>>>>I challenge anybody to take a look at the world around you and find me
a
pressurized structure (above 1 psi) in COMMERCIAL SERVICE which is not
one of those three shapes. >>>>

I can remember Zubrin talking about something similar. On a world of
substantial gravity, like the moon or mars, a hemispherical tent could be
used. The skirt of the tent, would be anchored several metres below the
ground, by the weight of the overlying soil. For small, low-pressure,
enclosed spaces (20-50m in diameter) this would seem to work reasonably
well. But there are severe limits to this technology. In order to minimise
the amount of digging, the method is only suitable for small enclosed
areas, where low atmospheric pressures are required. I get the feeling that
Zubrins fondness of low pressure atmospheres for many of his mission
scenarios, stems from the fact that it is much easier to construct habitats
if you are prepared to risk a low pressure environment.

Unfortunately, many of Zubrins calculations were overoptimistic. He
assumed that Kevlar sheeting would be used to construct such domes. Kevlar
is unsuitable for continuous loads, due to a slow creep related problem.
Zubrin also assumed the existence of a Kevlar that was 3-5 times stronger
than existing Kevlar. The safety factor that he assumed was 3, a margin
that would be considered too low by many pressure vessel experts.
I can remember discussing this problem on the Artemis project mailing
list. We were investigating the possibility of using a spherical, polymer
pressure vessel, in order to house a HEO manufacturing facility. The
initial mass estimate, from Zubrins calculations, put the mass of the 50m
diameter spherical pressure vessel, at 8 tonnes. After examination of the
various existing polymer materials, it was found that a Vectran pressure
vessel would be required. The mass of the vessel, assuming a reasonable
safety factor, was about 40 tonnes. This suggests that for initial
facilities, it might be worth while importing the pressure vessel from
Earth.

Tony

> I can remember Zubrin talking about something similar. On a world of
>substantial gravity, like the moon or mars, a hemispherical tent
could be
>used. The skirt of the tent, would be anchored several metres below the
>ground, by the weight of the overlying soil.

I haven't read Zubrin. So if this is what is meant by dome, I agree
that it would never work. I assumed by dome that we were talking
about a proper structure with a circular concrete base. The only
way this would work is by filling spheres half full of local soil
and burying them half-way down. Then it would look like a dome.

Mitchell James
mejames@...
http://www.InnerTransit.net (Email distribution for multilevel organizations)
http://www.InnerTransit.org (Homebase for collaborative engineering)

Zubrin also assumed the existence of a Kevlar that was 3-5 times stronger
than existing Kevlar.

I find that shocking, since O'Neill never went beyond current material strengths in any of hisengineering, and yet Zubrin has called O'Neill's work "absurd".

Regards,

Mike Combs

The only
way this would work is by filling spheres half full of local soil
and burying them half-way down. Then it would look like a dome.

Why throw away 50% of the useful volume ?

I still do not see any advantages of domes.

Even if we wanted a greenhouse dome, all we need are some shallow trays of dirt in the middle, we do not need to fill the entire lower half with soil.

And trays of custom hydroponic fluids (nutrient rich water) would be more useful than sterile Martian soil.

Cheers,

CR.

> In a message dated Mon, 25 Jun 2001 4:13:01 PM Eastern Daylight Time,
> Mitchell James mejames@... writes:
>
> The only
> way this would work is by filling spheres half full of local soil
> and burying them half-way down. Then it would look like a dome.
> ===================
>
> Why throw away 50% of the useful volume ?
>
> I still do not see any advantages of domes.

But Charles,

They look like SF paintings from the 50s. Just like our hero Dr.
Strangelove (excuse me -- Wernher von Braun) portrayed our future.

I apologize in advance to the true innocents offended by my sarcastic
humor.

Chuck Divine

>>>>I haven't read Zubrin. So if this is what is meant by dome, I agree
that it would never work. I assumed by dome that we were talking
about a proper structure with a circular concrete base. The only
way this would work is by filling spheres half full of local soil
and burying them half-way down. Then it would look like a dome.>>>>

Many of Zubrins ideas may seem flawed, but they are brilliant, none the
less. In various High Frontier concepts that I have studied, I have
included ideas or pieces of technology that Zubrin helped develop for his
Mars Direct plan. Zubrins ideas are not always well thought through or
backed up by practical science. On many occasions I have had to adapt his
ideas by filtering out engineering flaws. The case of his Kevlar 'dome' is
a good example. None the less, I would recommend his book 'The Case for
Mars'. If nothing else, reading the book should give you some idea as to
what we are up against. Zubrins 'Case for Mars' has probably done more to
wreak the 'High Frontier' than all else combined.

I have a few spare copies of the book. If you send me your mailing
address, I can post one to you. It makes interesting reading, but I
couldn't escape the impression that parts of it were amateurish.

Tony

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