Author Topic: Elon Musk: glass geodesic domes  (Read 98815 times)

Offline LMT

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Re: Glass geodesic domes
« Reply #20 on: 10/29/2016 01:14 am »
ETFE

Eden project does seem the most apt, the roof is a dynamic structure giving so much more that just protection from weather.

Sure seems that way.  ETFE's many useful properties have encouraged architects to design very imaginative ETFE structures on Earth.  (That one page displays ETFE "urban icebergs", a "double-fish" oasis, a pneumatic solar trough, a geodesic "bubble garden" with vein lights, and an "amphibious pavilion".  Wild work, certainly worth a look.) 

And under Mars' low gravity and negligible wind load... well, it would be interesting to see how architects might improve on the simple ETFE dome there.

Hydrogen from water, carbon from CO2, fluorine from?

From Earth, at least at first.  A 4-cushion, 300-m dome would need only 20-30 tons of Tefzel ETFE foil cargo.  Not bad, for a 2,000,000 m3 space. 

Mass-efficiency is another virtue of ETFE engineering, don't you think?
« Last Edit: 12/14/2016 06:49 pm by LMT »

Offline virnin

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Re: Glass geodesic domes
« Reply #21 on: 10/29/2016 01:33 am »
The panels are the same shape if the dome is based on an icosahedron. Each panel is an equilateral triangle.
Do you mean domes of only 20 faces? Once you tesselate and distort vertices to remain on a sphere obviously they must become something other than equilateral, simply because they were equilateral while perfectly planar.

To me the 20 face variation is not that interesting because the size you could transport would probably be even smaller than ITS volumes.
Each of the 20 faces can be arbitrarily large if they are constructed of smaller equilateral panels.  Yes, I understand that framing the sub-panels to keep each face flat will not be trivial but might prove easier than dealing with multiple shapes.

Offline KelvinZero

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Re: Glass geodesic domes
« Reply #22 on: 10/29/2016 02:20 am »
Each of the 20 faces can be arbitrarily large if they are constructed of smaller equilateral panels.  Yes, I understand that framing the sub-panels to keep each face flat will not be trivial but might prove easier than dealing with multiple shapes.
I was wondering about, say, using internal cabling to distribute the load, sort of like a suspension bridge. Im guessing variable sized faces really isn't such a big problem though.

In terms of arbitrarily  extendable shapes, another Idea I had was a constant size cell with bulging faces, eg cubical, or hexagonal cylinder, that can be joined or even stacked with adjoining faces removed. Again, cabling is used to distribute tension especially from top to bottom so it needs no anchoring. You could make an arbitrarily wide open area but there would always be columns down every ten meters or so, so you can't build a football field this way.

There would be creases on top that would gather dust, but you would probably actually fill these with dust deliberately to help weigh it down and create paths that can be walked over the roof. Traversing these paths a robot or person could manage dust build up very easily.

This approach would also give you the option of not removing internal faces, allowing you to extend without interfering with other sections and creating redundant levels of safety from decompression.
« Last Edit: 10/29/2016 02:27 am by KelvinZero »

Offline KelvinZero

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Re: Glass geodesic domes
« Reply #23 on: 10/29/2016 02:37 am »
Come to think of it, even if you can find a way to build larger volumes from a constant size face, you still have to use cabling or some other additional buttressing such as internal walls. This is because pressure vessels of greater volume need thicker walls to maintain the same pressure safely. I think I heard somewhere that the 'dry' mass ends up being proportional to the volume, not the surface area.

Offline LMT

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Re: Glass geodesic domes
« Reply #24 on: 10/29/2016 03:06 am »
Pressure Vessels

...pressure vessels of greater volume need thicker walls to maintain the same pressure safely. I think I heard somewhere that the 'dry' mass ends up being proportional to the volume, not the surface area.

You can get around that scaling law by holding the wall's interior and exterior pressures in close lockstep throughout construction and operation.  That is, don't build a pressure vessel.  It's easier said than done of course, but if accomplished it slashes the required mass, so I think it's a good target for the aspiring Mars architect to aim for.
« Last Edit: 12/14/2016 06:48 pm by LMT »

Offline Jimmy Murdok

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Re: Glass geodesic domes
« Reply #25 on: 10/29/2016 04:28 am »
Regarding pole length and types it depends on the frequency of the dome (or in how many triangles you want to distribute the structure). Few years ago I prepared a manual for the Mars Society Spain.
You can see the PDF at https://drive.google.com/open?id=0BzLuCXIhbPsdV3NsSEo1dlBVTlE
Below an extraction.
A couple of good dome calculators
http://www.desertdomes.com/domecalc.html
http://www.domerama.com/calculators/

Offline KelvinZero

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Re: Glass geodesic domes
« Reply #26 on: 10/29/2016 09:10 am »
You can get around that scaling law by holding the wall's interior and exterior pressures in close lockstep...
I think you are referring to building underwater, also a pet idea of mine.

To far off topic here though. Im even taking it a bit far off topic by mentioning shapes other than geodesic domes. This is really all about Elon Musk's Reddit AMA mention of geodesic domes.

Anyone got an opinion specifically on anchoring? To me the most obvious solution is to build almost-spheres not domes, with different, lighter materials for the bottom faces, probably flattened on the bottom because it is also filled up with soil. Either digging a hole for a true sphere or filling with processed, non-toxic soil mean you cannot just build this thing immediately though. It is more than just hopping out of your ITS and assembling the pieces, and hoping you read the instructions right and don't have any odd sized pieces left over.. :)

..that is also why I started to talk about cylinders etc.. I don't really get pressure tight, anchored domes as something easy to assemble, a very first step. I realise there are somewhat DIY domes on earth, but not pressurised and anchored.

Offline KelvinZero

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Re: Glass geodesic domes
« Reply #27 on: 10/29/2016 09:26 am »
How about a shape that is a sphere sort of pulled into a Torus by a central tall column? Im not attempting to solve the uniform parts here, just have something that can immediately be assembled on a flat surface. I think a dome is a bit of a waste in a way if you cannot have something to exploit that large empty volume in the center. This central cylindrical column could have a multistory building assembled around it over time, and also be capped by a smaller domed lookout area.

..this is not exactly pretty in my mind though. A dome is iconic.. this would be more like a really fat guy at the beach, or a pingpong ball nestled in a doughnut.
« Last Edit: 10/29/2016 09:31 am by KelvinZero »

Offline Oli

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Re: Glass geodesic domes
« Reply #28 on: 10/29/2016 01:41 pm »

You'd need a mind boggling amount of see-through glass for shielding.

E.g. ~33k m^3 of glass for a 100m diameter dome. Assuming 2m thickness.

Is glass actually any good for radiation shielding?

Also, keeping it clean (see-through) could be difficult, with all that Martian dust on the outside.

Offline scienceguy

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Re: Glass geodesic domes
« Reply #29 on: 10/29/2016 01:56 pm »
You don't need a mind-boggling amount of glass for shielding if you use sections of liquid water kept liquid by a layer of Martian air acting as heat insulation. Please see diagram.
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Online Robotbeat

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Re: Glass geodesic domes
« Reply #30 on: 10/29/2016 02:26 pm »
A totally glass dome, structurally efficient without concerning shielding, would be nice to have. You could stargaze in comfort on a bed of grass. I think that'd be wonderful, even if it wasn't where people spend most of their time (whether due to radiation concerns or just because other building types are more efficient). With all the lights off, it'd be much better than stargazing in most developed countries (due to light pollution there).
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Offline Mongo62

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Re: Glass geodesic domes
« Reply #31 on: 10/29/2016 02:29 pm »
Maybe a look at the actual, measured radiation dose rates on the surface of Mars would be useful, to see just how much of a problem we are facing.

The Martian surface radiation environment a comparison of models and MSL/RAD measurements

"The values derived from the different transport models for the total dose equivalent rates (0.510.60 mSv/d) as well as the dose rate in tissue (0.160.20 mGy/d) and the dose rate in silicon (0.130.16 mGy/d) agree within 20%."

To put that into perspective, Wikipedia says:

"The average radiation dose from an abdominal X-ray is 0.7 mGy, that from an abdominal CT scan is 8 mGy, that from a pelvic CT scan is 6 mGy, and that from a selective CT scan of the abdomen and the pelvis is 14 mGy."

The tissue dose rate is equivalent to 16-20 Rads per day (1 mGy ~ 1 mSv ~ 100 Rad), on the surface of Mars with no radiation protection. This is equivalent to a 365-day dose (at 0.18 mGy per day) of 65.7 mGy ~ 65.7 mSv ~ 6,570 Rads.

Compare this to measured dose rates on Earth, from this page:

Average American's total radiation exposure = 6.2 mSv/year
New York-Tokyo flights for airline crew = 9mSv/year
Smoking 1.5 packs/day = 13 mSv/year
Current average limit for nuclear workers = 20 mSv/year

So a person staying on the Martian surface without any radiation shielding for 365 days would get about 10 times the average American radiation exposure, and about 3 times the average limit for nuclear workers. Given that there would by necessity be some amount of shielding, in the form of pressure-containing glass if nothing else, I do not think that the risk would be excessive.
« Last Edit: 10/29/2016 02:32 pm by Mongo62 »

Offline Oli

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Re: Glass geodesic domes
« Reply #32 on: 10/29/2016 02:48 pm »
You don't need a mind-boggling amount of glass for shielding if you use sections of liquid water kept liquid by a layer of Martian air acting as heat insulation. Please see diagram.

True, liquid water would be an alternative. Not sure you actually need insulation, the heat of the dense internal air could be enough to keep it liquid.

Offline LMT

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Re: Glass geodesic domes
« Reply #33 on: 10/29/2016 03:16 pm »
Water & Glass

You don't need a mind-boggling amount of glass for shielding if you use sections of liquid water kept liquid by a layer of Martian air acting as heat insulation. Please see diagram.

Thanks for the clear illustration.  You could cut the dome's structural mass if the water or ice were exterior (supported freely), rather than interior (suspended and encased).  Pros/cons of that option? 

Also, who is insulating whom, necessarily?  You have air pockets insulating dome water, and that's certainly conceivable; but it can go other ways.  Dome infrared reflection, water, ice and air pockets can all provide useful insulation, and none of the insulators need be kept very warm themselves.  The only space that must be warm is the inhabited space. 

tl;dr  Many insulating configurations to consider.



And why glass?   What are its advantages in the Mars environment?

I know Elon tweeted "glass", so it's OP, but it's early days for SpaceX hab design, and much can change.  So why not ETFE or some other, lighter panel material? 

Quote from: Oli
Also, keeping it clean (see-through) could be difficult, with all that Martian dust on the outside.

ETFE is self-cleaning, btw.  Fluorine makes it super-slick.

« Last Edit: 12/14/2016 06:48 pm by LMT »

Offline spacenut

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Re: Glass geodesic domes
« Reply #34 on: 10/29/2016 03:45 pm »
If enough silica sand is found, it could be melted and triangular panes manufactured on Mars.  Assemble the carbon fiber frame, and insert the panes from the inside.  If one is broken by a meteor, it can be replaced from the inside.  A temporary patch over could be popped over the opening, until repairs can be made permanent.  Each dome sealed off from connecting tunnels or underground habitats and manufacturing areas. 

Plexiglas triangles could be made instead of glass for less breakage.  However winds could scratch the panes with sandstorms.  So, maybe a thin glass outer layer with Plexiglas under for protection from breakage and air escaping.  The Plexiglas being a plastic could give some radiation protection for the greenhouse workers. 

Offline RonM

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Re: Glass geodesic domes
« Reply #35 on: 10/29/2016 04:44 pm »
The dome needs to hold air pressure and add some radiation protection, but it doesn't need to be a shirtsleeve environment. Keep the buildings inside the dome well insulated and wear a coat or jacket while walking around the inside the dome. That would save energy trying to heat the dome. Frost on the inside of the dome might be a problem.

If the dome gets too warm from sunlight (which I doubt), then it shouldn't be made of glass.

Anyone have some approximate numbers we can use to determine the interior temperature of the dome?

Offline rarchimedes

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Re: Glass geodesic domes
« Reply #36 on: 10/29/2016 06:03 pm »
It is hard to imagine how a glass dome would be even desirable in any early stage of Mars exploration. Glass can certainly be created that has little expansion or contraction over very wide temperature ranges and that can control to some extent the wavelengths of light and radiation that can easily pass through it, but such specialized glass would be far beyond the manufacturing capabilities of early landers. And transporting it there is an absurd idea. Any people who are going to be on Mars for more than a few days will need the protection of Mars regolith, the more the better, but at least a couple of meters. Of course, a cave would be ideal.

Online lamontagne

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Re: Glass geodesic domes
« Reply #37 on: 10/29/2016 06:08 pm »
The dome needs to hold air pressure and add some radiation protection, but it doesn't need to be a shirtsleeve environment. Keep the buildings inside the dome well insulated and wear a coat or jacket while walking around the inside the dome. That would save energy trying to heat the dome. Frost on the inside of the dome might be a problem.

If the dome gets too warm from sunlight (which I doubt), then it shouldn't be made of glass.

Anyone have some approximate numbers we can use to determine the interior temperature of the dome?
The dome will essentially lose and gain energy by radiation alone (needs to be checked, this is a guess). Convection in the thin Martian atmosphere should be negligible.  So the glass needs to let visible light in during the day, and stop infrared from leaving during the night.  The structures within the dome will need to absorb energy as well.   So the temperature boils down to: can we reduce the radiation loses at night from the glass.  If we can, then the interior temperature can be pretty much anything.  There is no real point in keeping it low.
Using effective solar films, such as Solarban 70XL, we can reduce emissivity from 0,8 for ordinary glass to 0,02 for Low-e glass.  That should be a good start.  The further north, the more difficult keeping up the temperature will be, as the solar gain goes down.
The low-e film is ridiculously cheap, BTW.




Online Robotbeat

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Re: Glass geodesic domes
« Reply #38 on: 10/29/2016 07:13 pm »
Yeah, insulating a dome is as simple as using several panes, low-e coating, and some sort of inert filler (could be vacuum or krypton or argon).

If you're trying to radiation shield stuff, you'd want a thick plastic layer in between the glass (like safety glass but with a thicker plastic layer). Then in between panes, use a bunch of water. Make the plastic layer thick enough to insulate the water to keep it from freezing and to prevent condensation from forming on the glass. In fact, you might want to include some mild resistive heating element (transparent, like tin oxide) to keep any condensation from forming.

The plastic is a better insulator and radiation shield than glass and is lighter. It's also tougher. The glass maintains an optically clear surface and resists UV and scratching and discolorization of the plastic.
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Online docmordrid

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Re: Glass geodesic domes
« Reply #39 on: 10/29/2016 07:39 pm »
Thin sections of aluminium oxynitrate are bulletproof, 1.6 inch stop a up to a .50 BMG, and containing aluminum would offer some shielding benefit. Tough as nails.
« Last Edit: 10/29/2016 07:42 pm by docmordrid »
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