Attitudes toward Mars

>
> True for DOT, but over simplified. DOT regulations refer to
> containers that have no internal tension or external compression
> members and are designed to be bounced over rough roads in trucks
> going 70 MPH. More to the point, but difficult to refer to as

Also misleading, DOT regulations are a lot broader than that. They
also cover aircraft pressurized structures (via FAA). These standards
are all based on the ASME Boiler Code which was originally designed to
address the problem of ships boilers which exploded rather frequently.

> commercial, are NASA spacesuits. These are not single simple shapes
> but are complicated composites of simple conic sections. Conic shapes

To be a bit more precise, they are tapered cylinders.
Cone implies a flat surface at one end, nobody does that for pressure
vessels.
This conforms to the ASME standard of using purely hoop stresses in
pressurized structures.
The NASA space suits do not have any flat surfaces under presssure.

That is the key to this discussion which you missed.

Nobody does pressurized hemispheres.
That is because the flat surface results in a huge cantivlever with a
massive bending moment at the circle where the dome meets the floor.

> are only required where one wants to use the least amount of material
> for a given function. A meter thick wall of steel reinforced concrete
> surrounding a one meter volume at one atmosphere can be any possible
> shape including square. It is just way over designed.
>

Perhaps as an amusing thought experiment, but not for practical
applications.

Please provide us an example of a pressurized cuboid, 5 psi or above.

They do not exist in commercial usage.

What happens with flat surfaces is that the connecting wall cannot be of
a constant thickness.
To achieve a constant factor of safety (standard stress design
requirement) the wall has to be
tapered, becoming thicker closer to the join. This makes it very
expensive to manufacture.

That is why people do not do it.

It is much easier simply to use one of the tried and trusted shapes,
either sphere or cylinder (tapered cylinder is fine) or torus.

> An engineer told to build a Martian dome would just switch materials
> where the stress levels are too high for the original material. A

No he would not.

If he was a state licensed mechanical engineer, this would be his
reply....

"You want a pressurized dome ? What ever for ?
It will be a huge undertaking to design and analyze, let alone
manufacture it.
I cannot use hoop stresses to analyze it, so I will have to do the thing
with finite element analysis which complicates things considerably, and
gives a less accurate result.
There would also have to be a considerable amount of testing with
prototypes to validate the finite element computer model.

Why not simply use a sphere or cylinder ?
That way I can give you two or three times the volume for half the
material,
and get it done for you ten times as quickly, and cheaper too."

Mitchell, I have been there and done that.

For example, on one occassion in my day job as a NASA contractor I was
asked to devise a process for getting OSHA approval for a box shaped
pressure vessel for an experiment.
I had a long talk with the Chair of the ASME committee who wrote the
regs, and the fellow basically told me
it was a waste of time and money. We would be a lot better off
designing a conventional curved pressure vessel, that would be much much
cheaper to design and get approved.

So that is what we did. We did not have money to burn, who does ?
In the real world with real money you do pressure vessels with curved
surfaces.

> space colony wall may be made up of conic sections at the low level
> but look like a straight line from a larger point of view. The fact

What it "looks like" is not important from a pressure standpoint.

> that my "Inside Out"
> design is
> made up of concentric oblate torus doesn't really change the
> functionality and I can discuss it from a high level as a disk with
> multiple levels and worry about its multiple torus at a lower design
> level.
>

That design sounds good to me.

What has that got to do with pressurized domes ?