot of launches of Starship to put them all into
orbit. Cite:

https://www.businessinsider.com/spac...atellites-itc-
filing-30000-additional-42000-total-2019-10

So, 42,000 satellites need to be launched. Someone else online
estimated that you could stuff 325 Starlinks inside a Starship. So
that's about 130 launches of Starship. So if you launch four times per
week, that's 2.5 years to launch the entire constellation. So, SpaceX
is going to need *several* Starship/Super Booster combinations to meet
this high flight rate.

Depending on how much shielding they actually need with steel, the
math
may return to favouring carbon fibre or aluminium.

Bull****.

Going to LEO will work with heavy steel. But once they set the target to
Mars, they may need all the mass savings they can get.

Again, Musk has said stainless steel allows for a *lighter* Starship
design because the thermal protection system can be much lighter. It's
an excellent design trade. You keep hand waving without providing the
evidence that your assertions are true. I trust that SpaceX ran the
numbers and Musk is reporting the results of an actual engineering
analysis when he makes this point.

Also, the goal is to lower the cost of access to space. Cheap stainless
steel allows for that far more than something "exotic" and more
expensive like carbon fiber composites with heavier thermal protection.

Jeff
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