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SpaceX Vehicles and Missions => SpaceX Super Heavy/Starship (BFR/BFS) - Earth to Deep Space => Topic started by: KelvinZero on 10/28/2016 04:16 am

Title: Elon Musk: glass geodesic domes
Post by: KelvinZero on 10/28/2016 04:16 am
Question from /u/Ulysius

As a follow-up, considering the synodal reuse of the ITS spaceships, what form of permanent habitation do you foresee? Shipped modules or an (eventual) shift to in-situ resource utilization such as Martian rigolith/plastic-reinforced concrete structures?

Thank you for your time.



Answer from /u/ElonMuskOfficial

Initially, glass panes with carbon fiber frames to build geodesic domes on the surface, plus a lot of miner/tunneling droids. With the latter, you can build out a huge amount of pressurized space for industrial operations and leave the glass domes for green living space.
I thought this was worth it's own topic because it is about the only thing we have that is specifically SpaceX.
What do we know about this sort of construction?

Wouldn't cylinders be more convenient and adaptable? Cylinders have the advantage that you can make variable volumes by extending their length. You can cover area in a grid more efficiently. They don't need anchoring. You can align them north-south to get the best sun.

What sort of tools would be necessary for these domes? What sort of work? Is it people clambering around in spacesuits or one dedicated robot type?
Title: Re: Glass geodesic domes
Post by: RonM on 10/28/2016 04:40 am
On Earth, geodesic domes can have issues with leaking, but that might be do to the DIY construction. A well engineered system should be okay.

One great advantage of a geodesic dome based on a sphere is that all of the triangular sections are the same shape. That should make construction easier.

Like any other structure attached to the surface, it will be hard to hold it down against the internal air pressure.
Title: Re: Glass geodesic domes
Post by: KelvinZero on 10/28/2016 08:02 am
One great advantage of a geodesic dome based on a sphere is that all of the triangular sections are the same shape. That should make construction easier.
I hadn't thought about it till now, but I believe they are not all the same shape. Im not sure how few shape variations you can end up with.

https://en.wikipedia.org/wiki/Geodesic_dome.

This page mentions 6 edge sizes, but I dont know how many variations of triangle shape that represents.
http://geo-dome.co.uk/4v_tool.asp

You could pretty much construct an arbitrary cylinder diameter and length from a single triangle size though.. but Im not sure about closing the ends. That sounds similar to the dome problem.
Title: Re: Glass geodesic domes
Post by: guckyfan on 10/28/2016 08:12 am
You could pretty much construct an arbitrary cylinder diameter and length from a single triangle size though.. but Im not sure about closing the ends. That sounds similar to the dome problem.

You can use a fiber dome on top and maybe steel in the ground. No need to have the domes transparent.
Title: Re: Glass geodesic domes
Post by: docmordrid on 10/28/2016 12:10 pm
Translucent may be enough if it's a polyethylene, a pretty fair radiation shield and let's a bit of soft light in. Extra points if it's borated for neutrons.
Title: Re: Glass geodesic domes
Post by: AncientU on 10/28/2016 12:57 pm
You could pretty much construct an arbitrary cylinder diameter and length from a single triangle size though.. but Im not sure about closing the ends. That sounds similar to the dome problem.

You can use a fiber dome on top and maybe steel in the ground. No need to have the domes transparent.

No need?  Is that from an engineering perspective?

For humans living underground, transparent has a significant psychological advantage.  Seeing the sun, sky, landscape, and stars, planets, and Galaxy at night will be a unique contribution to mental health -- it certainly will be* for me.

* 8)
Title: Re: Glass geodesic domes
Post by: Robotbeat on 10/28/2016 02:02 pm
The whole point of a geodesic dome would be if you want it transparent, IMHO. Sphere minimizes surface area (i.e. Area of heavy glass windows) that need to be transported from Earth. Cylinders would be better for most other uses, and tunnels (if it really is as easy as people seem to think it is... I'm not convinced) would work, too.

There was a geodesic dome built in Antarctica that was brought in by transport planes and built locally. It lasted decades until it eventually had to be taken down due to loads from the ever-shifting Antarctic ice sheet (a problem you wouldn't have on Mars). The advantage is you can build enormous structures with just the material you can fit in a small volume for transport. Or, you could have a fairly small fabrication machine producing members locally.

And it's beautiful.

I think that is the main reason. I suspect that if this all works out, there will be a few domes built but then most buildings will be variations on cylinders or perhaps at a big enough scale you could just build a huge block building.

I tend to prefer inflatable domes. Enormous ones are already used on Earth for various uses.
Title: Re: Glass geodesic domes
Post by: vapour_nudge on 10/28/2016 02:12 pm
What about problems of heat loss in the below freezing temperatures? (A good question for KelvinZero 😄)
Title: Re: Glass geodesic domes
Post by: docmordrid on 10/28/2016 02:15 pm
IR reflective coatings w/double layer panels? A vacuum layer between them should be trivial.
Title: Re: Glass geodesic domes
Post by: Robotbeat on 10/28/2016 02:31 pm
Yes. If you had a reflective shade that went over the dome at night and retracted in the day, the dome could be heated entirely via the Sun.
Title: Re: Glass geodesic domes
Post by: RonM on 10/28/2016 02:36 pm
One great advantage of a geodesic dome based on a sphere is that all of the triangular sections are the same shape. That should make construction easier.
I hadn't thought about it till now, but I believe they are not all the same shape. Im not sure how few shape variations you can end up with.

https://en.wikipedia.org/wiki/Geodesic_dome.

This page mentions 6 edge sizes, but I dont know how many variations of triangle shape that represents.
http://geo-dome.co.uk/4v_tool.asp

You could pretty much construct an arbitrary cylinder diameter and length from a single triangle size though.. but Im not sure about closing the ends. That sounds similar to the dome problem.

The panels are the same shape if the dome is based on an icosahedron. Each panel is an equilateral triangle.

Other shapes are used to make better use of the available rectangular building supplies.

http://geo-dome.co.uk/wiki/article.asp?uname=29

Spend some time examining the pages you find.
Title: Re: Glass geodesic domes
Post by: Robotbeat on 10/28/2016 02:50 pm
Icosahedrons are the only ones that are based on identical equilateral triangles with identical vertices.
Title: Re: Glass geodesic domes
Post by: nacnud on 10/28/2016 03:23 pm
A big dome with individual buildings inside gives the freedom to build, demolish and rebuild as seen fit. Another option could be to build individual buildings and roof over the streets. This would require less roofing materials. Have a few examples of both.
Title: Re: Glass geodesic domes
Post by: Mongo62 on 10/28/2016 05:24 pm
I just wanted to point out that the National Geographic episode shows diagrams of geodesic domes (among other items) on the surface of Mars in two scenes at timestamps 2:25-2:32 and 29:15-29:54.

Given their placement in the video, I suspect that these might be borrowed from SpaceX plans for the early Mars settlement.
Title: Re: Glass geodesic domes
Post by: gosink on 10/28/2016 07:41 pm
Would heat loss be the problem - or would excess heat be the problem?  After all, Mars' atmosphere is nearly just a dusty vacuum.

I know they go through contortions when engineering the Mars rovers to make sure they don't get too cold at night, but would that remain the same for a building sized structure, presumably with all sorts of equipment running all night?
Title: Re: Glass geodesic domes
Post by: Robotbeat on 10/28/2016 07:43 pm
If the building was the size and activity of a large shopping mall, they'd be fine as long as they used good insulation (double pane, etc) on the panels.
Title: Re: Glass geodesic domes
Post by: KelvinZero on 10/28/2016 08:19 pm
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.
Title: Re: Glass geodesic domes
Post by: RonM on 10/28/2016 08:34 pm
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.

Oh, that's right. The cords do change when you distort the vertices. For practical domes with many panels, they can't be the same shape.
Title: Re: Glass geodesic domes
Post by: LMT on 10/28/2016 09:24 pm
Eden Project

A big dome with individual buildings inside gives the freedom to build, demolish and rebuild as seen fit. Another option could be to build individual buildings and roof over the streets. This would require less roofing materials. Have a few examples of both.

(http://forum.nasaspaceflight.com/index.php?action=dlattach;topic=41526.0;attach=1384761;image)

It does open up the space, doesn't it?

Your Eden Project greenhouse example seemed especially apt, at least to us.  We used Eden Project specs as a basis for the notional 2,000,000 m3 Lake Matthew domes (http://forum.nasaspaceflight.com/index.php?topic=40019.msg1515131#msg1515131). 



One unsung virtue of Eden Project ETFE engineering, potentially very important on Mars: 

It's cryogenic.



An architectural overview (http://www.webpages.uidaho.edu/arch504ukgreenarch/casestudies/edenproject1.pdf) of the Eden Project, with references.
Title: Re: Glass geodesic domes
Post by: nacnud on 10/28/2016 10:38 pm
Eden project does seem the most apt, the roof is a dynamic structure giving so much more that just protection from weather. Your thread is long and I've yet to read it all but given that in-situ resource utilisation is going to be vital where can one easily find fluorine on Mars?

Hydrogen from water, carbon from CO2, fluorine from?

Genuine question, no criticism intended.
Title: Re: Glass geodesic domes
Post by: LMT 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 (http://inhabitat.com/tag/etfe/) 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?
Title: Re: Glass geodesic domes
Post by: virnin 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.
Title: Re: Glass geodesic domes
Post by: KelvinZero 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.
Title: Re: Glass geodesic domes
Post by: KelvinZero 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.
Title: Re: Glass geodesic domes
Post by: LMT 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.
Title: Re: Glass geodesic domes
Post by: Jimmy Murdok 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 (https://drive.google.com/open?id=0BzLuCXIhbPsdV3NsSEo1dlBVTlE)
Below an extraction.
A couple of good dome calculators
http://www.desertdomes.com/domecalc.html (http://www.desertdomes.com/domecalc.html)
http://www.domerama.com/calculators/ (http://www.domerama.com/calculators/)
Title: Re: Glass geodesic domes
Post by: KelvinZero 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.
Title: Re: Glass geodesic domes
Post by: KelvinZero 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.
Title: Re: Glass geodesic domes
Post by: Oli 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.
Title: Re: Glass geodesic domes
Post by: scienceguy 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.
Title: Re: Glass geodesic domes
Post by: Robotbeat 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).
Title: Re: Glass geodesic domes
Post by: Mongo62 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 (http://www.swsc-journal.org/articles/swsc/pdf/2016/01/swsc150074.pdf)

"The values derived from the different transport models for the total dose equivalent rates (0.51–0.60 mSv/d) as well as the dose rate in tissue (0.16–0.20 mGy/d) and the dose rate in silicon (0.13–0.16 mGy/d) agree within 20%."

To put that into perspective, Wikipedia  (https://en.wikipedia.org/wiki/Gray_(unit))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 (http://radiationsurvival.blogspot.ca):

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.
Title: Re: Glass geodesic domes
Post by: Oli 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.
Title: Re: Glass geodesic domes
Post by: LMT 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 (https://www.chemours.com/Teflon_Industrial/en_US/assets/downloads/tefzel-etfe-film-properties.pdf), btw.  Fluorine makes it super-slick.

Title: Re: Glass geodesic domes
Post by: spacenut 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. 
Title: Re: Glass geodesic domes
Post by: RonM 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?
Title: Re: Glass geodesic domes
Post by: rarchimedes 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.
Title: Re: Glass geodesic domes
Post by: lamontagne 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.



Title: Re: Glass geodesic domes
Post by: Robotbeat 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.
Title: Re: Glass geodesic domes
Post by: docmordrid 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.
Title: Re: Glass geodesic domes
Post by: Robotbeat on 10/29/2016 07:41 pm
Aluminum is a crappy shielding material. Everything lighter on the Periodic Table is superior, including oxygen, nitrogen, carbon, and of course hydrogen.
Title: Re: Glass geodesic domes
Post by: docmordrid on 10/29/2016 07:54 pm
Aluminum is used in Earth-side radiation shielding. It's most effective against particles (alpha, beta) but is also used in gamma shields up to about 10 MeV. In diagnostic radiology it's used to filter soft x-rays downstream from the beam source.

Now add in the impact resistance.

We also need to consider how high the dome is, and the degree & gas mix used for pressurization. This because of 2 factors: the radiation 'flavors' and intensity will be reduced by the atmosphere in the dome, and the inverse square law. ISW won't be that significant, scatter from the dome won't be a point source due to overlapping, but some areas will get less than others.
Title: Re: Glass geodesic domes
Post by: KelvinZero on 10/29/2016 09:20 pm
Im mainly concerned with the initial prefab versions. My impression is that initially everything is shipped from earth and assembled on mars.. Only then is significant digging performed, and only after that significant manufacturing.

I think the intention is a prefab that can be immediately assembled on the surface.

Elon: "Initially, glass panes with carbon fiber frames to build geodesic domes on the surface, plus a lot of miner/tunneling droids. With the latter, you can build out a huge amount of pressurized space for industrial operations and leave the glass domes for green living space."

Water for shielding could be an option right from the beginning since it may be required for return propellent. There are various issues/alternatives around that but I am more concerned with prefab issues such as anchoring.
Title: Re: Glass geodesic domes
Post by: launchwatcher on 10/29/2016 10:14 pm
Conventional wisdom about geodesic domes on earth is that they tend to leak.   While they're mass efficient per unit of volume enclosed, they have a lot of facets and corners and edges.

Getting the seals between prefab panels right may well be a challenge - particularly at the (many) corners, where five or six triangular panels come together. 

Title: Re: Glass geodesic domes
Post by: Vultur on 10/30/2016 12:12 am
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.

Hardly. See Mongo62's post above - radiation levels on Mars surface are not that high.
Title: Re: Glass geodesic domes
Post by: MickQ on 10/30/2016 12:21 am
Conventional wisdom about geodesic domes on earth is that they tend to leak.   While they're mass efficient per unit of volume enclosed, they have a lot of facets and corners and edges.

Getting the seals between prefab panels right may well be a challenge - particularly at the (many) corners, where five or six triangular panels come together.

After assembly the dome could be partially pressurised and then a silicone rubber sealant applied to all the joints and corners on the inside.  Air pressure should push the sealant into all the leaks.  Keep increasing pressure and applying sealant until no more whiskers appear on the outside.

As to anchoring, what about a flat skirt extending 3 metres all around the structure and pile regolith on top.  Spray water onto it which will freeze and lock it in shape or alternately if the water content is high enough then just microwave while shaping to the required profile.
Title: Re: Glass geodesic domes
Post by: Robotbeat on 10/30/2016 01:08 am
Conventional wisdom about geodesic domes on earth is that they tend to leak.   While they're mass efficient per unit of volume enclosed, they have a lot of facets and corners and edges.

Getting the seals between prefab panels right may well be a challenge - particularly at the (many) corners, where five or six triangular panels come together.
That's an interesting point.
Title: Re: Glass geodesic domes
Post by: lamontagne on 10/30/2016 01:59 am
I have made a little spreadsheet of the solar heat gain for a day in a dome, vs the heat loss overnight.
If I am correct, the heat gain is much higher than the loss, even with non insulated glass.

So at first glance there is no need for any insulation. It might even be required to have some type of curtain during the day, or larger areas of opaque walls, to reduce the heat gain to manageable proportions.

My main assumption are that all energy is maintained in the dome (need energy absorbent walls for the interior surface areas) and that convection is negligible.  White walls inside the dome would reduce gain considerably, for example.

Title: Re: Glass geodesic domes
Post by: LMT on 10/30/2016 01:32 am
Iron, Lead, Glass, Boat

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.

Thanks for those numbers.  One important difference, when comparing Mars dose rates against dose rates on Earth:  the cosmic rays hitting Mars contain high charge and energy (HZE) particles, which may be more dangerous than the lower-energy radiation on Earth.  As noted in Cucinotta's 2014 Review of NASA Approach to Space Radiation Assessments for Mars Exploration (https://www.researchgate.net/profile/Francis_Cucinotta/publication/270343359_Review_of_NASA_Approach_to_Space_Radiation_Risk_Assessments_for_Mars_Exploration/links/54f472570cf24eb8794e8a9e.pdf):

Quote from: Cucinotta
Animal studies generally demonstrate that HZE particles have higher carcinogenic effectiveness than low-LET radiation. However, the number of studies of animal carcinogenesis made with HZE nuclei is extremely limited...

There are no human epidemiology data for HZE particles to estimate cancer risk or most other late effects with the exception of cataracts...

The shielding requirement for high-energy particles is just brutal.  As a quantitative hypothetical:  If shield construction were limited to a 1-meter maximum thickness, the only effective ISRU shield known to me, would be one of iron.  Aguayo et al. 2011, Fig. 38 (http://www.pnnl.gov/main/publications/external/technical_reports/PNNL-20693.pdf). 

And for the notional "glass geodesic dome"?  Well, a meter of iron cover would have "suboptimal" light transmission, obviously.  One option: a meter of lead is also effective shielding.  If PbO were transported as cargo it could in theory be incorporated into the manufacture of radiation-shielding glass on-site.  For example, this Schott RS 520 glass (http://www.schott.com/advanced_optics/english/products/optical-materials/special-materials/radiation-shielding-glasses/index.html). 

(http://www.schott.com/advanced_optics/media/keyvisual/scale/w759/radiation-shielding.jpg)

The basic RS 520 slab looks to be 1.6 m x 1.1 m x 0.2 m, having mass of 2 tons.  That's 1.4 tons of PbO, per slab.  Multiply by 5 slabs for a meter of shielding, then multiply by the number of panes in a dome--  Whoo. 

(https://cdn.meme.am/instances/250x250/69138981.jpg)
Title: Re: Glass geodesic domes
Post by: gospacex on 10/30/2016 06:33 am
The whole point of a geodesic dome would be if you want it transparent, IMHO. Sphere minimizes surface area (i.e. Area of heavy glass windows) that need to be transported from Earth. Cylinders would be better for most other uses, and tunnels (if it really is as easy as people seem to think it is... I'm not convinced) would work, too.

There was a geodesic dome built in Antarctica that was brought in by transport planes and built locally. It lasted decades until it eventually had to be taken down due to loads from the ever-shifting Antarctic ice sheet (a problem you wouldn't have on Mars). The advantage is you can build enormous structures with just the material you can fit in a small volume for transport. Or, you could have a fairly small fabrication machine producing members locally.

And it's beautiful.

Why the new Antarctic base has no geodesic dome?
Title: Re: Glass geodesic domes
Post by: guckyfan on 10/30/2016 07:29 am
One important difference, when comparing Mars dose rates against dose rates on Earth:  the cosmic rays hitting Mars contain high charge and energy (HZE) particles, which may be more dangerous than the lower-energy radiation on Earth.

Sievert are a weighted metric for biologic effects and include the higher risk due to high energy particles. As the effects of high energy particles are not very well known, it is a safe assumption that the effects are not undervalued. Much more likely they are overvalued as a cautionary measure.
Title: Re: Glass geodesic domes
Post by: guckyfan on 10/30/2016 07:36 am
About extremely thick radiation absorbing glass.

The purpose of these domes is very much aesthetic. That purpse would defeated by using such glass and would make it exceedingly expensive. So any radiation protection would be incorporated in buildings inside the dome, not the dome itself.
Title: Re: Glass geodesic domes
Post by: docmordrid on 10/30/2016 07:37 am
>
There was a geodesic dome built in Antarctica that was brought in by transport planes and built locally. It lasted decades until it eventually had to be taken down due to loads from the ever-shifting Antarctic ice sheet (a problem you wouldn't have on Mars). The advantage is you can build enormous structures with just the material you can fit in a small volume for transport. Or, you could have a fairly small fabrication machine producing members locally.

And it's beautiful.

Why the new Antarctic base has no geodesic dome?

As he said, shifting ice made for an unstable base. It did last 35 years though, and I don't see many glaciers on Mars away from the poles. Here's a brief story about the South Pole Dome.

https://antarcticsun.usap.gov/features/contenthandler.cfm?id=1984
Title: Re: Glass geodesic domes
Post by: KelvinZero on 10/30/2016 08:03 am
About extremely thick radiation absorbing glass.

The purpose of these domes is very much aesthetic. That purpse would defeated by using such glass and would make it exceedingly expensive. So any radiation protection would be incorporated in buildings inside the dome, not the dome itself.
Roof pools. I think swimming and diving would be really fun on Mars, you can dive from higher and go deeper without ear ache, and water ISRU has to be running right from the beginning. An hour a day using the pool wouldn't add much health risk, apart from drowning of course.
Title: Re: Glass geodesic domes
Post by: Oli on 10/30/2016 09:40 am
Why the new Antarctic base has no geodesic dome?

Likely because you only need buildings and not pressure vessels or large open spaces.
Title: Re: Glass geodesic domes
Post by: gospacex on 10/30/2016 12:26 pm
>
There was a geodesic dome built in Antarctica that was brought in by transport planes and built locally. It lasted decades until it eventually had to be taken down due to loads from the ever-shifting Antarctic ice sheet (a problem you wouldn't have on Mars). The advantage is you can build enormous structures with just the material you can fit in a small volume for transport. Or, you could have a fairly small fabrication machine producing members locally.

And it's beautiful.

Why the new Antarctic base has no geodesic dome?

As he said, shifting ice made for an unstable base. It did last 35 years though, and I don't see many glaciers on Mars away from the poles. Here's a brief story about the South Pole Dome.

https://antarcticsun.usap.gov/features/contenthandler.cfm?id=1984

There is ice sure enough, but the article does not say anything about *shifting* ice damaging the dome. From what I read elsewhere, the problem on the South Pole is that ice not so much shifts but accumulates, burying structures.

However, if the shifting ice was indeed a problem, still, the new base with elevated supports with ability to be jacked up still does not have a geodesic dome.

Geodesic dome could be built on a similar elevated base. It wasn't. I guess the practical experience of running old base had shown that there are no actual advantages to having one. The "boring" rectangular buildings with "small" windows work fine, and they are more practical to build.
Title: Re: Glass geodesic domes
Post by: Robotbeat on 10/30/2016 12:38 pm
Because the new building is specifically designed to withstand moving ice and blown snow.
Title: Re: Glass geodesic domes
Post by: Robotbeat on 10/30/2016 12:41 pm
Lead is one of the worst POSSIBLE shielding materials. Iron is also terrible.

GCRs are not X-rays or gammas. They're high energy particles. You want as low atomic mass as possible. Hydrogen is the ideal.
Title: Re: Glass geodesic domes
Post by: gospacex on 10/30/2016 01:43 pm
Because the new building is specifically designed to withstand moving ice and blown snow.

Why aren't they circular and round on the top, why are they rectangular? To me it disproves to idea that geodesic dome is advantageous. These guys actually tried it, and they don't want to repeat it.
Title: Re: Glass geodesic domes
Post by: LMT on 10/30/2016 02:21 pm
GCRs are not X-rays or gammas. They're high energy particles.

100+ MeV (https://msis.jsc.nasa.gov/sections/section05.htm#_5.7_RADIATION), yes. 

Lead is one of the worst POSSIBLE shielding materials. Iron is also terrible... 

You want as low atomic mass as possible. Hydrogen is the ideal.

Compare two notional meter-thick Mars ISRU shields, one of iron, one of water: Fig. 3 and Fig. 27 (http://www.pnnl.gov/main/publications/external/technical_reports/PNNL-20693.pdf), for example.  Which is the better shield against high-energy protons?
Title: Re: Glass geodesic domes
Post by: Robotbeat on 10/30/2016 02:35 pm
1) On a mass basis, water is far better. Something like lead would need to be brought from Earth. It'd be terrible.
2) that's not a good document to use because you can't look individually at the particles. Have to look at a spectrum. Please use a tool designed for space radiation an the secondaries it generates: http://oltaris.nasa.gov
Title: Re: Glass geodesic domes
Post by: Arb on 10/30/2016 02:41 pm
Let's keep this on topic folks; carbon fibre frame with glass panels is what Musk specified.

There are plenty of other threads for discussing radiation protection on Mars.

Ditto for your personal favourite fantasy Mars structure(s).
Title: Re: Glass geodesic domes
Post by: Robotbeat on 10/30/2016 02:44 pm
GCRs are not X-rays or gammas. They're high energy particles.

100+ MeV (https://msis.jsc.nasa.gov/sections/section05.htm#_5.7_RADIATION), yes. 

Lead is one of the worst POSSIBLE shielding materials. Iron is also terrible... 

You want as low atomic mass as possible. Hydrogen is the ideal.

Compare two notional meter-thick Mars ISRU shields, one of iron, one of water: Fig. 3 and Fig. 27 (http://www.pnnl.gov/main/publications/external/technical_reports/PNNL-20693.pdf), for example.  Which is the better shield against high-energy protons?
As an example as to why you need to use a tool like Oltaris instead, look at figures 1 and 25, which shows neutron flux. Neutrons are much worse than protons for biological effects, and as you can see, a meter of water does better than iron, plus it weighs an order of magnitude less. Also, look at the actual number of neutrons vs protons.

Please use a real tool like Oltaris, or at least a graph that use actual biological effective dose for the entire GCR spectrum at Mars, not just separate components.
Title: Re: Glass geodesic domes
Post by: LMT on 10/30/2016 02:48 pm
Dome Pool

About extremely thick radiation absorbing glass.

The purpose of these domes is very much aesthetic. That purpse would defeated by using such glass and would make it exceedingly expensive. So any radiation protection would be incorporated in buildings inside the dome, not the dome itself.
Roof pools. I think swimming and diving would be really fun on Mars, you can dive from higher and go deeper without ear ache, and water ISRU has to be running right from the beginning. An hour a day using the pool wouldn't add much health risk, apart from drowning of course.

Plus the health risk from your laser-sharks (http://forum.nasaspaceflight.com/index.php?topic=41427.msg1604169#msg1604169), presumably.  :)

But you know, if your dome's pool water were pumped up from the dome interior, it would be oxygen-rich at the dome surface, degassing only as it rose toward the pool surface, where pressure drops to ambient atmospheric pressure.

That is, for an exterior, protective pool.

One could conceive of a transparent netting in the pool, strung out horizontally 1 m above the dome surface.  It would prevent excursions above that depth.  Beneath the netting, conceivably cold-water fish could live in that oxygen-rich water, if the pool held several meters of shielding water above the netting.

Cold-water fish, or, if you preferred... ?

(https://bloomgist.files.wordpress.com/2016/08/the-oldest-greenland-shark-found-by-researchers-was-most-likely-around-392-years-old.jpg)

Title: Re: Glass geodesic domes
Post by: guckyfan on 10/30/2016 03:11 pm

But you know, if your dome's pool water were pumped up from the dome interior, it would be oxygen-rich at the dome surface, degassing only as it rose toward the pool surface, where pressure drops to ambient atmospheric pressure.

I hope you are just kidding. But I don't read your comment that way. English is not my first language. The pool would be on the roof of the building inside the dome. I have thought of using water this way for recreation and radiation shielding as well.
Title: Re: Glass geodesic domes
Post by: LMT on 10/30/2016 03:18 pm
GCRs are not X-rays or gammas. They're high energy particles.

100+ MeV (https://msis.jsc.nasa.gov/sections/section05.htm#_5.7_RADIATION), yes. 

Lead is one of the worst POSSIBLE shielding materials. Iron is also terrible... 

You want as low atomic mass as possible. Hydrogen is the ideal.

Compare two notional meter-thick Mars ISRU shields, one of iron, one of water: Fig. 3 and Fig. 27 (http://www.pnnl.gov/main/publications/external/technical_reports/PNNL-20693.pdf), for example.  Which is the better shield against high-energy protons?
As an example as to why you need to use a tool like Oltaris instead, look at figures 1 and 25, which shows neutron flux. Neutrons are much worse than protons for biological effects, and as you can see, a meter of water does better than iron, plus it weighs an order of magnitude less. Also, look at the actual number of neutrons vs protons.

Please use a real tool like Oltaris, or at least a graph that use actual biological effective dose for the entire GCR spectrum at Mars, not just separate components.

You're saying, "use a real tool", but it's the studies that help you make strong assertions, so you should include some study citations if you want to say more about radiation.  And as Arb says, there are other threads, np.
Title: Re: Glass geodesic domes
Post by: Robotbeat on 10/30/2016 06:01 pm
You really want me to link to all the studies used to validate Oltaris? Seems pointless.
Title: Re: Glass geodesic domes
Post by: DanielW on 10/30/2016 07:59 pm
A few notes. Icosahedrons can be further subdivided with each face being broken into 3 identical isosceles triangles. You would need two types of vertices and two types of edges, but your panels would all be the same.

Also if leaks are a problem why not make it intentionally leaky and inflate a thin transparent bladder inside?
Title: Re: Glass geodesic domes
Post by: TripD on 10/30/2016 09:31 pm
I know everyone wants water on the roof, but I opted for water at the bottom of the sphere.  Call me a traditionalist.  You could still have sharks with lasers though.
Title: Re: Glass geodesic domes
Post by: LMT on 10/30/2016 10:21 pm
Extended Aquaculture

But you know, if your dome's pool water were pumped up from the dome interior, it would be oxygen-rich at the dome surface, degassing only as it rose toward the pool surface, where pressure drops to ambient atmospheric pressure.

I hope you are just kidding. But I don't read your comment that way. English is not my first language. The pool would be on the roof of the building inside the dome. I have thought of using water this way for recreation and radiation shielding as well.

Why not outside the dome, to shield the entire facility?  At 0.7 kPa, the icy surface would sublimate only about as fast as water evaporates on Earth (http://onlinelibrary.wiley.com/doi/10.1029/2005GL023443/full).  That rate seems manageable.  And fish are fish.  So why not stock the water above the dome?  We could think of it as an "extended aquaculture", if that helps.
Title: Re: Glass geodesic domes
Post by: guckyfan on 10/30/2016 10:28 pm

Why not outside the dome, to shield the entire facility?

Because it would make the design and construction of the dome much more complicated. It also cannot shield the entire facility without making the whole dome idea basically moot because you no longer have an unobstructed view to the outside, which is the whole reason for the existence of such domes.
Title: Re: Glass geodesic domes
Post by: KelvinZero on 10/30/2016 10:34 pm
I don't think anyone has talked about anchoring yet? To me this is the elephant in the room for domes.

Options I see:

* Anchor into the ground. Maybe this isn't as hard as it seems?

* Bury a sphere. Involves digging a hemispherical hole or possibly exploiting a fortuitous crater.

* Don't bury a sphere. This isn't really a dome any more but I think it would look pretty. You just have to stop it rolling :)

* Create a truncated sphere by inverting a lower segment to become a domed floor. It would be strong, relying on compressive strength. The ring where the floor joins the  transparent dome might need extra reinforcing with cable. This rim could also be buried a bit in a shallow circular trench.

The last option could give you a nice moat for your laser sharks :)
Title: Re: Glass geodesic domes
Post by: LMT on 10/30/2016 10:49 pm
Dome Complexity

Why not [water] outside the dome, to shield the entire facility?

Because it would make the design and construction of the dome much more complicated.

But the water weight would reduce the anchoring forces (see KelvinZero (http://forum.nasaspaceflight.com/index.php?topic=41526.msg1604817#msg1604817)), while water protects against radiation, dust storms, dust devils, impactors and temperature extremes.  These hazards must be dealt with, one way or another, in the dome design.  (The problem of glass radiation protection (http://forum.nasaspaceflight.com/index.php?topic=41526.msg1604544#msg1604544) is vexing, and a potential source of design complexity, by itself.)  So it seems exterior water could actually decrease the overall complexity of the dome.
Title: Re: Glass geodesic domes
Post by: LMT on 10/30/2016 11:06 pm
Dome Anchor/Float

* Create a truncated sphere by inverting a lower segment to become a domed floor. It would be strong, relying on compressive strength. The ring where the floor joins the  transparent dome might need extra reinforcing with cable. This rim could also be buried a bit in a shallow circular trench.

The last option could give you a nice moat for your laser sharks :)

Compression ring: (http://forum.nasaspaceflight.com/index.php?topic=40019.msg1517447#msg1517447) a great way to distribute load, yes.

And if the air pressure and water pressure at the dome rim are equal, you don't need to bury the rim.  Just anchor it, and let it hang in suspension subaqueously.  Moon pool.  It would allow dome entry and exit without the hassle of airlock. 

For persons, I mean. 

OK, if you really want, then yes, for your sharks, too.

(60 kPa equalizes at about 15 m depth on Mars.)
Title: Re: Glass geodesic domes
Post by: lamontagne on 10/31/2016 12:01 am
Essentially the same idea as TripD, but on a larger scale.

Domes for exterior view, tunnels for working and sleeping and radiation protection.  The cliff might be volcanic rock, with a glacier a km or so to the left. 
Earlier domes have already been demolished and replaced with these.  As many swimming pools as you like.



Title: Re: Glass geodesic domes
Post by: Robotbeat on 10/31/2016 01:24 am
That's a pretty practical idea right there. Build into the side of a mountain or plateau. Pretty dome near the entrance, all the work goes on deep inside.
Title: Re: Glass geodesic domes
Post by: gosnold on 10/31/2016 08:40 am
Dome Anchor/Float

* Create a truncated sphere by inverting a lower segment to become a domed floor. It would be strong, relying on compressive strength. The ring where the floor joins the  transparent dome might need extra reinforcing with cable. This rim could also be buried a bit in a shallow circular trench.

The last option could give you a nice moat for your laser sharks :)

Compression ring: (http://forum.nasaspaceflight.com/index.php?topic=40019.msg1517447#msg1517447) a great way to distribute load, yes.

And if the air pressure and water pressure at the dome rim are equal, you don't need to bury the rim.  Just anchor it, and let it hang in suspension subaqueously.  Moon pool.  It would allow dome entry and exit without the hassle of airlock. 

For persons, I mean. 

OK, if you really want, then yes, for your sharks, too.

(60 kPa equalizes at about 15 m depth on Mars.)

You should consider making a complete diagram of your installation. Right now we can piece it together by reading the hints you spread in your posts, but that's tedious and few people will do it. And I imagine if you didn't want people to have an idea of the whole thing, you would not be talking about it.
Title: Re: Glass geodesic domes
Post by: KelvinZero on 10/31/2016 09:51 am
You should consider making a complete diagram of your installation. Right now we can piece it together by reading the hints you spread in your posts, but that's tedious and few people will do it. And I imagine if you didn't want people to have an idea of the whole thing, you would not be talking about it.
There is a thread devoted to wstewart's scheme somewhere. (edit: here (http://forum.nasaspaceflight.com/index.php?topic=40019.0)) Strangely, I also became obsessed with a similar idea, apparently entirely independently, and have probably overposted it in various incarnations. (edit: here (http://forum.nasaspaceflight.com/index.php?topic=40628.msg1564153#msg1564153)) People probably think we are Jekyll and Hyde :)

This thread though is meant to be specifically about Elon Musk's intentions, and a sort of dome that can be assembled quickly on the surface before serious mining etc goes on.. at least that was how I read the quote in the OP.

Has anyone else discussed the anchoring problem yet? This is the big wtf issue to me. As far as I know it is a very well known issue so Im surprised it hasnt been discussed vigourously.
Title: Re: Glass geodesic domes
Post by: guckyfan on 10/31/2016 10:32 am
Has anyone else discussed the anchoring problem yet? This is the big wtf issue to me. As far as I know it is a very well known issue so Im surprised it hasnt been discussed vigourously.

I have mentioned it frequently but never got much response. I favor self contained habitats that don't need anchoring. The lower portion could have heat insulation against the bedrock or regolith and be filled at least partly with regolith/soil which has a lot of mass and buffers temperature changes over the day and night cycle.

Edit: Usually responders argue that the forces be contained by cover of regolith or ice. Which is very hard to balance and neglects horizontal components of pressure forces. I also argue that any structure needs to be stable both pressurized and unpressurized, which self contained habitats do.
Title: Re: Glass geodesic domes
Post by: lamontagne on 10/31/2016 10:48 am
Has anyone else discussed the anchoring problem yet? This is the big wtf issue to me. As far as I know it is a very well known issue so Im surprised it hasnt been discussed vigourously.

I have mentioned it frequently but never got much response. I favor self contained habitats that don't need anchoring. The lower portion could have heat insulation against the bedrock or regolith and be filled at least partly with regolith/soil which has a lot of mass and buffers temperature changes over the day and night cycle.

Edit: Usually responders argue that the forces be contained by cover of regolith or ice. Which is very hard to balance and neglects horizontal components of pressure forces. I also argue that any structure needs to be stable both pressurized and unpressurized, which self contained habitats do.
Anchoring could be done using rock bolts, in the reverse process from pile driving on Earth.  You first calculate the force required, then you drive in a pile (or rock bolt) until the force required to drive in the pile is higher than the force required to pull it out, plus a safety factor.  You can then build the dome from those anchor points.  You also need to solidify the base of the dome for a few meters bellow grade do ensure against blow out, and that should be enough.
Title: Re: Glass geodesic domes
Post by: envy887 on 10/31/2016 01:35 pm
Has anyone else discussed the anchoring problem yet? This is the big wtf issue to me. As far as I know it is a very well known issue so Im surprised it hasnt been discussed vigourously.

I have mentioned it frequently but never got much response. I favor self contained habitats that don't need anchoring. The lower portion could have heat insulation against the bedrock or regolith and be filled at least partly with regolith/soil which has a lot of mass and buffers temperature changes over the day and night cycle.

Edit: Usually responders argue that the forces be contained by cover of regolith or ice. Which is very hard to balance and neglects horizontal components of pressure forces. I also argue that any structure needs to be stable both pressurized and unpressurized, which self contained habitats do.
Anchoring could be done using rock bolts, in the reverse process from pile driving on Earth.  You first calculate the force required, then you drive in a pile (or rock bolt) until the force required to drive in the pile is higher than the force required to pull it out, plus a safety factor.  You can then build the dome from those anchor points.  You also need to solidify the base of the dome for a few meters bellow grade do ensure against blow out, and that should be enough.

To hold 1 atmospheric pressure, the anchors would have to hold almost 10 tonnes of force per square meter of covered area. For example, a 200m diameter dome would exert 314,000 tonnes of upward force and need 500 tonnes of anchoring force PER METER of perimeter. Since area scales with the square of perimeter, anchoring a small dome is much easier than a large one.
Title: Re: Glass geodesic domes
Post by: LMT on 10/31/2016 01:47 pm
GSA

Dome Anchor/Float

* Create a truncated sphere by inverting a lower segment to become a domed floor. It would be strong, relying on compressive strength. The ring where the floor joins the  transparent dome might need extra reinforcing with cable. This rim could also be buried a bit in a shallow circular trench.

The last option could give you a nice moat for your laser sharks :)

Compression ring: (http://forum.nasaspaceflight.com/index.php?topic=40019.msg1517447#msg1517447) a great way to distribute load, yes.

And if the air pressure and water pressure at the dome rim are equal, you don't need to bury the rim.  Just anchor it, and let it hang in suspension subaqueously.  Moon pool.  It would allow dome entry and exit without the hassle of airlock. 

For persons, I mean. 

OK, if you really want, then yes, for your sharks, too.
 
(60 kPa equalizes at about 15 m depth on Mars.)

You should consider making a complete diagram of your installation. Right now we can piece it together by reading the hints you spread in your posts, but that's tedious and few people will do it. And I imagine if you didn't want people to have an idea of the whole thing, you would not be talking about it.

Other NSF domes look way cooler. :) 

If any NSF architects want free beer, one of my wannados is a GSA study of the Lake Matthew dome design, with staged analysis that steps incrementally from the modular open-air construction through anchored subaqueous flotation.  The build looks quite feasible, generally, but optimization could be... interesting.  We might post some notable GSA results here.

Anyway, in this thread we're looking at many dome ideas, and so I'm posting more generally.  If there's a Q that's very specific to Lake Matthew domes, you might raise it on the dedicated LM thread (http://forum.nasaspaceflight.com/index.php?topic=40019.0).  But topics like shielding, anchoring, moon pools, and even "extended aquaculture" could apply to Elon's domes, or others considered here.
Title: Re: Glass geodesic domes
Post by: lamontagne on 10/31/2016 02:07 pm
Has anyone else discussed the anchoring problem yet? This is the big wtf issue to me. As far as I know it is a very well known issue so Im surprised it hasnt been discussed vigourously.

I have mentioned it frequently but never got much response. I favor self contained habitats that don't need anchoring. The lower portion could have heat insulation against the bedrock or regolith and be filled at least partly with regolith/soil which has a lot of mass and buffers temperature changes over the day and night cycle.

Edit: Usually responders argue that the forces be contained by cover of regolith or ice. Which is very hard to balance and neglects horizontal components of pressure forces. I also argue that any structure needs to be stable both pressurized and unpressurized, which self contained habitats do.
Anchoring could be done using rock bolts, in the reverse process from pile driving on Earth.  You first calculate the force required, then you drive in a pile (or rock bolt) until the force required to drive in the pile is higher than the force required to pull it out, plus a safety factor.  You can then build the dome from those anchor points.  You also need to solidify the base of the dome for a few meters bellow grade do ensure against blow out, and that should be enough.

To hold 1 atmospheric pressure, the anchors would have to hold almost 10 tonnes of force per square meter of covered area. For example, a 200m diameter dome would exert 314,000 tonnes of upward force and need 500 tonnes of anchoring force PER METER of perimeter. Since area scales with the square of perimeter, anchoring a small dome is much easier than a large one.
500 tonnes per meter seems doable, but a little extreme.  After all, standard structural steel is 40 000 psi, or 20 tonnes per square inch.  So 25 square inch rods, or 6 inches in diameter (150mm), every half meter would give us a factor of safety of 2.

The domes illustrated are 150m in diameter, so perhaps just keep the six inch rods (250 tonnes per m).  Almost 1000 rods.  These would need to be driven down... 20 to 30m perhaps?  Or even a little more?  the dead weight of the dome would help a little, but probable not that much, or else the unpressurized structure would not be stable.  That would be about 500m3 of steel rods, or at  8000 kg/m3, 4000 tonnes of steel.  So definitively a local product would be best.  The weight of carbon fiber rods is rather daunting as well.  Big domes are something of a luxury item, obviously :-)
What might be a safe size for the window panes?  2 feet wide(600mm) for 1/2 inch (13mm)?

Title: Re: Glass geodesic domes
Post by: gospacex on 10/31/2016 02:13 pm
Dome Complexity

Why not [water] outside the dome, to shield the entire facility?

Because it would make the design and construction of the dome much more complicated.

But the water weight would reduce the anchoring forces (see KelvinZero (http://forum.nasaspaceflight.com/index.php?topic=41526.msg1604817#msg1604817)), while water protects against radiation, dust storms, dust devils, impactors and temperature extremes.  These hazards must be dealt with, one way or another, in the dome design.  (The problem of glass radiation protection (http://forum.nasaspaceflight.com/index.php?topic=41526.msg1604544#msg1604544) is vexing, and a potential source of design complexity, by itself.)  So it seems exterior water could actually decrease the overall complexity of the dome.

Excellent idea.

I would only suggest using a liquid with a somewhat higher melting point.

Say, SiO2. It's okay if it is not pure. Say, some iron and aluminum oxides, salts, etc.

You may say that it'll likely solidify (melting point ~1700 C), but your water pond is also meant to be iced over and thus won't be transparent, right? And solid regolith^W SiO2 will never leak from the dome roof. It will not cause corrosion. It's even more abundant than water.
Title: Re: Glass geodesic domes
Post by: gospacex on 10/31/2016 02:19 pm
That's a pretty practical idea right there. Build into the side of a mountain or plateau. Pretty dome near the entrance, all the work goes on deep inside.

Yeah, looks good. Remove the "pretty dome", and it looks excellent.

I agree with you - the base should be practical.
Building a huge dome just because it is pretty (and ignoring structural, safety, cost, and maintenance complications) is not.

Some sort of dome or other light-admitting structure may make sense for e.g. greenhouses, and if R&D indicates it's a better alternative than artificial light greenhouses, algae farms etc.
Title: Re: Glass geodesic domes
Post by: lamontagne on 10/31/2016 03:12 pm
That's a pretty practical idea right there. Build into the side of a mountain or plateau. Pretty dome near the entrance, all the work goes on deep inside.

Yeah, looks good. Remove the "pretty dome", and it looks excellent.

I agree with you - the base should be practical.
Building a huge dome just because it is pretty (and ignoring structural, safety, cost, and maintenance complications) is not.

Some sort of dome or other light-admitting structure may make sense for e.g. greenhouses, and if R&D indicates it's a better alternative than artificial light greenhouses, algae farms etc.
I don't ignore them.  The whole point of this thread is to discuss them and determine in what context they might make sense.  I'll gladly admit that the one shown are unreasonably large, but there may be a dimension that is not.  After all, requirements go down quickly with size.  These images originate in the Amazing Martian Habitat thread, so they are perhaps a bit too amazing  ;-)

Title: Re: Glass geodesic domes
Post by: francesco nicoli on 10/31/2016 03:20 pm
That's a pretty practical idea right there. Build into the side of a mountain or plateau. Pretty dome near the entrance, all the work goes on deep inside.

Yeah, looks good. Remove the "pretty dome", and it looks excellent.

I agree with you - the base should be practical.
Building a huge dome just because it is pretty (and ignoring structural, safety, cost, and maintenance complications) is not.

Some sort of dome or other light-admitting structure may make sense for e.g. greenhouses, and if R&D indicates it's a better alternative than artificial light greenhouses, algae farms etc.
I don't ignore them.  The whole point of this thread is to discuss them and determine in what context they might make sense.  I'll gladly admit that the one shown are unreasonably large, but there may be a dimension that is not.  After all, requirements go down quickly with size.  These images originate in the Amazing Martian Habitat thread, so they are perhaps a bit too amazing  ;-)

Not to be harsh, but we are not talking about nasa domes. we are talking about Musk's glass domes.
it should be clear by now that either they'll be pretty, or they won't be.
Title: Re: Glass geodesic domes
Post by: guckyfan on 10/31/2016 03:23 pm
500 tonnes per meter seems doable, but a little extreme.  After all, standard structural steel is 40 000 psi, or 20 tonnes per square inch.  So 25 square inch rods, or 6 inches in diameter (150mm), every half meter would give us a factor of safety of 2.

The problem to be solved is not the structural member. It is that an anchor has to be placed that will not be pulled out of the ground by that force. Probably doable if the underground is solid bedrock. But will the dome be on solid bedrock, when it is near a glacier? Also drilling in solid bedrock and fixing the anchor are again not trivial tasks if you need to place hundreds or maybe thousands of them?
Title: Re: Glass geodesic domes
Post by: LMT on 10/31/2016 03:44 pm
Water, Rock, Carbon

Dome Complexity

Why not [water] outside the dome, to shield the entire facility?

Because it would make the design and construction of the dome much more complicated.

But the water weight would reduce the anchoring forces (see KelvinZero (http://forum.nasaspaceflight.com/index.php?topic=41526.msg1604817#msg1604817)), while water protects against radiation, dust storms, dust devils, impactors and temperature extremes.  These hazards must be dealt with, one way or another, in the dome design.  (The problem of glass radiation protection (http://forum.nasaspaceflight.com/index.php?topic=41526.msg1604544#msg1604544) is vexing, and a potential source of design complexity, by itself.)  So it seems exterior water could actually decrease the overall complexity of the dome.

Excellent idea.

I would only suggest using a liquid with a somewhat higher melting point.

Say, SiO2. It's okay if it is not pure. Say, some iron and aluminum oxides, salts, etc.

You may say that it'll likely solidify (melting point ~1700 C), but your water pond is also meant to be iced over and thus won't be transparent, right? And solid regolith^W SiO2 will never leak from the dome roof. It will not cause corrosion. It's even more abundant than water.

Sure, and regolith makes a better ballast than water.  That's potentially very useful in countering air pressure, to reduce the anchoring forces as with envy887 and lamontagne.  How best to apply?

One idea:  a ballast ring

If water provides dome shielding, a ring track might be added for ballast.  It would stand above the water surface (and above the compression ring) to suspend ballast around the dome perimeter, for max weight and even distribution.  A 300 m diameter ring with 20 m track, containing 7 m of wet sand, would weigh ~1 billion N.  You'd subtract that weight from the anchoring force. 

And you'd still have your view.

Just one idea.



re: ice:  only in winter, unless you chose a polar site.  I think it's a fair working assumption that bulk water temperature should be maintained > 0 C spring-to-fall, especially if a natural-light garden is desired.



As for corrosion, we've seen that wastewater treatment plants have standardized on titanium alloy, which resists corrosive waters well.  Under treated water I'd think titanium alloy should have a long lifespan.   However carbon fiber frames would have about 1/3 the density.

Question:  does anyone have corrosion info on Elon's proposed carbon fiber?
Title: Re: Elon Musk: glass geodesic domes
Post by: Robotbeat on 10/31/2016 04:40 pm
Carbon fiber doesn't corrode. It's nearly inert. The plastic might, but generally it's fairly inert as well.
Title: Re: Elon Musk: glass geodesic domes
Post by: TripD on 10/31/2016 04:45 pm
The notion of using anchors worries me.  Under the loads described I would be very concerned about anchor points as failure modes especially on a long timeline.  The once covered bedrock is now exposed to day/night temperature swings and the weakened state caused by drilling the anchor point.  I would think that the dependability of manufactured components are much better understood.  You really cannot expect even a bedrock to be completely homogeneous throughout. 

Depending on a compression ring or a complete pressure sphere at least places known engineering and material strengths where you need them most.

Edit:   Better to play to the strength of rock. i.e. compression, not tension.
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 10/31/2016 05:55 pm
The notion of using anchors worries me.  Under the loads described I would be very concerned about anchor points as failure modes especially on a long timeline.  The once covered bedrock is now exposed to day/night temperature swings and the weakened state caused by drilling the anchor point.  I would think that the dependability of manufactured components are much better understood.  You really cannot expect even a bedrock to be completely homogeneous throughout. 

Depending on a compression ring or a complete pressure sphere at least places known engineering and material strengths where you need them most.

Edit:   Better to play to the strength of rock. i.e. compression, not tension.
We're really playing on the strength of steel.  If we put the rods deep enough, just the mass of the rock will be what keeps the dome in place.  Rather like reinforced concrete can operate quite well under tension.  But the rods would need to transmit their effort to at least 500 tonnes of rock per meter, and that's a lot of rock.

But yes, there are more risks, in particular with unknown rock, and with the heating of the rock from the habitat.
I guess the most reasonable solution is just to make a lot of much smaller spheres, and fill in the base up to a comfortable grade.  With water or soil, as per your illustration.  Perhaps something like a multiple roof greenhouse, with tension columns, would offer the maximum living area for minimum volume.  Rather like a city made of bubble wrap.
Or a city made from plastic pipe.  Wouldn't be a dome anymore though, so should go to the Amazing Habitat thread. 
Title: Re: Elon Musk: glass geodesic domes
Post by: LMT on 10/31/2016 06:07 pm
Carbon Fiber Degradation Due to Moisture

Carbon fiber doesn't corrode. It's nearly inert. The plastic might, but generally it's fairly inert as well.

Related problem:  carbon fiber composites tend to degrade via swelling and hydrolysis when exposed to moisture (https://fau.digital.flvc.org/islandora/object/fau%3A3482/datastream/OBJ/view/Durability_of_carbon_fiber_vinylester_composites_subjected_to_marine_environments_and_electrochemical_interactions.pdf). 

Quote
Weitsman et al [18] reported effects of fluids on the deformation, strength and durability of polymeric composites. They mentioned that sorption of fluids induces swelling in the polymeric phases, produces residual stress. More significantly, fluids can degrade polymers and fiber/matrix interface by chemical attack (hydrolysis). Reduction of up to 30% in the interfacial strength may occur in Graphite/epoxy systems. Exposure of fluids tends to shorten the fatigue life. Effect of fluids that penetrates the microcrack assists in the reduction of internal toughness, thereby lowering the levels of resistance to fracture. They concluded that fluids enhance the deformation of polymeric composites which must be considered in circumstances where stiffness and deflection are issues of concern…

Water is attracted by polar functional groups of heavily cross-linked epoxy and polyester resin molecules, the amount of water getting into the resin exceeds the amount of free volume spaces available, which leads to swelling of the resin [31]. As a result, the hydrogen bonds between polymer molecules are broken. This is known as plasticization and it leads to the fiber/matrix de-bonding. Due to non-uniformity of the moisture in the composite, matrix swelling is also non-uniform and these develop differential stress. Because of differential stresses, fiber/matrix de-bonding can be severe for glass and carbon fiber composites, where fibers are rigid.

Ouch.  Anyone know how the manufacturers of carbon fiber composites manage that problem?
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 10/31/2016 06:11 pm
Question from /u/Ulysius

As a follow-up, considering the synodal reuse of the ITS spaceships, what form of permanent habitation do you foresee? Shipped modules or an (eventual) shift to in-situ resource utilization such as Martian rigolith/plastic-reinforced concrete structures?

Thank you for your time.



Answer from /u/ElonMuskOfficial

Initially, glass panes with carbon fiber frames to build geodesic domes on the surface, plus a lot of miner/tunneling droids. With the latter, you can build out a huge amount of pressurized space for industrial operations and leave the glass domes for green living space.
I thought this was worth it's own topic because it is about the only thing we have that is specifically SpaceX.
What do we know about this sort of construction?

Wouldn't cylinders be more convenient and adaptable? Cylinders have the advantage that you can make variable volumes by extending their length. You can cover area in a grid more efficiently. They don't need anchoring. You can align them north-south to get the best sun.

What sort of tools would be necessary for these domes? What sort of work? Is it people clambering around in spacesuits or one dedicated robot type?

Too cool. I always thought glass would be one of the first locally-produced bulk engineering materials.

Initially of course it'll be imported from earth, but even that flat-packs really nicely.

EDIT:

The other being concrete...
Title: Re: Elon Musk: glass geodesic domes
Post by: LMT on 10/31/2016 07:33 pm
Anchors

What anchors might be best, in bedrock of uncertain properties?

Example:  Grout Bonded Anchors (http://www.williamsform.com/Contact_Us/PDFs/Ground_Engineering_Systems.pdf)  (brochure has a nifty flowchart btw, "Choosing an Appropriate Rock Anchor")  :)

These anchors work in most any rock, and can carry a working load of 4.4 million N per anchor.

(http://www.williamsform.com/Concrete_Anchors/Spin-Lock_Concrete_Anchors/Spin-Lock_Concrete_Installation/step_5_grouting_anchor_cad1.jpg)

Is there a better anchor method out there?
Title: Re: Elon Musk: glass geodesic domes
Post by: oiorionsbelt on 10/31/2016 08:03 pm
Instead of anchoring the dome to the ground, why not have an integrated floor and set the dome on top of the ground?
Title: Re: Elon Musk: glass geodesic domes
Post by: rarchimedes on 10/31/2016 08:15 pm
I'm having trouble with this whole concept. Geodesic domes or spheroids have strength only in the compressive mode. If you put pressure inside them, they blow apart like an unsupported balloon. The balloon distributes the forces equally at all points and has no weak points for leakage, while the dome has poorly distributed forces internally and literally almost infinite points and seams for leakage. Now if one were to build such a dome of lightweight and somewhat radiation filtering ETFE with appropriate coatings, and then invert that dome into a hole or onto an approximately circular berm, the weight of the dome would be expressed on the rim and at the peak, somewhat or completely mitigated by the pressure underneath. Additional regolith could be distributed above that rim to securely anchor it. The area under the dome could be initially filled with compressed Martian atmosphere, later to be converted to oxygen and nitrogen (provided by processing of local minerals). Certainly, that would provide a protected area for observation and plant growth. Without the protection of a sufficient atmosphere, such structures would be very vulnerable to incoming rocks, but at least the berms or excavation sides would protect from low angle projectiles. If I were planning to live on Mars, I would make such domes as small as possible concomitant with needs for lighted growing area. The ring around such would necessarily have to be provided with airlocks because of the danger of damage. If the atmosphere were left as largely CO2, it would be ideal for "farming".

Initially, all structures such as berms and initial habitats should be constructed of packed regolith made as close as possible to a form of concrete by extracted water and then coated internally with high strength plastic coatings, largely impermeable to air and water. Such coatings would be the most efficient construction materials to transport from off-planet. With 3-D printers, such coating materials could also be used to print many parts of any habitat. It may be noted here that such plastics in liquid form can have a relatively high hydrogen content and would thus be rather effective shielding materials in transit to Mars. I am unfamiliar with the difficulties of producing such polymeric materials as ISRU, but can only assume that with the presence of water, such manufacture would eventually be possible.

In any case, early transport of materials for such domes would be highly impractical. I would strongly suggest that initial needs for lighted areas be provided by translucent/transparent balloons attached to rings that can be rim weighted with regolith. All such areas would require locks to protect against projectile penetration. All living and working areas should be under sufficient regolith to protect all living on Mars.
Title: Re: Elon Musk: glass geodesic domes
Post by: Robotbeat on 10/31/2016 08:33 pm
Good point that geodesic domes are not necessarily optimized for tension. The design may need to be different. But a sphere is a fairly efficient shape for a pressure vessel, so an optimal structure could be developed.

The whole point of a glass dome is to have a very, very good view outside. Good enough for stargazing. So translucent won't do. Has to be high clarity. ETFE no good enough.

I think an inflatable dome is a really good idea for other purposes. But if you're building a glass dome, you're doing it for the view. Imagine a really big Cupola module but with better glass fill factor. The huge window on the ITS is a hint of what SpaceX is thinking of, I'd wager.
Title: Re: Elon Musk: glass geodesic domes
Post by: Robotbeat on 10/31/2016 09:04 pm
Plastics ISRU will be one of the first solids made by ISRU on Mars. Iron and sintered regolith, too.
Title: Re: Elon Musk: glass geodesic domes
Post by: guckyfan on 10/31/2016 09:13 pm
The whole point of a glass dome is to have a very, very good view outside. Good enough for stargazing. So translucent won't do. Has to be high clarity. ETFE no good enough.
................

The huge window on the ITS is a hint of what SpaceX is thinking of, I'd wager.

Absolutely. So covering with ice or any other method to maximise radiation protection also won't do. That is why I suggested, if buildings are built inside they would have internal roofs for radiation protection.

Also I as well thought immediately of the ITS window when I heard of geodesic domes for Mars.
Title: Re: Elon Musk: glass geodesic domes
Post by: Robotbeat on 10/31/2016 09:47 pm
Agreed.

I think there are ways to have significant radiation protection with a great view, but "glass dome" definitely isn't one of them. Glass dome will definitely not be radiation shielded other than what Mars herself will do.

Consider it good motivation to start thickening up the Martian atmosphere.
Title: Re: Elon Musk: glass geodesic domes
Post by: TripD on 10/31/2016 10:00 pm
Now I wonder how much light gets diminished/absorbed while passing through glass.  The reason I ask is that you could potentially have domes or half cylinders within domes or half cylinders.  This would allow for a step down of pressure between the outer and inner structures.
Title: Re: Elon Musk: glass geodesic domes
Post by: RonM on 10/31/2016 10:28 pm
The whole point of a glass dome is to have a very, very good view outside. Good enough for stargazing. So translucent won't do. Has to be high clarity. ETFE no good enough.
................

The huge window on the ITS is a hint of what SpaceX is thinking of, I'd wager.

Absolutely. So covering with ice or any other method to maximise radiation protection also won't do. That is why I suggested, if buildings are built inside they would have internal roofs for radiation protection.

Also I as well thought immediately of the ITS window when I heard of geodesic domes for Mars.

There's a psychological reason for a panoramic view through a glass dome. Once you leave Earth, you will not be able to go outside without a spacesuit and apparently spacesuits can be claustrophobic. When you are walking between the buildings under a glass dome, the vista beyond will make you feel like you are taking a stroll outside. Depending on the thickness of the panel supports, you might not even notice the geodesic framework if you don't think about it. Got to keep the colonists' spirit up.

Same concept will help on the ITS upper deck.
Title: Re: Elon Musk: glass geodesic domes
Post by: envy887 on 10/31/2016 10:38 pm
Instead of anchoring the dome to the ground, why not have an integrated floor and set the dome on top of the ground?
Because hemispheres are terrible pressure vessels. If it's not firmly anchored around the perimeter, the internal pressure will try to turn it into a sphere.
Title: Re: Elon Musk: glass geodesic domes
Post by: envy887 on 10/31/2016 10:42 pm
The whole point of a glass dome is to have a very, very good view outside. Good enough for stargazing. So translucent won't do. Has to be high clarity. ETFE no good enough.
................

The huge window on the ITS is a hint of what SpaceX is thinking of, I'd wager.

Absolutely. So covering with ice or any other method to maximise radiation protection also won't do. That is why I suggested, if buildings are built inside they would have internal roofs for radiation protection.

Also I as well thought immediately of the ITS window when I heard of geodesic domes for Mars.

The interior buildings would probably be buried for radiation protection and be separate pressure vessels to survive a possible dome depressurization. Actually, they would probably look a lot like tunnels.
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 10/31/2016 11:58 pm
I'm having trouble with this whole concept. Geodesic domes or spheroids have strength only in the compressive mode. If you put pressure inside them, they blow apart like an unsupported balloon. The balloon distributes the forces equally at all points and has no weak points for leakage, while the dome has poorly distributed forces internally and literally almost infinite points and seams for leakage. Now if one were to build such a dome of lightweight and somewhat radiation filtering ETFE with appropriate coatings, and then invert that dome into a hole or onto an approximately circular berm, the weight of the dome would be expressed on the rim and at the peak, somewhat or completely mitigated by the pressure underneath. Additional regolith could be distributed above that rim to securely anchor it. The area under the dome could be initially filled with compressed Martian atmosphere, later to be converted to oxygen and nitrogen (provided by processing of local minerals). Certainly, that would provide a protected area for observation and plant growth. Without the protection of a sufficient atmosphere, such structures would be very vulnerable to incoming rocks, but at least the berms or excavation sides would protect from low angle projectiles. If I were planning to live on Mars, I would make such domes as small as possible concomitant with needs for lighted growing area. The ring around such would necessarily have to be provided with airlocks because of the danger of damage. If the atmosphere were left as largely CO2, it would be ideal for "farming".

Initially, all structures such as berms and initial habitats should be constructed of packed regolith made as close as possible to a form of concrete by extracted water and then coated internally with high strength plastic coatings, largely impermeable to air and water. Such coatings would be the most efficient construction materials to transport from off-planet. With 3-D printers, such coating materials could also be used to print many parts of any habitat. It may be noted here that such plastics in liquid form can have a relatively high hydrogen content and would thus be rather effective shielding materials in transit to Mars. I am unfamiliar with the difficulties of producing such polymeric materials as ISRU, but can only assume that with the presence of water, such manufacture would eventually be possible.

In any case, early transport of materials for such domes would be highly impractical. I would strongly suggest that initial needs for lighted areas be provided by translucent/transparent balloons attached to rings that can be rim weighted with regolith. All such areas would require locks to protect against projectile penetration. All living and working areas should be under sufficient regolith to protect all living on Mars.

???

The panes are just acting like membranes, in the direction of dP.

The struts are either in tension or compression...

You could rely on the panes' edges to act as the struts

A half-dome needs to be either anchored down, or put on a thick slab which then effectively acts like the ground...

---

How do you construct a giant dome though?

Start with "struts-only", and then attach panes?

If attaching panes from both sides of the struts, you get a double layer for insulation...

Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 11/01/2016 12:01 am
Here is a variation on the dome, a double ellipsoid.
Think of it as the top and bottom of a propane tank, welded directly together.
Solves the anchor problem. Pretty good in tension, not as good as a sphere, but about the same as a cylinder wall. 

Requires some additional support structure though.  But much simpler than anchors.

As for glass how about the glass Tesla will be using for their solar tiles?  Seems pretty tough.

It's an ovoid or an ellipsoid?


Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 11/01/2016 12:17 am
I'm having trouble with this whole concept. Geodesic domes or spheroids have strength only in the compressive mode. If you put pressure inside them, they blow apart like an unsupported balloon. The balloon distributes the forces equally at all points and has no weak points for leakage, while the dome has poorly distributed forces internally and literally almost infinite points and seams for leakage. Now if one were to build such a dome of lightweight and somewhat radiation filtering ETFE with appropriate coatings, and then invert that dome into a hole or onto an approximately circular berm, the weight of the dome would be expressed on the rim and at the peak, somewhat or completely mitigated by the pressure underneath. Additional regolith could be distributed above that rim to securely anchor it. The area under the dome could be initially filled with compressed Martian atmosphere, later to be converted to oxygen and nitrogen (provided by processing of local minerals). Certainly, that would provide a protected area for observation and plant growth. Without the protection of a sufficient atmosphere, such structures would be very vulnerable to incoming rocks, but at least the berms or excavation sides would protect from low angle projectiles. If I were planning to live on Mars, I would make such domes as small as possible concomitant with needs for lighted growing area. The ring around such would necessarily have to be provided with airlocks because of the danger of damage. If the atmosphere were left as largely CO2, it would be ideal for "farming".

Initially, all structures such as berms and initial habitats should be constructed of packed regolith made as close as possible to a form of concrete by extracted water and then coated internally with high strength plastic coatings, largely impermeable to air and water. Such coatings would be the most efficient construction materials to transport from off-planet. With 3-D printers, such coating materials could also be used to print many parts of any habitat. It may be noted here that such plastics in liquid form can have a relatively high hydrogen content and would thus be rather effective shielding materials in transit to Mars. I am unfamiliar with the difficulties of producing such polymeric materials as ISRU, but can only assume that with the presence of water, such manufacture would eventually be possible.

In any case, early transport of materials for such domes would be highly impractical. I would strongly suggest that initial needs for lighted areas be provided by translucent/transparent balloons attached to rings that can be rim weighted with regolith. All such areas would require locks to protect against projectile penetration. All living and working areas should be under sufficient regolith to protect all living on Mars.

???

The panes are just acting like membranes, in the direction of dP.

The struts are either in tension or compression...

You could rely on the panes' edges to act as the struts

A half-dome needs to be either anchored down, or put on a thick slab which then effectively acts like the ground...

---

How do you construct a giant dome though?

Start with "struts-only", and then attach panes?

If attaching panes from both sides of the struts, you get a double layer for insulation...
You don't really need insulation, just low emissivity.  There is very little conduction to the thin martian atmosphere.

To build, you first set up the structure, then add the panes, then start the pressure and seal the leaks, would be my guess.
I don't think the panes are structural as far as tension goes.  They just serve to fill in between the structural members.
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 11/01/2016 12:32 am
The whole point of a glass dome is to have a very, very good view outside. Good enough for stargazing. So translucent won't do. Has to be high clarity. ETFE no good enough.
................

The huge window on the ITS is a hint of what SpaceX is thinking of, I'd wager.

Absolutely. So covering with ice or any other method to maximise radiation protection also won't do. That is why I suggested, if buildings are built inside they would have internal roofs for radiation protection.

Also I as well thought immediately of the ITS window when I heard of geodesic domes for Mars.

The interior buildings would probably be buried for radiation protection and be separate pressure vessels to survive a possible dome depressurization. Actually, they would probably look a lot like tunnels.
Subway stations, or underground hydro power stations are very similar.
Title: Re: Elon Musk: glass geodesic domes
Post by: Robotbeat on 11/01/2016 02:30 am
I don't think we'd have floating ellipsoids like that. They'll be anchored in the ground. Either with ballast or pilings.
Title: Re: Elon Musk: glass geodesic domes
Post by: LMT on 11/01/2016 03:49 am
Glass, Dome

The whole point of a glass dome is to have a very, very good view outside. Good enough for stargazing. So translucent won't do. Has to be high clarity. ETFE no good enough.
................

The huge window on the ITS is a hint of what SpaceX is thinking of, I'd wager.

Absolutely. So covering with ice or any other method to maximise radiation protection also won't do. That is why I suggested, if buildings are built inside they would have internal roofs for radiation protection.

Also I as well thought immediately of the ITS window when I heard of geodesic domes for Mars.

So if your goal were a pressurized dome having stargazing clarity, and you didn't care about radiation exposure or heat loss, what are the pane options?

The ISS cupola uses borosilicate glass.  Thermal-tempered borosilicate is also cryogenic, suitable on Mars.  Panes are produced commercially at 6 cm thickness.

If you manufactured borosilicate glass via silica ISRU ( ? ), and shipped only the B2O3 as cargo, a single ITS cargo of 450 tons would make panes to cover a hemispherical dome ~130 m in diameter.

If you shipped the finished panes from Earth, you'd need ~8 ITS cargo shipments.

Is there any way to improve those numbers?

(https://destinationspace.s3.amazonaws.com/images/Space-views-cupola_MkOyuxb.max-800x600.jpg)

(http://images.monolithic.org/img/2011/05/10/4dc92b85c29e068473000b49/medium/crn01.jpg)

(http://image.cdnllnwnl.xosnetwork.com/pics32/640/KI/KIWXXAWOVYAEENI.20120807235600.jpg)
Title: Re: Elon Musk: glass geodesic domes
Post by: Robotbeat on 11/01/2016 04:28 am
Boron absorbs neutrons so it might be marginally better from a radiation perspective to use more B2O3 in your glass mix.
Title: Re: Elon Musk: glass geodesic domes
Post by: guckyfan on 11/01/2016 06:59 am
Is there any way to improve those numbers?

If the habitat pressure is half earth sea level they can use less thick panes. They can build 20 or 30 m domes instead of such enormously large ones. They don't need micrometeorite protection. That may further decrease the needed thickness of the glass panes.

A little over 20m will allow building 4 storey high habitat buildings.
Title: Re: Elon Musk: glass geodesic domes
Post by: MP99 on 11/01/2016 08:09 am
Good point that geodesic domes are not necessarily optimized for tension. The design may need to be different. But a sphere is a fairly efficient shape for a pressure vessel, so an optimal structure could be developed.

Does it help if you string cables over the dome (along the struts)?

The cables provide the tension, and the panels channel the air pressure to the force transfer points at the corners of the panels.

My initial thought was that each cable would go over the zenith point, but that creates a major "congestion" point there.

I wonder if each cable runs at an angle - just along the run of the struts?

Cheers, Martin

Edit:- looks like that might work for this dome:-
http://forum.nasaspaceflight.com/index.php?topic=41526.msg1604803.msg#1604803
Title: Re: Elon Musk: glass geodesic domes
Post by: KelvinZero on 11/01/2016 08:29 am
Im really sticking on this anchoring thing. Im not saying it is impossible.. just that for the work of doing that it would be much easier and more reliable to just build a sphere.. and then you also have twice the volume. It could be in a crater, it could be dug in, it could be above ground sort of like  these gas tanks (https://en.wikipedia.org/wiki/Storage_tank) or this big liquid hydrogen tank (http://www.nasa.gov/content/liquid-hydrogen-the-fuel-of-choice-for-space-exploration)

Show me someone storing their pressurised gas in a dome anchored to the ground instead of a sphere and maybe I will change my mind.

It just seems to me like the whole concept is built on the misconception that you can just "dome some ground off" and start farming.. sort of like greenhouses. The ground would be the most artificial thing of it!

========

Going a bit off topic.. If the purpose of domes is aesthetics, you really want a seamless dome. That is an interesting engineering topic all of it's own.

I imagine you inflate something and then spray on layers either from the inside or outside. Or maybe you inflate something with two layers then fill up the gap between them. The technology is possibly science fiction, but if you could master the materials the construction could actually be a lot simpler than assembling pieces. You could probably automate it. Creating the feedstock from ISRU might be simpler than creating geodesic dome components. It is just a chemical. All the complex parts are in the machinery that come from earth.
Title: Re: Elon Musk: glass geodesic domes
Post by: guckyfan on 11/01/2016 08:30 am
I wonder if each cable runs at an angle - just along the run of the struts?

Cheers, Martin

The struts would be built for tension, I think.
Title: Re: Elon Musk: glass geodesic domes
Post by: envy887 on 11/01/2016 11:38 am
I wonder if each cable runs at an angle - just along the run of the struts?

Cheers, Martin

The struts would be built for tension, I think.

Yes, but cabling down allows the anchoring pressure to be spread over the area of the dome, rather than around the perimeter.  Unlike piled regolith or water on top, the cables would apply little to no force (as little as only their weight in .38g) if the dome accidentally depressurizes, so you don't have to worry about cave-ins.
Title: Re: Elon Musk: glass geodesic domes
Post by: LMT on 11/01/2016 12:31 pm
Zilch

Boron absorbs neutrons so it might be marginally better from a radiation perspective to use more B2O3 in your glass mix.

A marginal improvement on zilch is still zilch.  There is presently no useful 6 cm shield against cosmic rays and secondaries, encountered in transit or on the martian surface.  E.g., again, Aguayo et al. 2011 (http://www.pnnl.gov/main/publications/external/technical_reports/PNNL-20693.pdf):

Quote
There is little difference between the effect of borated [ed. 5%] polyethylene (BPE) on neutrons and that of PE. It is likely one would add boron to the polyethylene specifically for additional neutron shielding (because of boron’s neutron capture effects), however, this boron doping does not affect attenuation properties of the material at the energies of interest...

Useful boron neutron shielding (76% boron concrete) (https://www.jlab.org/news/stories/new-shielding-designed-put-block-neutrons), illustrated:

(https://www.jlab.org/sites/default/files/images/news/stories/JLB_5814.jpg)

And again, as Arb says, there are other threads for radiation posts.
Title: Re: Elon Musk: glass geodesic domes
Post by: Robotbeat on 11/01/2016 12:51 pm
However, Mars' environment is relatively more neutron rich than deep space. And I was simply answering the question of someone who asked if there was anything that could be done to improve.

The "boro" in borosilicate glass is some diboron trioxide that is already mixed in. You can make glad just from diboron trioxide which is like 40% boron. I was just suggesting if you had a choice, you may go for a bit more B2O3 in your glass if it isn't any trouble.

And there's something better: boron fibers actually have a very good specific strength, as good as carbon fiber.
Title: Re: Elon Musk: glass geodesic domes
Post by: LMT on 11/01/2016 01:19 pm
Breaking Glass

Is there any way to improve those numbers?

If the habitat pressure is half earth sea level they can use less thick panes.

ISS pressure is sea level, and cupola glass is, altogether, 9.4 cm thick.  And I don't know if failure modes scale linearly in borosilicate glass.  Can you find some numbers that would justify thinning dome glass below 6 cm, without risk of failure?
Title: Re: Elon Musk: glass geodesic domes
Post by: guckyfan on 11/01/2016 01:26 pm

ISS pressure is sea level, and cupola glass is, altogether, 9.4 cm thick.  And I don't know if failure modes scale linearly in borosilicate glass.  Can you find some numbers that would justify thinning dome glass below 6 cm, without risk of failure?

Find numbers to justify the assumption it doesn't. Besides the cupola is designed for LEO which is heavily infested with space debris, a much higher number than micro meteorites. At Mars with its atmosphere at low altitudes there are no micro meteorites. No need to protect from them.
Title: Re: Elon Musk: glass geodesic domes
Post by: Jcc on 11/01/2016 01:29 pm
Is there any way to improve those numbers?

If the habitat pressure is half earth sea level they can use less thick panes. They can build 20 or 30 m domes instead of such enormously large ones. They don't need micrometeorite protection. That may further decrease the needed thickness of the glass panes.

A little over 20m will allow building 4 storey high habitat buildings.

Lowering pressure is a good point and brings up some issues. You can increase the percent O2 above the nominal 20% in Earth's atmosphere and allow similar oxygenation despite living at lower pressure. That may be easier than obtaining 79% N2 to make up the air supply. Even so, it will be physiologically advantageous if people adapt to lower pressure the same as people living high in the Andes or Himalayas do on Earth. 0.5 Atm is equivalent to 5,477 m altitude, which is a bit over the limit of current human settlements. There is a village in Peru at 5100 m, but that is without enriched oxygen. People develop a much higher red blood cell count and other physiological adaptations.

Also related to physiological adaptations, Mars settlers will need to increase their tolerance of CO2. It will be necessary to exclude and scrub CO2 from breathable air, but usually the more perfect you need to make a system the more expensive and less fault tolerant it is.

Then, in the distant future when Mars has been "terraformed" with a thick atmosphere, and enough O2 for human survival, the Martians can finally take off their space suits and breath air that would kill an Earthling in 10 minutes.
 
Title: Re: Elon Musk: glass geodesic domes
Post by: LMT on 11/01/2016 02:13 pm
Breaking Glass


ISS pressure is sea level, and cupola glass is, altogether, 9.4 cm thick.  And I don't know if failure modes scale linearly in borosilicate glass.  Can you find some numbers that would justify thinning dome glass below 6 cm, without risk of failure?

Find numbers to justify the assumption it doesn't. Besides the cupola is designed for LEO which is heavily infested with space debris, a much higher number than micro meteorites. At Mars with its atmosphere at low altitudes there are no micro meteorites. No need to protect from them.

What assumption?  Borosilicate is manufactured in 6 cm panes for use in pressure windows, and cryogenics.  Seems reasonable for a Mars dome, and ISS cupola specs are ballpark.  If you imagine the panes can be thinned further, safely, it would be interesting to see some numbers on failure modes, to justify.  Otherwise there's no particular reason to assume it's possible. 

Remember, the panes would endure a temperature difference of up to 160 C across those few centimeters, and bumps happen.
Title: Re: Elon Musk: glass geodesic domes
Post by: Robotbeat on 11/01/2016 02:23 pm
Structural engineering is not magic. Of course if you reduce the pressure you can reduce thickness safely. You can also reduce thickness by using smaller panes or possibly curved panes.
Title: Re: Elon Musk: glass geodesic domes
Post by: envy887 on 11/01/2016 02:29 pm
I don't think we'd have floating ellipsoids like that. They'll be anchored in the ground. Either with ballast or pilings.

The cross-section area of a regolith ballast rim all the way around the dome perimeter scales linearly relative to the diameter of the dome. A 100m dome would need ~175 m2 cross-section, or a 10m dome ~17.5 m2 cross-section ballast rim to hold down 1 atmosphere.

Ground anchors up to 50 tonnes each appear entirely reasonable if bedrock is within reach; the number of anchors required per unit of perimeter length scales linearly with dome diameter: a 100m dome would need about 4 such anchors per meter of wall at the ground (1200 total), while a 25m dome would need 1 per meter (80 total) and a 10m dome only one every 2.5m (12 total) to hold down 1 atmosphere.

Either anchors or ballast is probably feasible for domes up to ~100m, with anchors preferable if there's shallow bedrock, and ballast preferable if there's a deeper layer of loose regolith.
Title: Re: Elon Musk: glass geodesic domes
Post by: envy887 on 11/01/2016 02:42 pm
What assumption?  Borosilicate is manufactured in 6 cm panes for use in pressure windows, and cryogenics.  Seems reasonable for a Mars dome, and ISS cupola specs are ballpark.  If you imagine the panes can be thinned further, safely, it would be interesting to see some numbers on failure modes, to justify.  Otherwise there's no particular reason to assume it's possible. 

Remember, the panes would endure a temperature difference of up to 160 C across those few centimeters, and bumps happen.

Borosilicate has rather poor mechanical properties in tension, particularly if it's scratched. Polycarbonate or layered polycarbonate-glass construction is considerably stronger, particularly in impact resistance. PC also has good temperature resistance and is a better insulator, although it would need an abrasion-resistant coating.

A 100m dome of tension-bearing Lexan panes would only weigh ~150 tonnes to contain 1 atmosphere, if the composite frames are of similar specific strength to the panes (and the frames should be 20-50 times stronger).
Title: Re: Elon Musk: glass geodesic domes
Post by: LMT on 11/01/2016 03:05 pm
Hockey Pucks

Structural engineering is not magic. Of course if you reduce the pressure you can reduce thickness safely. You can also reduce thickness by using smaller panes or possibly curved panes.

"Smaller panes..."  Smaller, relative to what?  The little ISS cupola top window is only 70.6 cm wide (http://esamultimedia.esa.int/docs/hsf_research/Climate_change_ISS_presentations/Cupola_Deloo.pdf).  Go smaller and you end up with a glass dome that's mostly frame, dotted with borosilicate hockey pucks.

As for the rest, let's not assume we can "shave a bit on the internet", when that shave cuts into uncertain safety margins.

(http://www.whatdoyouneed.com/glass-hockey-puck-paperweights.jpg)
Title: Re: Elon Musk: glass geodesic domes
Post by: Terra Incognita on 11/01/2016 03:06 pm

Lowering pressure is a good point and brings up some issues. You can increase the percent O2 above the nominal 20% in Earth's atmosphere and allow similar oxygenation despite living at lower pressure. That may be easier than obtaining 79% N2 to make up the air supply. Even so, it will be physiologically advantageous if people adapt to lower pressure the same as people living high in the Andes or Himalayas do on Earth. 0.5 Atm is equivalent to 5,477 m altitude, which is a bit over the limit of current human settlements. There is a village in Peru at 5100 m, but that is without enriched oxygen. People develop a much higher red blood cell count and other physiological adaptations.

Also related to physiological adaptations, Mars settlers will need to increase their tolerance of CO2. It will be necessary to exclude and scrub CO2 from breathable air, but usually the more perfect you need to make a system the more expensive and less fault tolerant it is.

It's not the absolute air pressure that people adapt to, its the partial pressure of Oxygen. The total air pressure only starts to become relevant below 21 KPa as you can no longer achieve sea level partial pressure of oxygen.
As has been pointed out earlier it's not a good idea to eliminate a buffer gas as you increase the fire risk.

Those populations in Peru have maladaptive responses including left heart failure from all the extra red blood cells thickening the blood. Lower air pressure holds less H2O which is partially why the air on a commercial plane is slightly unpleasant. Eventually, your airways dry and you get upper respiratory problems.

While some drop in air pressure would be tolerable I think we should be aiming for a nice sea level 100 KPa for a colony.

As for CO2, mammals are exquisitely sensitive to even very small changes in the gas and could only adapt to higher levels if those levels were tightly controlled. It will have to be filtered out. Eventually that can be done by plants quite efficiently.
Title: Re: Elon Musk: glass geodesic domes
Post by: Robotbeat on 11/01/2016 03:19 pm
So why don't people in Denver live in pressure domes?
Title: Re: Elon Musk: glass geodesic domes
Post by: LMT on 11/01/2016 04:24 pm
Polycarbonate or layered polycarbonate-glass construction is considerably stronger...

Unfortunately polycarbonate turns semi-brittle between -60 C and -80 C (http://link.springer.com/article/10.1007/BF00754478); i.e., daily. 

Cryogenic materials would seem to be necessary, where Mars domes are exposed to the elements.
Title: Re: Elon Musk: glass geodesic domes
Post by: LMT on 11/01/2016 07:20 pm
Anchors

I don't think we'd have floating ellipsoids like that. They'll be anchored in the ground. Either with ballast or pilings.

The cross-section area of a regolith ballast rim all the way around the dome perimeter scales linearly relative to the diameter of the dome. A 100m dome would need ~175 m2 cross-section, or a 10m dome ~17.5 m2 cross-section ballast rim to hold down 1 atmosphere.

Ground anchors up to 50 tonnes each appear entirely reasonable if bedrock is within reach; the number of anchors required per unit of perimeter length scales linearly with dome diameter: a 100m dome would need about 4 such anchors per meter of wall at the ground (1200 total), while a 25m dome would need 1 per meter (80 total) and a 10m dome only one every 2.5m (12 total) to hold down 1 atmosphere.

Either anchors or ballast is probably feasible for domes up to ~100m, with anchors preferable if there's shallow bedrock, and ballast preferable if there's a deeper layer of loose regolith.

I think the math for dome anchoring can work out even better than that, if regolith ballast and water/ice ballast are used in conjunction with notional grout-bonded titanium anchors.  One scenario:

- 300 m low-curvature dome, titanium with ETFE foil
- 5 m water/ice radiation cover
- perimeter ballast ring track 20 m wide, with 14 m wet sand
- 55 acres of suspended "hanging garden" with 0.3 m wet sand
- 60 kPa interior pressure

The net upward force on anchors would be ~400 million N.

Result:  At 4.4 million N per anchor, that calls for 90 anchors, spaced 10 m apart.  Titanium and grout (dry mass) cargo for all anchors would total ~120 tons.  If titanium is scavenged from expendable ITS plant airframe, the cargo is reduced to dry grout alone, at ~84 tons.

I think.

Illustration:  Williams Form Engineering, steel & grout Spin-Lock rock anchors:

(http://www.williamsform.com/Ground_Anchors/Spin-Lock_Rock_Anchors/spin-lock_viz_760.jpg)
Title: Re: Elon Musk: glass geodesic domes
Post by: Robotbeat on 11/02/2016 02:34 am
Polycarbonate or layered polycarbonate-glass construction is considerably stronger...

Unfortunately polycarbonate turns semi-brittle between -60 C and -80 C (http://link.springer.com/article/10.1007/BF00754478); i.e., daily. 

Cryogenic materials would seem to be necessary, where Mars domes are exposed to the elements.
There's not perfect contact between the done surface an the nearly vacuum Mars air. Additionally, the dome (like cupola or Shuttle Windows or Dragon windows or basically any modern home) will be multi panes. The outer layer will likely be glass coated at least due to UV protection and clarity.
Title: Re: Elon Musk: glass geodesic domes
Post by: Robotbeat on 11/02/2016 02:35 am
The inner surface of the dome won't be the same temperature as the internal air, either.
Title: Re: Elon Musk: glass geodesic domes
Post by: CriX on 11/02/2016 03:41 am
Are the domes necessarily pressurized?  They would still be valuable for their natural greenhouse properties and protection from dust, and the insider air would probably be electrically heated as well.  Though I'm not sure that standard Martian atmospheric pressure is enough for growing earth plants.  ... It would get rid of the anchoring problem at least and focus the sheltering efforts on the underground volumes.  Domes mostly for PR and agriculture?
Title: Re: Elon Musk: glass geodesic domes
Post by: Vultur on 11/02/2016 03:58 am
So why don't people in Denver live in pressure domes?

IIRC, the vast majority of people are entirely fine at up to 8000 ft (~0.74 atm). (That is the FAA limit for airliner cabins, btw.) Mexico City is ~7700 ft (~0.75 atm). by comparison; Denver is ~5000 ft (~0.83 atm).

Even being conservative, there should be no problems with Denver-equivalent pressure. And you can go a bit heavier on oxygen - yes, that increases fire risk somewhat, but IIRC lower total pressure also suppresses fire because the air doesn't transmit heat as well (or something like that...)


As for CO2, mammals are exquisitely sensitive to even very small changes in the gas


At least for humans... not that small of changes. "Natural" levels are about 300 ppm, current levels are about 400 ppm, 5000 ppm (0.5%) which is the OSHA permissible exposure limit, really serious toxicity is well into the percent range (tens of thousands of ppm).
Title: Re: Elon Musk: glass geodesic domes
Post by: guckyfan on 11/02/2016 06:18 am
At least for humans... not that small of changes. "Natural" levels are about 300 ppm, current levels are about 400 ppm, 5000 ppm (0.5%) which is the OSHA permissible exposure limit, really serious toxicity is well into the percent range (tens of thousands of ppm).

I don't know what the CO2 llevels on the ISS were or are. But they have reduced it recently because there is reason to think it is not microgravity, but CO2, that is behind the eye problems experienced by astronauts. So what is acceptable for days or even weeks, is not acceptable permanently.
Title: Re: Elon Musk: glass geodesic domes
Post by: MikeAtkinson on 11/02/2016 08:15 am
Its just occurred to me that we have seen a SpaceX glass dome segment.

Title: Re: Elon Musk: glass geodesic domes
Post by: Robotbeat on 11/02/2016 12:08 pm
Its just occurred to me that we have seen a SpaceX glass dome segment.
Yup. As long as they land with the window facing toward the equator, they could even grow some plants there, perhaps even starting in 2022. You could say Musk's greenhouse stunt has gotten a little more ambitious.
Title: Re: Elon Musk: glass geodesic domes
Post by: AbuSimbel on 11/02/2016 12:09 pm
With the recent solar roof announcement we also know that Tesla has an in-house high-tech glass engineering division, for both solar panels and automotive: the Tesla Glass division (https://electrek.co/2016/11/01/tesla-model-3-new-glass-in-house-elon-musk-tesla-glass-tech-group/). Maybe it will play a role? Maybe it's already involved in the development of ITS/Dragon 2?
Title: Re: Elon Musk: glass geodesic domes
Post by: envy887 on 11/02/2016 01:33 pm
Polycarbonate or layered polycarbonate-glass construction is considerably stronger...

Unfortunately polycarbonate turns semi-brittle between -60 C and -80 C (http://link.springer.com/article/10.1007/BF00754478); i.e., daily. 

Cryogenic materials would seem to be necessary, where Mars domes are exposed to the elements.

That's a non-issue for several reasons:

Glass is brittle at all temperatures, so PC becoming brittle over part of the operating range doesn't make it a worse choice.

The air in the dome is going to nominally be above 0C if they play to grow anything inside, so the inside surface of the panel will be warmer and highly impact resistant to some depth.

Polycarbonate does get more brittle with temperature, but it also gets harder and is actually much stronger in tension at low strain rates: https://www.curbellplastics.com/Research-Solutions/Technical-Resources/Technical-Resources/Plastic-Materials-in-Cryogenic-Environments During normal operation the panel will be at zero strain rate and can take enormous pressure (i.e. tensile) loads all the way down to -270 C.

So basically the only issue is when the dome is -50 C or less inside (either uninhabited or under construction) and struck by a micro-meteorite (or not-so-micro-meteorite). That doesn't seem like a real high risk, using weak in tension and more brittle glass doesn't reduce it in the least.
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 11/02/2016 02:13 pm
Polycarbonate or layered polycarbonate-glass construction is considerably stronger...

Unfortunately polycarbonate turns semi-brittle between -60 C and -80 C (http://link.springer.com/article/10.1007/BF00754478); i.e., daily. 

Cryogenic materials would seem to be necessary, where Mars domes are exposed to the elements.

That's a non-issue for several reasons:

Glass is brittle at all temperatures, so PC becoming brittle over part of the operating range doesn't make it a worse choice.

The air in the dome is going to nominally be above 0C if they play to grow anything inside, so the inside surface of the panel will be warmer and highly impact resistant to some depth.

Polycarbonate does get more brittle with temperature, but it also gets harder and is actually much stronger in tension at low strain rates: https://www.curbellplastics.com/Research-Solutions/Technical-Resources/Technical-Resources/Plastic-Materials-in-Cryogenic-Environments During normal operation the panel will be at zero strain rate and can take enormous pressure (i.e. tensile) loads all the way down to -270 C.

So basically the only issue is when the dome is -50 C or less inside (either uninhabited or under construction) and struck by a micro-meteorite (or not-so-micro-meteorite). That doesn't seem like a real high risk, using weak in tension and more brittle glass doesn't reduce it in the least.
Thanks for an interesting response.  What would take less energy to produce on site, glass from Mars sand (supposing a nearby source) or polycarbonates from... carbonate and salt deposits?
Title: Re: Elon Musk: glass geodesic domes
Post by: Robotbeat on 11/02/2016 02:16 pm
It'd be trickier to produce the glass than the plastic. That may or may not translate into power, but it does translate into time. Plastics will be produced long before glasses are.
Title: Re: Elon Musk: glass geodesic domes
Post by: JamesH65 on 11/02/2016 02:59 pm
It'd be trickier to produce the glass than the plastic. That may or may not translate into power, but it does translate into time. Plastics will be produced long before glasses are.

Why? Rough glass is pretty easy to produce, if you have sand. Polycarbonate not so easy, I would have thought. And you have to make the raw materials from the atmosphere first.
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/02/2016 03:02 pm
PC and other plastics can be produced from Methane.

Methane is the most energy intensive to produce.  Once you have it, creating longer molecules should be exothermic on the whole.


Polycarbonate or layered polycarbonate-glass construction is considerably stronger...

Unfortunately polycarbonate turns semi-brittle between -60 C and -80 C (http://link.springer.com/article/10.1007/BF00754478); i.e., daily. 

Cryogenic materials would seem to be necessary, where Mars domes are exposed to the elements.

That's a non-issue for several reasons:

Glass is brittle at all temperatures, so PC becoming brittle over part of the operating range doesn't make it a worse choice.

The air in the dome is going to nominally be above 0C if they play to grow anything inside, so the inside surface of the panel will be warmer and highly impact resistant to some depth.

Polycarbonate does get more brittle with temperature, but it also gets harder and is actually much stronger in tension at low strain rates: https://www.curbellplastics.com/Research-Solutions/Technical-Resources/Technical-Resources/Plastic-Materials-in-Cryogenic-Environments During normal operation the panel will be at zero strain rate and can take enormous pressure (i.e. tensile) loads all the way down to -270 C.

So basically the only issue is when the dome is -50 C or less inside (either uninhabited or under construction) and struck by a micro-meteorite (or not-so-micro-meteorite). That doesn't seem like a real high risk, using weak in tension and more brittle glass doesn't reduce it in the least.
Thanks for an interesting response.  What would take less energy to produce on site, glass from Mars sand (supposing a nearby source) or polycarbonates from... carbonate and salt deposits?
Title: Re: Elon Musk: glass geodesic domes
Post by: envy887 on 11/02/2016 03:21 pm
I'm not sure there are carbonate deposits on Mars, or aromatic organics of any kind for that matter. They can be catalytically synthesized from methane and water. I don't have a good understanding of whether that's more difficult or energy intensive than producing glass or steel. But unlike glass or steel, plastics and composites are light and relatively easy to ship from Earth for a while.

Early plastics production would probably focus on polyethylene, which is much easier to make from methane. A structure that looks like Earth greenhouses with nearly transparent HDPE film, plus wrapped UHMWPE fiber reinforcement for pressure containment should be feasible. That design is commonly used for transparent pressure hoses:
Title: Re: Elon Musk: glass geodesic domes
Post by: guckyfan on 11/02/2016 03:29 pm
Pressure on hoses for algae would be much lower than for water hoses on earth. So they could be thinner and with less reenforcement if any, so more transparent.
Title: Re: Elon Musk: glass geodesic domes
Post by: MikeAtkinson on 11/02/2016 04:09 pm
Its just occurred to me that we have seen a SpaceX glass dome segment.
Yup. As long as they land with the window facing toward the equator, they could even grow some plants there, perhaps even starting in 2022. You could say Musk's greenhouse stunt has gotten a little more ambitious.

What I meant is that this is like a segment of a 12 m diameter dome. Not exactly what SpaceX would use for a dome, but similar enough that you can see how they could create a dome.

Although there have been suggestions of 100+ m domes above, I think initial domes will be much smaller, in the 10-20 m diameter range. Partly because they will be much easier to anchor, partly because they will be easier to construct and because they are enough to enclose a hab, could be used as workshops/garages, and are suitable for agricultural experiments, etc.
Title: Re: Elon Musk: glass geodesic domes
Post by: Robotbeat on 11/02/2016 04:12 pm
You don't need "carbonates," almost the entire atmosphere is CO2 which you'd use as a feedstock. (There are a lot of chemistry steps there, but it can be done. I once figure out the whole synthesis process from Air, water to polycarbonate and similar plastics like PMMA.)

Rough glass (melted regolith) is useful for paving stones. But there's a huge difficulty in preparing high optical clarity glass with good structural properties. Float glass furnaces, etc. it'll happen but not before plastics production.
Title: Re: Elon Musk: glass geodesic domes
Post by: CraigLieb on 11/02/2016 05:47 pm
Transparent Aluminum...  its a real thing now...

http://screenrant.com/star-trek-transparent-aluminum-real/
Title: Re: Elon Musk: glass geodesic domes
Post by: Robotbeat on 11/02/2016 06:23 pm
A big thing with glass is that good structural glass requires a lot of different materials that must be mined and of high quality. Plastics of many different kinds can be made with basically just air and water (& sophisticated chemistry).
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/02/2016 06:52 pm
Look up Acrylic on Wikipedia - can be synthesized from CHO precursors.

It's a great material to work on, a bit touchy on machining, but great for thermoforming and solvent bonding.

I wonder if that's what Musk is cooking.
Title: Re: Elon Musk: glass geodesic domes
Post by: envy887 on 11/02/2016 07:27 pm
Acrylic is nice for UV resistance and is reasonably strong, but has poor impact resistance compared to polycarbonate. It's still lighter, stronger, and tougher than glass.

Aluminum oxynitride is great stuff. The only issue I can see with that is it's quite expensive and a 12" by 12" window is considered "large". Also the manufacturing capacity to produce large quantities of large panels is currently about a million times less than PC and acrylic,
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/02/2016 08:35 pm
Acrylic is nice for UV resistance and is reasonably strong, but has poor impact resistance compared to polycarbonate. It's still lighter, stronger, and tougher than glass.

Aluminum oxynitride is great stuff. The only issue I can see with that is it's quite expensive and a 12" by 12" window is considered "large". Also the manufacturing capacity to produce large quantities of large panels is currently about a million times less than PC and acrylic,

I've worked with both... Bullet resistant windows are Acrylic, since it's easier to make thick panes out of of it.
PC is easier to machine, but very difficult to bond.

Thermoforming Acrylic is a dream, and if you want to give the panes just a touch of 3D curvature, not a problem.

If the struts are painted with an acrylic coat, you can solvent bond to them for a seamless connection.

Also easy to add acrylic "goo" and patches as a gap filler, hole fixer, etc.
Title: Re: Elon Musk: glass geodesic domes
Post by: Robotbeat on 11/02/2016 08:47 pm
PMMA is easier to make than polycarbonate via ISRU.
Title: Re: Elon Musk: glass geodesic domes
Post by: Space Ghost 1962 on 11/02/2016 09:28 pm
Plastics don't function well in a Mars surface environment. It's not just the UV.

Some plastics will combust with certain components of the dust (one example - urea is often used as a filler/stabilizer - explodes with perchlorates). The dust has a high static charge that's difficult to dissipate, it abrades coatings/surfaces and leads to interesting photochemical reactions, some of which could fissure thick structural plastic members. Acrylics are in this camp.

And I haven't gotten to the alkali salts issues yet either. PTFE and HDPE fair well but long term exposure likely will see embrittlement/erosion issues. Polycarbonates and thermal cycling would face similar issues. Thermosetting plastics might hold up better on Mars than they do on Earth.

So be careful here on materials.

One material that will be ideal - Aluminium oxynitride (http://www.surmet.com/technology/alon-optical-ceramics/).

edit:auto-incorrect strikes ;)
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/02/2016 11:37 pm
Plastics don't function well in a Mars surface environment. It's not just the UV.

Some plastics will combust with certain components of the dust (one example - urea is often used as a filler/stabilizer - explodes with perchlorates). The dust has a high static charge that's difficult to dissipate, it abrades coatings/surfaces and leads to interesting photochemical reactions, some of which could fissure thick structural plastic members. Acrylics are in this camp.

And I haven't gotten to the alkali salts issues yet either. PTFE and HDPE fair well but long term exposure likely will see embrittlement/erosion issues. Polycarbonates and thermal cycling would face similar issues. Thermosetting plastics might hold up better on Mars than they do on Earth.

So be careful here on materials.

One material that will be ideal - Aluminium oxynitride (http://www.surmet.com/technology/alon-optical-ceramics/).

edit:auto-incorrect strikes ;)

Thickness is your friend against surface phenomena.  Large panes for a pressurized dome, especially factoring in ballistic protection, are going to be a few inches thick.

Surface issues can be dealt with by cleaning and re-coating.

Fire...  from dust on the outside?  In a 1% CO2 environment?


Title: Re: Elon Musk: glass geodesic domes
Post by: Robotbeat on 11/02/2016 11:45 pm
Yeah, no way there are enough perchlorates to make anything explode. And if there was, you could mine that perchlorate deposit as an energy source! Perchlorates will exothermically release oxygen if heated and given the right catalyst.
Title: Re: Elon Musk: glass geodesic domes
Post by: KelvinZero on 11/03/2016 05:52 am
You can look at the Wikipedia page "Pressure vessels".  There is a nice, short overwrap pressure vessel.  Or you can look at the propane pressure tank on your barbecue, if you have one. It's pretty stuby.
The vessel will keep its shape because there are no compression forces, all forces push equally towards the exterior and the walls are under pure tension. But yes, an ellipsoid is less mass efficient that sphere.  The strain in about double that of a sphere, or almost equal to that of a cylinder.  So this allows manufacturers to use the same thickness throughout.
Ok: it linked to this: https://en.wikipedia.org/wiki/Head_(vessel)
"Vessel dished ends are mostly used in storage or pressure vessels in industry. These ends, which in upright vessels are the bottom and the top, use less space than a hemisphere (which is the ideal form for pressure containments) while requiring only a slightly thicker wall."

..so it is suboptimal, but apparently only a bit. Im surprised. Does this rely on any 'unbendiness' of the walls? Would these maintain their shape if infinitly strong in tensile strength but fully flexible?.. I think I can see that is true now by imagining constant length chords across the dome. Tensile strength requirements go up, approaching infinity as they approach flatness, but it is not about bendiness (I really should look up the technical term for that :) )
Oops, that was discussion I had intended to post in this thread. I hate it when people pursue their pet peeve over multiple threads simultaneously.

Two points and I think I will consider this 'anchoring' problem answered with this flattened pressure vessel approach:

(1) A sphere gives better volume/mass than a flattened sphere, but is it possible that at a certain deformation, the flattened sphere gives a larger single flat area per mass? You could argue that a high roof is not so useful. After all, if what you want is sky scrapers, they could stick out the top anyway and be their own pressure vessels. No one needs to hang out windows on floors a hundred stories up.

(2) As a compromise between a sphere and flattened sphere, and especially if it turns out a flattened sphere does not give better single flat area/mass, what if the top half is a sphere and the lower half is as flattened as practical? It might be practical to flatten that one spot quite a bit because the entire mass of your dome is resting on it, and also this lower half could be of a different, non-transparent, perhaps cheaper material. A bit of regolith can be filled in around it later or it can have short legs around the rim, or it could be put in a shallow crater. In any case it could be a lot less digging than to half-bury a sphere and less work and less vertigo-inducing than a full height sphere on the surface.

This compromise might make a sort-of dome-like thing a reasonable quickly assemblable design for any ground type after all.
Title: Re: Elon Musk: glass geodesic domes
Post by: LMT on 11/03/2016 06:10 am
Toughing It Out

Polycarbonate or layered polycarbonate-glass construction is considerably stronger...

Unfortunately polycarbonate turns semi-brittle between -60 C and -80 C (http://link.springer.com/article/10.1007/BF00754478); i.e., daily. 

Cryogenic materials would seem to be necessary, where Mars domes are exposed to the elements.

That's a non-issue for several reasons:

Glass is brittle at all temperatures, so PC becoming brittle over part of the operating range doesn't make it a worse choice.

The air in the dome is going to nominally be above 0C if they play to grow anything inside, so the inside surface of the panel will be warmer and highly impact resistant to some depth.

Polycarbonate does get more brittle with temperature, but it also gets harder and is actually much stronger in tension at low strain rates: https://www.curbellplastics.com/Research-Solutions/Technical-Resources/Technical-Resources/Plastic-Materials-in-Cryogenic-Environments During normal operation the panel will be at zero strain rate and can take enormous pressure (i.e. tensile) loads all the way down to -270 C.

So basically the only issue is when the dome is -50 C or less inside (either uninhabited or under construction) and struck by a micro-meteorite (or not-so-micro-meteorite). That doesn't seem like a real high risk, using weak in tension and more brittle glass doesn't reduce it in the least.

Reading that ref. more conservatively in another thread (http://forum.nasaspaceflight.com/index.php?topic=41427.msg1605888#msg1605888).  Failure modes due to reduced toughness; just seems like a bad idea.
Title: Re: Elon Musk: glass geodesic domes
Post by: MikeAtkinson on 11/03/2016 07:43 am

One material that will be ideal - Aluminium oxynitride (http://www.surmet.com/technology/alon-optical-ceramics/).

edit:auto-incorrect strikes ;)

Another material is Magnesium aluminate (Spinel) which may be sintered from powder into various shapes.

It looks like both Aluminium oxynitride and Magnesium aluminate are difficult to work with and processing them into usable structures is likely to be heavily encumbered with patents.
Title: Re: Elon Musk: glass geodesic domes
Post by: envy887 on 11/03/2016 01:01 pm
Glass is the least tough potential pane material at any temperature, so the worries about PC toughness are completely unfounded.
Title: Re: Elon Musk: glass geodesic domes
Post by: Robotbeat on 11/03/2016 01:12 pm
I notice a cert Amount of concern trolling in this thread that keeps pulling things off topic. First assumption here has to be that rational engineers will be designing this thing.
Title: Re: Elon Musk: glass geodesic domes
Post by: philw1776 on 11/03/2016 04:16 pm
Plastics don't function well in a Mars surface environment. It's not just the UV.

Some plastics will combust with certain components of the dust (one example - urea is often used as a filler/stabilizer - explodes with perchlorates). The dust has a high static charge that's difficult to dissipate, it abrades coatings/surfaces and leads to interesting photochemical reactions, some of which could fissure thick structural plastic members.

Appreciate this important safety tip. 

There goes my idea of having surface suits just expel urine like whizzing outdoors in my backyard woods.
Title: Re: Elon Musk: glass geodesic domes
Post by: LMT on 11/03/2016 10:14 pm
"Mars is hard."  Plastic is easier?

Plastics don't function well in a Mars surface environment. It's not just the UV.

Some plastics will combust with certain components of the dust (one example - urea is often used as a filler/stabilizer - explodes with perchlorates). The dust has a high static charge that's difficult to dissipate, it abrades coatings/surfaces and leads to interesting photochemical reactions, some of which could fissure thick structural plastic members. Acrylics are in this camp.

And I haven't gotten to the alkali salts issues yet either. PTFE and HDPE fair well but long term exposure likely will see embrittlement/erosion issues. Polycarbonates and thermal cycling would face similar issues. Thermosetting plastics might hold up better on Mars than they do on Earth.

So be careful here on materials.

One material that will be ideal - Aluminium oxynitride (http://www.surmet.com/technology/alon-optical-ceramics/).

"Mars is hard", yeah.  And hard on materials.  I hear there's an Xtreme Materials Properties Database (http://llis.nasa.gov/lesson/1858) somewhere in the JPL garage.  Maybe somebody will throw a copy at us sometime.  Meanwhile, bar's open.

If a dome facility fully blocks UV and also cleans inputs thoroughly, plastics should have a long service life inside.  ISRU low- and high-density plastics could kit out much of a dome's interior, saving immense cargo.  What are good ways to manufacture?

As MeekGee noted, methane production is a given, and polyethylene plastic can be produced from the methane.  Is that the best start?  I'll mention the Newlight AirCarbon (https://newlight.com/aircarbon/) process, that produces PHA plastic (http://f2.hs-hannover.de/fileadmin/media/doc/ifbb/Bioplastics_Magazine__03_11__Vol._6_S._43-45.pdf) from methane and CO2, via biocatalytics. 

Notably, PHA plastics can be UV stable.  UV flux on Mars is comparable to Earth's, but skewed (http://mars.jpl.nasa.gov/mgs/sci/fifthconf99/6128.pdf) toward more damaging UVB and UVC wavelengths, so UV stability is uncertain on Mars.  Still, PHA seems an improvement on polyethylene plastic in this regard.

If the methanotrophic biocatalyst is easily cultivated, this NewCarbon process might be a contender.  Newlight patent applications (http://www.patentsencyclopedia.com/assignee/newlight-technologies-llc/).

What are the other contenders?

https://www.youtube.com/watch?v=Hghly5Kdt8A
Title: Re: Elon Musk: glass geodesic domes
Post by: KelvinZero on 11/04/2016 09:17 pm
Im interested in the mechanics of assembling this prefab dome.. looking forward to people actually trialling it on earth. Perhaps Elon Musk could sell them :-)

I had a bunch of ideas for assembly. Decided to biff most of them. No mat for the bottom. No bladder. This is not scalable enough.

Ideas I am sticking with:
*Assemble a circular ring first, a bit like a trampoline. It might have legs or it might be built over a depression. Probably a bit of both.
*Underside is a semielliptical surface. It is constructed similar to the upper faces but probably with something cheaper and lighter than the glass panes. It's skeleton has to be strong enough to withstand full pressure but the individual panes can gain some support by having regolith packed under them.
*Upper side is a geodesic dome, perhaps a bit more than half a sphere.

This leaves the problem of making it 100% airtight. Only idea I have there is that I bet we could spot these leaks easily from outside with some sort of IR vision.

Also, assembling something like this with spacesuits and ladders does not seem likely. What sort of equipment is required there? Would also need something to move regolith etc if it is not simply built with legs all the way to the ground.
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/05/2016 11:04 pm
Acrylic is "glass"...

And you'd like to use a material that is initially shipped from earth, and later made in situ.

Both Regular Si glass and Acrylic fit the bill.
Title: Re: Elon Musk: glass geodesic domes
Post by: KelvinZero on 11/06/2016 10:19 pm
Hey did the people who set up this think about the practicality of a geodesic dome? Do they have answers to the anchoring questions etc?

http://www.npr.org/sections/thetwo-way/2016/08/29/491794937/mars-mission-crew-emerges-from-yearlong-simulation-in-hawaii

Title: Re: Elon Musk: glass geodesic domes
Post by: TripD on 11/07/2016 12:12 am
One more go around.  A toroid at sea level pressure and an open space at some reduced pressure that still allows for growing varying plants.
Title: Re: Elon Musk: glass geodesic domes
Post by: oldAtlas_Eguy on 11/07/2016 07:48 pm
Hey did the people who set up this think about the practicality of a geodesic dome? Do they have answers to the anchoring questions etc?

http://www.npr.org/sections/thetwo-way/2016/08/29/491794937/mars-mission-crew-emerges-from-yearlong-simulation-in-hawaii
If you create a geodesic dome as a sphere where it is partially filled processed regolith or even just the lower half as storage industrial space with a thin soil cover no anchors are required because the structure is its own anchor being a sphere.
Title: Re: Elon Musk: glass geodesic domes
Post by: KelvinZero on 11/07/2016 08:00 pm
Hey did the people who set up this think about the practicality of a geodesic dome? Do they have answers to the anchoring questions etc?

http://www.npr.org/sections/thetwo-way/2016/08/29/491794937/mars-mission-crew-emerges-from-yearlong-simulation-in-hawaii
If you create a geodesic dome as a sphere where it is partially filled processed regolith or even just the lower half as storage industrial space with a thin soil cover no anchors are required because the structure is its own anchor being a sphere.
That is my conclusion at the moment. Im actually inspired by all this 3d to mock up some domes based on NASA hydrogen storage tanks: https://www.nasaspaceflight.com/2016/10/ksc-groundwork-sls-block-1b-upgrades/

The extra depth is actually useful for extra shielding, and the lower sides give great windows for looking out at your immediate surroundings whereas upper sloping walls are mainly good for looking at sky :) .. The upper half can give you room to kick a football but the lower half could be divided into levels with nicer views.
Title: Re: Elon Musk: glass geodesic domes
Post by: Robotbeat on 11/07/2016 09:10 pm
Wasting half the structure as its own anchor is easier conceptually but anchors are done all the time with suspension bridges and other construction on Earth. Just because it's easier to put on a napkin sketch doesn't mean we should steer the architecture in that direction. Just use anchors &/or ballast.
Title: Re: Elon Musk: glass geodesic domes
Post by: KelvinZero on 11/08/2016 01:17 am
Wasting half the structure as its own anchor is easier conceptually but anchors are done all the time with suspension bridges and other construction on Earth. Just because it's easier to put on a napkin sketch doesn't mean we should steer the architecture in that direction. Just use anchors &/or ballast.
How you wasting half the structure? By doubling the structure you are doubling the volume.. then on top of that you are saving whatever structure and infrastructure and work and surveying would have been needed for the anchors.

As a counter example, why do people not seem to use anchoring for pressure vessels on earth?
Title: Re: Elon Musk: glass geodesic domes
Post by: Robotbeat on 11/08/2016 01:47 am
They do. See large pressurized sports domes for baseball and tennis and football/soccer, for instance. Extremely high pressure vessels like for gas storage dont, but that's a completely different purpose. We're not storing gas, we're housing people.
Title: Re: Elon Musk: glass geodesic domes
Post by: KelvinZero on 11/08/2016 02:45 am
They do. See large pressurized sports domes for baseball and tennis and football/soccer, for instance. Extremely high pressure vessels like for gas storage dont, but that's a completely different purpose. We're not storing gas, we're housing people.
You mean this?
https://en.wikipedia.org/wiki/Air-supported_structure

But in that case isn't the pressure per square meter just to support a square meter of tent-like material? Wouldn't that just be a few kilograms? (or maybe to withstand any wind force, but that is a different sort of problem since wind force generally pushing inwards or sideways I would have thought.)

On mars we are talking a pressure of around ten earth-tons weight per square meter, which on Mars means about 30 tons of mass to anchor each square meter.
Title: Re: Elon Musk: glass geodesic domes
Post by: Robotbeat on 11/08/2016 03:02 am
They do. See large pressurized sports domes for baseball and tennis and football/soccer, for instance. Extremely high pressure vessels like for gas storage dont, but that's a completely different purpose. We're not storing gas, we're housing people.
You mean this?
https://en.wikipedia.org/wiki/Air-supported_structure

But in that case isn't the pressure per square meter just to support a square meter of tent-like material? Wouldn't that just be a few kilograms? (or maybe to withstand any wind force, but that is a different sort of problem since wind force generally pushing inwards or sideways I would have thought.)

On mars we are talking a pressure of around ten earth-tons weight per square meter, which on Mars means about 30 tons of mass to anchor each square meter.
They are high enough pressure that they require anchoring against the internal pressure as well.

The pressure they are pressurized at is ~0.35psi.

If you're comparing to big spheres used as pressure vessels to store natural gas, those are roughly 3500psi.

We're interested in something in between. Probably about 7-12psi (similar oxygen level as Denver or slightly less, but with slightly higher relative concentration of oxygen, a combination which gives slightly better fire safety than sea level while reducing structural loads and reducing danger of getting the bends in case of rapid decompression).
Title: Re: Elon Musk: glass geodesic domes
Post by: KelvinZero on 11/08/2016 03:56 am
10 tons is an easier number to remember though :)

But ok, 10psi is still about 30 times more than 0.35, and on mars there _might_ be another factor of 3 problem due to lighter gravity. It might be a 100 times more difficult therefore. I guess potentially that is no problem if you are relying on the tensile strength of some monolithic chunk of stone that you are anchoring to, though I don't like having to rely on the geology like that if I don't have to.

So what do you see as the advantage of a dome over a sphere? I argued above that the sphere actually takes less structure (and infrastructure and surveying and work) for the same volume.

I really like the fact you can just assemble this thing on the surface so I would need a solid reason to not go with a fully enclosed pressure vessel, at least initially*

I actually like the shape of a sphere, if there is not a serious mass penalty. The upper side gives you room to kick a football. The lower side gives you good room for working space with awesome views of both your doorstep right up to the horizon. I don't think the upper half of domes divide into levels as well. It is fine to truncate the sphere at the bottom a bit if you like. You probably would pay very little for that.

*There is one case where I think a dome can be very well anchored and provide infinite volume for structure, but that is for the future after significant mining. That is when your dome is really a cylinder with a hemispherical cap, with the cylinder part using the entire earth for strength, and furthermore the bottom of the cylinder connected to something even larger tens of meters down. There is no way that is budging.
Title: Re: Elon Musk: glass geodesic domes
Post by: Robotbeat on 11/08/2016 04:36 am
No. you drive a deep anchor into the ground. Imagine an anchor deep into the soil that expands at the lowest depth. you're relying on the mass of the soil/ground or possibly compressive strength, not the rock tensile strength.
Title: Re: Elon Musk: glass geodesic domes
Post by: KelvinZero on 11/08/2016 05:14 am
No. you drive a deep anchor into the ground. Imagine an anchor deep into the soil that expands at the lowest depth. you're relying on the mass of the soil/ground or possibly compressive strength, not the rock tensile strength.
You are saying 'no' to the only point I brought up in your favour :)

I figure the area the rim has to support is 0.5R area, ie with a 100 meter wide dome R=50 so a 1 meter segment of rim has to support 25 square meters, or about 250 earth-tons of pressure (sticking with my sealevel approximation) which implies about x3 = 750 tons of mars rock to hold down that 1 meter.

That is probably not as bad as it sounds. I don't know the math here. Im guessing that even if you anchored in sand the influence of the anchor would widen in a cone. You are sharing this mass with your neighbouring anchors so you end up with only a triangular slice all of your own. (proportional to the square of the depth, not the cube) My laymans assumptions imply that maybe the depth you have to drill is nothing like a kilometer, more on the order of ten meters.. extremely rough assumptions though.

Im sure you can do it. But why not just go with the sphere: double the volume for double the transported mass, ie same volume to mass ratio and none of this fiddling around. Just assemble it.
Title: Re: Elon Musk: glass geodesic domes
Post by: GregA on 11/08/2016 05:15 am
In terms of pane shape, I think it's fair to look at the observation window in the BFS to see the vague thoughts the designers may be imagining with Mars plans. They're all triangular (https://www.youtube.com/watch?v=0qo78R_yYFA?t=11s)

With the recent solar roof announcement we also know that Tesla has an in-house high-tech glass engineering division, for both solar panels and automotive: the Tesla Glass division (https://electrek.co/2016/11/01/tesla-model-3-new-glass-in-house-elon-musk-tesla-glass-tech-group/). Maybe it will play a role? Maybe it's already involved in the development of ITS/Dragon 2?
I was wondering if anyone would mention that. Absolutely.

Here we have Tesla working on stronger glass options for the cars, the technology now also used as roofing tiles - including shapes that have to intertwine with each other. They're designed to be good insulators, and the car glass fits into a metal framework, and then has to handle the twists and turns of car movements - all useful learnings for triangular panes in domes. There's talk of carbon fibre car bodies in future.

Also the solar versions of the tiles incorporate cells which are opaque, though Elon has joked about the car's glass roof generating some power (there's some debate on whether it was a joke). MIT has produced fully transparent solar cells which would be far more useful to them (and of course you could expect EM would like the glass to absorb any other radiation possible and convert it to energy, but we all know that's limited.)

Anyway, all interesting intersections with the glass domes of Mars. If they start constructing the glass at the gigafactory that'll show more of their interest in this I think.
Title: Re: Elon Musk: glass geodesic domes
Post by: Robotbeat on 11/08/2016 05:26 am
No. you drive a deep anchor into the ground. Imagine an anchor deep into the soil that expands at the lowest depth. you're relying on the mass of the soil/ground or possibly compressive strength, not the rock tensile strength.
You are saying 'no' to the only point I brought up in your favour :)

I figure the area the rim has to support is 0.5R area, ie with a 100 meter wide dome R=50 so a 1 meter segment of rim has to support 25 square meters, or about 250 earth-tons of pressure (sticking with my sealevel approximation) which implies about x3 = 750 tons of mars rock to hold down that 1 meter.

That is probably not as bad as it sounds. I don't know the math here. Im guessing that even if you anchored in sand the influence of the anchor would widen in a cone. You are sharing this mass with your neighbouring anchors so you end up with only a triangular slice all of your own. (proportional to the square of the depth, not the cube) My laymans assumptions imply that maybe the depth you have to drill is nothing like a kilometer, more on the order of ten meters.. extremely rough assumptions though.

Im sure you can do it. But why not just go with the sphere: double the volume for double the transported mass, ie same volume to mass ratio and none of this fiddling around. Just assemble it.
Because now you have a lot more structure just to hold everything up instead of being flat on the ground.
Title: Re: Elon Musk: glass geodesic domes
Post by: KelvinZero on 11/08/2016 07:15 am
Because now you have a lot more structure just to hold everything up instead of being flat on the ground.
Mainly you just have to stop it rolling :)

I think you are sort of trolling now. You really can't think of low mass ways around this that you probably have to do anyway, or are just trivial?

Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 11/08/2016 01:05 pm
Because now you have a lot more structure just to hold everything up instead of being flat on the ground.
Mainly you just have to stop it rolling :)

I think you are sort of trolling now. You really can't think of low mass ways around this that you probably have to do anyway, or are just trivial?
A flat floor could be used, in particular for smaller domes. 
for a rough guess, you need to calculate the force on the floor area, at 10t/m2 or less at lower pressure, then divide this by the number of beams you can fit into the space.  Each beam end corresponds to the bottom of a structural member that holds the glass panes.
The beam needs to resist the bending moment of an end load. My guess is 6 inch beams for a 12 foot dome, then they grow quickly as the domes get bigger.

I like the full sphere on legs ides, or partly buried bottom, with the lower part serving as water tank and technical area, with clean/dirty water, air tanks, air recycler, electrical apparatus, batteries, potato storage ;-) 
No anchoring is required in such a case, Martian winds are a negligible force, except in novels.
Title: Re: Elon Musk: glass geodesic domes
Post by: KelvinZero on 11/08/2016 07:50 pm
I like the full sphere on legs ides, or partly buried bottom, with the lower part serving as water tank and technical area, with clean/dirty water, air tanks, air recycler, electrical apparatus, batteries, potato storage ;-) 
No anchoring is required in such a case, Martian winds are a negligible force, except in novels.
I really have to get back into Blender one day ;)

Legs, flattened bottom, partially buried or regolith piled up. Maybe a mix of all 3.5 of those options.

There is also another thing you need: a way to get into it. This implies airlocks and other pressurised volumes. Assume these are connected externally and it is easy to imagine these also forming a stable base.

If you want to be a purist you could postulate the smaller volumes are spheres also. The only point of that is to mathematically argue that this extra structure does not imply extra mass per enclosed volume.

I imagine fat cylindrical legs that are also your airlocks and perhaps stairways. (An engineer might rule out that last one. Maybe it would threaten the strength of the geodesic dome)
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/08/2016 08:04 pm
Because now you have a lot more structure just to hold everything up instead of being flat on the ground.
Mainly you just have to stop it rolling :)

I think you are sort of trolling now. You really can't think of low mass ways around this that you probably have to do anyway, or are just trivial?

He's not trolling, he's just making sense.

You're talking about a very deep excavation (craters don't have the right aspect ratio) and then foundation to keep the mass distributed so as not to buckle your sphere.

Deep earth anchors are dirt(!) simple.   you percussion pound them in, they expand deep underneath, you consider the "friction cone" above them as their load limit, and done.   They are used all the time.

If you're scared, you can double them up.

You still need to "pour a pad", but this saves you the hassle of building a ginormous floor.

----

Advanced option -  if you want agriculture, you pressurize your dome with CO2, and make slightly-pressurized dwellings inside that have N2O2 atmosphere.  You can then go into the dome with merely a respirator, and if your dwellings can hold pressure, you have double protection while inside of them.
Title: Re: Elon Musk: glass geodesic domes
Post by: GregA on 11/08/2016 10:06 pm
You're talking about a very deep excavation (craters don't have the right aspect ratio) and then foundation to keep the mass distributed so as not to buckle your sphere.
I suspect Musk is focussed on ease of construction. Lots of standard size glass means it's transportable, interchangeable if needed, and later manufacturable on Mars.

He's described underground dwelling for humans, robots for digging, with the domes on the surface for crops right? It implies
a) he thinks the digging a hole is doable
b) automated construction as much as possible
c) he's not thinking of habitats in the domes. These are underground.
d) a farm-based dome will need the soil to be engineered for crops anyway.
e) entry to the dome will sometimes come from underground, not the surface

So I wouldn't discount the idea of a spherical design.
Title: Re: Elon Musk: glass geodesic domes
Post by: KelvinZero on 11/08/2016 11:15 pm
He's not trolling, he's just making sense.

You're talking about a very deep excavation (craters don't have the right aspect ratio) and then foundation to keep the mass distributed so as not to buckle your sphere.

Deep earth anchors are dirt(!) simple.   you percussion pound them in, they expand deep underneath, you consider the "friction cone" above them as their load limit, and done.   They are used all the time.

If you're scared, you can double them up.

You still need to "pour a pad", but this saves you the hassle of building a ginormous floor.
I really did think this was obvious but I listed examples of how to trivially fix this above. For me the most obvious is to combine larger and smaller pressure volumes, such as your airlock volumes that provide access, but there are also the other 3.5 methods mentions. I really dont see them as involving much digging. I think you might be envisioning having to escavate the entire bottom half !! Draw a circle and see how little you have to bury to get a wide base.. maybe 1/8 the height and much less than that in volume? but in any case two of the ideas mentioned require no digging.

Having the floor "for free" does not save you any mass. A sphere is two hemispheres. For double the structure you get double the volume. The sphere-based habitat gives you the same volume per wall cargo, but is still cheaper and less complex because there are no anchors or floor proofing to master. You just assemble it.

I don't really know much about deep earth anchors. This is actually an interesting topic to me because my (very rough) calculations suggested you might need like ten meters. That is an interesting value to me because it is also what is required for getting to the ice at glaciers near the equator, it is speculated. It is great if that sort of boring is trivial. I did point out that you don't get an entire friction cone though. Because you have many anchors side by side, each just gets a friction 'triangular wedge" of mass it can exploit to hold itself down.

I admit there is plenty I do not know there. But before getting into all that, what actual advantage do you get if you add all these additional complexities? Not more volume.
Title: Re: Elon Musk: glass geodesic domes
Post by: KelvinZero on 11/09/2016 02:13 am
Given that this friction cone is a real thing, it gave me confidence to do a bit of math using some simplified numbers.
-----
Earth pressure = 10 tons per square meter
Soil density = 3 tons per m3.
Mars gravity = 1/3 earth's (for simplicity)

Thus volume of soil needed to anchor a square meter is 10 m3

Thus the volume of soil needed to anchor a dome is
Vrequired = ∏*R2*10 (m3)
-----
The volume anchored by a row of neighbouring anchors is
Vanchored =(area of a triangular wedge) * length of row
which I am going to assume holds even if the row is bent in a curve.

The area of the triangular wedge is
area(D, T) = D2*tan(T))
where D is the depth and T is the cone of friction angle.

The length of the row is equal to the circumference of the dome, ie 2*∏*R so
Vanchored = D2*tan(T)) * (2*∏*R)
----
Equating the two:
Vanchored = Vrequired
D2*tan(T)) * (2*∏*R) = ∏*R2*10 (m3)
Which I think solves to:

Limit for a large number of anchors:
Anchor depth for a mars dome of radius R,  and soil cone of friction angle T:
D = Sqrt(5R/tan(T))
(assumes 3t/m3 soil density, gravity = 1/3 earth, sea-level pressure and no safety margin)

If we arbitrarily set T = 45° and R = 50, I get a depth of 16 meters for our anchors.
----
EDIT

In hindsight you probably do not need a large number of anchors to hold the edge down. You can probably just have stiff edge or similar. A discrete number means your friction cones would not need to overlap.

For a discrete number of anchors and using the same assumptions (density of soil etc) I get

D3 = (30R2)/(N.tan(T))
where N is number of anchors, assuming no overlap.

eg for N = 6, R=50 and T=45° I get a depth of about 23 meters.
(and for T=45°, this is also the radius of the friction cone. These just fit into the verticies of a hexagon of 50 meter sides without overlapping)

Note these values assume no safety margin. Maybe they would be sufficient for half pressure?. Also some of the assumptions and approximations begin to break down under R=50, and the actual requirements would be harder than suggested.
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/09/2016 08:48 am
Quicker:

http://www.platipus-anchors.com/applications/civil-engineering-and-construction/bat-anchor-2/

And apply the gravity factor.

If you make a proper pad, it takes care of some of the redundancy, and these anchors are testable to make sure they're not slowly losing strength.
Title: Re: Elon Musk: glass geodesic domes
Post by: KelvinZero on 11/09/2016 09:39 am
Quicker:

http://www.platipus-anchors.com/applications/civil-engineering-and-construction/bat-anchor-2/

And apply the gravity factor.

If you make a proper pad, it takes care of some of the redundancy, and these anchors are testable to make sure they're not slowly losing strength.
Was that aimed at me? you sent me to a page with ground anchors in the 75-200kN range. Did you mean I should sign up for the calculator? I hate plugging my address in randomly around the place and these really don't seem of the right scale. That would equate to 2.8 to 7.6 earth-tons of pressure on Mars, depending on the soil. Earth sea level pressure is 10 tons/square meter. You could hold down your shadow, but not much more than that.

Edit: If you have a login for that calculator, find out what sort of single anchor you need to hold down 40,000 tons. (400,000 kN). With six of those you could probably hold down your 100 meter diameter dome in Mars gravity (with no safety margin).
They might also tell you what equipment you need to install it, which would be interesting.
Title: Re: Elon Musk: glass geodesic domes
Post by: MickQ on 11/09/2016 10:26 am
Imagine a 20mt diameter sphere. The lower 1/4 of the structure is an engineered metallic "bowl" incorporating 4 or 6 legs.  Half of the legs contain airlocks and any connection points for outside services and the other legs are full of ballast or storage tanks or backup power/ECLSS etc.  In the bottom of the metal portion are elevators and/or stairs down to underground habitation/workshop/storage/garage facilities.  With all this bolted together I think minimal anchoring would be needed as the whole structure is a pressure vessel.
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/09/2016 12:41 pm
Quicker:

http://www.platipus-anchors.com/applications/civil-engineering-and-construction/bat-anchor-2/

And apply the gravity factor.

If you make a proper pad, it takes care of some of the redundancy, and these anchors are testable to make sure they're not slowly losing strength.
Was that aimed at me? you sent me to a page with ground anchors in the 75-200kN range. Did you mean I should sign up for the calculator? I hate plugging my address in randomly around the place and these really don't seem of the right scale. That would equate to 2.8 to 7.6 earth-tons of pressure on Mars, depending on the soil. Earth sea level pressure is 10 tons/square meter. You could hold down your shadow, but not much more than that.

Edit: If you have a login for that calculator, find out what sort of single anchor you need to hold down 40,000 tons. (400,000 kN). With six of those you could probably hold down your 100 meter diameter dome in Mars gravity (with no safety margin).
They might also tell you what equipment you need to install it, which would be interesting.
We saying that load rated products exist.

If you're going to prep the floor, you will place as many of these around the perimeter as you need.

So I guess what I'm saying is that anchoring is not a giant problem.

Knowing that, you can evaluate the digging project which is not impossible either, in comparison.

Title: Re: Elon Musk: glass geodesic domes
Post by: KelvinZero on 11/09/2016 07:44 pm
Quote
Edit: If you have a login for that calculator, find out what sort of single anchor you need to hold down 40,000 tons. (400,000 kN). With six of those you could probably hold down your 100 meter diameter dome in Mars gravity (with no safety margin).
They might also tell you what equipment you need to install it, which would be interesting.
We saying that load rated products exist.
If you're going to prep the floor, you will place as many of these around the perimeter as you need.
So I guess what I'm saying is that anchoring is not a giant problem.
Knowing that, you can evaluate the digging project which is not impossible either, in comparison.

I feel like you are not reading anything I said.

* Digging equals zero, if you are worried about it. (two of the sphere suggestions have no digging)
* Of course load rated products exist. Can someone look up the price for six 40,000-ton anchors and what we need to install them?
* You can't just place as many as you need. That is the whole point of my page of math. Just read the highlighted conclusions. The cones of the mass they are pulling on begin to overlap. 6 is optimal if the angle of the cone is 45°
* And finally, What I am saying is not even all negative. The math suggests that for larger domes it gets easier. I am not just spouting words to reach predefined conclusions.
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/09/2016 07:51 pm
Quote
Edit: If you have a login for that calculator, find out what sort of single anchor you need to hold down 40,000 tons. (400,000 kN). With six of those you could probably hold down your 100 meter diameter dome in Mars gravity (with no safety margin).
They might also tell you what equipment you need to install it, which would be interesting.
We saying that load rated products exist.
If you're going to prep the floor, you will place as many of these around the perimeter as you need.
So I guess what I'm saying is that anchoring is not a giant problem.
Knowing that, you can evaluate the digging project which is not impossible either, in comparison.

I feel like you are not reading anything I said.

* Digging equals zero, if you are worried about it. (two of the sphere suggestions have no digging)
* Of course load rated products exist. Can someone look up the price for six 40,000-ton anchors and what we need to install them?
* You can't just place as many as you need. That is the whole point of my page of math. Just read the highlighted conclusions. The cones of the mass they are pulling on begin to overlap. 6 is optimal if the angle of the cone is 45°
* And finally, What I am saying is not even all negative. The math suggests that for larger domes it gets easier. I am not just spouting words to reach predefined conclusions.

Dude - I only wrote 4 lines, and didn't reach any conclusions, only laid out constraints...  Deep breaths...

The cones can overlap somewhat btw, it's ok. 

Title: Re: Elon Musk: glass geodesic domes
Post by: KelvinZero on 11/09/2016 09:15 pm
Dude - I only wrote 4 lines, and didn't reach any conclusions, only laid out constraints...  Deep breaths...

The cones can overlap somewhat btw, it's ok.
You should run for President.   :o

I think we are going around in circles here.  The math above covers the degree to which cones can overlap. One of my examples is for continuous overlap if anyone is interested.

I also did an example with 6x40kiloton anchors for a mars dome of 100m diameter. The main weakness was my arbitrary choice of 45° for the cone of mass it could pull on. If anyone can dig up info for a real 40kiloton anchor and what we need to install it  this could give a good estimate of the minimum requirements. I haven't included a safety margin but perhaps we get that by aiming lower than 1 atm.

Another thing we can probably resolve: What volume would an initial habitat be? I am guessing you want to fit it on a single flight (and possibly more than one but lets go for the maximum).

Any takers? Im guessing this is basically the question of the typical mass per volume, since this will be a constant with volume. Then we just specify a sensible number for what ITS can deliver. Do we want to deliver one with every crewed flight or assume a dedicated flight?
Title: Re: Elon Musk: glass geodesic domes
Post by: Robotbeat on 11/09/2016 09:38 pm
You can put the anchors in at somewhat of an angle, too.
Title: Re: Elon Musk: glass geodesic domes
Post by: KelvinZero on 11/09/2016 11:37 pm
You can put the anchors in at somewhat of an angle, too.
That is a good idea.

Another idea I had revolved around a single anchor in the centre that is also your shaft down for mining. I was mistaken before in thinking that you had to hold down the edges in detail. Hold down the center and the edges will hold themselves down. *

This would be fairly straightforward if the shaft is created early on, which seems reasonable since we probably will be boring for return fuel before putting effort into domes.

Any suggestion on the mass to volume ratio, and how much ITS cargo mass could reasonably be dedicated to this in a single flight? This value is the same for sphere or anchored hemisphere anyway.

* sort of like a toilet plunger. :)
Title: Re: Elon Musk: glass geodesic domes
Post by: KelvinZero on 11/10/2016 12:38 am
Hey guys, look at this. I think this might be an example of flattening the bottom of the sphere as was one suggestion. Some images imply this is not an embedded sphere.
double membrane gas storage image search (https://www.google.co.nz/search?q=double+membrane+gas+storage+tank&espv=2&biw=1069&bih=515&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiP24iMhZ3QAhWRNpQKHRyZBHUQ_AUIBigB)

It is possible that these designs are for holding liquid with some gas on top? needs more investigation. Im not sure if it is relevant.

On reading some more, I think these might be classes of https://en.wikipedia.org/wiki/Gas_holder and not actually about storing pressure.
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/10/2016 01:46 am
You can put the anchors in at somewhat of an angle, too.
That is a good idea.

Another idea I had revolved around a single anchor in the centre that is also your shaft down for mining. I was mistaken before in thinking that you had to hold down the edges in detail. Hold down the center and the edges will hold themselves down. *

This would be fairly straightforward if the shaft is created early on, which seems reasonable since we probably will be boring for return fuel before putting effort into domes.

Any suggestion on the mass to volume ratio, and how much ITS cargo mass could reasonably be dedicated to this in a single flight? This value is the same for sphere or anchored hemisphere anyway.

* sort of like a toilet plunger. :)

An anchor in the middle doesn't help you for a flat floor.  There's no fear of the thing "flying away".  The problem is the membrane mode on the floor, so you want to anchor the perimeter, or else have a very rigid pad.

A somewhat curved floor adds a LOT of strength in bending, so if you were to use a crater, and make a floor that follows it, it'll be a lot harder for the floor to fail in bending.

That's it - my four lines are up.
Title: Re: Elon Musk: glass geodesic domes
Post by: envy887 on 11/10/2016 02:12 am
An anchor in the middle helps if it's cabled up to the ceiling.
Title: Re: Elon Musk: glass geodesic domes
Post by: KelvinZero on 11/10/2016 03:42 am
An anchor in the middle helps if it's cabled up to the ceiling.
Yeah it is basically like a plunger to unblock drains. You can use that to force water down as well as to suck back.

In the short term I still wouldnt go this way, but longer term I think these shafts down can trivially be seen as sufficient to demonstrate anchoring is possible. Why not have six? This also means six entrances to the underworld from your dome. You could share these anchor shafts between neighboring domes forming a hexagonal grid. Im hazy what pressure tight walls look like where two domes meet but Im sure that is solvable, or maybe you have no wall separating them at all. This is an effectively unlimited open area dotted in pillars at regular intervals. Instead of 6 and hexagons you could also go with 4 and squares.

Eitherway, something like this, but glass.
cistern in the portuguese fortress of el jadida (http://www.alamy.com/stock-photo-cistern-in-the-portuguese-fortress-of-el-jadida-morocco-61858175.html)

. So long as your underlying structure is at least 10 meters deep and covers the same basic area as your dome you have enough to anchor yourself. Make it 30 meters deep to be safe.

This is getting more into a topic for the other thread since it is obviously far beyond a prefab delivered by the ITS.
Title: Re: Elon Musk: glass geodesic domes
Post by: guckyfan on 11/10/2016 06:25 am
An anchor in the middle helps if it's cabled up to the ceiling.

I had thought about a building in the center. The roof becomes part of the dome and has thick and heavy shielding. The dome can be anchored there and the building takes some of the tensile force. Or the roof is heavy enough to balance this force.
Title: Re: Elon Musk: glass geodesic domes
Post by: Radical_Ignorant on 11/10/2016 07:03 am
I'm little confused by some parts of this discussion. Who cares about volume? It's about flat area where people can walk, plants can grow.
What for you need volume? Nobody build houses with 50m high ceilings. And if there is no access to top surface (sunshine) it's better to go underground for lot of reasons.
So it's about aingle flat plane area with access to sunshine.
Title: Re: Elon Musk: glass geodesic domes
Post by: guckyfan on 11/10/2016 07:33 am
Pressure calls for a dome shaped volume. A large volume has the added advantage, that pressure drops quite slowly, when a pane fails. And why not build a highrise in the center?  It also gives height for a few large trees, not necessary but a nice to have.

Densely populated with a highrise and some free space around it sound good to me.
Title: Re: Elon Musk: glass geodesic domes
Post by: KelvinZero on 11/10/2016 08:06 am
I'm little confused by some parts of this discussion. Who cares about volume? It's about flat area where people can walk, plants can grow.
What for you need volume? Nobody build houses with 50m high ceilings. And if there is no access to top surface (sunshine) it's better to go underground for lot of reasons.
So it's about aingle flat plane area with access to sunshine.
That is a reasonable point, and a clear advantage of domes over spheres and possibly flattened domes over hemispherical ones, but IMO volume is more relevant for several reasons.

* Even on earth we are considering vertical farming, and for that matter vertical living in our cities. All the things driving this in earth cities will be massively more relevant on mars.
* Having half the area facing the sun is not a big problem. It would be easy to use reflectors to get some more light in. You may want to anyway since Mars gets less light than Earth. Reflectors are far far cheaper and less critical than the same area of geodesic glass dome.

As for going underground, I actually agree largely, but remember this subject is about quickly assembled domes before significant mining can have taken place. At least that is how I interpreted Elon's remarks in the OP.

*Bearing that in mind, the taller shape of a sphere can give you better immediate radiation protection compared to a dome. I picture a central living and working area to be in the form of a multistory building with a pool on the roof. Water is something you will have in abundance before even the first dome is assembled. The ITS needs tanker loads of water for ISRU to get home.

All things being equal I would probably choose domes over spheres too. You get a larger single flat area and it is at right there at ground level. I just think a self enclosed pressure vessel is far more convenient for something you assemble as a prefab early on. Later, definitely with the digging. Also once you have dug down and have actual factories and things down there you will have awesomely good anchors for your domes.
Title: Re: Elon Musk: glass geodesic domes
Post by: Radical_Ignorant on 11/10/2016 08:51 pm
High place is good. Reasonably high. People will need to have a walk. But 10-20 meters is well enough. Building 100m diameter sphere - can't imagine any good reason for that. At least early on. Later as well. Having 30m tall tree when you can walk only 50 meters in any direction would only increase feeling of claustrophobia IMHO.
Radiation. Go underground for sleep and work and lot of activities. Way cheaper to dig hole. And it's safer.
Title: Re: Elon Musk: glass geodesic domes
Post by: Radical_Ignorant on 11/10/2016 09:29 pm
And I believe main question is: what for. There is no way to envision/predict anything without taking purpose into consideration.
Domes can be imagined as early small shelters. 20m radious. Do you imagine living few years in such space? Most activities would have to be done outside. Lot of communication between those domes. Plenty of airlocking. That's just ineffective. That's temorary only solution for few years.
Then you can build few domes. Say 50m in diameter. Each of them has shaft to underground. Domes can grow underground with time and became connected by tunnels. Caves for factories, workshops, sleeping quarters can be digged. Long term domes will became something like cupola on ISS or Central Park in NY.
Or... they can be wide and used for agriculture. I have no idea if that's economicaly better than to grow plants underground. Probably yes.
Or it can be mix of two.
Anyway my opinion is that all those small places from movies and NASA renderings are extremely inefective solutions driven by lack of vision. Building surface city under one dome is one time effort - not feasible until very late into development of colony and still poor in radiation shielding. It's not about research station for few brave scientist. It's not about "been there, checked that, learned that, go home".
It has to be growable. Start small so it's possible to start and then dig more to grow place or attach modules. Attaching spheres is... sounds weird, but then plenty of things will sound/look weird from Earthling perspective.
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/10/2016 10:32 pm
I like the high domes.

I agree that volume is not the metric, but I like the open space.

A dome only has the high ceiling height in the center.  So build secondary dwellings on the perimeter, and leave the center area open and high.  That's a good set up, for a long-term environment.

When the domes get REALLY large, the dwelling ring can be 1 story on the outside, and two stories on the second-outer ring.  Still gorgeous, and leaves room for you brain to breath.

I still like a two-layer pressurization scheme.  Dwelling slightly over pressurized, but capable of coping with a dome failure.


Title: Re: Elon Musk: glass geodesic domes
Post by: GregA on 11/10/2016 10:55 pm
Yes spheres would be tall. You could have tiered layers, like a shelter in the middle for other needs, so outside would look more like an artificial hill, you'd want a good use of all space somehow.

I always liked donut/torus shapes. Also very strong. But you can't make thousands of standard triangle windows to put them together.
Title: Re: Elon Musk: glass geodesic domes
Post by: rakaydos on 11/11/2016 12:34 am
Accordig to Wolfram alpha, 1mx1mx2m of glass Quartz weighs 5 metric tonnes.

Could a dome of 2meter thick, localy produced mars-glass be floated on a partial atmospheric pressure dome?
Title: Re: Elon Musk: glass geodesic domes
Post by: KelvinZero on 11/11/2016 12:34 am
High place is good. Reasonably high. People will need to have a walk. But 10-20 meters is well enough. Building 100m diameter sphere - can't imagine any good reason for that. At least early on. Later as well. Having 30m tall tree when you can walk only 50 meters in any direction would only increase feeling of claustrophobia IMHO.
Radiation. Go underground for sleep and work and lot of activities. Way cheaper to dig hole. And it's safer.
Yes 100 meter didn't come from anywhere in particular. It is just a round number and also that anchoring gets proportionally easier and easier with larger domes.

Can anyone provide a guess at the volume per weight? And the cargo that could reasonably be transported in an early ITS flight? These numbers should be pretty solid, and exactly the same for Sphere and Dome.

I am most interested in what I consider these early prefab versions, and what sort of radius we are looking at.

For example Bigelow b330 is 330m3 for 20 tons. (I have no idea if that would over or underestimate a glass geodesic sphere that is designed for decades).. but anyway that implies 16.5 m3 per ton.

Lets say 300 tons to mars (this link says 330 is possible: https://en.wikipedia.org/wiki/Interplanetary_Transport_System)

so that is almost 5000 m3. From that I get about a 27 meter dome (13.4m high) or 21 meter sphere.

Even if the b330 approximation is off by a factor of two it gives a ballpark figure. Probably no where near a 100m sphere. That would have 125 times more volume (and therefore more mass) than a 20m sphere.
Title: Re: Elon Musk: glass geodesic domes
Post by: Robotbeat on 11/11/2016 12:46 am
Trees is definitely one reason. There's going to be a lot of green in this glass dome.

In the South Pole Station dome, they had two story buildings inside. In SpaceX Hawthorne, there's basically a 4 story building inside. Ideally you'd have even higher for access via cranes, etc.

It feels good to have a spacious interior if going outside is as hard as it is on Mars.

You could potentially even do something like this every once in a while:
https://www.youtube.com/watch?v=uCj5CUaaeZ4
Title: Re: Elon Musk: glass geodesic domes
Post by: KelvinZero on 11/11/2016 01:20 am
Initially, a vertical farm with an organic sort of design, sort of like a tree with walkways, could be a nice way to exploit that high ceiling without making it claustrophobic. The stairways could also support vines.

Something like that could green up quite quickly, eg between one ITS flight and the next.
 
Title: Re: Elon Musk: glass geodesic domes
Post by: envy887 on 11/11/2016 01:33 am
Bigelow is including a lot more than structure in that 20 tonnes, and has to worry about MMOD damage which isn't really an issue on Mars surface.

A 100m seamless polycarbonate dome designed to 200 kPa would only mass about 120 tonnes. Carbon fiber frames would increase the strength and reduce the mass, as they are much stronger than polycarbonate. You can probably double that for anchor and for structure mass... But a big dome should fit on one ITS flight.
Title: Re: Elon Musk: glass geodesic domes
Post by: TripD on 11/11/2016 02:10 am
I just don't see the excavation as a deal breaker for a sphere.  The construction could be done in any oversize depression and later back filled if desired with tailings from any processed regolith.  It would require that the sphere be built with its own lower bulwark but supporting frames would need to be built anyway for the internal levels.
Title: Re: Elon Musk: glass geodesic domes
Post by: KelvinZero on 11/11/2016 02:50 am
A 100m seamless polycarbonate dome designed to 200 kPa would only mass about 120 tonnes.
Awesome! Got a reference? I would like to play around with the numbers.

edit: https://en.wikipedia.org/wiki/Pressure_vessel#Spherical_vessel
never mind..looks like I just need to figure out what these 'density' and 'stress' values are. I think it is this:

https://en.wikipedia.org/wiki/Polycarbonate
Tensile strength (σt)   55–75 MPa
Density (ρ)   1.20–1.22 g/cm3

Here is a bunch more: https://en.wikipedia.org/wiki/Ultimate_tensile_strength#Typical_tensile_strengths

edit2: Rats. Im getting a mass about 10 times greater. Can anyone spot a flaw?
For sphere
M = (3/2)PV(𝛒/𝛔) ..where
P = 1 atm = 101325 (pascal)
𝛒 = density of material = 1.22g/cm3 = 1220kg/m3
𝛔 = 75MPa = 75,000,000 (pascal)
..leading to M = 2.5V, or 2.5kg per m3

A sphere of 50m radius is about 523,000 m2 leading to about 1300 tons.

Title: Re: Elon Musk: glass geodesic domes
Post by: CapitalistOppressor on 11/11/2016 02:52 am
Either a dome or a sphere seems to be a workable solution. 

I really like the elegance and simplicity of a partially buried sphere, especially for smaller, initial dwellings, while a dome seems like a better solution for a very large space.

As a potential homesteader, I'm not too keen on the idea of having to hire a specialized crew to come out and properly anchor my dome (the geological survey alone will kill my budget). But digging a large hole and snapping together a prefab pressure sphere is right up my alley.

In contrast, as a city planner I doubt I'd be too interested in excavating a giant hole when I have specialized crews on hand who could easily, and economically, anchor the huge dome I've been planning for the entertainment district.
Title: Re: Elon Musk: glass geodesic domes
Post by: envy887 on 11/11/2016 12:37 pm
...
edit2: Rats. Im getting a mass about 10 times greater. Can anyone spot a flaw?
For sphere
M = (3/2)PV(𝛒/𝛔) ..where
P = 1 atm = 101325 (pascal)
𝛒 = density of material = 1.22g/cm3 = 1220kg/m3
𝛔 = 75MPa = 75,000,000 (pascal)
..leading to M = 2.5V, or 2.5kg per m3

A sphere of 50m radius is about 523,000 m2 leading to about 1300 tons.

This is right. I though I was calculating for a 50m radius, not diameter - and only for a hemisphere, not a whole sphere, but anchors and floor structure add mass too.

Mass increases as radius3, so a 100m dome will mass 8x more than a 50m dome.
Title: Re: Elon Musk: glass geodesic domes
Post by: rakaydos on 11/11/2016 03:12 pm
If we're talking about anchoring the dome down... Is there any reason the "dome" shouldnt be a flat glass celing over a crater? Or even inverted downward from the rim of the crater?

My understandig was that the sharp corner along the rim is a weak point there. But it's also the point easiest to reinforce. The massive internal overpressure will do more than "float" any conventional dome, it will hold any convex structure in extreme tension.

A Concave, downward bulging "dome" meanwhile lets the internal overpressure hold it in COMPRESSION, which is significantly easier on a number of cheap building materials.
Title: Re: Elon Musk: glass geodesic domes
Post by: Robotbeat on 11/11/2016 03:31 pm
Tension is much better, actually. Making basalt fibers is cheap and would be incre strong.

One reason tension is much, much better is you don't need to add a bunch of mass to prevent buckling like you do with compression.

Compression << tension.
Title: Re: Elon Musk: glass geodesic domes
Post by: oldAtlas_Eguy on 11/12/2016 01:31 am
The two different classes of building materials have different associated loading. A rock/concrete like material works best in compression while metals or fibrous material works better in tension.

Glass though could work well in tension or compression based on thickness. Since most likely the panes will be significantly thick, having the panes be slightly bulge inward causing the pane to be in compression against its mounts makes seals and other features of the structure to work better. The pane in compression and the frame in tension. Plus glass in compression is less likely to shatter and blowout when cracked.
Title: Re: Elon Musk: glass geodesic domes
Post by: Robotbeat on 11/12/2016 01:44 am
No, for large structures like we're talking about, buckling becomes dominant for compressive loads. That means a lot of mass.

Tension is better. Much, much better.
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/12/2016 02:10 am
No, for large structures like we're talking about, buckling becomes dominant for compressive loads. That means a lot of mass.

Tension is better. Much, much better.

oAEG is right in principle, and glass is a wonderful material, but yeah - for a pressure dome like this, a tensile structure is more resilient.

Suppose you want agriculture inside the dome.  What's the game plan?

Do you anchor the perimeter, then seal the dome to the local ground?  I see a number of solutions here, it actually gets pretty interesting.

Title: Re: Elon Musk: glass geodesic domes
Post by: guckyfan on 11/12/2016 02:17 am
Suppose you want agriculture inside the dome.  What's the game plan?

My understanding was the geodesic domes are to be attractive to people. Including some plants, maybe ornamental, maybe some useful plants.

Greenhouses would be more functional. Shape like the Nissen huts seem right to me. They can be stretched long and have less hard structural requirements.
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/12/2016 01:24 pm
Suppose you want agriculture inside the dome.  What's the game plan?

My understanding was the geodesic domes are to be attractive to people. Including some plants, maybe ornamental, maybe some useful plants.

Greenhouses would be more functional. Shape like the Nissen huts seem right to me. They can be stretched long and have less hard structural requirements.

So while not knowing what they have in mind, I'm thinking again about a largish dome, with dwelling built as secondary structures near the perimeter, and open space in the middle. (Plus maybe a shaft entrance.)

Here's an example of potential sizing

The dwelling tube is 5 m diameter, giving a 3 m tall by 5 m wide living space with 1 m tall service areas top and bottom

The dome is 25 m diameter, so 12.5 m high in this configuration.

The tube has a pitch diameter of 20 m, so is approx 60 m long - enough  for ten 6 m long "rooms".

A secondary "corridor/utility" tube can be run inside, with pitch diameter of ~10 m, so that normally you don't go through the rooms.

This will make for a reasonable dwelling for 10-20 people? 

For larger domes, I'd go with less than 180 degrees, (so that the anchors are driven in at an angle) because the height begins to be excessive.

A cute question is "how do you get out".

My guess is that one of the rooms is an airlock (with suiting and clean-up facilities), and opens to the outside through the dome wall.  Or the air lock is on the outside of the dome wall.
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/12/2016 01:54 pm
For more breathing space, this is a 50 m dome, but only about 120 degrees, so is 16 m tall.

The tubes are still 5 m in diameter, except are now twice as long.

This size makes it possible to have some agriculture in the center "patio", which is 25 m in diameter.

The anchors here will be driven at about 30 degree to the vertical.
Title: Re: Elon Musk: glass geodesic domes
Post by: TripD on 11/12/2016 05:22 pm
So, the notion of using anchors is to preclude any excavation?  I briefly thought of an alternative to horizontally aligned tubes for habitats within the dome (smaller domes along the perimeter with 2nd level and connecting corridors all underground), then realized that is defeating the purpose of the anchoring to begin with?
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/12/2016 08:49 pm
IMO excavation is great and lots of it will be done.

Dome are for surface living, agriculture, etc.

Anchors are one of two ways to prevent the dome from rocketing into the sky...

It uses Mars as the floor of the dome, and you need to make a connection somehow - so deep earth tensile anchors (see the link to commercial products upthread), and some poured peripheral belt for sealing.  (You can even put a fully-hermetic flexible ground barrier sheet, but it's not load bearing.  Mars is your structural  floor)

The alternative is to make a structural floor.  Either a strong flat floor (e.g. thick poured pad), a full spherical floor, or a curved floor.

EDIT: The larger dome, with no structural floor, can look like this:
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/12/2016 10:03 pm
There's a bit of overlap between this thread and the habitats thread.

What I doodles is my impression of what's reasonable for "stage 1" work.

Meaning - crews arrive in ITS ships, and need to set up a first base.

They first use inflatable 5 m tubes and set up the torus habitats.  (With outward facing windows, for sanity. I'd hate to  live in an enclosed tube - this is not the ISS)

Then they erect a dome around the torus, from flat panes that were brought from earth.

This is very far from the much larger domes envisioned in the other thread, which would be "stage 2" structures, hopefully with a large fraction of in-situ material content.  (Whether glass or plastics)
Title: Re: Elon Musk: glass geodesic domes
Post by: KelvinZero on 11/12/2016 10:56 pm
I want to keep this separate from the general habitats thread by focusing on what can be transported in an ITS mission and matches Elon's remark. I believe this means a prefab that can be operational before significant mining. (edit: but we can argue sufficient mining to fill an ITS with return propellent has already been mastered) Significant mining can be part of the design, but your habitat apparently has to keep your miners alive in the interim. Ideally justify things with weights and argue how it can fit in with early missions. Then we could list all the other equipment and the work involved, speculate on issues working in spacesuits or dedicated teleoperated assembly.

There is a huge amount to cover on just this one narrow initial prefab topic. The General thread is more about the endpoint I think, plus some flights of fancy of course. If a topic here starts sounding like the general thread, inspect it for issues like weight and ITS cargo hold requirements, early small mission crews vs later 100 person crews and so on.

As a reminder, here is the initial quote this thread is based on.

Question from /u/Ulysius
As a follow-up, considering the synodal reuse of the ITS spaceships, what form of permanent habitation do you foresee? Shipped modules or an (eventual) shift to in-situ resource utilization such as Martian rigolith/plastic-reinforced concrete structures?

Answer from /u/ElonMuskOfficial
Initially, glass panes with carbon fiber frames to build geodesic domes on the surface, plus a lot of miner/tunneling droids. With the latter, you can build out a huge amount of pressurized space for industrial operations and leave the glass domes for green living space.
Title: Re: Elon Musk: glass geodesic domes
Post by: TripD on 11/12/2016 11:51 pm
Quote
snip....  (With outward facing windows, for sanity. I'd hate to  live in an enclosed tube - this is not the ISS)

I'd add, make the upper half of the torus glass to avoid becoming a shade wall for the interior growing zone.
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 11/13/2016 04:45 am
The larger dome, with no structural floor, can look like this:
(https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=41526.0;attach=1387679;image) (https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=41526.0;attach=1387679;image)

The dome is being pushed upwards by nearly 20,000 tonnes of force, or about 125 tonnes per linear metre of circumference.

An additional 50,000 tonnes for force is pushing outwards, which, given the way domes distribute force, will be trying to bend the dome out horizontally at the base circumference, or about 300 tonnes per linear metre.

Surely it would be easier to just use a pressure vessel?
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/13/2016 05:04 am
The anchors perfectly mimic the struts that would have been there had the dome been a perfect sphere. That's why they are tangent.

If you can't build it with struts, you can't build it at all.

----------

That said, cables or struts, that's a LOT of force...  Steel cables that can take it are 2" thick (If placed every meter)

Carbon fiber would be even thicker (though lighter)

So yeah - we know pressure vessels get harder with size, whether you use anchors or struts.

Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 11/13/2016 05:23 am
The anchors

400+ tonnes of force per linear metre of circumference for a mere 50mx16m dome. Rock anchors require a certain spacing based on conical force distribution. The cones can't overlap. You can't just jam them in cheek by jowl.

It might be a solvable problem, but why have the problem in the first place? People seem to be making a lot of effort just to have a dome for the sake of having a "dome".

(The weight of the dome itself is trivial compared to the forces involved.)
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/13/2016 05:52 am
I get 100, not 400 tons/meter.

So the tradeoff is this:

100 ton anchors (with 2" steel cable) every meter over a 120 m circumference, or

A 1200 m2 hole, about 16 m deep in the middle (for the bottom 1/3 of the sphere), and ~3x the structural frame, whose struts (if using m-scale tiles) are also 2" steel cable equivalent.  And also 3x the skin. (Panes)

Quite a choice...

The anchors

400+ tonnes of force per linear metre of circumference for a mere 50mx16m dome. Rock anchors require a certain spacing based on conical force distribution. The cones can't overlap. You can't just jam them in cheek by jowl.

It might be a solvable problem, but why have the problem in the first place? People seem to be making a lot of effort just to have a dome for the sake of having a "dome".

(The weight of the dome itself is trivial compared to the forces involved.)
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/13/2016 06:01 am
Another possibility is to run a trencher on the perimeter.

(http://www.mastenbroek.com/products/deep-trenching/)

This can be automated, and if you can concrete the resultant peripheral belt, you get a continuous anchor that will easily do 100 ton/meter (much more), give you a nice continuous line to seal to, etc.
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 11/13/2016 06:13 am
I get 100, not 400 tons/meter.

70,000 odd tonnes of force, 20,000 tonnes vertical, the other 50,000 tonnes are trying to turn your dome into a sheet. (Given the way domes transmit forces, the 50,000 tonnes will be a horizontal outward force around the circumference. 300-odd tonnes per linear metre.) The latter is an easier problem than the vertical anchoring, but it can't be ignored.

if you can concrete the resultant peripheral belt, you get a continuous anchor that will easily do 100 ton/meter (much more)

100 tonnes-force per metre on Mars is 300 tonnes mass. I'm just not seeing how you can create a non-overlapping conic for each anchor that can bind that much material per linear metre. Remember, all the anchor is doing is transferring the tension to the surrounding rock (or concrete). You still need enough mass within the force-cone to hold the dome down.
Title: Re: Elon Musk: glass geodesic domes
Post by: Radical_Ignorant on 11/13/2016 08:28 am
I'm not catching the idea of struts/anchoring problem.
Why not put some dead weight at the bottom. I heard Italians did something similar with their famous tower in Pisa. Anyway you need to apply force working downward. You can do that by anchoring but as well by adding weight. Why not?
Title: Re: Elon Musk: glass geodesic domes
Post by: KelvinZero on 11/13/2016 09:02 am
I'm not catching the idea of struts/anchoring problem.
Why not put some dead weight at the bottom. I heard Italians did something similar with their famous tower in Pisa. Anyway you need to apply force working downward. You can do that by anchoring but as well by adding weight. Why not?
It is worth reading the thread and responding to the specific objections with numbers.

Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/13/2016 12:42 pm
Another possibility is to run a trencher on the perimeter.

(http://www.mastenbroek.com/products/deep-trenching/)

This can be automated, and if you can concrete the resultant peripheral belt, you get a continuous anchor that will easily do 100 ton/meter (much more), give you a nice continuous line to seal to, etc.
You can't add the forces in different directions.  If you draw a great circle on the sphere, the vertical tensile force, is simple the pressure (say 100 kPa) times the area, divided by the circumference.

Since it is part of a sphere, by symmetry, the same is true for any partial dome, as long as you anchor it in a tangential manner.

Those trenchers in the picture could go 8 meters deep.

If the friction angle is 30 degrees, each linear meter has a volume of dirt equal to 1*h*h/2, so let's call it 0.5h^2 ton force per m.

If you want ~100, you need h=15m..


Given these numbers, the trench doesn't make sense, so for an earth mount, back to anchors, since they clearly create a similar shape (the overlapping cones creating a triangular prism) and you can reach greater depth with a lot less equipment.

I'd still use a shallow trench as part of the prep work, but only as a convenient way to anchor too.

-----

However, these numbers also give me pause.

This is an enormous amount of material.

Even for the shallow dome, which is only 1/3 (or less) that of the full dome.

I'd estimate, very roughly, 5000 m of strut, comparable to 2" steel cable.

Lots of connectors, since there are few continuous runs in a geodesic dome.

Not so easy to make connectors for 100 tons when your length scale is only 1 m... 

And if you increase the length scale, (larger panes) you need even thicker struts...

This is getting interesting. (This applies equally to the full dome.)

I get 100, not 400 tons/meter.

70,000 odd tonnes of force, 20,000 tonnes vertical, the other 50,000 tonnes are trying to turn your dome into a sheet. (Given the way domes transmit forces, the 50,000 tonnes will be a horizontal outward force around the circumference. 300-odd tonnes per linear metre.) The latter is an easier problem than the vertical anchoring, but it can't be ignored.

if you can concrete the resultant peripheral belt, you get a continuous anchor that will easily do 100 ton/meter (much more)

100 tonnes-force per metre on Mars is 300 tonnes mass. I'm just not seeing how you can create a non-overlapping conic for each anchor that can bind that much material per linear metre. Remember, all the anchor is doing is transferring the tension to the surrounding rock (or concrete). You still need enough mass within the force-cone to hold the dome down.
Title: Re: Elon Musk: glass geodesic domes
Post by: MikeAtkinson on 11/13/2016 01:37 pm
Here is a very basic spherical dome design. 16 apartments (8 at about 28m3 floor area and 8 with less). I've not shown access to the different levels but that would be through stairs.

Communal volume would include cooking/dining area, meeting rooms, etc. perhaps using mezzanine level(s).

Grow area on the top would have crops, it is not intended to provide a large number of calories, rather as a nice garden environment for the domes occupants.

Tunnel underneath would probably be deeper. It would be the main method of reaching other facilities.

The airlock is mainly for occasional use and emergencies.

The utilities area would also double as an emergency shelter (solar storms, leaks, fire, etc.) and can be pressurised separately from the rest of the dome.

Utilities (water, comms, electricity, gasses, sewage?) are carried in pipes in the tunnel. This allows shirt-sleeve access to them for maintenance.

Larger spherical domes would allow more levels and more floor area, but I think starting with something this size is a good idea, eventually something this size would make an excellent home for a single family.
Title: Re: Elon Musk: glass geodesic domes
Post by: TripD on 11/13/2016 05:39 pm
Spheres are so damned inconvenient!
Title: Re: Elon Musk: glass geodesic domes
Post by: Robotbeat on 11/13/2016 05:59 pm
Bah. He said geodesic glass domes, not spherical apartments. We're getting further and further away from Musk's statements.

Don't subdivide the thing up like a house. Make it look like domes all over the world like the gardens in the UK and the South Pole dome. A vast internal space where there's free air. Buildings placed inside /maybe/, probably lots of growing things. If it's just an apartment, might as well make a lot of long tubes.
Title: Re: Elon Musk: glass geodesic domes
Post by: KelvinZero on 11/13/2016 06:37 pm
Bah. He said geodesic glass domes, not spherical apartments. We're getting further and further away from Musk's statements.

Don't subdivide the thing up like a house. Make it look like domes all over the world like the gardens in the UK and the South Pole dome. A vast internal space where there's free air. Buildings placed inside /maybe/, probably lots of growing things. If it's just an apartment, might as well make a lot of long tubes.
I don't understand why you keep giving opinions and avoiding numbers. The sphere is not drift: the anchoring problem is right there in our face. It has to be the #1 topic until someone produces some numbers that make anchoring an attractive, not eyebrow raising, option.

Besides, some geodesic "domes" on earth are actually spheres. Certainly a lot of them are much more than a hemisphere.

Look at this link. Observe that the first two examples are really pretty close to spheres.
https://en.wikipedia.org/wiki/Geodesic_dome

The real question is whether it is a pressure vessel in its own right or relys on anchoring. There are many off-sphere, a bit more domelike variations to choose from if you think "sphere" violates the spirit of "dome".
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/13/2016 06:39 pm
Bah. He said geodesic glass domes, not spherical apartments. We're getting further and further away from Musk's statements.

Don't subdivide the thing up like a house. Make it look like domes all over the world like the gardens in the UK and the South Pole dome. A vast internal space where there's free air. Buildings placed inside /maybe/, probably lots of growing things. If it's just an apartment, might as well make a lot of long tubes.
And smaller.  Those numbers on the 50m dome are really large.

Down to 25 and smaller, then maybe the trenching works.  (Or a combination of a peripheral trench with anchors at its bottom)

But I have to admit, I'm not ruling out full spheres sitting 1/3 below grade.  There's up sides to that too.

I'm mostly trying to figure out how to make the struts in such a way that it actually works, can hold the huge tension, seal with the panes, etc.

And how to deal with a failed strut.
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 11/13/2016 06:40 pm
Why not put some dead weight at the bottom. [...] You can do that by anchoring but as well by adding weight. Why not?

That would work. You can also pile weight on top of the dome, which is the usual solution if we don't care about sunlight, since it's also thermal mass, radiation protection, etc, and reduces the risk of blow-outs if the tensile structure fails. But Musk wants glass...

The problem with weight at the bottom is the amount of mass required. For the 50m dome that MeekGeek proffered, the vertical component alone is 20,000 tonnes. The dome has around 157m of circumference, so that's just over 125 tonnes per linear metre. Say 130 tonnes to give us some reserve. 130 tonnes every single metre around the dome.

That's tonnes-force, of course. Ie, 1.3 MN. On Mars, gravity is 0.38g, so you need 2.6 times the mass to achieve the same force. Over 50,000 tonnes in total, or around 340 tonnes of mass for every single metre around the perimeter.

The density of lead is around 11 tonnes/m³, so if you used lead weights, you're looking at a wall ~30m high by 1m deep, or 15m high by 2m deep. That's still a pretty substantial wall, the dome is only 16m high. You can go wider, but you need to transmit the forces out to the outer part of the wall, and lead isn't good at holding structural loads. We're better off with steel. Steel drops us to 8 tonnes/m³, so if the steel is welded together, we're looking at something like a wall 6m high by 7m deep. Realistically, you'd use the steel as the dome, rather than waste it as dead-weight.

But until the colony has a fully fledged steelworks, with enough capacity to waste 50,000 tonnes of steel on a single 50m dome, you'd have to bring that 50,000 tonnes with you, which is... impractical. So realistically we're limited to "dumb" materials that we can source locally. Either rock or sintered/cemented regolith.

Solid rock or concrete varies between 2 & 3 tonnes/m³. Using the standard 2.4t/m³ for concrete, we need 140x1m. Or 12m high, 12m wide.

Except that the force would just tear out the bolts holding your dome to the wall. So you're need some kind of deep anchor system to bind the wall and the dome together.

In which case, you might as well use the rock already beneath dome and anchor directly to that.

QED.

[edit: "on top of the top", well, yeah.]
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/13/2016 07:08 pm
The pile-dirt option is just like anchors, but with a lot more complexity...  You need to excavate and then back-fill as much dirt as there was above the anchor...

But if you can trench to only 3 m, then reach in and drive an anchor 10 m further in, you're got a nice factor of safety, and also a nice thick belt that can help with load distribution.

------

I still wonder though...  With 1000s of struts... There's a chance of one failing...  What happens to the dome if you eliminate one strut?
Title: Re: Elon Musk: glass geodesic domes
Post by: TripD on 11/13/2016 07:23 pm
Just as a visual cue and not to argue sphere verses dome.  The outer shell is radius 25m and the individual habitats are of radius 5m.  Not a lot of open space in between.
Title: Re: Elon Musk: glass geodesic domes
Post by: MP99 on 11/13/2016 07:33 pm


Why not put some dead weight at the bottom. [...] You can do that by anchoring but as well by adding weight. Why not?

That would work. You can also pile weight on top of the dome, which is the usual solution if we don't care about sunlight, since it's also thermal mass, radiation protection, etc, and reduces the risk of blow-outs if the tensile structure fails.

But, if you do get a blowout, then the dome collapses onto the inhabitants, because you're relying on the air pressure to support it.

Cheers, Martin
Title: Re: Elon Musk: glass geodesic domes
Post by: MP99 on 11/13/2016 07:38 pm
The worry that I have about a dome is that the tremendous pressure will blow through the regolith under the dome. A single weakness anywhere in the perimeter will cause a failure.

Think of the parable of the boy with his finger in a leak in a dyke.

ISTM that "dome" is probably shorthand for a sphere nestling in a suitable crater.

Cheers, Martin
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/13/2016 08:32 pm
The force is tremendous, the pressure is only 1 atm or less.

The dome does not rely on pressure to stay erect.  It can resist the pressure in tension, and can support its much much lower weight in compression.

I feel confident that a medium depth trench, with anchors from its bottom, gives a technical solution to both anchoring and sealing.
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 11/13/2016 08:45 pm
Here is a very basic spherical dome design.

Mike, I agree with Robotbeat, spherical domes don't belong here. I suggest re-posting it in the other habitat thread (https://forum.nasaspaceflight.com/index.php?topic=41427.0).


[...]

While you could interpret Musk's comment to include a geodesic sphere, IMO you should use the narrower interpretation until he himself drops a hint otherwise.

I strongly suspect, like so many Mars advocates, he really is picturing a lightly sealed hemisphere sitting on Mars rock, thinking mainly of compressive loads, and grossly underestimates the anchoring force requiring.

Hence I think it's worth focusing on the issue of "build a glass dome".


And smaller.  Those numbers on the 50m dome are really large.
Down to 25 and smaller, then maybe the trenching works. (Or a combination of a peripheral trench with anchors at its bottom)

However, as you go smaller, think how many people each dome could realistically house. And how much work is required to build the dome and its foundations/anchors.

Is the labour/occupant ratio worthwhile?

(Also, how long will it take to build? Hence what is the maximum doubling-rate of the colony?)

With 1000s of struts... There's a chance of one failing...  What happens to the dome if you eliminate one strut?

The neighbouring struts must be able to handle their own loads plus the loads from the failed strut. Otherwise the initial failure will also overload the neighbouring struts, which themselves fail, pushing even more load onto the next set of struts, causing a rippling failure across the entire structure.

How much you over-engineer it depends on how long you want it to last without significant maintenance, given that any material will weaken over time.


You can also pile weight on top of the dome, which [...] reduces the risk of blow-outs if the tensile structure fails.
But, if you do get a blowout, then the dome collapses onto the inhabitants, because you're relying on the air pressure to support it.

If you get a blow-out, everyone in the dome is dead anyway.

However, if you get a failure of a single panel in a dome with a regolith covering, the air has to leak through the regolith which will slow the rate of the leak, hence it won't really be a "blow-out". That gives you more time to evacuate, and maybe even enough time to repair.

[And if at least the first layer of the covering material is sintered/cemented into blocks, you can arrange it to settle into a compressive dome as the pressure inside drops. Compressive domes are a vastly easier problem to solve than pressurised ones.]

Of course a covered dome is also off-topic.
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/13/2016 09:23 pm
This is the 50m dome with appropriately deep anchors.

At this depth, I don't know whether the percussion-driven anchors still work, but a portable tiltable driller can go 20 m without breaking a sweat almost anywhere.  Once drilled, you need to create an anchor cavity at the bottom, and you have your anchor.  Then repeat 120 times around the perimeter.

But yeah, automated.



 
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 11/13/2016 09:44 pm
[I'm posting out of sync with your posts.]

You can't add the forces in different directions.  If you draw a great circle on the sphere, the vertical tensile force, is simple the pressure (say 100 kPa) times the area, divided by the circumference.

I'm not adding, I'm subtracting. The total pressure on a 50m dome is nearly 73,000 tonnes. You're only dealing with the vertical component.

If you draw a great circle on the sphere ...

...then when mapped back on the dome, every single line passes through the "cut" edge.

Therefore every one of those 70+ thousand tonnes of force passes into the rim.

Around 20,000 tonnes of force is vertical, which you're anchoring against with tangential anchors.

But there's another 50,000 tonnes that will be trying to open the dome out like a sheet. That creates a perpendicular, outward, tensile force in a ring around the base.

The easiest way to deal with that would be to increase the tensile strength of a ring around the base, capable of withstanding the 50,000 tonnes. Ie, increase the thickness of the struts as they approach the base. Interestingly, it turns the dome into something more like a traditional compression dome, thickest at the base and thinnest at the apex.

Alternatively you could also use rock anchors to balance the horizontal force, this time perpendicular to the rim instead of tangential. Adding the two components back together, you'd end up with a single set of anchors with a drilling angle of just under 40° inwards of vertical.

And, of course, you could go back to the trench idea, turn the outward force into a compressive load on the surrounding rock. It just means you are burying part of your dome, but it might help with the seal. Essentially allow the wall of the dome to flex out and press against the rock, creating a seal.

All in all, less difficult to deal with than the vertical force, IMO, but it still needs to be remembered.

And it bring us back to the question of how much material are you really saving, compared to a slightly flattened spherical pressure vessel or our old friend the cylindrical tube?

Even for the shallow dome, which is only 1/3 (or less) that of the full dome.

1/9th for 120°.

And if you increase the length scale, (larger panes) you need even thicker struts...

And thicker glass.
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/13/2016 09:49 pm
This is the same 50m dome, partially dug.

Lots more volume to do stuff in, but you'll need to build up a lot of multi-level structures.

About 4x the structural skin, and no anchors.

My instinct says it likes the ground-anchored domes, but I can't make an absolute call.

One up-side of digging is that for a similar total volume, you can go with a smaller dome, and then the structural requirements are easier for the dome structure.

Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/13/2016 09:52 pm
[I'm posting out of sync with your posts.]

You can't add the forces in different directions.  If you draw a great circle on the sphere, the vertical tensile force, is simple the pressure (say 100 kPa) times the area, divided by the circumference.

I'm not adding, I'm subtracting. The total pressure on a 50m dome is nearly 73,000 tonnes. You're only dealing with the vertical component.

If you draw a great circle on the sphere ...

...then when mapped back on the dome, every single line passes through the "cut" edge.

Therefore every one of those 70+ thousand tonnes of force passes into the rim.

Around 20,000 tonnes of force is vertical, which you're anchoring against with tangential anchors.

But there's another 50,000 tonnes that will be trying to open the dome out like a sheet. That creates a perpendicular, outward, tensile force in a ring around the base.

The easiest way to deal with that would be to increase the tensile strength of a ring around the base, capable of withstanding the 50,000 tonnes. Ie, increase the thickness of the struts as they approach the base. Interestingly, it turns the dome into something more like a traditional compression dome, thickest at the base and thinnest at the apex.

Alternatively you could also use rock anchors to balance the horizontal force, this time perpendicular to the rim instead of tangential. Adding the two components back together, you'd end up with a single set of anchors with a drilling angle of just under 40° inwards of vertical.

And, of course, you could go back to the trench idea, turn the outward force into a compressive load on the surrounding rock. It just means you are burying part of your dome, but it might help with the seal. Essentially allow the wall of the dome to flex out and press against the rock, creating a seal.

All in all, less difficult to deal with than the vertical force, IMO, but it still needs to be remembered.

And it bring us back to the question of how much material are you really saving, compared to a slightly flattened spherical pressure vessel or our old friend the cylindrical tube?

Even for the shallow dome, which is only 1/3 (or less) that of the full dome.

1/9th for 120°.

And if you increase the length scale, (larger panes) you need even thicker struts...

And thicker glass.

At the interface line, there are circumferential forces, which are still taken up by the structural hoop of the dome, and force perpendicular to them (vertical if it's a 180-degree dome) that are simply pressure*area/circumference.

The anchors only take that latter force.

If the dome were to continue to become a full sphere, the struts would be taking the same force.

Given how large these forces are, for a large dome, it basically doesn't care about its own weight.

However an interesting difference is that if depressurized, a dome will stand just fine.  A full sphere that's partially supported at the bottom will likely buckle.
Title: Re: Elon Musk: glass geodesic domes
Post by: MikeAtkinson on 11/13/2016 10:19 pm
Here is a very basic spherical dome design.

Mike, I agree with Robotbeat, spherical domes don't belong here. I suggest re-posting it in the other habitat thread (https://forum.nasaspaceflight.com/index.php?topic=41427.0).


Respectfully disagree.

Spherical domes have several advantages for initial habitats. The major one is that there is little in the way of site preparation and no anchors. The entire dome can be constructed on Earth and shipped as a flatpack, and then assembled on Mars. Importantly it can be fully assembled and tested on Earth. It doesn't depend on subsurface rock types or if they are fractured by cratering, or if there is ground water/ice. There can be one design that can be used with confidence in different locations on Mars.
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 11/13/2016 10:24 pm
At the interface line, there are circumferential forces, which are still taken up by the structural hoop of the dome, and force perpendicular to them (vertical if it's a 180-degree dome) that are simply pressure*area/circumference.

When you have a line of force around an intact great-circle, the entire circle is under nice linear tension. When you cut the circle, the force is a bending moment at the edges.

In the case of a dome, you are cutting every great-circle, so the entire force load passes through the rim, not just the vertical component.

Imagine if you hung a bulk-mass from the apex of the dome sufficient to overcome the vertical force. The air-pressure will still be pushing horizontally out on the side walls, and all of that load still ends up at the perimeter. If the perimeter was still attached to the rest of a sphere, it would translate into a tensile, linear load. But separated, it is experienced as a bending force.

Spherical domes have several advantages for initial habitats.

Sure, but this isn't the "initial habitat" thread, it's in direct response to Musk's "glass geodesic domes" comment.
Title: Re: Elon Musk: glass geodesic domes
Post by: KelvinZero on 11/13/2016 10:56 pm

[...]
While you could interpret Musk's comment to include a geodesic sphere, IMO you should use the narrower interpretation until he himself drops a hint otherwise.

I strongly suspect, like so many Mars advocates, he really is picturing a lightly sealed hemisphere sitting on Mars rock, thinking mainly of compressive loads, and grossly underestimates the anchoring force requiring.

Hence I think it's worth focusing on the issue of "build a glass dome".
The term is commonly attached to shapes that are more than a hemisphere, for example the first two examples here. https://en.wikipedia.org/wiki/Geodesic_dome. Im perfectly ok with flattening the bottom a bit. various ways to do that. Or I could just relabel the bottom portion of the sphere as the anchor. Musk certainly did not specify the method of anchoring. It could be in a hole from earlier, necessary, excavation such as for ISRU fuel.

There are many detail beyond that which are the same in either case. The volume per transported wall are the same. The assembly of the wall is pretty much the same. We can discuss all that freely, and ground anchoring proponents can resolve the additional requirements for anchoring really whenever they feel like getting on to that.
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/13/2016 11:23 pm
I don't think so.

The key is that the foundation has to mimic the "missing 2/3" of the full sphere.

In a full sphere, i doesn't matter where you cut, it's always in pure tension - no bending moment.

So you cut your dome, look at what the "other side" of the cut would have been doing, and set your perimeter the same way - which is why I have my anchors tangent to the surface.


At the interface line, there are circumferential forces, which are still taken up by the structural hoop of the dome, and force perpendicular to them (vertical if it's a 180-degree dome) that are simply pressure*area/circumference.

When you have a line of force around an intact great-circle, the entire circle is under nice linear tension. When you cut the circle, the force is a bending moment at the edges.

In the case of a dome, you are cutting every great-circle, so the entire force load passes through the rim, not just the vertical component.

Imagine if you hung a bulk-mass from the apex of the dome sufficient to overcome the vertical force. The air-pressure will still be pushing horizontally out on the side walls, and all of that load still ends up at the perimeter. If the perimeter was still attached to the rest of a sphere, it would translate into a tensile, linear load. But separated, it is experienced as a bending force.

Spherical domes have several advantages for initial habitats.

Sure, but this isn't the "initial habitat" thread, it's in direct response to Musk's "glass geodesic domes" comment.
Title: Re: Elon Musk: glass geodesic domes
Post by: LMT on 11/13/2016 11:31 pm
Tie Supports

Imagine if you hung a bulk-mass from the apex of the dome sufficient to overcome the vertical force. The air-pressure will still be pushing horizontally out on the side walls, and all of that load still ends up at the perimeter.

Generally speaking, when the ground can't handle the anticipated horizontal load, architects sometimes add tie supports.  They connect across the base, to carry horizontal load internally within the structure.  It's just a mass-efficient way to handle load. 

You might calculate for example with Spectra rope (https://www.honeywell-spectra.com/?document=fiber-capability-guide&download=1), which could be manufactured from polyethylene in situ.
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/13/2016 11:38 pm
So about this "how to actually build it" thing....

Let's consider triangles that are ~1 m on the side, with edges that have to carry, in a 50 m dome, ~100 tons or 1E6 N. (give or take).

How do we build this, mechanically?

Approach 1:  Build an edge-only dome using struts (and some pinned connectors), then attach non structural (but pressure bearing) panes.

This was my first guess, but the main problem is robustness. If you lose even one strut, the whole thing fails.

Second, by the time you are done with the 6-way pinned connections, it's very difficult to seal to.

Third, the panes weigh a lot, and all that mass is wasted.


Approach 2: Use structural panes.

Build the domes out of panes, not struts. The panes attach along their common edges, not just at the vertices.

Take simple acrylic, with a yield strength of 60 MPa.   If you have an entire 1 m edge to work with, you need an edge width of 16 cm to carry the 100 tons.

But Carbon Composite is 10x stronger, in an isotropic fabric...  So you can have 1.6 cm carry the load.  or, maybe 10 cm if you use a network that is 85% open and much lighter, and sandwich it between two thin acrylic sheets..

Doesn't matter exactly. There are a several ways to make a structural pane. The point is - you have a load bearing pane, with edge connectors, and no stresses near the vertices (important!)

One advantage is that each connection is only between two entities (along the common edges) and not 6 - much easier.

The other advantage is that you have built in redundancy.  You can lose a pane, and all you really have is a hole.  The entire thing doesn't collapse.  (I think!)

Title: Re: Elon Musk: glass geodesic domes
Post by: Robotbeat on 11/14/2016 12:31 am
The heavy part of the dome will be the glass panels. The structure won't be too bad, though sealing the triangles may be annoying. But anchors just need to be deep enough that their friction cones have enough surface area on the non-overlapping side. It's fine that they overlap, it's just that the overlapping area doesn't count so much. As long as the total weight of the volume of the soil in all the cones is equal to the pressure times bottom area of the dome, you're fine.

To ensure this, you just need long enough cables. Cables made out of the right material can have an extremely good strength to density ratio, like 4GPa/(g/cc). Much stronger than the Windows or the quasi-isotropic Carbon fiber composite of the frame, which would be around 0.4GPa/(g/cc) (much worse for the glass due to knock-downs for stress concentrations). Then the anchors themselves, but if the cables are long, the anchors will be a minority of the mass.

So the anchors and cables would be much less mass than a whole sphere. Also, realize that you still have to solve the problem of how to properly rest on the soil and walk around on the sphere.


And there's another thing: you could have a vertical cable in the center of the dome anchored deep underground. This could carry some of the load as well. The dome wouldn't have to be so high for a given area.
Title: Re: Elon Musk: glass geodesic domes
Post by: TripD on 11/14/2016 01:25 am
Would the use of structural panes lend themselves to single replacement after the dome is built?

Couldn't the overlap issue of friction cones be alleviated by staggering the depth of them?  I would be more concerned with how the failure of one effects the other, otherwise.
Title: Re: Elon Musk: glass geodesic domes
Post by: LMT on 11/14/2016 01:42 am
Anchors Away

If you pick a commercial ground engineering system (http://www.williamsform.com/Contact_Us/PDFs/Ground_Engineering_Systems.pdf) and run the numbers, you can really advance the NSF dome anchoring designs.  Just sayin'.
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/14/2016 02:15 am
The heavy part of the dome will be the glass panels. The structure won't be too bad, though sealing the triangles may be annoying. But anchors just need to be deep enough that their friction cones have enough surface area on the non-overlapping side. It's fine that they overlap, it's just that the overlapping area doesn't count so much. As long as the total weight of the volume of the soil in all the cones is equal to the pressure times bottom area of the dome, you're fine.

To ensure this, you just need long enough cables. Cables made out of the right material can have an extremely good strength to density ratio, like 4GPa/(g/cc). Much stronger than the Windows or the quasi-isotropic Carbon fiber composite of the frame, which would be around 0.4GPa/(g/cc) (much worse for the glass due to knock-downs for stress concentrations). Then the anchors themselves, but if the cables are long, the anchors will be a minority of the mass.

So the anchors and cables would be much less mass than a whole sphere. Also, realize that you still have to solve the problem of how to properly rest on the soil and walk around on the sphere.


And there's another thing: you could have a vertical cable in the center of the dome anchored deep underground. This could carry some of the load as well. The dome wouldn't have to be so high for a given area.

The panels will be heavy, but they don't look like they can offset the force from the pressure differential.

Looking at the depth of the anchors, don't think of them as cones.  Just figure on an inverted triangular prism running around the perimeter - we're talking about anchors that are 1 m apart, and some 15 m deep.

With a friction angle of 30 degrees, you get a 15 m wide triangle (ignoring for a second the tilt angle.

I'm guessing because this is so critical, they'll go even deeper - margin is your friend, and it's a lot cheaper to drill just a little bit deeper then it is to pick up the pieces afterwards if an anchor fails...   
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 11/14/2016 02:34 am
To ensure this, you just need long enough cables. Cables made out of the right material can have an extremely good strength to density ratio, like 4GPa/(g/cc). Much stronger than the Windows or the quasi-isotropic Carbon fiber composite of the frame, which would be around 0.4GPa/(g/cc)

The anchors, by definition, have to hold the same load as the frame. If the anchor-cables are so mass-efficient, why wouldn't you just use them as the tensile frame as well?
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/14/2016 03:21 am
Anchors Away

If you pick a commercial ground engineering system (http://www.williamsform.com/Contact_Us/PDFs/Ground_Engineering_Systems.pdf) and run the numbers, you can really advance the NSF dome anchoring designs.  Just sayin'.

That cheating.   Trying to have fun first
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/14/2016 03:27 am
Would the use of structural panes lend themselves to single replacement after the dome is built?

Couldn't the overlap issue of friction cones be alleviated by staggering the depth of them?  I would be more concerned with how the failure of one effects the other, otherwise.

I think you can make the tiles replaceable.  I depends on the edge-to-edge connector. 

I'm thinking about tiles that have a composite net core, in two layers.  Near the edge, to core is doubled over, and the tile has a thicker peripheral flange. 

So now you can grab the edge with a metal connector, and the tile doesn't lose strength near its edge.

The metal connector can be a one-piece slide-on, or a two part bolt-on. The latter type allows replacement.

Title: Re: Elon Musk: glass geodesic domes
Post by: KelvinZero on 11/14/2016 07:37 am
Borehole digging could be a relevant topic. I think this could be a good way to get water early on. (bore into glacier near equator until reach ice, somehow cycle hot water through or perhaps have a heater.

If you can dig really deep holes then anchoring becomes pretty plausible I imagine. Here is an interesting quote:
https://en.wikipedia.org/wiki/Borehole#History
"Borehole drilling has a long history. Han Dynasty China (202 BC – 220 AD) used deep borehole drilling for mining and other projects. Chinese borehole sites could reach as deep as 600 m"

This range also helps when we don't really know if we will hit the supposed glacier ice at ten meters or a bit deeper.

I have always heard that boring is really hard, at least robotically, and I still can't really imagine sending an ITS without real confidence of hitting water and that it contains no surprises that will mess up your ISRU equipment. But in any case one way or another we have to assume this is solved already for this discussion.

I guess we can find good numbers for weight and labour for equipment like this.

(note: I think we could demonstrate that if the depth of the anchor needed to be more than 0.5𝛑R then it would weigh a fair bit more than the lower half of a sphere.. as well as not providing that double volume. This is argued by conceptually cutting the lower sphere into strips and comparing these to anchor cables.)
Title: Re: Elon Musk: glass geodesic domes
Post by: mfck on 11/14/2016 09:58 am
Does the dome have to be sealed, as in 100% air tight pressure vessel or is it enough to have it at positive pressure(PP)? I mean, considering that ISRU fuel production is a hard requirement to land people (iirc), industrial scale O2 and N2 production and CO2 processing would already be there when they start to dome up.

Wouldn't a PP, open system, dome relax the structural requirements, particularly the anchoring PITA at hand?

Yes, you can't have short sleeve / breathable environment from that way, but you can have a much more benign one under the dome:

Less dust, thermal balance, attenuated radiation and pressure environment... Could probably grow stuff at low (1/2atm?) pressure and reduce the personal protection to rebreather and MCP suits....

Yes, it's wasteful, but I suggest to allow an abundance in some resource, else this whole enterprise is, probably, doomed if it has to squeeze every margin. Energy abundance would seem the most beneficial (I.e nuclear vs PV), allowing ISRU overproduction, which can't be bad, fuel and ECLSS wise.
Title: Re: Elon Musk: glass geodesic domes
Post by: francesco nicoli on 11/14/2016 10:29 am
Does the dome have to be sealed, as in 100% air tight pressure vessel or is it enough to have it at positive pressure(PP)? I mean, considering that ISRU fuel production is a hard requirement to land people (iirc), industrial scale O2 and N2 production and CO2 processing would already be there when they start to dome up.

Wouldn't a PP, open system, dome relax the structural requirements, particularly the anchoring PITA at hand?

Yes, you can't have short sleeve / breathable environment from that way, but you can have a much more benign one under the dome:

Less dust, thermal balance, attenuated radiation and pressure environment... Could probably grow stuff at low (1/2atm?) pressure and reduce the personal protection to rebreather and MCP suits....

Yes, it's wasteful, but I suggest to allow an abundance in some resource, else this whole enterprise is, probably, doomed if it has to squeeze every margin. Energy abundance would seem the most beneficial (I.e nuclear vs PV), allowing ISRU overproduction, which can't be bad, fuel and ECLSS wise.

what's the point in building a gigantic glass dome ifyou cannot really going around it without a mask?
Title: Re: Elon Musk: glass geodesic domes
Post by: mfck on 11/14/2016 10:51 am
Does the dome have to be sealed, as in 100% air tight pressure vessel or is it enough to have it at positive pressure(PP)? I mean, considering that ISRU fuel production is a hard requirement to land people (iirc), industrial scale O2 and N2 production and CO2 processing would already be there when they start to dome up.

Wouldn't a PP, open system, dome relax the structural requirements, particularly the anchoring PITA at hand?

Yes, you can't have short sleeve / breathable environment from that way, but you can have a much more benign one under the dome:

Less dust, thermal balance, attenuated radiation and pressure environment... Could probably grow stuff at low (1/2atm?) pressure and reduce the personal protection to rebreather and MCP suits....

Yes, it's wasteful, but I suggest to allow an abundance in some resource, else this whole enterprise is, probably, doomed if it has to squeeze every margin. Energy abundance would seem the most beneficial (I.e nuclear vs PV), allowing ISRU overproduction, which can't be bad, fuel and ECLSS wise.

what's the point in building a gigantic glass dome ifyou cannot really going around it without a mask?
It's in the quote... 
Title: Re: Elon Musk: glass geodesic domes
Post by: Ionmars on 11/14/2016 12:45 pm
Semantics:
In some cases, the difference between an anchored dome and a sphere could be in the words chosen. Consider a dome with anchors that are extensions of the struts that contain the panes. Now bend those anchors back under the dome in a curve that mirrors the curve of the dome above. They continue until they meet each other in the middle of the structure and are joined together.  The anchors would be interlaced with struts, like the topside structure, but solid material would be employed between the anchors rather than window panes. As suggested earlier, the bottom 1/3 could be back-filled with regolith. We could then name the underside structure the self-connected anchors of a dome or the underside of a sphere.

This could also be accomplished with MeekGee's interlocking panes as structural elements.
Title: Re: Elon Musk: glass geodesic domes
Post by: Ionmars on 11/14/2016 01:24 pm
Multipurpose:
Assume a dome/sphere structure like I described above. The first purpose os to provide viewing of the outside panorama.
As purpose number 2 we could addd features that would utilize this volume as a central park. Fill the bottom 1/3 with water to form a pond. Provide floating walkways that meander across the surface. Add a deck in the center large enough for a bandstand or village meeting place.

Purpose number 3 could be raising fish in the pond as a supplemental protein source.

Number 4. Build vertical tubes anchored in the bottom of the pond that rise high above the surface. Pump water from the bottom of the pond and sprinkle it into the air. This serves to aerate the water for the benefit of the fish and fountains for the people.

Number 5. Hang plants and vines up and down the tubes. Grapes and tomatoes for food supplements and flowers for aesthetics.

You could probably improve on this list. 
Title: Re: Elon Musk: glass geodesic domes
Post by: envy887 on 11/14/2016 01:28 pm
To ensure this, you just need long enough cables. Cables made out of the right material can have an extremely good strength to density ratio, like 4GPa/(g/cc). Much stronger than the Windows or the quasi-isotropic Carbon fiber composite of the frame, which would be around 0.4GPa/(g/cc)

The anchors, by definition, have to hold the same load as the frame. If the anchor-cables are so mass-efficient, why wouldn't you just use them as the tensile frame as well?

The frame elements can't be in pure uniaxial tension like a cable. They will be pulled equally in 2 directions at every point. And they also have to hold compression loads when the dome is depressurized. So fibers aren't an option unless they are in a composite, which reduces the overall and specific strength.
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/14/2016 02:36 pm
Does the dome have to be sealed, as in 100% air tight pressure vessel or is it enough to have it at positive pressure(PP)? I mean, considering that ISRU fuel production is a hard requirement to land people (iirc), industrial scale O2 and N2 production and CO2 processing would already be there when they start to dome up.

Wouldn't a PP, open system, dome relax the structural requirements, particularly the anchoring PITA at hand?

Yes, you can't have short sleeve / breathable environment from that way, but you can have a much more benign one under the dome:

Less dust, thermal balance, attenuated radiation and pressure environment... Could probably grow stuff at low (1/2atm?) pressure and reduce the personal protection to rebreather and MCP suits....

Yes, it's wasteful, but I suggest to allow an abundance in some resource, else this whole enterprise is, probably, doomed if it has to squeeze every margin. Energy abundance would seem the most beneficial (I.e nuclear vs PV), allowing ISRU overproduction, which can't be bad, fuel and ECLSS wise.
I think sealing will not be a problem. An inner rubber skirt (non load bearing) would do it. You can even have a full rubber sheet, and only seal to the ground  if you do ground penetrations.

But I do think that the habitats have to be pressure vessels, and doors from the habitats to the dome should be airtight and normally closed.

A failed pane will not cause insta- depressurization.

I see the colonists first building the torus, and then building the dome while living in the torus.

After the dome is up, maybe the atmosphere in the dome is high in CO2 (how much is still ok for people) and maybe you have the ability to pump in CO2 to keep pressure if there a small leak. (Though that's a large pump).

All this talk about drilling, and pumping, and ISRU...  That's a lot of power.  Just sayin'.
Title: Re: Elon Musk: glass geodesic domes
Post by: guckyfan on 11/14/2016 06:46 pm
But I do think that the habitats have to be pressure vessels, and doors from the habitats to the dome should be airtight and normally closed.

I think, emergency shelters would be good enough. No need to build the whole habitats pressure resistant.
Title: Re: Elon Musk: glass geodesic domes
Post by: TripD on 11/14/2016 07:13 pm
But I do think that the habitats have to be pressure vessels, and doors from the habitats to the dome should be airtight and normally closed.

I think, emergency shelters would be good enough. No need to build the whole habitats pressure resistant.

Except for the structural benefit to having a lower pressure in the outer dome .  As for emergency shelters, there will be access ways to other parts of the colony which would provide a safe place for evacuation.
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/14/2016 07:21 pm
But I do think that the habitats have to be pressure vessels, and doors from the habitats to the dome should be airtight and normally closed.

I think, emergency shelters would be good enough. No need to build the whole habitats pressure resistant.

I'd wait till there are a few domes standing for a few years before being too confident.

If the habitats are a secondary pressurized volume, dome failures will have a lot lower cost in lives.

It doesn't mean you have to airlock in and out of them - just close the door behind you... 

And if you build the habitats first, and only afterwards erect the dome, then this will be a natural outcome of this strategy anyway.

At this point, emergency shelters are only for people that are, at the time, outside the habitats but inside the dome.  I think that's more prudent.
Title: Re: Elon Musk: glass geodesic domes
Post by: Ionmars on 11/14/2016 08:43 pm
...
...
...
After the dome is up, maybe the atmosphere in the dome is high in CO2 (how much is still ok for people) and maybe you have the ability to pump in CO2 to keep pressure if there a small leak. (Though that's a large pump).
...
According to Wikipedia “In concentrations up to 1% (10,000 ppm), it will make some people feel drowsy and give the lungs a stuffy feeling. Concentrations of 7% to 10% (70,000 to 100,000 ppm) may cause suffocation, even in the presence of sufficient oxygen, manifesting as dizziness, headache, visual and hearing dysfunction, and unconsciousness within a few minutes to an hour.”

Surprisingly, very high CO2 levels may also become detrimental to plants. According to HydroFarm (speaking about CO2 enrichment for plants) “Above 2,000 PPM, CO2 starts to become toxic to plants and above 4,000 PPM it becomes toxic to people.” It appears that CO2 levels should be controlled whenever living organisms are involved.
https://www.hydrofarm.com/resources/articles/co2_enrichment.php
Title: Re: Elon Musk: glass geodesic domes
Post by: DreamyPickle on 11/14/2016 09:02 pm
One potential use for low-pressure domes would be agriculture with natural light. I know it's possible to grow plants indoors using artificial light but a proper evaluation would have to compare the amount of mass and volume shipped from Earth for the same amount of food calorie growth capacity. Natural light might win over because you would need to ship fewer solar panels and electric lights.

While Elon said "domes" this doesn't need to refer specifically to half-spheres anchored on flat rock. For agriculture in particular a tall dome would not be useful, surface is far more important. For habitation you can have a much higher dome (almost a complete sphere) which is completely filled in with platforms at every level. The internal construction can be very light-weight because not only is gravity lower but you can anchor each floor to the dome's structure with cables.

I'm confused about how anchoring would work. Don't you need a pressure vessel to go all around the bottom anyway, to prevent the atmosphere from diffusing through the soil? And even assuming you make the ground level impermeable somehow, wouldn't the joint between the dome wall and the ground become a point of high stress and risk cracking? Intuitively it seems it would make more sense to design the bottom as a very flattened pressure vessel head (https://en.wikipedia.org/wiki/Head_(vessel)). The base could be excavated in advance to the proper shape to avoid having to add additional supports.
Title: Re: Elon Musk: glass geodesic domes
Post by: Robotbeat on 11/14/2016 09:04 pm
Yeah, even at 1000ppm, CO2 can slow down some mental tasks. This is is a problem for poorly ventilate building on Earth. And so at the same ventilation levels, it becomes more of a problem if your outside CO2 levels are higher. You could rightfully say that rising CO2 levels are making us dumber. By the end of the century with levels at 900ppm (and higher in cities), this could be an issue even outdoors as the veneraforming of Earth continues.

But I digress. Yeah, you want to keep CO2 levels down near 350ppm or lower to maintain peak mental acuity. The slight extra power for the CO2 scrubbers is worth it, IMHO.

Here is the experiment which showed that:
http://ehp.niehs.nih.gov/wp-content/uploads/advpub/2015/10/ehp.1510037.acco.pdf
Title: Re: Elon Musk: glass geodesic domes
Post by: Ionmars on 11/14/2016 09:07 pm
...
...
...
It doesn't mean you have to airlock in and out of them - just close the door behind you... 
...
...
If the difference between habitat air pressure and under-the-dome air pressure is is only 1 psi, then for a standard small door of 30 inches by 80 inches you have (30)(80)(1) = 2400 pounds pressure resistance. You will need a lot of adrenalin to open that door!  :)
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/15/2016 12:13 am
...
...
...
It doesn't mean you have to airlock in and out of them - just close the door behind you... 
...
...
If the difference between habitat air pressure and under-the-dome air pressure is is only 1 psi, then for a standard small door of 30 inches by 80 inches you have (30)(80)(1) = 2400 pounds pressure resistance. You will need a lot of adrenalin to open that door!  :)

That was tongue in cheek. I know what a hatch looks like.  But it's still very different than having an airlock.

Point it - as long as conditions are normal, you can walk in and out of the habitat pretty easily.  I mean even if it were an airlock, you wouldn't need to cycle it - you'd just go through two doors.

But if you have a dome failure and rapid loss of pressure, you'd save a LOT of people if all those that are in the habitats are protected.

10 years later, when you're confident that these domes never fail, sure.  But still - you'd want air tight door on the entrance to your tunnels, right? 

What the domes give you is the ability to do agriculture, service machinery, build large structures - in a shirtsleeve environment.  And go for strolls.

And those working under the dome are always cognizant of the nearest quick shelter.

But I'd really be hesitant to just expose the entire population to that risk 24/7.

---

Edit:  Just imagine how easier it is to do maintenance on this drill rig while under a dome, then put on a suit and drive it outside, compared with servicing it in a suit.  (Not to mention if you have pressure cabin on it, though you might want the ability to hop-off hop-on while working outside)
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/15/2016 12:45 am
...
...
...
It doesn't mean you have to airlock in and out of them - just close the door behind you... 
...
...
If the difference between habitat air pressure and under-the-dome air pressure is is only 1 psi, then for a standard small door of 30 inches by 80 inches you have (30)(80)(1) = 2400 pounds pressure resistance. You will need a lot of adrenalin to open that door!  :)

Positive pressure should be a very small fraction of a PSI, and you don't have to build your door like a house door...   

Have you never been to slightly overpressurized tent?

And besides, folks out there are explaining why outside CO2 levels can be high anyway so you don't even need that.    Even zero dP is fine if the atmospheres are identical.

Title: Re: Elon Musk: glass geodesic domes
Post by: Lumina on 11/15/2016 03:14 am
Point it - as long as conditions are normal, you can walk in and out of the habitat pretty easily.  I mean even if it were an airlock, you wouldn't need to cycle it - you'd just go through two doors.

But if you have a dome failure and rapid loss of pressure, you'd save a LOT of people if all those that are in the habitats are protected.

10 years later, when you're confident that these domes never fail, sure.  But still - you'd want air tight door on the entrance to your tunnels, right?

Agreed, and this might be one reason why Elon Musk spoke of tunnels at the same time as he spoke of domes. Domes look sexier and serve clear purposes, but they will not be the only answer because a dome's life (on Mars...) will be measured in what, decades? Whereas tunnels can be stable for centuries and so they will have far less risk and far fewer problems.
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/15/2016 03:51 am
Point it - as long as conditions are normal, you can walk in and out of the habitat pretty easily.  I mean even if it were an airlock, you wouldn't need to cycle it - you'd just go through two doors.

But if you have a dome failure and rapid loss of pressure, you'd save a LOT of people if all those that are in the habitats are protected.

10 years later, when you're confident that these domes never fail, sure.  But still - you'd want air tight door on the entrance to your tunnels, right?

Agreed, and this might be one reason why Elon Musk spoke of tunnels at the same time as he spoke of domes. Domes look sexier and serve clear purposes, but they will not be the only answer because a dome's life (on Mars...) will be measured in what, decades? Whereas tunnels can be stable for centuries and so they will have far less risk and far fewer problems.

"Clear purpose" - got it!

I wonder if they'll find large salt deposits they can quickly mine in...

As for dome lifetime, yeah, there's a lifetime, and an MTBF...  And if you have many domes on the surface, you need the MTBF to be much larger than the service life of the dome...

------------------

Or... a large mesh of small domes.  Maybe down to 5-10 m diameter, so basically single rooms or single habitats.

At that size, sure, use full spheres. Dig down 2-4 m, and bury most of the bottom half of the sphere.  That I buy.

Much thinner glass, much easier struts.  in a 10 m sphere, you can still grow a tree...

Spheres are connected by transfer tubes, so you can isolate a damaged Sphere, and so failures are not catastrophic to the colony.

You'll have to service your equipment in underground caverns, but that's fine.

From 50 m to 5-10 m, we reduced the force in the struts from 100 tons / m to 10-20 tons /m

That's much more manageable.

Title: Re: Elon Musk: glass geodesic domes
Post by: Robotbeat on 11/15/2016 06:23 am
A cable made of high performance material like Zylon or Carbon fiber about an inch and a half in diameter can support a load of 450 tons. I don't see the big problem, here...
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/15/2016 06:51 am
A cable made of high performance material like Zylon or Carbon fiber about an inch and a half in diameter can support a load of 450 tons. I don't see the big problem, here...

Are you talking about the anchors?

I think the anchors are solvable for a 50 m dome as I've shown, but it's still problematic, for all the reasons recounted above.

You need to be pretty cocky to think that 120 100-ton anchors supporting a critical structure are "no big problem"....   Cables (both synthetic and wire rope) are really tricky to work with as structural elements.

Full spheres do make sense in smaller sizes.  You're not wasting height, and the structure is a lot simpler.

There's no reason not to do both, but recognize the drawbacks of each.
Title: Re: Elon Musk: glass geodesic domes
Post by: Robotbeat on 11/15/2016 12:31 pm
Considering the forces involved, I'd argue cables are much simpler than the composite frame of a geodesic sphere.

I think you're letting yourself become enamored with the buried sphere idea. I don't think it's as slam dunk as that. If you want a simple and practical pressure vessel you should look at cylinders since they are not completely made of compound curves like a sphere.
Title: Re: Elon Musk: glass geodesic domes
Post by: Robotbeat on 11/15/2016 12:37 pm
Also, a half sphere is probably not the optimal shape for a dome. A flattened half-sphere can be built such that there are no hoop stresses in one direction, which simplifies construction and makes it a lot easier to use very high strength to weight ratio cables as the main resisting force of the structure.

Think of a Mylar party balloon. As can be seen by the bunching, there is no hoop stress around the perimeter. NASA recently tested an inflatable airlock concept called MESH based on this idea. The lack of hoop stress made it possible to put a sealable zipper parallel to the tension cables. They also showed a completely redundant cable structure is also possible for the concept.
Title: Re: Elon Musk: glass geodesic domes
Post by: francesco nicoli on 11/15/2016 01:01 pm
Does the dome have to be sealed, as in 100% air tight pressure vessel or is it enough to have it at positive pressure(PP)? I mean, considering that ISRU fuel production is a hard requirement to land people (iirc), industrial scale O2 and N2 production and CO2 processing would already be there when they start to dome up.

Wouldn't a PP, open system, dome relax the structural requirements, particularly the anchoring PITA at hand?

Yes, you can't have short sleeve / breathable environment from that way, but you can have a much more benign one under the dome:

Less dust, thermal balance, attenuated radiation and pressure environment... Could probably grow stuff at low (1/2atm?) pressure and reduce the personal protection to rebreather and MCP suits....

Yes, it's wasteful, but I suggest to allow an abundance in some resource, else this whole enterprise is, probably, doomed if it has to squeeze every margin. Energy abundance would seem the most beneficial (I.e nuclear vs PV), allowing ISRU overproduction, which can't be bad, fuel and ECLSS wise.

what's the point in building a gigantic glass dome ifyou cannot really going around it without a mask?
It's in the quote...

The quote just lists a series of things yu could do in an unpressurised system. I don't quite see how doing it in a gigantic but umpressurised dome makes doing them easier or cheaper than in other structures. Even a non-pressurised dome is a non-neglegible effort. the marginal cost/effort of making it pressurized is probably minimal compared with the marginal cost/effort of moving from doing all the things you list in a different way, to build up a full unpressurised dome. In italian we say "you have gone up to 30, you can go 31".
Title: Re: Elon Musk: glass geodesic domes
Post by: mfck on 11/15/2016 01:15 pm


Does the dome have to be sealed, as in 100% air tight pressure vessel or is it enough to have it at positive pressure(PP)? I mean, considering that ISRU fuel production is a hard requirement to land people (iirc), industrial scale O2 and N2 production and CO2 processing would already be there when they start to dome up.

Wouldn't a PP, open system, dome relax the structural requirements, particularly the anchoring PITA at hand?

Yes, you can't have short sleeve / breathable environment from that way, but you can have a much more benign one under the dome:

Less dust, thermal balance, attenuated radiation and pressure environment... Could probably grow stuff at low (1/2atm?) pressure and reduce the personal protection to rebreather and MCP suits....

Yes, it's wasteful, but I suggest to allow an abundance in some resource, else this whole enterprise is, probably, doomed if it has to squeeze every margin. Energy abundance would seem the most beneficial (I.e nuclear vs PV), allowing ISRU overproduction, which can't be bad, fuel and ECLSS wise.

what's the point in building a gigantic glass dome ifyou cannot really going around it without a mask?
It's in the quote...

The quote just lists a series of things yu could do in an unpressurised system. I don't quite see how doing it in a gigantic but umpressurised dome makes doing them easier or cheaper than in other structures. Even a non-pressurised dome is a non-neglegible effort. the marginal cost/effort of making it pressurized is probably minimal compared with the marginal cost/effort of moving from doing all the things you list in a different way, to build up a full unpressurised dome. In italian we say "you have gone up to 30, you can go 31".

Unless it's a day in a month. Count the number of probables in your post, what's your point?
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/15/2016 01:29 pm
Considering the forces involved, I'd argue cables are much simpler than the composite frame of a geodesic sphere.

I think you're letting yourself become enamored with the buried sphere idea. I don't think it's as slam dunk as that. If you want a simple and practical pressure vessel you should look at cylinders since they are not completely made of compound curves like a sphere.

This is not a "war of ideas"...  Both ideas have their up-sides and drawbacks, and in the trade-offs, the "dig-and-sphere" wins for smaller sizes, since its main drawbacks (wasteful, amount of dirt moved) are minimized.

As for cables, can you describe how you're envisioning the dome built?  How do you handle the connection points, What is the construction process?
Title: Re: Elon Musk: glass geodesic domes
Post by: francesco nicoli on 11/15/2016 07:33 pm


Does the dome have to be sealed, as in 100% air tight pressure vessel or is it enough to have it at positive pressure(PP)? I mean, considering that ISRU fuel production is a hard requirement to land people (iirc), industrial scale O2 and N2 production and CO2 processing would already be there when they start to dome up.

Wouldn't a PP, open system, dome relax the structural requirements, particularly the anchoring PITA at hand?

Yes, you can't have short sleeve / breathable environment from that way, but you can have a much more benign one under the dome:

Less dust, thermal balance, attenuated radiation and pressure environment... Could probably grow stuff at low (1/2atm?) pressure and reduce the personal protection to rebreather and MCP suits....

Yes, it's wasteful, but I suggest to allow an abundance in some resource, else this whole enterprise is, probably, doomed if it has to squeeze every margin. Energy abundance would seem the most beneficial (I.e nuclear vs PV), allowing ISRU overproduction, which can't be bad, fuel and ECLSS wise.

what's the point in building a gigantic glass dome ifyou cannot really going around it without a mask?
It's in the quote...

The quote just lists a series of things yu could do in an unpressurised system. I don't quite see how doing it in a gigantic but umpressurised dome makes doing them easier or cheaper than in other structures. Even a non-pressurised dome is a non-neglegible effort. the marginal cost/effort of making it pressurized is probably minimal compared with the marginal cost/effort of moving from doing all the things you list in a different way, to build up a full unpressurised dome. In italian we say "you have gone up to 30, you can go 31".

Unless it's a day in a month. Count the number of probables in your post, what's your point?


point is pretty straightforward. You can do all the stuff you cited with a third of a bazillion. Doing that in a giganting non-pressurized dome will bring your costs up from half a bazillion to a full bazillion, for doing essentially the same stuff. At that point, is worthy to spend a bazillion + x to make the dome pressurized.


Quote

 Count the number of probables in your post


like if the thread were scarce in ifs' and whethers'. Man, you are talking of gigantic glass domes on a different planet where we have never even landed a human being once. If you don't have ifs, you are a fool.

Title: Re: Elon Musk: glass geodesic domes
Post by: KelvinZero on 11/15/2016 07:39 pm
As for cables, can you describe how you're envisioning the dome built?  How do you handle the connection points, What is the construction process?

I have also been wondering about this. It probably won't be people in bulky ISS-like suits climbing 10-meter ladders with a glass pane in one hand. :)
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/15/2016 07:55 pm
As for cables, can you describe how you're envisioning the dome built?  How do you handle the connection points, What is the construction process?

I have also been wondering about this. It probably won't be people in bulky ISS-like suits climbing 10-meter ladders with a glass pane in one hand. :)
I'm trying to figure out some scheme for it, just for kicks.

Imagine you have a spherical mandrel on earth, and you make a high strength fishing net over it. (From some high strength fibrous material).

When you make it, make it in three Gores, so you can roll it for shipping.

On Mars, reconnect the gores, and then use a low pressure bladder to somehow inflate it to shape, then find a way to tile it....  It's not hopeless....

But remember how cables stretch, and figure out how to mediate between the fishing net and the tiles... 

I'm still with a tile based construction, and thinking about making one here at home...

Title: Re: Elon Musk: glass geodesic domes
Post by: mfck on 11/15/2016 08:03 pm


...
If you don't have ifs, you are a fool.
...

Agreed, though worth noting, that having ifs does not mean you're not a fool.
Title: Re: Elon Musk: glass geodesic domes
Post by: envy887 on 11/15/2016 08:14 pm
As for cables, can you describe how you're envisioning the dome built?  How do you handle the connection points, What is the construction process?

I have also been wondering about this. It probably won't be people in bulky ISS-like suits climbing 10-meter ladders with a glass pane in one hand. :)
I'm trying to figure out some scheme for it, just for kicks.

Imagine you have a spherical mandrel on earth, and you make a high strength fishing net over it. (From some high strength fibrous material).

When you make it, make it in three Gores, so you can roll it for shipping.

On Mars, reconnect the gores, and then use a low pressure bladder to somehow inflate it to shape, then find a way to tile it....  It's not hopeless....

But remember how cables stretch, and figure out how to mediate between the fishing net and the tiles... 

I'm still with a tile based construction, and thinking about making one here at home...

Use a multilayer flexible acrylic construction. Ship it in rolls of individual layers, seam it to together on site, and inflate one layer at a time under the net. Increase the pressure as you add each layer.
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/15/2016 09:05 pm
As for cables, can you describe how you're envisioning the dome built?  How do you handle the connection points, What is the construction process?

I have also been wondering about this. It probably won't be people in bulky ISS-like suits climbing 10-meter ladders with a glass pane in one hand. :)
I'm trying to figure out some scheme for it, just for kicks.

Imagine you have a spherical mandrel on earth, and you make a high strength fishing net over it. (From some high strength fibrous material).

When you make it, make it in three Gores, so you can roll it for shipping.

On Mars, reconnect the gores, and then use a low pressure bladder to somehow inflate it to shape, then find a way to tile it....  It's not hopeless....

But remember how cables stretch, and figure out how to mediate between the fishing net and the tiles... 

I'm still with a tile based construction, and thinking about making one here at home...

Use a multilayer flexible acrylic construction. Ship it in rolls of individual layers, seam it to together on site, and inflate one layer at a time under the net. Increase the pressure as you add each layer.

So if you look at a facility on earth that manufactures LTAs, (and you'll need a higher level of QA than that), you'll see hangar-sized rooms, huge amount of controlled space - it's not so easy to fabricate 50 m precision spherical bladders like these.

Remember you just landed with a handful of BFSs at best. You may have remote controlled tools like a drill rig or a dozer, but they are small, and power is at a premium.

So you live in the BFS, it's crowded, and you need to start building.

Easiest thing is to dig a 10 m diameter, 4 m deep domed hole (which might, just might, can be done autonomously), and then build a sphere from a kit and just let it sit there.The hole is just a passive hole.

Already, you're making BFS-sized enclosures, without needing any facilities, and so you have more room to breath, but still not enough room for major projects...

Next step is a 50 m dome (say 120-degree) - which requires more complicated earth work (drill, anchor, concrete, repeat 120 times) but worth it since you get nice "walking room", and a first place to keep you equipment in, equipment that you'll need to start building tunnels.

Once you get underground, the dirt's the limit in terms of usable space, and the domes become you agriculture centers.


Title: Re: Elon Musk: glass geodesic domes
Post by: KelvinZero on 11/16/2016 12:20 am
It occurs to me that these kitset domes could be really fun.

I mean, you probably would not make them of the same space-age materials, but I can imagine some knockoff that would never hold pressure being on sale from somewhere. I guess more on the 6-meter wide, 3 meter high scale. The principle of how it assembles (easily!) could be the same.

About a final seal, maybe all it needs is the right sort of tape, dispensed from a conventional tape gun? Im imagining one of those materials that is between solid and liquid. It just squeezes into any gap under pressure. You have got to be able to lay one layer over another without the hint of a gap.
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 11/16/2016 04:04 am
To ensure this, you just need long enough cables. Cables made out of the right material can have an extremely good strength to density ratio, like 4GPa/(g/cc). Much stronger than the Windows or the quasi-isotropic Carbon fiber composite of the frame, which would be around 0.4GPa/(g/cc)
The anchors, by definition, have to hold the same load as the frame. If the anchor-cables are so mass-efficient, why wouldn't you just use them as the tensile frame as well?
The frame elements can't be in pure uniaxial tension like a cable. They will be pulled equally in 2 directions at every point.

Why can't you use a web of cables?

If the strength of cables really is an order-of-magnitude greater, it seems ridiculous not to.

And they also have to hold compression loads when the dome is depressurized. So fibers aren't an option unless they are in a composite, which reduces the overall and specific strength.

The compression load when unpressurised is trivial compared to the tensile force at 1atm.

So under the net you can have a vastly weaker structure that is fully self-supporting when unpressurised.

When pressurised, it is held down by the net, so it only has to withstand the force between the main cables, over a distance of less than a metre say (in a 50m structure. A few inches per pane in a 5m dome.) Just as in the composite-frame example, the glass panels themselves only supports the stress over their short span, not the overall structural stress.
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 11/16/2016 04:14 am
It occurs to me that these kitset domes could be really fun.
[...] I can imagine some knockoff that would never hold pressure being on sale from somewhere. I guess more on the 6-meter wide, 3 meter high scale. The principle of how it assembles (easily!) could be the same.
About a final seal, maybe all it needs is the right sort of tape, dispensed from a conventional tape gun? Im imagining one of those materials that is between solid and liquid. It just squeezes into any gap under pressure. You have got to be able to lay one layer over another without the hint of a gap.

You could make something like this using duct-tape as both the panel-sealer and tensile support (in the place of the cable-webbing I mentioned in the previous post). Duct-tape stretches, so it wouldn't last long, but something more durable like speed-tape might allow a seasonal structure at relatively low cost.

It just needs a standard, easily copied design that eliminates hoop-forces in selected areas to allow velcro-able "airlocks" made the same way. Everything else is available at your local hardware store.

(Build it before it snows to create an access corridor between the house and the driveway/shed/etc. Or even large enough to cover the entire driveway. Once snow "sets", it should be largely self-supporting, so the positive pressure shouldn't be significant if you have the right shape. Work with the snow to reduce the area that you need to shovel.)

Wildly off-topic of course.
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 11/16/2016 06:13 am
After the dome is up, maybe the atmosphere in the dome is high in CO2 (how much is still ok for people) and maybe you have the ability to pump in CO2 to keep pressure if there a small leak.

To make Ionmars' comment more explicit: the intolerance to CO2 concentration increases vastly quicker than the danger from low pressure. You can tolerate a 10% drop in atmospheric pressure and still easily function well enough to run to the nearest emergency airlock/pressure-safe-shelter/etc. But you can't function if you replace that lost pressure with CO2.

To emphasise another part of Ionmars' comment, plants are more sensitive to high CO2 levels than people. Especially as people can tolerate no CO2, but plants can't. Plants need a much, much narrow band of CO2 levels than humans. And AIUI, the band gets narrower if you lower the atmospheric pressure, making it even harder to keep the plants healthy.

Like domes-on-Mars, people seem to picture plants as easier to keep alive than people. "Have a low-pressure dome with plants."
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 11/16/2016 06:18 am
Does the dome have to be sealed, as in 100% air tight pressure vessel or is it enough to have it at positive pressure(PP)?
Wouldn't a PP, open system, dome relax the structural requirements, particularly the anchoring PITA at hand?
Could probably grow stuff at low (1/2atm?) pressure

The anchor requirements are fairly linear with pressure. Half atmos doesn't save enough, IMO. You probably only see enough real benefits below 0.1atm to justify the hassle of not being at 1atm.

Likewise, the rate of permitted air loss would have to be fairly high before you see any meaningful reduction in sealing requirements. Much higher than you can replace from processed air, hence higher than you can allow to leak daily from a plant-compatible atmosphere.



Re: Big domes with little domes, with littler habs inside them.

I've always liked the idea of having a giant low-tech outer structure (and yes, I'm usually picturing domes) that is partially pressurised with Martian atmosphere. A purely inflatable dome (a tent), with large soft-lock airlocks, so you can bring entire vehicles inside at night/winter. You can have most of your systems inside, even comms gear, the whole works; perhaps reducing design requirements and making maintenance easier. Etc etc...

But the numbers don't work (IMO) unless the majority of the structure can be ISRU-manufactured at little cost, and is very simple to put up.

(Ie, it only works if the structure is "free".)

The whole point of a low pressure (and especially Mars air) dome is to allow you to drastically increase the area-under-cover at low cost. But large domes increase the anchoring requirements exponentially.

The force on the anchors decreases linearly with pressure, but the total force increases exponentially with radius. Combine the two scaling effects and 0.1 atm lets you increase the radius by 3 times for the same anchoring requirements. 0.01 atm lets you increase the size 10-fold.

Is there enough advantage from a 0.01 atm atmosphere to not just have a smaller structure at a full 1atm?
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/16/2016 06:45 am
Does the dome have to be sealed, as in 100% air tight pressure vessel or is it enough to have it at positive pressure(PP)?
Wouldn't a PP, open system, dome relax the structural requirements, particularly the anchoring PITA at hand?
Could probably grow stuff at low (1/2atm?) pressure

The anchor requirements are fairly linear with pressure. Half atmos doesn't save enough, IMO. You probably only see enough real benefits below 0.1atm to justify the hassle of not being at 1atm.

Likewise, the rate of permitted air loss would have to be fairly high before you see any meaningful reduction in sealing requirements. Much higher than you can replace from processed air, hence higher than you can allow to leak daily from a plant-compatible atmosphere.



Re: Big domes with little domes, with littler habs inside them.

I've always liked the idea of having a giant low-tech outer structure (and yes, I'm usually picturing domes) that is partially pressurised with Martian atmosphere. A purely inflatable dome (a tent), with large soft-lock airlocks, so you can bring entire vehicles inside at night/winter. You can have most of your systems inside, even comms gear, the whole works; perhaps reducing design requirements and making maintenance easier. Etc etc...

But the numbers don't work (IMO) unless the majority of the structure can be ISRU-manufactured at little cost, and is very simple to put up.

(Ie, it only works if the structure is "free".)

The whole point of a low pressure (and especially Mars air) dome is to allow you to drastically increase the area-under-cover at low cost. But large domes increase the anchoring requirements exponentially.

The force on the anchors decreases linearly with pressure, but the total force increases exponentially with radius. Combine the two scaling effects and 0.1 atm lets you increase the radius by 3 times for the same anchoring requirements. 0.01 atm lets you increase the size 10-fold.

Is there enough advantage from a 0.01 atm atmosphere to not just have a smaller structure at a full 1atm?
Exponentially?
Title: Re: Elon Musk: glass geodesic domes
Post by: guckyfan on 11/16/2016 07:18 am
I have suggested very large domes of very thin sheets. Just pressurized enough to stand up. They would act like greenhouses, very much reducing temperature swings inside, which would be good for any equipment. No appreciable increase of pressure but protection from harsh UV and keeping IR inside.
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 11/16/2016 09:08 am
The force on the anchors decreases linearly with pressure, but the total force increases exponentially with radius. Combine the two scaling effects and 0.1 atm lets you increase the radius by 3 times for the same anchoring requirements. 0.01 atm lets you increase the size 10-fold.
Exponentially?

2 is an exponent.
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/16/2016 02:22 pm
The force on the anchors decreases linearly with pressure, but the total force increases exponentially with radius. Combine the two scaling effects and 0.1 atm lets you increase the radius by 3 times for the same anchoring requirements. 0.01 atm lets you increase the size 10-fold.
Exponentially?

2 is an exponent.
:o
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 11/16/2016 04:39 pm
Does the dome have to be sealed, as in 100% air tight pressure vessel or is it enough to have it at positive pressure(PP)?
Wouldn't a PP, open system, dome relax the structural requirements, particularly the anchoring PITA at hand?
Could probably grow stuff at low (1/2atm?) pressure

The anchor requirements are fairly linear with pressure. Half atmos doesn't save enough, IMO. You probably only see enough real benefits below 0.1atm to justify the hassle of not being at 1atm.

Likewise, the rate of permitted air loss would have to be fairly high before you see any meaningful reduction in sealing requirements. Much higher than you can replace from processed air, hence higher than you can allow to leak daily from a plant-compatible atmosphere.



Re: Big domes with little domes, with littler habs inside them.

I've always liked the idea of having a giant low-tech outer structure (and yes, I'm usually picturing domes) that is partially pressurised with Martian atmosphere. A purely inflatable dome (a tent), with large soft-lock airlocks, so you can bring entire vehicles inside at night/winter. You can have most of your systems inside, even comms gear, the whole works; perhaps reducing design requirements and making maintenance easier. Etc etc...

But the numbers don't work (IMO) unless the majority of the structure can be ISRU-manufactured at little cost, and is very simple to put up.

(Ie, it only works if the structure is "free".)

The whole point of a low pressure (and especially Mars air) dome is to allow you to drastically increase the area-under-cover at low cost. But large domes increase the anchoring requirements exponentially.

The force on the anchors decreases linearly with pressure, but the total force increases exponentially with radius. Combine the two scaling effects and 0.1 atm lets you increase the radius by 3 times for the same anchoring requirements. 0.01 atm lets you increase the size 10-fold.

Is there enough advantage from a 0.01 atm atmosphere to not just have a smaller structure at a full 1atm?
Don't think there would be much advantage from the pressure, but there might be some interest in keeping equipment warm.  As the main cooling on Mars will be radiative, a dome, or more likely an open ended cylinder, with low-e coating and transparent walls, combined with infra red heaters might be a simple way of keeping heavy equipment warm and avoiding problems with freezing plastics, overly thick oil and such.  This type of dome would be rather like garages in northern climate mines.  No need for air pressure, in fact, just a fancy dome tent, really.
Title: Re: Elon Musk: glass geodesic domes
Post by: guckyfan on 11/16/2016 05:59 pm
Don't think there would be much advantage from the pressure, but there might be some interest in keeping equipment warm.  As the main cooling on Mars will be radiative, a dome, or more likely an open ended cylinder, with low-e coating and transparent walls, combined with infra red heaters might be a simple way of keeping heavy equipment warm and avoiding problems with freezing plastics, overly thick oil and such.  This type of dome would be rather like garages in northern climate mines.  No need for air pressure, in fact, just a fancy dome tent, really.

For heating there is the sun. The dome or tent only needs to keep the infrared in. The ground will warm up over time and keep the temperature from dropping too much over night.
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 11/17/2016 04:20 pm
Don't think there would be much advantage from the pressure, but there might be some interest in keeping equipment warm.  As the main cooling on Mars will be radiative, a dome, or more likely an open ended cylinder, with low-e coating and transparent walls, combined with infra red heaters might be a simple way of keeping heavy equipment warm and avoiding problems with freezing plastics, overly thick oil and such.  This type of dome would be rather like garages in northern climate mines.  No need for air pressure, in fact, just a fancy dome tent, really.

For heating there is the sun. The dome or tent only needs to keep the infrared in. The ground will warm up over time and keep the temperature from dropping too much over night.
Yes, I agree the infra red radiators may be overkill. In the middle of the Mars winter perhaps?  Might perhaps serve as a dust free enclosure as well, or at least a dust reduction area.
Title: Re: Elon Musk: glass geodesic domes
Post by: guckyfan on 11/17/2016 05:30 pm
Yes, I agree the infra red radiators may be overkill. In the middle of the Mars winter perhaps?  Might perhaps serve as a dust free enclosure as well, or at least a dust reduction area.

Much depends on how wide a temperature swing would be acceptable. Maybe different for domes with different purposes. Even with no heating the swings would be very much reduced. During summer they will probably need cooling, so lots of air flow.
Title: Re: Elon Musk: glass geodesic domes
Post by: Ionmars on 11/18/2016 12:11 pm
Reading the excellent posts on this thread leads me to propose a modified geodesic dome structure. This type of dome may be built on a larger scale yet provide higher safety margins. In this approach we would construct a series of very heavy-duty circular hoops as structural elements of the dome that are over-designed for tensional forces. The super-hoops would also have to be super-anchored, perhaps continuing under the dome and joining together underneath. The portions that contact the ground will have the support of the planetary mass and may be built lighter. I have sketched this idea in the attached file. The surface areas between these “super-hoops” will be filled with the same type of structural members and transparent panels as in the standard dome. 

The idea is to create super-strong members that can be treated mathematically the same as the ground surface itself.  The stress felt by the edges of the panes and the members holding them is not due to the tension stress of the entire dome, but just the smaller areas between the super-hoops. How much distance can we allow between the super-hoops to build the size dome that we want? How thick must the hoops be?

I realize that this approach requires a compromise of the beauty of the traditional geodesic dome. However, it may be a compromise worth considering for the sake of safety, especially if one thinks of the modified dome as having a poignant design appeal of its own. (Provided the rendering is much better than this crude sketch.)
Title: Re: Elon Musk: glass geodesic domes
Post by: KelvinZero on 11/18/2016 09:25 pm
In this approach we would construct a series of very heavy-duty circular hoops as structural elements of the dome that are over-designed for tensional forces..
I think a geodesic dome is sort of defined as being optimised for strong hoops.

No way can I do the math to compare your proposal to a traditional geodesic. I just say, absolutely. Hand it to the mathematicians to give us an optimally hooped dome, whatever that is.

Until proven otherwise I think we tend to assume geodesic but I don't think anyone is proposing going geodesic for aesthetic reasons if the math points to something else. At least we would have to see it and decide it was really really ugly.  :)
Title: Re: Elon Musk: glass geodesic domes
Post by: Ionmars on 11/19/2016 04:09 pm
I could probably do the math eventually, but I was hoping a better mathematician would happen by.
Title: Re: Elon Musk: glass geodesic domes
Post by: Rei on 11/19/2016 04:43 pm
Quote
For heating there is the sun. The dome or tent only needs to keep the infrared in. The ground will warm up over time and keep the temperature from dropping too much over night.

Greenhouses don't actually work that way (I've built multiple greenhouses).  Even on Earth, radiative heat loss occurs way too fast vs. how fast heat transfers in and out of the soil.  On Mars it would be even worse.  Plus, unless they have a very insulating glazing (aka, low light transmission, making the already-low light conditions even worse), in an environment like Mars they're not even going to be able to stay warm during the day from sunlight alone.

If you do have surplus heat during the day, it's possible to design active heat storage systems, where you vent air through heat exchangers into water or soil.  This of course means extra mass, and requires excess daytime heat.

If you have excess heat from another process (for example, nuclear reactor), then obviously you can just pump that in as your heat source. We do that here in Iceland with geothermal water.  But if what you have is electricity, by far the best way you can supply it is through lights.  Mars is low-light to begin with, and in bad dust storms can spend weeks in even lower light conditions.  Crops need vast amounts of light energy, way more than most people who've never grown them under artificial light envision.  This much lighting gives off large amounts of heat.  Some crops grow well in 24/7 lighting.  Others need staggered lighting, at least during certain parts of their growth cycle to induce flowering/fruiting.
Title: Re: Elon Musk: glass geodesic domes
Post by: Rei on 11/19/2016 04:47 pm
Reading the excellent posts on this thread leads me to propose a modified geodesic dome structure

That design will be vulnerable to torsion and lateral stress.  A geodesic by design resists torsion and stress equally from all directions.

That doesn't make them perfect.  From a mass perspective, the optimal shape involves trusses.  Geodesics are simpler to build than truss structures, but the bending moment of inertia is proportional to the thickness of a beam to its, what, third power?  Haven't done a FEA run in half a year so I'm a bit rusty  ;)  But basically if you want to maximize stress and minimize mass, you have a heirarchy of structural members, with small numbers of those of the greater thickness, leading to greater numbers of less thickness, and so forth, all the way to the glazing.

Of course, your lowest mass structures are pressure-supported.
Title: Re: Elon Musk: glass geodesic domes
Post by: guckyfan on 11/19/2016 04:52 pm
Quote
For heating there is the sun. The dome or tent only needs to keep the infrared in. The ground will warm up over time and keep the temperature from dropping too much over night.

Greenhouses don't actually work that way (I've built multiple greenhouses).  Even on Earth, radiative heat loss occurs way too fast vs. how fast heat transfers in and out of the soil.  On Mars it would be even worse.  Plus, unless they have a very insulating glazing (aka, low light transmission, making the already-low light conditions even worse), in an environment like Mars they're not even going to be able to stay warm during the day from sunlight alone.

Greenhouses on earth don't lose their heat through radiation. The glass cover of a greenhouse stops that. Plastic might not, but glass does. Glass greenouses lose heat due to atmospheric convection. Not so much on Mars with its thin atmosphere.

Title: Re: Elon Musk: glass geodesic domes
Post by: rds100 on 11/19/2016 05:07 pm

Domes sound fancy, but what about good old fashioned pyramids? To me it seems much easier to work with (and produce) flat surfaces.
Title: Re: Elon Musk: glass geodesic domes
Post by: Rei on 11/19/2016 05:09 pm
Hmm, I'm just thinking of glazing mounting here.  There's going to be some significant engineering work to do vs. Earth-based systems, traditional systems for handling thermal expansion and changes in loading stress aren't pressuretight.  The glazing basically floats within channels (with expansion gaps), which may or may not be sealed with silicone sealant, but are allowed to slide and breathe.  Spacecraft already deal with windows to some extent, but not to the extent of a greenhouse. 

The gas in-between the outer and inner layer(s) of the glazing raises interesting questions.  Here on Earth for polycarbonate panels for example we use an impermeable tape on the top end of the channels, and a permeable "dust tape" on the bottom that lets any water that condenses inside drain out (the top end goes underneath a ridge cap or overhang, while the bottom end is often buried slightly in the ground).  Mars doesn't have much water vapour, but it does have a little.  Anything that does freeze inside will never drain out, as water can't form a liquid on Mars conditions.  You might be able to bake it out though.  I sure hope the dust would never find a way in - you'd never get it out.  In an extreme case, such as a winter night, you could face CO2 freezing out, although it'd later thaw on its own.  You could instead go with a pressuretight approach for the inter-layer spacing, but that'd be more mass, more risk, and potentially more shipping volume (depending on the type of glazing).

Surely all solvable, but not the same as on Earth.  Again, approach of pressure-supported film greenhouses (including pressure-based glazing layer spacing) looks to be simplest and lowest mass (as you control the gas you're pumping into the inter-layer glazing space).
Title: Re: Elon Musk: glass geodesic domes
Post by: LMT on 11/19/2016 05:12 pm
Quote
For heating there is the sun. The dome or tent only needs to keep the infrared in. The ground will warm up over time and keep the temperature from dropping too much over night.

Greenhouses don't actually work that way (I've built multiple greenhouses).  Even on Earth, radiative heat loss occurs way too fast vs. how fast heat transfers in and out of the soil.  On Mars it would be even worse.  Plus, unless they have a very insulating glazing (aka, low light transmission, making the already-low light conditions even worse), in an environment like Mars they're not even going to be able to stay warm during the day from sunlight alone.

Greenhouses on earth don't lose their heat through radiation. The glass cover of a greenhouse stops that. Plastic might not, but glass does. Glass greenouses lose heat due to atmospheric convection. Not so much on Mars with its thin atmosphere.

For ref., cross-posting useful Mars dome heat loss calcs (http://forum.nasaspaceflight.com/index.php?topic=41427.msg1605830#msg1605830) from lamontagne.
Title: Re: Elon Musk: glass geodesic domes
Post by: Rei on 11/19/2016 05:46 pm
Greenhouses on earth don't lose their heat through radiation. The glass cover of a greenhouse stops that. Plastic might not, but glass does. Glass greenouses lose heat due to atmospheric convection. Not so much on Mars with its thin atmosphere.

I'll admit that my greenhouse work on Earth has been with plastic, and glass is a much better IR blocker than most plastics. I've read quite a few papers on Mars greenhouses, and all of them are in agreement about what I wrote about heating needs for Martian greenhouses.  Here's a random example:

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20050182966.pdf

p.101

That is to say: on Mars, almost all greenhouse heat loss is through radiation. Even with perfect blocking of IR through the glazing itself, the outer layer radiates the heat away.  The rate of heat loss is rapid, to the point that even during the day it's hard to keep up, and at night there's no reasonable way to keep up without supplemental heat.

Radiative heat loss is proportional to the temperature to the fourth power.  On Earth, half of your radiative heat exchange is with the ground, which is only slightly colder than the greenhouse (and on cloudy days, you're exchanging with the clouds).  On Mars, it's far cooler, and you're overwhelmingly exchanging directly with space above.  So you get almost nothing back.
Title: Re: Elon Musk: glass geodesic domes
Post by: guckyfan on 11/19/2016 07:27 pm
I have seen a greenhouse design with mass buffer to store heat over night. It is doable. Though if the greenhouse is small and the ratio between surface and volume is not good it would not be enough. Sun would still provide a major part of the heat.
Title: Re: Elon Musk: glass geodesic domes
Post by: Jcc on 11/19/2016 07:35 pm
How about insulating blankets that pull up at night and down in the morning?
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 11/19/2016 07:35 pm
Greenhouses on earth don't lose their heat through radiation. The glass cover of a greenhouse stops that. Plastic might not, but glass does. Glass greenouses lose heat due to atmospheric convection. Not so much on Mars with its thin atmosphere.

I'll admit that my greenhouse work on Earth has been with plastic, and glass is a much better IR blocker than most plastics. I've read quite a few papers on Mars greenhouses, and all of them are in agreement about what I wrote about heating needs for Martian greenhouses.  Here's a random example:

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20050182966.pdf

p.101

That is to say: on Mars, almost all greenhouse heat loss is through radiation. Even with perfect blocking of IR through the glazing itself, the outer layer radiates the heat away.  The rate of heat loss is rapid, to the point that even during the day it's hard to keep up, and at night there's no reasonable way to keep up without supplemental heat.

Radiative heat loss is proportional to the temperature to the fourth power.  On Earth, half of your radiative heat exchange is with the ground, which is only slightly colder than the greenhouse (and on cloudy days, you're exchanging with the clouds).  On Mars, it's far cooler, and you're overwhelmingly exchanging directly with space above.  So you get almost nothing back.
Thanks for the paper.  Very interesting.  I agree radiative heat loss is dominant in most cases.  I had no idea Martian atmosphere was so opaque, reducing illumination by 30% at the best of times.
I stand by my calculation that a second layer of glass with a film reduces radiative heat loss dramatically. The paper seems to only look at single layer materials. I have accounted for a 20% reduction in heat gain due to opacity of the glass, but that may be optimistic.
Changing the input because of extra opacity still leaves double glazed domes thermally positive most of the time, if my assumption that most of the incoming heat is conserved, either as sensible heat in materials or as latent heat in water evaporation from plants, is correct.
BTW i've just finished designing the HVAC for a very interesting project, a Medical grade cannabis growing facility, with 12x 600m2 grow rooms.  Its totally enclosed and makes no attempt at all at solar input.  The building has a 12h on 12h off cycle, with a tremendous heat load, most of the time.  It needs cooling all the time, and if the lights stay on and the cooling stops the plants die within the hour.  About 1000W per m2 of lighting power, so very close to the solar constant.  50% of the load is latent load, to drive evaporation and nutriment absorption.  I've found it an interesting analog to what we want to do  ;-)

Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 11/19/2016 07:38 pm
How about insulating blankets that pull up at night and down in the morning?

Yes, most/all greenhouses in Quebec, Canada, which has a number of analogies with Mars  ;-)  have them. Many of the are motorized with light sensors.  Glass greenhouses are no longer built, by the way, at least around here.  Plastic film is much cheaper.  Usually 2 layer, with fans do drive air into the layers.
Title: Re: Elon Musk: glass geodesic domes
Post by: LMT on 11/19/2016 07:53 pm
I have seen a greenhouse design with mass buffer to store heat over night. It is doable. Though if the greenhouse is small and the ratio between surface and volume is not good it would not be enough. Sun would still provide a major part of the heat.

A sunlit pond makes an excellent buffer.  Even better than, say, basalt, having 5x the specific heat capacity and 1.7x the energy density.
Title: Re: Elon Musk: glass geodesic domes
Post by: KelvinZero on 11/19/2016 07:57 pm
Domes sound fancy, but what about good old fashioned pyramids? To me it seems much easier to work with (and produce) flat surfaces.
This is probably off topic here because this spaceX thread is specifically about a comment Elon Musk made about domes.

On the face of it pyramids and flat surfaces seem crazy for holding pressure but I was thinking vaguely about starting a topic specifically on a cellular space-filling polyhedra sort of design that can be extended incrementally.

The strength comes from an internal lattice of struts so on a large scale it could be for example a pyramid or any shape you like.. sort of like Minecraft  :)

It is even possible the windows could be fairly flat because their strength might come from cables internally. There is an interesting design problem that you might want internal faces that could withstand pressure loss on either side. I would guess you could do better than just doubling up everything.

The cells might be a uniform 10x10m, but you could create interesting internal volumes by removing some internal faces.
Title: Re: Elon Musk: glass geodesic domes
Post by: guckyfan on 11/19/2016 08:30 pm
How about insulating blankets that pull up at night and down in the morning?

Yes, most/all greenhouses in Quebec, Canada, which has a number of analogies with Mars  ;-)  have them. Many of the are motorized with light sensors.  Glass greenhouses are no longer built, by the way, at least around here.  Plastic film is much cheaper.  Usually 2 layer, with fans do drive air into the layers.

Yes it could be high tensile plastic. I know that plastic beer bottles are sputtered from the inside with a thin layer of glass. The glass makes the PET bottles impermeable to oxygen which would otherwise spoil the taste of the beer quickly. I wonder if that thin layer is good enough to reflect infrared as effective as glass panes. The process can't be expensive or they could not use it for cheap beer bottles.
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 11/20/2016 12:54 am
Hmm, I'm just thinking of glazing mounting here. There's going to be some significant engineering work to do vs. Earth-based systems, traditional systems for handling thermal expansion and changes in loading stress aren't pressuretight. The glazing basically floats within channels (with expansion gaps)

You could potentially have a similar "floating" pane system, because of the pressure difference. Essentially use the force against the panes to press them against the frame. (A slightly flexible gasket between the two to provide the final air-seal.) Ie, the panes wouldn't be locked in place by anything accept air-pressure. The panes would then be able to thermally expand laterally with the same expansion gaps between panes.

(Think of the old coaster-under-the-inverted-glass-of-water trick.)

You need brackets/clips to hold the panes in place when the structure is unpressurised, obviously, but that's trivial compared to the pressurised loads.

Mars doesn't have much water vapour, but it does have a little.  Anything that does freeze inside will never drain out, as water can't form a liquid on Mars conditions.

During the day, peak-summer, the temperature of the outer layer will eventually match the inside of the greenhouse, regardless of the insulation.

Again, approach of pressure-supported film greenhouses (including pressure-based glazing layer spacing) looks to be simplest and lowest mass (as you control the gas you're pumping into the inter-layer glazing space).

It wouldn't be "film" if it needs to support 10 tonnes per square metre.
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 11/20/2016 12:55 am
Yes it could be high tensile plastic. I know that plastic beer bottles are sputtered from the inside with a thin layer of glass. The glass makes the PET bottles impermeable to oxygen which would otherwise spoil the taste of the beer quickly. I wonder if that thin layer is good enough to reflect infrared as effective as glass panes. The process can't be expensive or they could not use it for cheap beer bottles.

That would solve a number of problems. If you can trap your HT polymer under a flexible but still gas-impermeable layer of glass, you don't have to worry about vacuum outgasing enbrittlement; that opens up the entire menu of materials for the panels. Light, strong, vacuum-tolerant, gas-tight, IR-trapping. Win.

Domes sound fancy, but what about good old fashioned pyramids? To me it seems much easier to work with (and produce) flat surfaces.

Pyramids are compressive structures. Remember, the issue is that we're dealing with a pressure vessel.

(It's weird - stick a hab in space and everyone intuitively gets it. But the moment you put it on a surface, everyone goes back to thinking of unpressurised (or lightly pressurised) Earth structures.)

Likewise...

Of course, your lowest mass structures are pressure-supported.

This won't be "pressure supported", it will be a pressure vessel.

(Unless it's covered with 20+ metres of regolith, water or ice. Or made of several metres thickness solid steel.)
Title: Re: Elon Musk: glass geodesic domes
Post by: Robotbeat on 11/20/2016 04:17 am
Air supported structures are also pressure vessels and are under tension. You can make a pure tension structure lighter than one with flexure and compressive loads.
Title: Re: Elon Musk: glass geodesic domes
Post by: guckyfan on 11/20/2016 07:42 am
It wouldn't be "film" if it needs to support 10 tonnes per square metre.

Very recently we had a discussion on micrometeorite damage. There was mention of a document about a greenhouse tunnel design. It used "film" given in micron thickness, reenforced for tensile strength with a high tension fiber mesh. The fibers would take most of the tension and also act to stop the spread of leaks.

Maybe Robotbeat remembers better than me, where exactly it was.
Title: Re: Elon Musk: glass geodesic domes
Post by: KelvinZero on 11/20/2016 07:34 pm
Very recently we had a discussion on micrometeorite damage. There was mention of a document about a greenhouse tunnel design. It used "film" given in micron thickness, reenforced for tensile strength with a high tension fiber mesh. The fibers would take most of the tension and also act to stop the spread of leaks.

Way back here I calculated 2.5kg/m3 for polycarbonate.

https://en.wikipedia.org/wiki/Polycarbonate
...
..leading to M = 2.5V, or 2.5kg per m3

It is quite possible that I screwed up putting the numbers in. Also I don't actually know anything polycarbonate compared to other choices.

However I think this is the right direction: Come up with a kg/m3 number we can all use. It is the exact same number whether we are discussing sphere or dome, small or large. The mass of a pressure vessel scales with the volume, not the surface area. It is a very general, reusable result.

Do the people who are more familiar with the math agree? And if so, what value should we use, for what material? (I think my result was for exactly 1atm.. what pressure and what safety margin should we assume?)

Title: Re: Elon Musk: glass geodesic domes
Post by: MikeAtkinson on 11/21/2016 06:05 pm
I don't disagree in principle, but most of the strength will be in the struts, not the panels. So quite a bit less mass if using carbon fiber composite struts.
Title: Re: Elon Musk: glass geodesic domes
Post by: KelvinZero on 11/21/2016 06:35 pm
I don't disagree in principle, but most of the strength will be in the struts, not the panels. So quite a bit less mass if using carbon fiber composite struts.
Thats at me right? Yep that number probably isn't for the ideal material. You probably also have to factor in a safety margin which I didn't (unless you assume less than 1atm which is reasonable). I don't know what the right material, pressure or safety margin is so 2.5kg/m3 has no particular reason to be correct.
Title: Re: Elon Musk: glass geodesic domes
Post by: TripD on 11/21/2016 08:04 pm
If the plan for a blown out pane is to patch and fix before evacuating the atmosphere I would imagine that there has to be a significant structural margin in the struts.  If a temporary plate is going to fill the void while the pane is replaced I don't see any way around this patching plate slamming against the struts.
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 11/21/2016 10:12 pm
If the plan for a blown out pane is to patch and fix before evacuating the atmosphere I would imagine that there has to be a significant structural margin in the struts.  If a temporary plate is going to fill the void while the pane is replaced I don't see any way around this patching plate slamming against the struts.
There can also be a fair amount of torque on a beam that has lost a plate on one side.  My guess is that the plate seats will be as close as possible to the center-line of the structural beams, to reduce this torque.
Perhaps the hole could be filled using something less rigid than a spare plate, such as a strong foam blanket (some form of material that absorbs energy) with some carbon fiber rods, much wider than the typical structural space that could be 'thrown over' the hole from a distance? 
Title: Re: Elon Musk: glass geodesic domes
Post by: TripD on 11/22/2016 03:18 am
Spreading out the load seems a good idea in general.  How about a robotic sealer that tracks along a group of six panes and sits down slowly as it has a large valve to allow a softer action.

Edit/

   This same bot could be used on the outside to clean off dust, otherwise it might end up being the little bot that never gets used.  :o
Title: Re: Elon Musk: glass geodesic domes
Post by: Ionmars on 11/22/2016 02:18 pm
Spreading out the load seems a good idea in general.  How about a robotic sealer that tracks along a group of six panes and sits down slowly as it has a large valve to allow a softer action.

Edit/

   This same bot could be used on the outside to clean off dust, otherwise it might end up being the little bot that never gets used.  :o
A replacement panel for a leaking or blown-out panel should approach the damage area from the inside of the dome rather than the outside. This way the rush of air to the outside would draw the replacement panel towards the old panel frame. This rather than fighting against the current.

The outside bot could pass the replacement panel edgewise through a frame opening to the inside and insert from there.
Edit: This may require a thin wire loop embedded in the middle of each panel. Then the outside bot could be put to work during construction. Once the framework was built, the outside bot could install every panel.
Title: Re: Elon Musk: glass geodesic domes
Post by: LMT on 11/22/2016 03:45 pm
SpiderBot

Spreading out the load seems a good idea in general.  How about a robotic sealer that tracks along a group of six panes and sits down slowly as it has a large valve to allow a softer action.

Edit/

   This same bot could be used on the outside to clean off dust, otherwise it might end up being the little bot that never gets used.  :o

"SpiderBot, SpiderBot.  Does whatever a SpiderBot does." 

Ref. (http://simpsons.wikia.com/wiki/Spider-Pig_(song))

https://www.youtube.com/watch?v=86EAzvXrESg
Title: Re: Elon Musk: glass geodesic domes
Post by: TripD on 11/22/2016 03:45 pm
@Ionmars   Yah it doesn't show perspective very well, but the view shown is actually on the inside.  Sorry about the confusion.
Title: Re: Elon Musk: glass geodesic domes
Post by: Ionmars on 11/23/2016 07:21 am
@Ionmars   Yah it doesn't show perspective very well, but the view shown is actually on the inside.  Sorry about the confusion.
Sounds good.
Skunkworks will still have a challenge to transfer this technology from an airship to a dome on Mars; particularly where  trusses are employed between panels. The machine couldn't slide over the surface without bumping into ridges. No doubt you will find a good solution and I hope you will have the chance to develop it. :)
Title: Re: Elon Musk: glass geodesic domes
Post by: Ionmars on 11/23/2016 08:47 am
This post is a follow-up to my previous Reply #313 in this thread. Here I present a better sketch of the modified dome structure and a further modification. The idea is to employ a series of “super-hoops” that are over-designed to resist tension forces. In this way we can design the paneled areas to resist the tensional forces between these hoops and not for the total force against the entire dome. Note that the hoops over the center of the dome are the largest and therefore have been made thicker (stronger) as compared to those near the periphery.

The new change is that the panel coverings between hoops are not flat, but are dome-shaped. This is analogous to a domed roof over a tunnel, but here the domed tunnel is draped over the larger dome structure. The reason is that smaller domed roofs can resist greater tensional force. In this example the distance between hoops is arbitrarily set to 40 meters, a distance that a domed-roof could span with a good safety margin. The result is a large dome of about 230 meters.
Title: Re: Elon Musk: glass geodesic domes
Post by: Rei on 11/23/2016 10:59 am
This post is a follow-up to my previous Reply #313 in this thread. Here I present a better sketch of the modified dome structure and a further modification. The idea is to employ a series of “super-hoops” that are over-designed to resist tension forces.

Just like I wrote last time:

Quote
That design will be vulnerable to torsion and lateral stress.  A geodesic by design resists torsion and stress equally from all directions.

That doesn't make them perfect.  From a mass perspective, the optimal shape involves trusses.  Geodesics are simpler to build than truss structures, but the bending moment of inertia is proportional to the thickness of a beam to its, what, third power?  Haven't done a FEA run in half a year so I'm a bit rusty  ;)  But basically if you want to maximize stress and minimize mass, you have a heirarchy of structural members, with small numbers of those of the greater thickness, leading to greater numbers of less thickness, and so forth, all the way to the glazing.

Of course, your lowest mass structures are pressure-supported.

The last time I designed a greenhouse, it was an isogrid, about twice as long as it was wide, so I tried using the asymmetry to allow me to focus reinforcements predominantly on the narrow axis.  It didn't work, even in that "easier" case.  The shape tries to twist or lean and overload the weaker elements on the long axis.

The same will happen to you here, but even moreso.  If you try to put all of your strength on one axis, it'll transfer to the weak elements and overstress them.

Also: it's nice and easy to draw a bunch of random elements.  It's a whole different ballgame when you have to actually join them together in a buildable fashion.  And account for the strength of the joints in your FEA run.
Title: Re: Elon Musk: glass geodesic domes
Post by: Rei on 11/23/2016 11:15 am
On the upside: unlike on Earth, most of your stress on Mars is self-loading.  Your wind / snow and even dust loads will be very small.  And of course gravity is lower.  Only in cases where you want to pile regolith on top do you have to deal with heavy loadings per square meter.

Anchoring will be a pain, however.  Maybe earth screws?  Better pick an area that's not shallowly underlain by bedrock...

Just thinking about the environment... I'm betting that corrosion between dissimilar metals is going to be huge.  Normally your panels basically act like charge collectors even on Earth, accelerating corrosion between, for example, an aluminum frame and stainless bolts, or whatnot.  But on Mars they'll be far more effective at it.  Every last element that contacts every last other element better be very resistant to galvanic corrosion, w/proper isolation.

(I know some people have talked about CF-framing.... I've never heard of anyone making a CF-framed greenhouse, so I have no clue how well that'd actually work.  They make fiberglass greenhouses (I never have), which are good in some regards, but vulnerable to UV and are flammable.  But CF with an advanced binder might be able to work around that (at significantly greater material cost - but that's typical for space applications)
Title: Re: Elon Musk: glass geodesic domes
Post by: LMT on 11/23/2016 02:01 pm
Storm Corrosion (Of Love & Emotion)

Just thinking about the environment... I'm betting that corrosion between dissimilar metals is going to be huge.  Normally your panels basically act like charge collectors even on Earth, accelerating corrosion between, for example, an aluminum frame and stainless bolts, or whatnot.  But on Mars they'll be far more effective at it.  Every last element that contacts every last other element better be very resistant to galvanic corrosion, w/proper isolation.

Yeah, I recall Stan-1967 joked about setting up an electroplating shop.  ISRU++.  (Hi Stan.)

Cathodic protection would seem necessary.  I think magnesium anodes (http://www.martyranodes.com/content/martyr-products-services/pleasurecraft-anodes/Mag.php) should protect common frame metals:  titanium, aluminum, iron (with ISRU), whether above ground or underwater.  Carbon fiber also, I guess, judging from C electronegativity; though carbon fiber suffers underwater for other reasons (https://forum.nasaspaceflight.com/index.php?topic=41526.msg1605042#msg1605042).

Magnesium would be sacrificed rapidly at the anodes.  I suppose it could be reprocessed, or else replenished relatively easily from basaltic sand, via for example the Calera CO2 sequestration process (http://adsabs.harvard.edu/abs/2010AGUFMGC31C0889J), which one might use for Ca/Mg fertilizer production (http://forum.nasaspaceflight.com/index.php?topic=35877.msg1579199#msg1579199) anyway.

https://www.youtube.com/watch?v=RAlC75xG4qU

https://www.youtube.com/watch?v=xTBsaOjbLKE
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/23/2016 02:54 pm
On the upside: unlike on Earth, most of your stress on Mars is self-loading.  Your wind / snow and even dust loads will be very small.  And of course gravity is lower.  Only in cases where you want to pile regolith on top do you have to deal with heavy loadings per square meter.

Anchoring will be a pain, however.  Maybe earth screws?  Better pick an area that's not shallowly underlain by bedrock...

Just thinking about the environment... I'm betting that corrosion between dissimilar metals is going to be huge.  Normally your panels basically act like charge collectors even on Earth, accelerating corrosion between, for example, an aluminum frame and stainless bolts, or whatnot.  But on Mars they'll be far more effective at it.  Every last element that contacts every last other element better be very resistant to galvanic corrosion, w/proper isolation.

(I know some people have talked about CF-framing.... I've never heard of anyone making a CF-framed greenhouse, so I have no clue how well that'd actually work.  They make fiberglass greenhouses (I never have), which are good in some regards, but vulnerable to UV and are flammable.  But CF with an advanced binder might be able to work around that (at significantly greater material cost - but that's typical for space applications)
Because his is more of a giant pressure vessel than a greenhouse.  And the bigger it gets, the harder it is to build.

Title: Re: Elon Musk: glass geodesic domes
Post by: Oersted on 11/23/2016 03:47 pm

Domes sound fancy, but what about good old fashioned pyramids? To me it seems much easier to work with (and produce) flat surfaces.

A geodesic dome is composed of flat surfaces and very few different elements. That is the beauty of it.
Title: Re: Elon Musk: glass geodesic domes
Post by: Ionmars on 11/23/2016 07:28 pm
...
...
The last time I designed a greenhouse, it was an isogrid, about twice as long as it was wide, so I tried using the asymmetry to allow me to focus reinforcements predominantly on the narrow axis.  It didn't work, even in that "easier" case.  The shape tries to twist or lean and overload the weaker elements on the long axis.

The same will happen to you here, but even moreso.  If you try to put all of your strength on one axis, it'll transfer to the weak elements and overstress them.

Also: it's nice and easy to draw a bunch of random elements.  It's a whole different ballgame when you have to actually join them together in a buildable fashion.  And account for the strength of the joints in your FEA run.
Thanks for sharing your experience. My intuition and some of the earlier posts were wrong. So as the size of dome increases you should only increase the thickness and strength of all members equally. Eventually the members are so thick as to crowd out any usable glass panes. Se la vie, Elon.
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/23/2016 10:07 pm
...
...
The last time I designed a greenhouse, it was an isogrid, about twice as long as it was wide, so I tried using the asymmetry to allow me to focus reinforcements predominantly on the narrow axis.  It didn't work, even in that "easier" case.  The shape tries to twist or lean and overload the weaker elements on the long axis.

The same will happen to you here, but even moreso.  If you try to put all of your strength on one axis, it'll transfer to the weak elements and overstress them.

Also: it's nice and easy to draw a bunch of random elements.  It's a whole different ballgame when you have to actually join them together in a buildable fashion.  And account for the strength of the joints in your FEA run.
Thanks for sharing your experience. My intuition and some of the earlier posts were wrong. So as the size of dome increases you should only increase the thickness and strength of all members equally. Eventually the members are so thick as to crowd out any usable glass panes. Se la vie, Elon.

Actually the struts can grow linearly in width, and linearly in thickness, giving you what your need w/o reducing the fraction of "open sky".

However, as you grow in diameter, you start paying a lot for unused volume.  You then start looking at partial domes, so at least you're not wasting skin, but structurally, you don't get get a break.  a 50 m diameter 120-dome and 180-dome requires the same thickness.

So this really moves you towards a large number of smaller units, and if you're in the 5-10 m range, full spheres start gaining an advantage compared to just domes.

So I'm predicting a combination of both:  up to 50 m diameter partial domes, and up to 10 m diameter full spheres.

For larger enclosed volumes - subtropolis-type excavations.  Maybe even in salt deposits.


Title: Re: Elon Musk: glass geodesic domes
Post by: Rei on 11/23/2016 10:20 pm
...
...
The last time I designed a greenhouse, it was an isogrid, about twice as long as it was wide, so I tried using the asymmetry to allow me to focus reinforcements predominantly on the narrow axis.  It didn't work, even in that "easier" case.  The shape tries to twist or lean and overload the weaker elements on the long axis.

The same will happen to you here, but even moreso.  If you try to put all of your strength on one axis, it'll transfer to the weak elements and overstress them.

Also: it's nice and easy to draw a bunch of random elements.  It's a whole different ballgame when you have to actually join them together in a buildable fashion.  And account for the strength of the joints in your FEA run.
Thanks for sharing your experience. My intuition and some of the earlier posts were wrong. So as the size of dome increases you should only increase the thickness and strength of all members equally. Eventually the members are so thick as to crowd out any usable glass panes. Se la vie, Elon.

Not exactly.  Again, I've mainly dealt with plastic, but with polycarbonate panels, if you want longer spans, you simply use thicker panels.  Increase the panel thickness and you increase its bending moment of inertia, proportional to the third power of the thickness.  Now, there are practical issues to take into account; if the gap between the two layers gets too large, it loses insulative ability because gas moves around too readily, so you start having to add more layers.  In addition to the number of layers having light-absorbing properties, each additional layer also has an inherent degree of scattering/reflection.  So for example, here in Iceland, which is rather low light by Earth standards, but with relatively mild winters and cheap heating, double layer is usually optimal, which caps you off at about 12mm panels.  But in a place like Minnesota where light is more abundant but heating problems more challenging, you'd probably want at least three layers, if not more.

With your structural elements, the same scaling factors apply.  Increase the thickness a little bit on a given beam axis, the moment of inertia increases dramatically on that axis.  So this is what you have to work against the problems of increasing spans, wherein your stress increases proportional to the third power and your deformation to the fourth power.  Now, your mass increases a lot as you start increasing the dimensions of a beam on each axis, so what you do if that becomes too much of a problem is you instead make trusses, which dramatically increases the effective thickness of the "beam" (now truss).  But of course that comes at a the cost of a lot more joints, which is more engineering work, construction work, complexity, etc.  And on and on it goes.

Basically, there's countless options when it comes to construction, and lots of tradeoffs.  So you define your parameters - what sort of dimensions you want, what sort of spans, what your environmental conditions are, what your construction methods will be, etc, and then you work through progressive iterations to find what is - as a whole - the optimal solution.

I'll point out that I haven't done any work with structures where you have an elevated internal pressure.  As a general rule, optimized structures in tension tend to be lighter than ones in compression, so it's understandable why NASA has done a lot of looking into inflatable greenhouses.  A lot of such papers I've seen for "inflated" structures these days tend to focus on plastic films (of a variety of types) reinforced with a high tensile matrix, often most vectran.  Your typical non-biaxially oriented plastic may have a couple dozen MPa tensile strength (higher for more crystalline plastics, lower for non-crystalline, in general).  A biaxially oriented one may be in the ballpark of 200MPa or so.  But high strength unaxial fibers are several GPa.  So obviously you want the stresses born by fibers, but with broader sheeting in-between.  And generally you want a multlayer sheet because each type of layer provides different properties - tensile strength, elastic modulus, gas permeability (often different between water vs. other compounds), UV resistance, abrasion resistance, fog resistance / antifouling, transparency in different parts of the spectrum, and so on.  And these parameters often vary tremendously - permeability differences can be across many orders of magnitude, for example.  Then there's issues of manufacturing, bonding, packaging (foldability), and on and on...  :)

Title: Re: Elon Musk: glass geodesic domes
Post by: LMT on 11/24/2016 02:46 am
No(de) Limits

Noodling a basic Thistle Dome GSA: 

Abaqus CAE pops out a structural module with ballpark properties.  But a full Thistle Dome with hundreds of modules and fine mesh / realistic stresses will blow past the Abaqus Student Edition limit of 1000 nodes. 

Question:  Anybody seen or heard tell of a comparable structural shareware with unlimited nodes?

Computing time isn't a problem.  Mesh oversimplification is a full-stop problem, on even a tiny dome segment.

https://www.youtube.com/watch?v=EKBstPFnyMY
Title: Re: Elon Musk: glass geodesic domes
Post by: oiorionsbelt on 11/25/2016 11:34 pm
There has been a lot of discussion about anchoring these domes but as they will be pressurized, how would they be sealed where the dome meets the regolith?
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 11/25/2016 11:47 pm
There has been a lot of discussion about anchoring these domes but as they will be pressurized, how would they be sealed where the dome meets the regolith?
Either the wall is buried a few feet down,or there is an airtight membrane brought in towards the center of the floor.
Title: Re: Elon Musk: glass geodesic domes
Post by: oiorionsbelt on 11/26/2016 12:00 am
There has been a lot of discussion about anchoring these domes but as they will be pressurized, how would they be sealed where the dome meets the regolith?
Either the wall is buried a few feet down,or there is an airtight membrane brought in towards the center of the floor.
Could a "ridgid floor" solve both sealing and anchoring issues?
Title: Re: Elon Musk: glass geodesic domes
Post by: oiorionsbelt on 11/26/2016 12:02 am
Something along these lines perhaps.
https://www.technologyreview.com/s/545216/materials-scientists-make-martian-concrete/
Title: Re: Elon Musk: glass geodesic domes
Post by: Aussie_Space_Nut on 11/26/2016 12:40 am
I wanted to try and get my head around these Geodesic Domes so I decided to model one up. I chose a "Kite" shape as only 1 panel shape is reguired for a sphere, or 3 panel shapes for a half dome. (The Kite panel and both its LH and RH half.)

My thinking was a flat pack dome/sphere.

I found that the Kite panel became too large, IMHO, for large 100 metre domes.

I think though they could be used to finish either end of a "Tube" style dwelling. But even then the interface between the half dome and the tube becomes a problem due to the "facets" of the dome meeting the smooth curve of the tube.

In the end I think the whole Geodesic idea is great for "Cool Looking Architecture" here on Earth but for Mars is simply impractical. Not saying it cant be done, I just dont think it can be done easily. Happy to be proved wrong though!

Title: Re: Elon Musk: glass geodesic domes
Post by: Aussie_Space_Nut on 11/26/2016 12:45 am
For my second dome attempt I tried panels which all had the same edge length. A Triangel, Square and Pentagon plus their LH & RH half panels. My conclusions were same as before. The panels just get too big to handle.

Title: Re: Elon Musk: glass geodesic domes
Post by: LMT on 11/26/2016 01:49 am
I found that the Kite panel became too large, IMHO, for large 100 metre domes...  In the end I think the whole Geodesic idea is great for "Cool Looking Architecture" here on Earth but for Mars is simply impractical. Not saying it cant be done, I just dont think it can be done easily. Happy to be proved wrong though!

Just noting an artistic scaling similarity in National Geographic's "Mars".  Their largest geodesic at "Olympus Town (http://www.architecturaldigest.com/story/mars-set-design-national-geographic)" is a cramped common area dome, ~15 m diameter. 

So is this the largest hab the show's advisers thought practical as a geodesic?  Was there a kinematic scaling problem, such as the scaling of pressure vessel wall thickness with radius? 

Or is it just a TV budget thing? 

(https://assets.wired.com/photos/w_1534/wp-content/uploads/2016/10/3956_MARS_31MAY2016NATGEO.jpg)
Title: Re: Elon Musk: glass geodesic domes
Post by: Aussie_Space_Nut on 11/26/2016 03:02 am
Geodesic Dome website I found helpful.

https://simplydifferently.org/Geodesic_Polyhedra?page=0
Title: Re: Elon Musk: glass geodesic domes
Post by: Aussie_Space_Nut on 11/26/2016 11:22 am
I thought I would try 1 more. I used the equal edge length pentagon, square & triangle. However I divided up the pentagon into triangles and the square into triangles. This gave me 3 basic triangles of similar size.

Title: Re: Elon Musk: glass geodesic domes
Post by: Aussie_Space_Nut on 11/26/2016 12:05 pm
Yes, scaling up. Because it's a pressure vessel I think the discussion about high loads for large domes at the base is fair enough.

As others have said I think you could make a pressurised sphere easily enough if you make it small enough that your panels are easy to manage.

Half domes I'm not so sure.

And here is the thing, if your sphere is small why bother going Geodesic? You might as well just use plain old segments of a sphere. Probably much easier to make.

So what is the great attraction regarding geodesic spheres/domes?

Why aren't all our large pressure vessels here on Earth geodesic in shape?

I think we fantasize about geodesic shapes because they look cool. I'm beginning to wonder if that is the sole reason for employing them in futuristic designs. :-)
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 11/26/2016 03:18 pm
Yes, scaling up. Because it's a pressure vessel I think the discussion about high loads for large domes at the base is fair enough.

As others have said I think you could make a pressurised sphere easily enough if you make it small enough that your panels are easy to manage.

Half domes I'm not so sure.

And here is the thing, if your sphere is small why bother going Geodesic? You might as well just use plain old segments of a sphere. Probably much easier to make.

So what is the great attraction regarding geodesic spheres/domes?

Why aren't all our large pressure vessels here on Earth geodesic in shape?

I think we fantasize about geodesic shapes because they look cool. I'm beginning to wonder if that is the sole reason for employing them in futuristic designs. :-)
It's the flat packing and relatively small panes that are attractive.

Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 11/26/2016 07:59 pm
Yes, scaling up. Because it's a pressure vessel I think the discussion about high loads for large domes at the base is fair enough.

As others have said I think you could make a pressurised sphere easily enough if you make it small enough that your panels are easy to manage.

Half domes I'm not so sure.

And here is the thing, if your sphere is small why bother going Geodesic? You might as well just use plain old segments of a sphere. Probably much easier to make.

So what is the great attraction regarding geodesic spheres/domes?

Why aren't all our large pressure vessels here on Earth geodesic in shape?

I think we fantasize about geodesic shapes because they look cool. I'm beginning to wonder if that is the sole reason for employing them in futuristic designs. :-)
We don't use geodesic domes because our pressure vessels are made from weldable ductile materials, i.e. steel, and not glass :-)  IF we made steel domes on Mars, they wouldn't be geodesic either. 
We also don't use them because we can use large flat sheets to cover areas, and these are cheaper to build. Geodesic domes are interesting in just a few special cases, Martian domes may be one of them.
I wouldn't be surprised though if we could get about the same results with domes that used principal and secondary structures, and a lot of variously sized glass panes.  Admittedly, for tension structures, the advantages of I beams mostly go away.

Title: Re: Elon Musk: glass geodesic domes
Post by: DusanC on 12/09/2016 12:27 pm
IMHO inflatable half cylindrical structures are better, something like bubble insulated greenhouses:

(http://www.solarbubblebuild.com/bubble_greenhouse_test_cell/img/test_cell.jpg)

Upsides:
1. Lower mass/usable surface ratio- I emphasize this as domes have large unused volume above, if you want to use it you have to make additional construction and you block sunlight;
2. Easier construction;
3. You can make segments easier so that damage in one segment doesn't depressurize everything;
4. Easier to expand;

Active bubble foam insulation between double outer wall is a great way to manage temperature, it works like this:

(http://www.solaripedia.com/images/large/2413.gif)
Title: Re: Elon Musk: glass geodesic domes
Post by: KelvinZero on 12/09/2016 05:36 pm
This particular forum is spaceX-specific, and the thread OP about a specific Elon comment about glass geodesic domes.

That looks quite interesting and might deserve it's own thread. There was a big discussion about retaining heat (I think it was in the mars power thread, in the Mars forum). My only other comment is that you would go full cylinder. The pressure is about 10 tons per square meter and your diagram looks like it could be adapted to a full cylinder quite readily due to all that stuff going on in the bottom half. No need to mess around with tent pegs :-)

Title: Re: Elon Musk: glass geodesic domes
Post by: DusanC on 12/09/2016 08:18 pm
This particular forum is spaceX-specific, and the thread OP about a specific Elon comment about glass geodesic domes.
I know, just wanted to show that IMHO this is one of Elons ''It's a cool idea, but in few years we'll probably do something totaly different'' statements.

That looks quite interesting and might deserve it's own thread. There was a big discussion about retaining heat (I think it was in the mars power thread, in the Mars forum). My only other comment is that you would go full cylinder. The pressure is about 10 tons per square meter and your diagram looks like it could be adapted to a full cylinder quite readily due to all that stuff going on in the bottom half. No need to mess around with tent pegs :-)
Just stole the image of google search, enough to show the idea ;)
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 12/10/2016 05:54 pm
[...]

Repost your comment in the more general habitat thread: Envisioning Amazing Martian Habitats (https://forum.nasaspaceflight.com/index.php?topic=41427.0)
Title: Re: Elon Musk: glass geodesic domes
Post by: mapp3d on 01/16/2019 11:42 am
Good morning,
I've been collaborating for some time on a blog of a geodesic domes company, and I'd like to write an article about Elon Musk's crystal domes, would any of you have or could you give me more information and photos about this project?

Thank you very much in advance, and if anyone is interested in reading more articles about geodesic domes, I leave here the link to the website with which I collaborate.
https://www.geodomes.es (https://www.geodomes.es)
If it is not allowed to add a link, I ask the moderators to edit the article, since it is not my intention to spam.
Title: Re: Elon Musk: glass geodesic domes
Post by: Ludus on 01/19/2019 07:23 pm
Elon seems to have become pretty fond of Sprung structures.
https://www.sprung.com/?gclid=CjwKCAiAsoviBRAoEiwATm8OYCVyOjyINPnYJXYc8JriLT7sRoFnt9h3JBGTqyU_mjRT_j3Pt1HSZBoCE28QAvD_BwE (https://www.sprung.com/?gclid=CjwKCAiAsoviBRAoEiwATm8OYCVyOjyINPnYJXYc8JriLT7sRoFnt9h3JBGTqyU_mjRT_j3Pt1HSZBoCE28QAvD_BwE)

They’ve shown up at Tesla in Fremont for an assembly line, at the Long Beach site and in Boca Chica. They might adapt to Mars too.
Title: Re: Elon Musk: glass geodesic domes
Post by: nacnud on 01/19/2019 07:35 pm
With the difference in pressure wouldn't a sprung structure on Mars effectively be an inverted version of a sprung structure on Earth. You would have cables holding in a fabric membrane on Mars in rather that ridged spars holding a fabric membrane out on Earth.
Title: Re: Elon Musk: glass geodesic domes
Post by: docmordrid on 01/19/2019 08:28 pm
>
You would have cables holding in a fabric membrane on Mars in rather that ridged spars holding a fabric membrane out on Earth.

More likely the Sprung frame or a mesh on the outside and fabric walls inside.  Extra points if said mesh can produce a magnetosphere.
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 01/19/2019 09:34 pm
With pressure on the inside, you don't need a sprung structure, it'll be entirely tensile.

Although you might have a minimal frame to support the unpressurised mass of the pressure-vessel during construction, and depressurised maintenance. But that can involve removable internal supports, scaffolding, it doesn't actually have to be self-supporting open spans.
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 01/19/2019 10:11 pm
Or, work the Sprung on making pressurized domes.  The overall design will be different, but the devil's in the details and they have a lot of real-life experience.

Just like the Caldwell water tower company.
Title: Re: Elon Musk: glass geodesic domes
Post by: docmordrid on 01/19/2019 10:16 pm
Or, work the Sprung on making pressurized domes.  The overall design will be different, but the devil's in the details and they have a lot of real-life experience.

Just like the Caldwell water tower company.

Sprung has Arctic experience,

https://www.sprung.com/case-study/arctic-watch-wilderness-lodge/
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 01/19/2019 10:55 pm
Or, work the Sprung on making pressurized domes. The overall design will be different, but the devil's in the details and they have a lot of real-life experience.

Yes, Sprung, capital-S, the company, might have the skills to design a pressure vessel suitable for Mars. But it won't be based on the "sprung" spans, little-s, that their existing buildings are based around. The second sentence was the point I was trying to make.

People have a tendency to point at a picture of pretty much any novel Earth-structure and shout "on Mars!" But it's meaningless if you don't look at how that structure works on Earth, look at the problem it's trying to solve, and ask whether that's at all related to the completely different requirements you need on Mars. There's nothing about Sprung's self-supporting buildings, or geodesic domes to bring it back to the topic, or domes in general, that makes them suitable for Mars just because they vaguely resemble the sci-fi images we all know and love.

Does Sprung (the company) have the engineering skills to design a Mars-hab? Maybe. Does their experience with building clever compressive structures on Earth give them any more insight that any other company with structural engineering experience on Earth? No.
Title: Re: Elon Musk: glass geodesic domes
Post by: Slarty1080 on 01/20/2019 12:27 am
With pressure on the inside, you don't need a sprung structure, it'll be entirely tensile.

Although you might have a minimal frame to support the unpressurised mass of the pressure-vessel during construction, and depressurised maintenance. But that can involve removable internal supports, scaffolding, it doesn't actually have to be self-supporting open spans.

Very true. I think some people has missed this point and don't see pressure as being a major issue. Here's one way to help visualise the pressure at work here:

Think of a big 2-3m deep swimming pool on Earth with a glass bottom looking down into a basement. How big a free span would you be comfortable with in that basement?

Turn that upside down and that's the sort of pressure the Mars dome would have to contain. It's manageable but it's a considerable force especially if you are considering a very large dome.

Title: Re: Elon Musk: glass geodesic domes
Post by: Ludus on 01/20/2019 06:48 am
Sprung is just a family name. The company goes back to the nineteenth century making light prefab structures though.
Title: Re: Elon Musk: glass geodesic domes
Post by: meekGee on 01/20/2019 01:03 pm
Or, work the Sprung on making pressurized domes. The overall design will be different, but the devil's in the details and they have a lot of real-life experience.

Yes, Sprung, capital-S, the company, might have the skills to design a pressure vessel suitable for Mars. But it won't be based on the "sprung" spans, little-s, that their existing buildings are based around. The second sentence was the point I was trying to make.

People have a tendency to point at a picture of pretty much any novel Earth-structure and shout "on Mars!" But it's meaningless if you don't look at how that structure works on Earth, look at the problem it's trying to solve, and ask whether that's at all related to the completely different requirements you need on Mars. There's nothing about Sprung's self-supporting buildings, or geodesic domes to bring it back to the topic, or domes in general, that makes them suitable for Mars just because they vaguely resemble the sci-fi images we all know and love.

Does Sprung (the company) have the engineering skills to design a Mars-hab? Maybe. Does their experience with building clever compressive structures on Earth give them any more insight that any other company with structural engineering experience on Earth? No.
Again, the overall geometry is not applicable.  But that's only a small portion of their know-how.

Lightweight durable skins, connecting such skins to rigid members in a way that's compatible with being deployed outdoors, the beam structure itself, the logistics of transport and deployment - all very applicable if they have the passion to go there.
Title: Re: Elon Musk: glass geodesic domes
Post by: spacenut on 01/20/2019 03:28 pm
What would it take to be able to manufacture glass on Mars to avoid transporting from earth?  Natural gas (Methane) for melting the silicone can be made for rocket fuel and maybe some used to manufacture glass.  Can it be made like safety glass on car windshields on Mars?  Making the glass panels small and double pane to interlock in a geodesic dome or tunnel would allow for easier repair without depressurizing the habitat. 
Title: Re: Elon Musk: glass geodesic domes
Post by: Jcc on 01/20/2019 05:46 pm
What would it take to be able to manufacture glass on Mars to avoid transporting from earth?  Natural gas (Methane) for melting the silicone can be made for rocket fuel and maybe some used to manufacture glass.  Can it be made like safety glass on car windshields on Mars?  Making the glass panels small and double pane to interlock in a geodesic dome or tunnel would allow for easier repair without depressurizing the habitat.

For applications that require a large amount of heat, how about direct solar thermal:
https://en.m.wikipedia.org/wiki/Ivanpah_Solar_Power_Facility

(Applications like glass making, iron refining, etc.)
Title: Re: Elon Musk: glass geodesic domes
Post by: spacenut on 01/20/2019 05:59 pm
Electric melting of glass is not efficient, electric heat is not efficient in general, at least on earth.  A gas furnace can melt glass easier, unless solar can be concentrated directy on the silicone, or directly on iron, aluminum etc and can get hot enough.  The plant you referenced got the water to 550° C.  Pretty hot, but silicone melts at 1,400° C, while aluminum is 660° C.  Can a reflective solar plant on Mars get as hot as it does on earth?
Title: Re: Elon Musk: glass geodesic domes
Post by: AC in NC on 01/20/2019 06:16 pm
ISTM that challenges are:

Clean raw material:   http://planete-mars.com/a-mars-colony-a-tentative-technical-analysis/14/

Quote
Glass and ceramics
Mars clays should enable the manufacture of ceramics, while silica, ubiquitous, will allow producing glass. One problem though: the Martian silica will be obtained from a sand rich in Fe2O3 iron oxide (hematite) that we must get rid of if we want to get a good optical quality glass. This can be done by reducing Fe2O3 with carbon monoxide and segregating the iron thus obtained. From glass, we can also manufacture glass fiber, useful for elaborating composites.

Energy:  https://www.lowtechmagazine.com/what-is-the-embodied-energy-of-materials.html

Quote
Energy to Produce Glass per KG(from sand, etc): 18-35 MJ (5 to 9.7 KWhrs)
Title: Re: Elon Musk: glass geodesic domes
Post by: Jcc on 01/20/2019 06:56 pm
Electric melting of glass is not efficient, electric heat is not efficient in general, at least on earth.  A gas furnace can melt glass easier, unless solar can be concentrated directy on the silicone, or directly on iron, aluminum etc and can get hot enough.  The plant you referenced got the water to 550° C.  Pretty hot, but silicone melts at 1,400° C, while aluminum is 660° C.  Can a reflective solar plant on Mars get as hot as it does on earth?

There's this: https://www.youtube.com/watch?v=L2dvwdbQshQ

But mainly I was thinking of using direct solar to "preheat" the materials to bring them closer to the temperature needed and reducing the amount of electric or combustion heating.
Title: Re: Elon Musk: glass geodesic domes
Post by: RonM on 01/20/2019 08:20 pm
Electric melting of glass is not efficient, electric heat is not efficient in general, at least on earth.  A gas furnace can melt glass easier, unless solar can be concentrated directy on the silicone, or directly on iron, aluminum etc and can get hot enough.  The plant you referenced got the water to 550° C.  Pretty hot, but silicone melts at 1,400° C, while aluminum is 660° C.  Can a reflective solar plant on Mars get as hot as it does on earth?

Industrial solar furnace would work. Focused properly, they can easily melt glass. But an industrial solar furnace would use a lot of large mirrors, especially on Mars. Look at the size of the example on Wikipedia.

https://en.wikipedia.org/wiki/Solar_furnace
Title: Re: Elon Musk: glass geodesic domes
Post by: Slarty1080 on 01/20/2019 08:28 pm
Electric melting of glass is not efficient, electric heat is not efficient in general, at least on earth.  A gas furnace can melt glass easier, unless solar can be concentrated directy on the silicone, or directly on iron, aluminum etc and can get hot enough.  The plant you referenced got the water to 550° C.  Pretty hot, but silicone melts at 1,400° C, while aluminum is 660° C.  Can a reflective solar plant on Mars get as hot as it does on earth?
I think you mean silica (silicon dioxide)
Title: Re: Elon Musk: glass geodesic domes
Post by: nacnud on 01/20/2019 09:14 pm
A light furnace can heat things as hot as the thing that emits the light, which in this case is the surface of the sun, so 3500°C.
Title: Re: Elon Musk: glass geodesic domes
Post by: RobLynn on 01/20/2019 09:54 pm
A light furnace can heat things as hot as the thing that emits the light, which in this case is the surface of the sun, so 3500°C.

Could probably find a lot of uses for a big Martian mirror field placed on a steep equator-facing hill side.

Could be redirected for occasional high-power localised needs like baking soil for volatiles, or rovers so that they didn't need such large batteries or panels themselves.  Could melt areas of the surface to create smooth roadways or landing pads or to provide primary energy input to materials and chemical processing.

And the rest of the time could be used for enhancing green-house operation.
Title: Re: Elon Musk: glass geodesic domes
Post by: Jcc on 01/20/2019 11:18 pm
Also melting of ice in the soil and steam disillusion of brine to pure water.

Which you can drink while living in glass geodesic domes (back on topic).
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 01/20/2019 11:45 pm
Making glass from raw materials is a complex process, requiring enough chemicals and purification steps, many which will need to be different enough on Mars, that picking a heat-source will be the smallest issue to solve.
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 01/21/2019 03:00 am
Electric melting of glass is not efficient, electric heat is not efficient in general, at least on earth.  A gas furnace can melt glass easier, unless solar can be concentrated directy on the silicone, or directly on iron, aluminum etc and can get hot enough.  The plant you referenced got the water to 550° C.  Pretty hot, but silicone melts at 1,400° C, while aluminum is 660° C.  Can a reflective solar plant on Mars get as hot as it does on earth?
Got to disagree on this:
http://ietd.iipnetwork.org/content/electric-melting
Electric furnaces are much more logical on Mars than gas fed ones, since the gas on MArs comes from electricity in the first place.
Title: Re: Elon Musk: glass geodesic domes
Post by: Lampyridae on 01/21/2019 12:12 pm
Making glass from raw materials is a complex process, requiring enough chemicals and purification steps, many which will need to be different enough on Mars, that picking a heat-source will be the smallest issue to solve.

Glass can be pure silica, ie fused quartz but that is harder to deal with than the soda-lime glass windows are normally made out of (~25% additives by wt). I expect they would be more like bottle glass due to condensation and lifetime issues (the additives are water soluble and degrades over time). And as you mentioned there are many steps in getting even to powdered silica feedstock.

It'll probably use a flotation glass method (liquid glass on liquid metal bed), and here the gravity may even help because normally molten glass spreads until it's 6mm thick. We may find the gravity lets it settle at 1.8mm thick. Now just that statement alone shows just how much work is ahead. The first manned expedition would probably have a bunch of little mining, refining and manufacturing experiments just to see how everything works on Mars, along with little prototypes of structures.

The domes themselves need not be spheres. In addition to flattened spheres, you can also subtract dome sections from domes. By doing this, you sacrifice the internal volume but keep the surface area constant, reducing stress on the dome's surface.
Title: Re: Elon Musk: glass geodesic domes
Post by: CuddlyRocket on 01/21/2019 06:20 pm
Electric melting of glass is not efficient, electric heat is not efficient in general, at least on earth.  A gas furnace can melt glass easier, unless solar can be concentrated directy on the silicone, or directly on iron, aluminum etc and can get hot enough.  The plant you referenced got the water to 550° C.  Pretty hot, but silicone melts at 1,400° C, while aluminum is 660° C.  Can a reflective solar plant on Mars get as hot as it does on earth?

I think you mean silica (silicon dioxide)

He certainly didn't mean silicone! :)
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 01/22/2019 06:01 am
Making glass from raw materials is a complex process, requiring enough chemicals and purification steps, many which will need to be different enough on Mars, that picking a heat-source will be the smallest issue to solve.
Glass can be pure silica,

Except even high quality sand is not pure silica.

Getting from sand to silica is a complex, chemical hungry process. With enough steps (remembering that you have to make everything else you use) that the step "heat the purified silica until it melts" is such a trivial step, it can be ignored or treated as solved in a thread like this one. It's everything else that needs to be fleshed out.

[edit: Oops, didn't see this sentence in your comment: "And as you mentioned there are many steps in getting even to powdered silica feedstock." D'oh.]

flotation glass method (liquid glass on liquid metal bed), and here the gravity may even help because normally molten glass spreads until it's 6mm thick. We may find the gravity lets it settle at 1.8mm thick.

What's the reasoning for the latter? I would assume the minimum thickness is a function of gravity and surface tension. Less gravity, the greater the effect of surface tension and so the thicker the glass panes (without further rolling/stretching.)
Title: Re: Elon Musk: glass geodesic domes
Post by: rarchimedes on 01/22/2019 06:23 am
Every once in a while, Elon spouts off on a subject without spending the time and brain cells to have control of the subject. Geodesics only work as compression structures. I suppose one could dump a geodesic dome, inverted, into a well or trench, but that would not be volumetrically efficient and would require anchoring to prevent unintended blowouts. In addition, such a negative structure would have difficulty providing the desired insolation. Without a fairly thick layer of water or other filter, illuminated surfaces would merely become sterile due to ionizing radiation. To work safely, mirrors or light tubes would be necessary. I would suggest that in the absence of a mitigating atmosphere to significantly protect from all but the lightest of objects, no atmosphere containing volume should be directly exposed to incoming objects, considering the risks of unpredictable loss of that atmosphere. That way, significant mass could be interposed, with mirrors to bring in light/heat. Since it seems unlikely that reasonable amounts of glass can be brought in or produced in the short to medium term, early habitats should be largely buried or installed in caves, with artificial lighting where light is needed. The most likely early, in situ solids to be produced on Mars are ceramics, then metals, with mirror coatings easily transported and applied. In some perfect world, the constituents of usable glass to be produced with a rational level of effort on Mars will jump up and make themselves available. Lacking that highly unlikely discovery, we need to proceed as I have noted here. The one absolute necessity for human survival on Mars is H2O and lots of it. The corollary to that is the amount of energy necessary to process that water. The only rational and dependable source of that energy is nuclear, as sufficient solar panels or concentrated solar for all needs seems more than a stretch. I would recommend a liquid metal/thorium reactor for the best longevity and safety. Such a reactor would not be pressurized and would be passively safe and could work beautifully in a vacuum or near vacuum environment. 
Title: Re: Elon Musk: glass geodesic domes
Post by: rarchimedes on 01/22/2019 06:45 am
I missed a point. Yes, methane and oxygen can be probably separated/combined from the existing atmosphere and water in quantities sufficient for rocket fuel, but I doubt that sufficient can be obtained to make glass. It may even turn out that hydrolox is the only reasonably efficient rocket fuel. Any way you figure it, it will be quite a while before sufficient energy is available to make glass of reasonable quality for any purpose. Just off the top of my head, I suspect that thicknesses of frozen water will make the best windows for quite some time, as well as providing good radiation protection. We might want to take along some surface films to reduce deliquescence and/or evaporation.
Title: Re: Elon Musk: glass geodesic domes
Post by: JamesH65 on 01/22/2019 11:56 am
I missed a point. Yes, methane and oxygen can be probably separated/combined from the existing atmosphere and water in quantities sufficient for rocket fuel, but I doubt that sufficient can be obtained to make glass. It may even turn out that hydrolox is the only reasonably efficient rocket fuel. Any way you figure it, it will be quite a while before sufficient energy is available to make glass of reasonable quality for any purpose. Just off the top of my head, I suspect that thicknesses of frozen water will make the best windows for quite some time, as well as providing good radiation protection. We might want to take along some surface films to reduce deliquescence and/or evaporation.

You also missed paragraphs which would make your post a lot more readable.
Title: Re: Elon Musk: glass geodesic domes
Post by: Lampyridae on 01/22/2019 12:22 pm
Making glass from raw materials is a complex process, requiring enough chemicals and purification steps, many which will need to be different enough on Mars, that picking a heat-source will be the smallest issue to solve.
Glass can be pure silica,

Except even high quality sand is not pure silica.

Getting from sand to silica is a complex, chemical hungry process. With enough steps (remembering that you have to make everything else you use) that the step "heat the purified silica until it melts" is such a trivial step, it can be ignored or treated as solved in a thread like this one. It's everything else that needs to be fleshed out.

Yeah, I'm not disagreeing with you... pretty much said the same thing. What I'm saying is that it's possible to make glass, the ancient Phoenicians did it, but it depends what kind of glass. Beads and jugs are a far cry even from the glass bricks of the 1800s used for natural lighting.

Quote
flotation glass method (liquid glass on liquid metal bed), and here the gravity may even help because normally molten glass spreads until it's 6mm thick. We may find the gravity lets it settle at 1.8mm thick.

What's the reasoning for the latter? I would assume the minimum thickness is a function of gravity and surface tension. Less gravity, the greater the effect of surface tension and so the thicker the glass panes (without further rolling/stretching.)

That would be my assumption, yes. Well, we don't have anything other than a theoretical grasp of how industrial processes would work in reduced gravity so it would be good to find out how this stuff actually works. Glass fibres grown (extruded?) in zero gravity can be extremely pure with minimal stresses, so perhaps glass made on Mars might be a bit stronger than the same glass made on Earth.
Title: Re: Elon Musk: glass geodesic domes
Post by: Slarty1080 on 01/22/2019 12:45 pm
I missed a point. Yes, methane and oxygen can be probably separated/combined from the existing atmosphere and water in quantities sufficient for rocket fuel, but I doubt that sufficient can be obtained to make glass. It may even turn out that hydrolox is the only reasonably efficient rocket fuel. Any way you figure it, it will be quite a while before sufficient energy is available to make glass of reasonable quality for any purpose. Just off the top of my head, I suspect that thicknesses of frozen water will make the best windows for quite some time, as well as providing good radiation protection. We might want to take along some surface films to reduce deliquescence and/or evaporation.

I assume you mean there won't be sufficient methane and oxygen to be burnt and used as a heat source for melting glass. Correct that won't be happening.

I can't see glass being manufactured on Mars for a long time due to the manufacturing difficulties, exacerbated by high levels of iron contamination that would need to be removed.

Some form of plastic is much more likely given that modest extensions to the propellant ISRU equipment could provide a range of basic feed stocks needed.

Using water ice as a roofing material might work. A comfortably pressurised living environment should easily be able to support a few metres of ice above it that could be protected from evaporation by a thin layer of plastic film and with some careful processing it should be possible to make the ice nearly transparent.

Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 01/23/2019 12:31 am
I missed a point. Yes, methane and oxygen can be probably separated/combined from the existing atmosphere and water in quantities sufficient for rocket fuel, but I doubt that sufficient can be obtained to make glass. It may even turn out that hydrolox is the only reasonably efficient rocket fuel. Any way you figure it, it will be quite a while before sufficient energy is available to make glass of reasonable quality for any purpose. Just off the top of my head, I suspect that thicknesses of frozen water will make the best windows for quite some time, as well as providing good radiation protection. We might want to take along some surface films to reduce deliquescence and/or evaporation.

I assume you mean there won't be sufficient methane and oxygen to be burnt and used as a heat source for melting glass. Correct that won't be happening.

I can't see glass being manufactured on Mars for a long time due to the manufacturing difficulties, exacerbated by high levels of iron contamination that would need to be removed.

Some form of plastic is much more likely given that modest extensions to the propellant ISRU equipment could provide a range of basic feed stocks needed.

Using water ice as a roofing material might work. A comfortably pressurised living environment should easily be able to support a few metres of ice above it that could be protected from evaporation by a thin layer of plastic film and with some careful processing it should be possible to make the ice nearly transparent.
Iron is a contaminant, but it's also a ressource.  Iron ore, at least here in Quebec, is essentially SiO2 and Fe2O3.  So you have both your source of sand and of iron, for the steel of the actual dome structure.
There is little need for the dome to be actually geodesic, pretty much any tension structure will do better to transmit strain to whatever keeps the dome in place.  The glass panes are pretty much in bending, but being hyperstatically supported all around, the strain is not that hig of the width of the glass is not too large.

I would expect a MArs colony to start using glass and steel as soon as possible.  Although the energy need is high, it is tiny compared to the need for return fuel production or food. 

The joined fancy globe is not a dome, but it is glass and steel on Mars.  Each glass section acts as a hemispherical pressure vessel, with double walls to reduce heat loss.  It should not be all that heavy for such a large structure, as the gravity is lower and there are no real wind forces.  About 100m wide.

As far as energy goes, I've joined a little table of the energy use I propose for a fairly advanced colony of 1000 people.  For about 500 tonnes of glass and 500 tonnes of steel per year, incredibly tiny numbers by Earth standards, the fraction of the colony power is not all that great.  I expect a project like this too much of a  stretch, but as a marvel similar to the products of World Fairs and such, perhaps when the colony has a few thouthand more people.
There are a number of tables providing the intrinsic energy of materials, if you want to check my numbers :-)

Oups, sky is a bit too blue  ;-)
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 01/23/2019 12:36 am
Not so blue.  2000 to 3000 tonnes?  Plus some concrete structure.
Title: Re: Elon Musk: glass geodesic domes
Post by: Slarty1080 on 01/23/2019 11:32 am
The "Separation" box in your diagram covers a mutitude of issues. How will this be carried out?
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 01/23/2019 09:55 pm
The "Separation" box in your diagram covers a mutitude of issues. How will this be carried out?
Crushing, milling, floating and separating, plus chemical interactions come to mind.  There will be a dozen processes that need to be worked out, but I can give a small sample of what will need to be done for a case that I know a little about: Iron Ore.
Iron ore in Quebec mines is mostly separated by crushing the rock into a very fine powder using ball mills.  At a certain size of particle, most of the grains are either pure silica, or pure iron ore, and are fine enough to be transported by water as a slurry.  As both these materials are quite inert chemically, they are separated out mechanically in separation spiral.  The spirals are literally rubber lined chutes with a very precisely placed groove, and the velocity is such that the sand goes up the edge and the heavier iron ore goes down the groove, and they separate.  This is not an exact science, and before a mine is build they will create prototype spirals and test them out to get the groove exactly right.
Now on Mars, that will change because the gravity is lower, and most likely the separation will be less effective.  So whatever is used will need to be tested, then modified until it produces decent results.  Perhaps there will be contaminants, such as salts, that need to be removed first by dilution, for example.
I expect the first ships to carry very complete material testing labs, as well as geologists with exploration vehicles.
The geologists will find ore deposits with the most useful combinations, and the labs will use small grinders, sieves, chemical reactants and such to create working prototypes for separation.
Then craft persons will create small working prototypes, perhaps good for a few pounds a day, and tinker with them until they work.
They will then create larger versions, hoping they scale properly, and if this works they will replicate them until they have a useful production line.  A few hundreds tonnes a year is ridiculously small by today's standards for pretty much any industrial process but that's all they need for a while.
The lab will keep working to improve the process, and the machines will get larger and larger.

This process has led, over time, to 250 tonne trucks and 10 000 horsepower SAG mills.  But it starts quite small.  In many cases little more than a set up on a bench lab.  I fondly remember getting a project, early in my career, for moving a proof of concept plant.  I thought it would be a large undertaking but finally is was just moving a bench lab on castor wheels and hooking up water  :-).  Small test equipment is available of the shelf in a multitude of configurations.

All the elements required for glass and steel domes are on Mars.  In many cases they are actually together in the same rock formations.  Even Soda ash can be manufactured, if it turn out not to exist naturally.  And probably not for all that much energy.

Title: Re: Elon Musk: glass geodesic domes
Post by: Slarty1080 on 01/23/2019 11:14 pm
No doubt in the fullness of time much of this will be possible. But it will take a lot of time because there is so little infrastructure available on Mars.

For example the purification of Silica: mechanical separation, transportation and especially milling will involve moving parts in contact with abrasive materials and consequent wear. So a lot of spare parts will be required and these will have to come all the way from Earth initially.

There are different ways to purify silica depending on how pure the original feed stock is. In the case of Mars I think it is likely to require extensive treatment to remove many impurities such as iron.

Here is an example
https://hobbychemistry.wordpress.com/2015/04/11/pure-silicon-dioxide-from-sand/ (https://hobbychemistry.wordpress.com/2015/04/11/pure-silicon-dioxide-from-sand/)

There are other ways which use other chemicals, but the takeaway here is the consumption of chemicals in this case hydrochloric acid and sodium hydroxide and the production of wastes in this case dirty hydrochloric acid and acid washings.

The hydrochloric acid and sodium hydroxide have to come from Earth initially. Yes these might also be made on Mars but in order to do so even more chemistry is involved with more chemical processing feed stocks and waste streams.
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 01/24/2019 12:40 am
No doubt in the fullness of time much of this will be possible. But it will take a lot of time because there is so little infrastructure available on Mars.

For example the purification of Silica: mechanical separation, transportation and especially milling will involve moving parts in contact with abrasive materials and consequent wear. So a lot of spare parts will be required and these will have to come all the way from Earth initially.

There are different ways to purify silica depending on how pure the original feed stock is. In the case of Mars I think it is likely to require extensive treatment to remove many impurities such as iron.

Here is an example
https://hobbychemistry.wordpress.com/2015/04/11/pure-silicon-dioxide-from-sand/ (https://hobbychemistry.wordpress.com/2015/04/11/pure-silicon-dioxide-from-sand/)

There are other ways which use other chemicals, but the takeaway here is the consumption of chemicals in this case hydrochloric acid and sodium hydroxide and the production of wastes in this case dirty hydrochloric acid and acid washings.

The hydrochloric acid and sodium hydroxide have to come from Earth initially. Yes these might also be made on Mars but in order to do so even more chemistry is involved with more chemical processing feed stocks and waste streams.
Lovely chemistry but way overkill. 
https://www.explainthatstuff.com/glass.html
Naturally occuring sand banks in many places on Earth can provide practically pure silica.  This should exist on Mars as well, with wind and water separation having been active in the past.
Iron Ore is is fact a good source of silica.  So if you find a nice concentration of iron ore, and separate it to get the iron, you also get the silica.  You can getty very effective mechanical separation, and even more effective magnetic separation.

It all starts with good geologists!

You can buy a nice 2 tonne per hour+ ball mill from here:
http://www.zenithmills.com/products/
With a 20 kW motor I expect is that is masses around 2-5 tonnes.
My guess is that for a single 100 tonne Starship cargo load, you can get hoppers, feeders, mills and furnaces, both for iron, steel and glass for a 2000 tonnes per year production.  I'm particularly excited by hydrogen reduction for iron production.  Seems a perfect for for a planet with no coal.
You will need to recycle a small part of your production to make new balls, and to replate the interior oy your ball mill.  The actual bearings, motors and such are good for decades.  Rubber might be a problem if no local production is possible.  But a few tonnes of rubber should go a long way.


Title: Re: Elon Musk: glass geodesic domes
Post by: biosehnsucht on 01/24/2019 12:54 am
From the description of having to fine tune the mechanical separation method for iron ore, it seems like magnetic is the way to go.
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 01/24/2019 01:10 am
From the description of having to fine tune the mechanical separation method for iron ore, it seems like magnetic is the way to go.
The process people were quite excited by rare Earth magnets, I remember they needed to be careful not to overheat them.  If we can do the separation work directly without the very fine crushing and water separation, so much the better.  It won't be a direct application of Earth equipment, but after some initial test I don't see why we couldn't use  adapted existing equipment rather than create from scratch.
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 01/24/2019 01:24 am
By the way if you use a boring machine or a roadheader to bore into sandstone contaminated with iron, you get your iron, your glass precursor and probably some water all nicely broken down as feedstock.
Title: Re: Elon Musk: glass geodesic domes
Post by: rarchimedes on 01/24/2019 01:43 am
I missed a point. Yes, methane and oxygen can be probably separated/combined from the existing atmosphere and water in quantities sufficient for rocket fuel, but I doubt that sufficient can be obtained to make glass. It may even turn out that hydrolox is the only reasonably efficient rocket fuel. Any way you figure it, it will be quite a while before sufficient energy is available to make glass of reasonable quality for any purpose. Just off the top of my head, I suspect that thicknesses of frozen water will make the best windows for quite some time, as well as providing good radiation protection. We might want to take along some surface films to reduce deliquescence and/or evaporation.

You also missed paragraphs which would make your post a lot more readable.
Depends upon the reader. In a forum such as this, one reads the entire thread and tries to cover as much of it as is reasonable, to move the conversation along. That might require one paragraph per sentence or sentence per paragraph.

Edit/Lar: removed inappropriate tone.
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 01/24/2019 03:52 am
Lovely chemistry but way overkill.
https://www.explainthatstuff.com/glass.html
Naturally occuring sand banks in many places on Earth can provide practically pure silica.

The link you provided was something intended for children, it... simplifies. Even the highest grades of silica sand, above 99%, have to be further mechanically and chemically processed in order to produce silica suitable for clear glass.

If you want to make ceramics, golf-traps, and coloured glass-beads, then sure, you can use the high grade sand as-is. But if you want to make panes of optically clear glass, you have to chemically treat the sand through repeated stages to remove impurities, such as iron, aluminium, titanium, chromium, etc. "Magnets" will only separate grains of iron from grains of silica, not separate iron contamination within silica grains.

I've never tried it myself, but I've watched people (both IRL, but obviously online) make their own steel, their own aluminium, and their own clear glass. The latter is the hardest, most exacting, most frustrating process I've seen them try, even without trying to float panes.
Title: Re: Elon Musk: glass geodesic domes
Post by: JamesH65 on 01/24/2019 10:49 am
I missed a point. Yes, methane and oxygen can be probably separated/combined from the existing atmosphere and water in quantities sufficient for rocket fuel, but I doubt that sufficient can be obtained to make glass. It may even turn out that hydrolox is the only reasonably efficient rocket fuel. Any way you figure it, it will be quite a while before sufficient energy is available to make glass of reasonable quality for any purpose. Just off the top of my head, I suspect that thicknesses of frozen water will make the best windows for quite some time, as well as providing good radiation protection. We might want to take along some surface films to reduce deliquescence and/or evaporation.

You also missed paragraphs which would make your post a lot more readable.
Depends upon the reader. In a forum such as this, one reads the entire thread and tries to cover as much of it as is reasonable, to move the conversation along. That might require one paragraph per sentence or sentence per paragraph. I have a better idea. Why don't you organize your posts in a manner that suits you and I will do the same for myself. Since you have figured out what I meant sufficiently that you know where I should have broken the post into paragraphs, why don't you put out your interpretation so that I can further enlighten you. In other words, with what size spoon should I feed you.

I didn't read your whole post, because it wasn't paragraphed, and I like, many other readers, find huge chunks of unparagraphed text very difficult to read*, and, more importantly, comprehend. Parapgrahs were invented for a reason, but since you decided to behave unpleasantly instead of taking some well intentioned and simple advice on board, I guess you don't care whether people read your posts or not.


* hence the shortcut TL;DR.
Title: Re: Elon Musk: glass geodesic domes
Post by: Lampyridae on 01/24/2019 11:11 am
Lovely chemistry but way overkill.
https://www.explainthatstuff.com/glass.html
Naturally occuring sand banks in many places on Earth can provide practically pure silica.

The link you provided was something intended for children, it... simplifies. Even the highest grades of silica sand, above 99%, have to be further mechanically and chemically processed in order to produce silica suitable for clear glass.

If you want to make ceramics, golf-traps, and coloured glass-beads, then sure, you can use the high grade sand as-is. But if you want to make panes of optically clear glass, you have to chemically treat the sand through repeated stages to remove impurities, such as iron, aluminium, titanium, chromium, etc. "Magnets" will only separate grains of iron from grains of silica, not separate iron contamination within silica grains.

I've never tried it myself, but I've watched people (both IRL, but obviously online) make their own steel, their own aluminium, and their own clear glass. The latter is the hardest, most exacting, most frustrating process I've seen them try, even without trying to float panes.

I seem to recall the colonists in Kim Stanley Robinson's Red Mars struggling to make glass and winding up with uneven little discoloured panes. I've seen some attempts at making ISRU glass which boil down to melting regolith to make some obsidian. I've also seen a paper discussing uses for ferrosilicon after oxygen extraction from regolith. That might be a pathway to pure silicon. But at this stage all the ISRU research boils down to propellants and making mud space huts.

Making transparent ice (not that I've done it) seems a lot easier, just requiring clean water, controlled temperatures and shaving off the top few cm. Sandwich between regular glass or plastic from Earth and done.

Alternatively, import pure Earth silicon, oxidise it and melt it? Cut shipping costs by almost a third.

In the 17th century, one ingredient in glass making was seaweed (burnt to ash). Also, there were various plants that provided the sodium carbonate (which is why glasswort looks not at all glassy).
http://www.verre-histoire.org/colloques/innovations/pages/p301_01_dungworth.html

It was replaced with the LeBlanc process which generates the soda lime for glass from sea salt, sulphuric acid and carbon.
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 01/24/2019 12:06 pm
Lovely chemistry but way overkill.
https://www.explainthatstuff.com/glass.html
Naturally occuring sand banks in many places on Earth can provide practically pure silica.

The link you provided was something intended for children, it... simplifies. Even the highest grades of silica sand, above 99%, have to be further mechanically and chemically processed in order to produce silica suitable for clear glass.

If you want to make ceramics, golf-traps, and coloured glass-beads, then sure, you can use the high grade sand as-is. But if you want to make panes of optically clear glass, you have to chemically treat the sand through repeated stages to remove impurities, such as iron, aluminium, titanium, chromium, etc. "Magnets" will only separate grains of iron from grains of silica, not separate iron contamination within silica grains.

I've never tried it myself, but I've watched people (both IRL, but obviously online) make their own steel, their own aluminium, and their own clear glass. The latter is the hardest, most exacting, most frustrating process I've seen them try, even without trying to float panes.

I want to make relatively clear glass to use in 'geodesic' domes made of glass and steel. 
I expect floated glass, about 2 feet wide but ideally 3, 1/2 inch thick should be sufficiently strong for the task.
I would like this to be available the synod after the colony starts in earnest.  This is an Elon Musk thread, so large ships, plenty of supplies, ambitious scale.  Not a smart person in a garage, or a lone astronaut in a dinky station, but an effort from a large corporation backed by universities and lots of money, where all the difficult bits can be built on Earth and shipped to Mars.
I would like to produce about 500 tonnes per year for a 1000 person colony, and then scale up as the colony grows.

The question that needs to be answered is: What goes into the little box named 'Processing' in the graphic of the colony process diagram.
Is it missing major external inputs? Inputs that make it impossible?  Large quantities on non recycled acids, for example.
Does it represent a huge 500 tonne machine that cannot be brought from Earth?
Does it involve significant steps that require it to be broken down into smaller steps, at the 'scale' of the diagram?

I used the referenced 'How it's made' text because it didn't show a significant pre treatment of the minerals, and it seemed to be complete, although simple.  I have not seen anywhere an explanation of the exact preparation process of glass feedstock that details the purification process, therefore I assumed it was fairly trivial. I may have been wrong, I often am.

I use tables of embodied energy in building materials that shows glass has much lower energy requirements than plastics.   These tables are not perfectly reliable, and some obviously have built in biases, however glass energy is always lower than plastics.





Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 01/24/2019 12:38 pm
The question that needs to be answered is: What goes into the little box named 'Processing'

AIUI, it varies wildly depending on what exactly is in the source sand, there isn't a single method because there isn't a single set of contaminants. Even the way the contaminants contaminate will vary, depending on whether it's as a mix of different types of grain, a coating on the silica grains, or in the silica crystals themselves. Or a combination of all three.

It might be an acid wash, dissolving the contaminant, or a series of acids, each targeting one contaminant. (Treat with acid#1, rinse, dry, re-grind, treat with acid#2, rinse, dry, re-grind...) Or you might treat the sand with something to bond with the contaminant to make it hydrophobic, then add a detergent wash, the contaminant ends up in the foam that can be scraped or washed off.
Title: Re: Elon Musk: glass geodesic domes
Post by: Lampyridae on 01/24/2019 01:01 pm
The question that needs to be answered is: What goes into the little box named 'Processing'

AIUI, it varies wildly depending on what exactly is in the source sand, there isn't a single method because there isn't a single set of contaminants. Even the way the contaminants contaminate will vary, depending on whether it's as a mix of different types of grain, a coating on the silica grains, or in the silica crystals themselves. Or a combination of all three.

It might be an acid wash, dissolving the contaminant, or a series of acids, each targeting one contaminant. (Treat with acid#1, rinse, dry, re-grind, treat with acid#2, rinse, dry, re-grind...) Or you might treat the sand with something to bond with the contaminant to make it hydrophobic, then add a detergent wash, the contaminant ends up in the foam that can be scraped or washed off.

All of which will require a fairly large, semi-pressurised facility as well. I'm envisioning something very big, with large bulk material airlocks and a suit-pressure pressurisation (enabling humans to walk around with oxygen masks).

Curiosity found nearly pure silica in Gale crater, can't recall offhand what the contaminants were though.
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 01/24/2019 01:16 pm
The question that needs to be answered is: What goes into the little box named 'Processing'

AIUI, it varies wildly depending on what exactly is in the source sand, there isn't a single method because there isn't a single set of contaminants. Even the way the contaminants contaminate will vary, depending on whether it's as a mix of different types of grain, a coating on the silica grains, or in the silica crystals themselves. Or a combination of all three.

It might be an acid wash, dissolving the contaminant, or a series of acids, each targeting one contaminant. (Treat with acid#1, rinse, dry, re-grind, treat with acid#2, rinse, dry, re-grind...) Or you might treat the sand with something to bond with the contaminant to make it hydrophobic, then add a detergent wash, the contaminant ends up in the foam that can be scraped or washed off.
This is all quite possible, but what is actually done, in real plants?  And not require much energy?  Grinding requires a lot of energy.  Sand is pre-ground, that's one of the reasons it's used.
I made the usual Google search and came up with the joined report.  It mentions some sands, in particular those with clays, need to be washed, but as far as I can see, many sands can be used directly.  The report is old, but as far as I can see that's a good point rather than a defect :-)
The process diagrams that a search bring up also do not show an acid wash, or any particular treatment of the silica feedstock.  So either it is done elsewhere at the source, and the glass-works receive pre-treated sand, or it is not required.  I understand we don't want to oversimplify things, but we shouldn't overcomplicate them either.
If the fist step is: Find adequate sand within a reasonable distance, and the box remains a simple box, then that seems the most reasonable solution.  That means the SiO2 will come from a mine and not from digging in sandstone, and that would be a valuable input for the overall process diagram, making it a little less naive.

As far as processing goes, I expect it should be done in a large pressurized enclosure, it's a 1000 person colony, after all.  Airlocks can be quite small, rotary airlocks could provide rapid input with minimum air loss if they feed a pressure vessel style hopper with a vacuum pump operating in batches.
Title: Re: Elon Musk: glass geodesic domes
Post by: Lampyridae on 01/24/2019 01:41 pm
Got the PDF of the silica find here:

https://repository.si.edu/bitstream/handle/10088/20568/min_Squyres_et_al_2008_Science_320_1063-1067.pdf?sequence=1&isAllowed=y

I made the usual Google search and came up with the joined report.  It mentions some sands, in particular those with clays, need to be washed, but as far as I can see, many sands can be used directly.  The report is old, but as far as I can see that's a good point rather than a defect :-)

I see a lot of stains on this. How many Bothans died to bring us this information?

It's good, solid information though that actually gives us something to work on. I doubt we'll find pure sand though, but opal and quartz deposits may be doable.
Title: Re: Elon Musk: glass geodesic domes
Post by: Tulse on 01/24/2019 02:13 pm
Do we want glass to see out of, or just to provide illumination from the outside?  If the latter, how much processing can be dispensed with and still produce something translucent (but not transparent)?
Title: Re: Elon Musk: glass geodesic domes
Post by: guckyfan on 01/24/2019 02:34 pm
Do we want glass to see out of, or just to provide illumination from the outside?  If the latter, how much processing can be dispensed with and still produce something translucent (but not transparent)?

I am convinced it is for psychological reasons, so to look out, while having plants inside grown with natural light.

Edit: the same line of thougt that induces Elon to have this large window on Starship.
Title: Re: Elon Musk: glass geodesic domes
Post by: spacenut on 01/24/2019 02:58 pm
Windows and plant are like comfort food.  People in Washington and Oregon have a higher suicide rate than the rest of the US.  Psychiatrists think it is because of all the cloudy and rainy days they have.  Sunlight is refreshing, even if looking out over a desert.  Windows on Starship and on Mars will help the well being of long space travel and colonists on Mars. 

Initially I think long arched greenhouse structures or standard angled roof structures will be easier to build in space suits, before a large geodesic dome.  Colonists would also be able to have an air pipe going down the center top to blow off dust. 
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 01/24/2019 04:46 pm
Windows and plant are like comfort food.  People in Washington and Oregon have a higher suicide rate than the rest of the US.  Psychiatrists think it is because of all the cloudy and rainy days they have.  Sunlight is refreshing, even if looking out over a desert.  Windows on Starship and on Mars will help the well being of long space travel and colonists on Mars. 

Initially I think long arched greenhouse structures or standard angled roof structures will be easier to build in space suits, before a large geodesic dome.  Colonists would also be able to have an air pipe going down the center top to blow off dust.
Anything built initially will come from Earth and can be 'perfect'.  Flat high strength glass seems like a no brainer for habitats in pretty much any quantity, and clear plastics might be just as good and lighter. 
The process questions arise latter when you want to stop depending on Earth.  As a colony and not as a base. And due to the very high transport costs you want to do this as soon as practically possible, while balancing the requirements against the requirements for other in situ processes.  Since most construction on Earth is concrete and steel, making these first seems like priority.  As there are carbonates on Mars, it seems possible.
Ceramics are super interesting as they are low energy, production wise, and provide a lot of visual interest and good surface qualities for in situ production.  I think glass comes after that, so still pretty high on the priority list.

A glass dome is really a steel dome.  The glass is non structural.  Filler, in a sense.  Glass and concrete are extremely similar, in a way, as they are both made from larges parts of silica.  Concrete in a 1:3,6 mix could be 90% silica after all, higher than soda glass itself at 70% silica.  And soda glass can be made at 30 MPa in tensile strength, while concrete is more in the 2 MPa range.  So there is probably not that much of a difference between using one or the other, if fact glass may be cheaper in some ways, if the production costs are reasonable.

I think a real weakness of glass domes may be the large number of joints that need to be sealed, and their exposure to ultraviolet radiation on the surface of Mars, leading possibly to rapid decay of the sealants.


Title: Re: Elon Musk: glass geodesic domes
Post by: Slarty1080 on 01/24/2019 09:41 pm
No doubt in the fullness of time much of this will be possible. But it will take a lot of time because there is so little infrastructure available on Mars.

For example the purification of Silica: mechanical separation, transportation and especially milling will involve moving parts in contact with abrasive materials and consequent wear. So a lot of spare parts will be required and these will have to come all the way from Earth initially.

There are different ways to purify silica depending on how pure the original feed stock is. In the case of Mars I think it is likely to require extensive treatment to remove many impurities such as iron.

Here is an example
https://hobbychemistry.wordpress.com/2015/04/11/pure-silicon-dioxide-from-sand/ (https://hobbychemistry.wordpress.com/2015/04/11/pure-silicon-dioxide-from-sand/)

There are other ways which use other chemicals, but the takeaway here is the consumption of chemicals in this case hydrochloric acid and sodium hydroxide and the production of wastes in this case dirty hydrochloric acid and acid washings.

The hydrochloric acid and sodium hydroxide have to come from Earth initially. Yes these might also be made on Mars but in order to do so even more chemistry is involved with more chemical processing feed stocks and waste streams.
Lovely chemistry but way overkill. 
https://www.explainthatstuff.com/glass.html
Naturally occuring sand banks in many places on Earth can provide practically pure silica.  This should exist on Mars as well, with wind and water separation having been active in the past.
Iron Ore is is fact a good source of silica.  So if you find a nice concentration of iron ore, and separate it to get the iron, you also get the silica.  You can getty very effective mechanical separation, and even more effective magnetic separation.

It all starts with good geologists!

You can buy a nice 2 tonne per hour+ ball mill from here:
http://www.zenithmills.com/products/
With a 20 kW motor I expect is that is masses around 2-5 tonnes.
My guess is that for a single 100 tonne Starship cargo load, you can get hoppers, feeders, mills and furnaces, both for iron, steel and glass for a 2000 tonnes per year production.  I'm particularly excited by hydrogen reduction for iron production.  Seems a perfect for for a planet with no coal.
You will need to recycle a small part of your production to make new balls, and to replate the interior oy your ball mill.  The actual bearings, motors and such are good for decades.  Rubber might be a problem if no local production is possible.  But a few tonnes of rubber should go a long way.

Well I hope the pure silica you are hoping for is available on Mars, but I suspect not. It might have been available hundreds of millions (or more likely billions) of years ago but since then there must have been a lot of global dust storms and there is a lot of iron on Mars along with a great many other materials such as olivine, pyroxene and feldspar blowing around. Judging by the chemical analysis so far the regolith is quite a mixture also including calcium perchlorate and much else:

https://en.wikipedia.org/wiki/Martian_soil

Even if there is some hidden dune of pure silica somewhere it will take some finding and the priorities for the Mars base will be a suitable surface at low elevation with an abundant source of water not silica.

I'm not saying that there is no silica there, there is and in abundance, it’s just that its mixed with a lot of other minerals and silicates. The geology of Mars is very different from that on Earth. Also Red iron oxide Fe2O3 is only very weakly magnetic and other compounds of iron are not magnetic at all.

I doubt that rubber would last very long on Mars; some sort of plastic substitute will be needed and will need replacement.

I will grant you that the equipment could be brought in but the problem of the chemical purification remains. According to your link sodium carbonate, calcium carbonate and possibly boron oxide will also be required. Unless these are imported from Earth sources of these compounds will also have to be found or more likely they will themselves need to be synthesised and purified from whatever materials that are available that contain the correct elements.
Title: Re: Elon Musk: glass geodesic domes
Post by: Lar on 01/25/2019 01:35 am
(fan) There is another thread (or 3) for chemical processing, but I'm struck by the need to be able to reconstitute reagents at scale, for a wide variety of reagents... For example if something gets sulfuric or hydrochloric acid washed, that acid is now "dirty" in that some of it has been changed, and the solution is now carrying dissolved salts of what was etched away.

Those salts present an opportunity, if their elements are useful for anything, (for example, removing perchlorates potentially sources chlorine (used in the very hydrochloric acid that might be etching other things) if you have the energy to process them),  but nevertheless every process has to be closed loop or very close. Energy balances will be very important.

(mod) Did a bit of tidying. User rarchimedes is out of line bucking back at people pointing out that his walls of text are impenetrable, but some of the comments in response also went by the bye.
Title: Re: Elon Musk: glass geodesic domes
Post by: Slarty1080 on 01/25/2019 02:28 am
(fan) There is another thread (or 3) for chemical processing, but I'm struck by the need to be able to reconstitute reagents at scale, for a wide variety of reagents... For example if something gets sulfuric or hydrochloric acid washed, that acid is now "dirty" in that some of it has been changed, and the solution is now carrying dissolved salts of what was etched away.

Those salts present an opportunity, if their elements are useful for anything, (for example, removing perchlorates potentially sources chlorine (used in the very hydrochloric acid that might be etching other things) if you have the energy to process them),  but nevertheless every process has to be closed loop or very close. Energy balances will be very important.

(mod) Did a bit of tidying. User rarchimedes is out of line bucking back at people pointing out that his walls of text are impenetrable, but some of the comments in response also went by the bye.

Must check those threads, in fact there might be scope for a related thread elsewhere. I though this particular point was very relevant here as the topic involves glass and the difficulties of purification should not be underestimated. You are right to say that there are opportunities, but the chemical composition of Martian regolith is very different from that of most soils on Earth and different processes will be required to process it in many cases. For example sulphur might be used in concrete as a binding agent and windows might be made from polyethylene protected by water ice.
Title: Re: Elon Musk: glass geodesic domes
Post by: Lar on 01/25/2019 04:22 am
I'm too lazy to chase them down but yeah, good reading. Agree that the particular points raised were relevant. I just think it's interesting that every solvent, every reagent, every waste product has to be dealt with carefully. You can't have open loop (use the etchant once to make one PCB, then discard) processes. Some very clever chemical and process engineering will be needed. And as you say, a lot of the feedstocks will be different. Requiring lots of research and labwork and tinkering and scaleups.
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 01/25/2019 07:34 am
Do we want glass to see out of, or just to provide illumination from the outside?  If the latter, how much processing can be dispensed with and still produce something translucent (but not transparent)?
I am convinced it is for psychological reasons, so to look out, while having plants inside grown with natural light.

However, you don't necessarily need to look up to achieve the psychological impact. You might get away with a few clear shelled look-outs for the night-time view, plus a row of clear-glass around the main hab for the daytime landscape gazing. With the rest of the glass being translucent, even slightly opaque panels. As long as it lets enough light through, plants don't care. We use translucent plastic in commercial greenhouses.

So you might be able to have crappy, ISRU glass for the bulk of the structure, and higher clarity Earth-made glass for the looking-out-bits.



Others,
Re: Ice.

I'm happy to scowl at the idea of using glass (especially first generation ISRU glass) for a large pressurised vessel. (And of course, remain a broken record regarding domes and pressure.) But I can't see (ha) that ice, thin enough to be translucent, cold enough to not sublimate, is going to be an improvement.
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 01/25/2019 07:35 am
The question that needs to be answered is: What goes into the little box named 'Processing'
AIUI, it varies wildly depending on what exactly is in the source sand, there isn't a single method because there isn't a single set of contaminants.
This is all quite possible, but what is actually done, in real plants?

The thing that I said. It varies. Depending on the contaminants. There isn't a single recipe. My examples were things I've seen mentioned in regard to purifying silica sand for glass making. Glass makers just buy processed silica of the purity and grain-size required for the job.

Some contaminants are merely colourants, others are opacitants, so (from what I'm reading) you can sometimes offset some naturally occurring contamination by adding yet another salt that counters the colour of the contaminant. Magnesium oxide removes some of the colour of chrome oxide, IIRC, saving you from having to remove the chrome itself because neither salt is an opacitant.

The added salt needs to be very pure, of course, but the amounts are fairly small, tenths of a percent. So once you know the detailed composition of your best Martian silica source, you can ship in a few tonnes of customised additives from Earth to produce a thousand tonnes of clear glass. If you can do that, it will be easier than needing entirely separate processes to produce or recycle enough of the reagents needed to remove the contaminant.

But it all depends how pure the silica source it and what the contaminants are.

Are you assuming pure silica-glass and just wearing the energy cost, or are you looking for a substitute for limestone for soda-glass? (And accepting the industrial cost of finding sodium carbonate.)

Grinding requires a lot of energy.  Sand is pre-ground, that's one of the reasons it's used.

I've seen that sandstone is also used to make silica-sand, if it has the right purity. Purity wins over issues like grinding, apparently.

Everything I've seen seems to be water hungry, though. Lots of washing/rinsing stages. Water is king on Mars, again.

As far as processing goes, I expect it should be done in a large pressurized enclosure, it's a 1000 person colony, after all.

Yeah, there's an interesting trade between the cost of adding pressurised volume and the cost of not having it. Similarly, is the hassle of dealing with equipment in a partial vacuum more than the hassle of dealing with the heat coming off the kilns inside a pressure vessel?
Title: Re: Elon Musk: glass geodesic domes
Post by: Lampyridae on 01/25/2019 08:56 am

Well I hope the pure silica you are hoping for is available on Mars, but I suspect not. It might have been available hundreds of millions (or more likely billions) of years ago but since then there must have been a lot of global dust storms and there is a lot of iron on Mars along with a great many other materials such as olivine, pyroxene and feldspar blowing around. Judging by the chemical analysis so far the regolith is quite a mixture also including calcium perchlorate and much else:

https://en.wikipedia.org/wiki/Martian_soil

Even if there is some hidden dune of pure silica somewhere it will take some finding and the priorities for the Mars base will be a suitable surface at low elevation with an abundant source of water not silica.

I have mentioned that pure silica has been found on Mars by the rovers (Opportunity IIRC found 99% pure stuff, nodules). See the PDF I linked.

Now, an actual Mars colony will not be some Starcraft base built right next to a Vespene geyser and a crystal field. Your resources will be quite scattered, your silica sands may not necessarily be within 100km. You will need field survey stations, mining outposts, charging station (someone detailed in Steampunk Mars thread I think) large ore trucks and so on. I'm working on a GIS-based Masters proposal for this. The main resource the colony will probably want to sit on is lots of water.

Quote
I'm not saying that there is no silica there, there is and in abundance, it’s just that its mixed with a lot of other minerals and silicates. The geology of Mars is very different from that on Earth. Also Red iron oxide Fe2O3 is only very weakly magnetic and other compounds of iron are not magnetic at all.

I doubt that rubber would last very long on Mars; some sort of plastic substitute will be needed and will need replacement.

I will grant you that the equipment could be brought in but the problem of the chemical purification remains. According to your link sodium carbonate, calcium carbonate and possibly boron oxide will also be required. Unless these are imported from Earth sources of these compounds will also have to be found or more likely they will themselves need to be synthesised and purified from whatever materials that are available that contain the correct elements.


Boron oxide is only really required for pyrex. Pyrex is nice but they don't use it for spacecraft windows which are aluminosilicate or fused silica.

Anyway, if plain glass really is a problem then the processing can simply tap into the aluminium feedstock and make alumina (transparent sapphire) which is much harder than making straight glass, limits the size (but not thickness) but allows you to skip the need for pure, refined sand. But I don't think it's worth it personally, it's very energy intensive and the stuff is made in blobs which need to be cut and polished to shape.
Title: Re: Elon Musk: glass geodesic domes
Post by: Lampyridae on 01/25/2019 09:39 am
Silica-rich soil from Gusev crater:

(https://www.nasa.gov/images/content/176734main_pia09403-512.jpg)

About 90% silica. https://www.nasa.gov/mission_pages/mer/images/pia09403.html

https://repository.si.edu/bitstream/handle/10088/20568/min_Squyres_et_al_2008_Science_320_1063-1067.pdf?sequence=1&isAllowed=y

Removing the effects of soil covering the target, the silica found was opalescent, with 98% Si, 1.5% TiO2, 0.3% Cr2O3, some trace Ni and Zn. The TiO2 and Cr2O3 may or may not be representative of other deposits on Mars (sample size of 1...); the silica formed from hot spring conditions.

(https://img.purch.com/h/1400/aHR0cDovL3d3dy5zcGFjZS5jb20vaW1hZ2VzL2kvMDAwLzA2MC8yNjMvb3JpZ2luYWwvc3Bpcml0LXBvc3NpYmxlLW1hcnMtYmlvc2lnbmF0dXJlcy5qcGc=)

The TiO2 would give a slightly white-blue colouration (if at all noticeable) and would be a very effective UV blocker, and the Cr2O3 would add a greenish tint of about beer bottle opacity. Note what appears to be a greenish colouration to the soil but with no human eyes to see it who can really tell?

Chrome oxide %age effect on tint:

http://www1.metalurji.org.tr/immc2016/192.pdf

So we need <0.1% Cr2O3 and probably like <0.001% for decent window glass. Or, add salts to balance it out, like Paul451 mentioned.

Some other colour effects:

https://www.lehigh.edu/imi/teched/GlassProcess/Lectures/Lecture04_Shelby_ColoredGlass.pdf

Iron can get away with a fairly high %age - 0.5% hardly has any effect.
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 01/25/2019 12:45 pm
Wow, great information!
So I will give in and go for a Silica mine, rather than extract it from the same sandstone as the base.
As my first try was a bit too extravagant, here is the Lampyridae II dome.  Glass and steel, about 100 tonnes in all, excepting the internal structure and trees.

The ore hauler in the front is my solution to the resource problem.  At 20 tonnes per trip, 2 trips per day, 100 km each, it can carry in 40 x 200 = 8000 tonnes of various ores per year with plenty of down time for maintenance.
That's enough for all the special needs of the colony.  The very large volume items such as rock and water really need to come from the colony site, however.
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 01/25/2019 12:56 pm
A few views of the Marvel.
The idea is that a colony will want to build Marvels, from time to time, and not only purely utilitarian structures.
A park and a point of view.  Not too live in, too much radiation, but a few minutes up to a few hours per day.

The architecture is inspired by the nest stadium in China.
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 01/25/2019 01:22 pm
The question that needs to be answered is: What goes into the little box named 'Processing'
AIUI, it varies wildly depending on what exactly is in the source sand, there isn't a single method because there isn't a single set of contaminants.
This is all quite possible, but what is actually done, in real plants?

The thing that I said. It varies. Depending on the contaminants. There isn't a single recipe. My examples were things I've seen mentioned in regard to purifying silica sand for glass making. Glass makers just buy processed silica of the purity and grain-size required for the job.

Some contaminants are merely colourants, others are opacitants, so (from what I'm reading) you can sometimes offset some naturally occurring contamination by adding yet another salt that counters the colour of the contaminant. Magnesium oxide removes some of the colour of chrome oxide, IIRC, saving you from having to remove the chrome itself because neither salt is an opacitant.

The added salt needs to be very pure, of course, but the amounts are fairly small, tenths of a percent. So once you know the detailed composition of your best Martian silica source, you can ship in a few tonnes of customised additives from Earth to produce a thousand tonnes of clear glass. If you can do that, it will be easier than needing entirely separate processes to produce or recycle enough of the reagents needed to remove the contaminant.

But it all depends how pure the silica source it and what the contaminants are.

Are you assuming pure silica-glass and just wearing the energy cost, or are you looking for a substitute for limestone for soda-glass? (And accepting the industrial cost of finding sodium carbonate.)

Grinding requires a lot of energy.  Sand is pre-ground, that's one of the reasons it's used.

I've seen that sandstone is also used to make silica-sand, if it has the right purity. Purity wins over issues like grinding, apparently.

Everything I've seen seems to be water hungry, though. Lots of washing/rinsing stages. Water is king on Mars, again.

As far as processing goes, I expect it should be done in a large pressurized enclosure, it's a 1000 person colony, after all.

Yeah, there's an interesting trade between the cost of adding pressurised volume and the cost of not having it. Similarly, is the hassle of dealing with equipment in a partial vacuum more than the hassle of dealing with the heat coming off the kilns inside a pressure vessel?
I'm assuming substitutes are found for all items, so standard Soda glass.  Soda can be produced from salt, so even of there are no soda mines it can be created on site. 
Banished to the salt mines of Mars!!! has a nice ring to it, I find.
Sandstone is very easy to grind, most of the time, and compared to Basalt or granite, since it really wants to break down and become sand again.  As long as it hasn't been heated too much and turned into something else.  Guess it isn't sandstone anymore at that point.
Water is definitively the no 1 resource, for heating cooling and getting stuff in solution or suspension for separation.  Getting back to my diagram of a few posts back, I really think I need to have two water reserves, one industrial and one potable.  I guess the potable water might come from the Sabatier reaction, that produces a lot of water along with the methane, that should be quite pure.
Geting back to domes, a geodesic dome doesn't have to be perfectly hemispherical.  So even the rather extravagant shape I show might have a geodesic structure, although I'm not certain it's required.  Simple hoop shapes should be just as good for a pressure vessel.

Title: Re: Elon Musk: glass geodesic domes
Post by: Lampyridae on 01/25/2019 01:45 pm
Wow, great information!
So I will give in and go for a Silica mine, rather than extract it from the same sandstone as the base.
As my first try was a bit too extravagant, here is the Lampyridae II dome.  Glass and steel, about 100 tonnes in all, excepting the internal structure and trees.

The ore hauler in the front is my solution to the resource problem.  At 20 tonnes per trip, 2 trips per day, 100 km each, it can carry in 40 x 200 = 8000 tonnes of various ores per year with plenty of down time for maintenance.
That's enough for all the special needs of the colony.  The very large volume items such as rock and water really need to come from the colony site, however.


Looking good! A dome needn't have 100% transparent coverage or be absolutely gigantic to convey an outdoors feeling. This one is about maybe 20m in diameter, with the panes about 1.5m-2m across. The struts are plywood but could easily be concrete. I figure you could easily halve the diameter, put some plants in and still have a reasonable outdoorsy feel for the colonists and to promote the colony's image back on Earth.

EDIT: looking at this, I realised that one of the reasons why it seems so open is that its colour blends in with the ground. A Mars dome could use an ochre colour to match the more distant hills, making it feel more like you are sitting in the open inside some kind of geological feature.

(https://images.adsttc.com/media/images/515e/5811/b3fc/4bc5/2600/0191/large_jpg/IMG_1892.jpg?1365137422)

https://www.archdaily.com/355536/roskilde-dome-2012-kristoffer-tejlgaard/515e5811b3fc4bc526000191-roskilde-dome-2012-kristoffer-tejlgaard-image

When you get to monstrously large domes like The Tropicals Dome in Germany (300x200x100m) outside views kind of become irrelevant because you are in the outside (though it has huge ETFE window because the plants kept dying). That kind of thing I guess could be made with translucent concrete or illuminated with light pipes projecting onto interior panels, creating a blurry outdoors view.
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 01/25/2019 02:04 pm
Humidity control is likely to be a serious problem in a tropical, or even a cooler climate Mars dome.  You need to keep the glass temperature bellow the dew point ant at -50 and colder at night that will be difficult.
I have been thinking these domes would really have double glass panes, with reflective films on the inner and outer panes to increase the interior surface temperature.

The outside pane doesn't need to be load or pressure bearing, the near vacuum of Mars atmosphere beats any gas that could be inserted there.  It's more of a thermal control item.

The amount of light will go down, and that's another reason I expect Mars domes will be more 'decorative' and psychological than really practical. There may actually be a need for supplementary artificial light, that could be turned on for a period.  OR else mostly use shade plants.

A feature of the German dome highlights one of the problems of greenhouses: there are shades that reduce the light, I expect to avoid overheating during the day.  Most greenhouses I know of in our area (Quebec, Canada) need to be open in summer, something that is not possible on Mars.
Title: Re: Elon Musk: glass geodesic domes
Post by: Slarty1080 on 01/25/2019 02:08 pm
In response to several posts:
Concerning alumina: are there any pure alumina deposits available on Mars? If not then that would not really solve the problem as alumina would also need to be refined.

Concerning the pure silica: I'm impressed that silica of such high purity is available anywhere on Mars, although the glass created would be green due to the chromium impurities present as you suggest. Without materials like calcium and sodium carbonates the melting point would also be 1600+ degrees C so it won't be cheap on the electricity front and might not be that handy for the initial settlement either.

Concerning what is actually done in real plants (on Earth): is not necessarily what would be done in a real plant on Mars. Some sands on Earth may be used directly (I don’t know) but conditions are different on Mars. Silica deposits on Earth may well be higher purity and be in the right particle size due to more recent wet weathering, but handling will be different in reduced gravity near vacuum dry conditions with very fine particles where electrostatic attraction may well clog up the works. And in the one reported case of high purity silica we have to go on chromium contamination is significant.


Title: Re: Elon Musk: glass geodesic domes
Post by: edzieba on 01/25/2019 02:12 pm
Does glass give a significant mechanical advantage over plastics? Water is assumed to be available as a feedstock (for life-support and ISRU propellant) as is CO2 from the atmosphere, so generating polymers 'from scratch' is an option (or with processes like Methane -> Ethane -> Etylene -> Polythene), with little to no additional preprocessing of feedstocks over that required for life-support and ISRU use. At least in initial stages of colonisation, it would make more sense to use resources that have already been gathered rather than set up mining and processing operations.
Title: Re: Elon Musk: glass geodesic domes
Post by: RonM on 01/25/2019 02:39 pm
UV degrades plastic. Glass is a better longterm solution, assuming it's available.
Title: Re: Elon Musk: glass geodesic domes
Post by: spacenut on 01/25/2019 02:50 pm
If windows or domes are made of some type of plastic, wouldn't etching from sandstorms be a problem?  Also, a large building or open area doesn't have to have glass on top, but around the sides so people can see outside, like lots of windows.  then have a shutter system to close over these windows in sandstorms or solar flare activity headed towards Mars. 

Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 01/25/2019 03:25 pm
Does glass give a significant mechanical advantage over plastics? Water is assumed to be available as a feedstock (for life-support and ISRU propellant) as is CO2 from the atmosphere, so generating polymers 'from scratch' is an option (or with processes like Methane -> Ethane -> Etylene -> Polythene), with little to no additional preprocessing of feedstocks over that required for life-support and ISRU use. At least in initial stages of colonisation, it would make more sense to use resources that have already been gathered rather than set up mining and processing operations.
Plastics require far more energy on Mars than glass, IMHO.  Plastics would be made from methane, that is made from hydrogen.  Making the hydrogen is the most energy intense process of the early colony, as the oxygen-hydrogen bond is so strong.  That's why it's such a good fuel, BTW.

You might make plastics from algae tanks and oil, but even then the embodied energy is way higher than for glass. 

The interesting thing about glass is that it is made from an oxide, SiO2.  That means it doesn't need to be broken down in the glass making process.  In fact, if there is a use for the heat from the cooling of the glass, the actual energy used for glass making is even lower than what is usually found in  embodied energy tables, as these assume the energy for cooling the glass is lost to atmosphere.  Reasonable on Earth, but a real waste on Mars.  You would at least use the cooling of the finished glass to preheat the sand and other materials. 
In an ideal system, glass making would in fact use almost no energy, as there is very little energy added to the substance.  But of course recycling energy in a glass furnace is probably very far from 100% efficient. 20% maybe?
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 01/25/2019 03:35 pm
BTW, transportation on Mars, with practically no air resistance, lower gravity (less tire flex) and probably no driver will be ridiculously inexpensive.  As soon as passable dirt roads are found/built, of course.  So the distance of the source minerals for the glass or iron ore to build the domes in not necessarily that big a deal.
Title: Re: Elon Musk: glass geodesic domes
Post by: Lar on 01/25/2019 05:14 pm
Plastics might be a good interim solution until the industrial base and range of feedstocks has expanded significantly...  Glass might be more energy efficient but for very early stage production, the amount of new equipment needed might dominate the trades

on the other hand getting solar cell production up and running quickly might be so important that making glass is an easy by product of wafer production?
Title: Re: Elon Musk: glass geodesic domes
Post by: Slarty1080 on 01/25/2019 07:26 pm
Does glass give a significant mechanical advantage over plastics? Water is assumed to be available as a feedstock (for life-support and ISRU propellant) as is CO2 from the atmosphere, so generating polymers 'from scratch' is an option (or with processes like Methane -> Ethane -> Etylene -> Polythene), with little to no additional preprocessing of feedstocks over that required for life-support and ISRU use. At least in initial stages of colonisation, it would make more sense to use resources that have already been gathered rather than set up mining and processing operations.
Plastics require far more energy on Mars than glass, IMHO.  Plastics would be made from methane, that is made from hydrogen.  Making the hydrogen is the most energy intense process of the early colony, as the oxygen-hydrogen bond is so strong.  That's why it's such a good fuel, BTW.

You might make plastics from algae tanks and oil, but even then the embodied energy is way higher than for glass. 

The interesting thing about glass is that it is made from an oxide, SiO2.  That means it doesn't need to be broken down in the glass making process.  In fact, if there is a use for the heat from the cooling of the glass, the actual energy used for glass making is even lower than what is usually found in  embodied energy tables, as these assume the energy for cooling the glass is lost to atmosphere.  Reasonable on Earth, but a real waste on Mars.  You would at least use the cooling of the finished glass to preheat the sand and other materials. 
In an ideal system, glass making would in fact use almost no energy, as there is very little energy added to the substance.  But of course recycling energy in a glass furnace is probably very far from 100% efficient. 20% maybe?
Plastics will require a lot of energy for sure due to the use of hydrogen CO2 + H2 > CO +H2O then 2CO + 2H2 > C2H2 + H20, But so will glass. Unless there is a source of high quality sodium/ calcium carbonate or an equivalent we are talking silica glass with a very high melting point 1600 deg C so a lot of energy will be needed and the impurities in the silica such as chromium need to be dealt wit to avoid bottle green glass.
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 01/25/2019 07:59 pm
Does glass give a significant mechanical advantage over plastics? Water is assumed to be available as a feedstock (for life-support and ISRU propellant) as is CO2 from the atmosphere, so generating polymers 'from scratch' is an option (or with processes like Methane -> Ethane -> Etylene -> Polythene), with little to no additional preprocessing of feedstocks over that required for life-support and ISRU use. At least in initial stages of colonisation, it would make more sense to use resources that have already been gathered rather than set up mining and processing operations.
Plastics require far more energy on Mars than glass, IMHO.  Plastics would be made from methane, that is made from hydrogen.  Making the hydrogen is the most energy intense process of the early colony, as the oxygen-hydrogen bond is so strong.  That's why it's such a good fuel, BTW.

You might make plastics from algae tanks and oil, but even then the embodied energy is way higher than for glass. 

The interesting thing about glass is that it is made from an oxide, SiO2.  That means it doesn't need to be broken down in the glass making process.  In fact, if there is a use for the heat from the cooling of the glass, the actual energy used for glass making is even lower than what is usually found in  embodied energy tables, as these assume the energy for cooling the glass is lost to atmosphere.  Reasonable on Earth, but a real waste on Mars.  You would at least use the cooling of the finished glass to preheat the sand and other materials. 
In an ideal system, glass making would in fact use almost no energy, as there is very little energy added to the substance.  But of course recycling energy in a glass furnace is probably very far from 100% efficient. 20% maybe?
Plastics will require a lot of energy for sure due to the use of hydrogen CO2 + H2 > CO +H2O then 2CO + 2H2 > C2H2 + H20, But so will glass. Unless there is a source of high quality sodium/ calcium carbonate or an equivalent we are talking silica glass with a very high melting point 1600 deg C so a lot of energy will be needed and the impurities in the silica such as chromium need to be dealt wit to avoid bottle green glass.
It's not an obvious concept, but unless there is a permanent phase change or a chemical reaction, heating doesn't really require much energy, as long as you can recover the heat and reduce heat losses.  On Earth, very few industries bother because energy is so cheap, but on Mars there will be a great incentive to use energy efficient solutions. 
Probably not new solutions, BTW, just solutions that are not cost effective here, but would be there.

There will be sodium sources, it's a very common geological process of evaporation that we know happened on Mars.  And some has been seen from orbit.  Finding all required elements nicely concentrated in a reasonable distance will be a lot of footwork by geologist though.  Calcium carbonate has also been detected from orbit, so there should be concentrated sources as well.  Chromium is perhaps not all that common in the lithosphere, so there would be areas without it.  Wikipedia tells me it's 500 times less abundant than Iron, so light green glass is more likely :-)
https://en.wikipedia.org/wiki/Abundance_of_elements_in_Earth%27s_crust

Glass is Oxygen, Silicium, Sodium, Calcium and Aluminium.  So a mix of no 1,2,3,5,6.  The only one we want to remove is 4, Iron.  It's literally made of all of the most common elements available.  You know, I'm beginning to really like the stuff.
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 01/26/2019 07:04 am
Re: Silica vs soda glass.

It's probably worth remembering that pure silica glass has low thermal expansion compared to soda glass. Given the day/night variation, combined with how tight you want the gas-seals to be, you need to match the thermal properties to the frame. (Also, I believe pure silica glass is stronger than soda glass.)

Re: double glazing.

I think you'd have a bunch of layers for redundancy and thermal management, with less and less pressure between the layers as you move outwards, and enough strength that you can lose (break) any one layer without overstressing the next. Each layer would also be a laminate with plastic to lessen the chance that an impact goes through all layers. The outside of the outer layer would have an anti-abrasion coating. The inside of the inside layer might have a hydrophobic coating.
Title: Re: Elon Musk: glass geodesic domes
Post by: Lar on 01/26/2019 01:59 pm
Many many layers sounds good but the plumbing to maintain 5-10 different incremental pressures might be complex. Or would it be done with each pane and sealed as a unit so it was a sandwich of 5-10 layers that looked superficially like a glass brick from the side?

What would be a good anti abrasion coating? What if the answer was limited to "easy early stage ISRU" (whatever that means to you)?
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 01/26/2019 03:22 pm
Here is an image of my suggested frame arrangement.

Lot's of empty space that acts as an insulator, a vacuum flask, in a sense.
Minimum conduction, although a thermal break might be nice, if feasible.  The may be cold spots due to conduction in the walls.
Thick inner glass, for strength.
Thinner outer glass, that really serves to hold the low E films to reduce radiation.  Acts as multi layer insulation.  Calculated the same way.
https://en.wikipedia.org/wiki/Multi-layer_insulation

The frame would be extruded, or folded and welded from a flat plate.
Would need to look at the corners, the most likely spots for leaks.
The shape hides the sealant from most ultra violets, I hope.

The inner window is pressed into place by atmospheric pressure, and cannot pop out.  The outer glass is screwed into place to hold the glass, but has no real structural purpose.

How tough is 1/2 inch glass?  Seems to me it would be really hard to break.
The inner glass has to stand up to 10 tonnes, and is 1m across.
Anyone have a handy formulae for the strain in a flat plate resting on all four sides, with a spreaded out uniform load?

If the inner glass pane breaks, the outer pane can hold pressure, but leaks.  So repairs are required but can be done from the inside.

For scratches, we might laser sinter on a layer of pure silica, or even a thin layer of alumina?  Probaly too complex though.
Might simple replace the outer panes when transparency goes down too much.  This needs to be done from the outside, but only, perhaps, once a decade?
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 01/26/2019 05:29 pm
Modified so that the glass always lays flat on the frame despite changes in angles.
Will require good cutting and welding at the angles.

Added multilayer insulation to stop heat loss through the frame.
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 01/26/2019 11:45 pm
Many many layers sounds good but the plumbing to maintain 5-10 different incremental pressures might be complex.

You aren't using pumps to continually modify their pressure. It's once-and-done during assembly. If it leaks, you have to pop that whole pane and reseal anyway.

Or would it be done with each pane and sealed as a unit so it was a sandwich of 5-10 layers that looked superficially like a glass brick from the side?

Not a brick, but yes multiple layers in a single, pre-assembled, sealed panel. (Span-width depending on the strength of the glass.) Similarly to how double/triple-glazed panels are made on Earth. (As below.)

Given the low production numbers, you can presumably assemble the layers directly, one layer at a time, into the main structural frame, as Lamontagne has shown. But I think being able to put everything together in a clean controlled environment on the ground, working at a convenient height in a pressurised area, and then merely hoisting each assembled unit into the main frame, would be easier than doing the detailed assembly work one layer at a time on the frame, in EVA suits, at height.

What would be a good anti abrasion coating?

AIUI, usually just a thin layer of glass doped with another metal-oxide(s).

Although, given the recyclability of glass, they might just accept a shorter lifespan and replace them more often, throwing the old panes into the cullet, old frames into the iron-works. (Larger amounts of a single generalised thing over smaller amounts of many specialised things.) That's especially the case if they expect to replace entire structures often due to the expansion of the settlement.



(https://www.homeinsulations.co.za/wp-content/uploads/2016/12/double-glazing-in-south-africa-1024x1024.jpg)
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 01/27/2019 01:57 am
I don't really think we need 5 layers of windows.

There is an interesting product called safety film, manufactured by 3M, that would be just fine for our nice domes.
I've joined a brochure.  At 0,2mm thick, we can afford to bring it all the way from Earth.  It was used recently in a project I worked on.  We didn't try to break the windows though.  There is a video as well.
https://www.youtube.com/watch?v=cZy4DJHM_fs

Plus another video on Youtube with a bad person shooting through the window.  That I can't copy here, presumably because it is scary.

By putting a low-e film on the inside of the exterior glass, radiation can be reduced by a very large value,  97% if I understand the product literature correctly.  Meaning that a single layer of film will reduce heat loss to practically nothing, as the near vacuum between the two panes eliminates most convection.   This film is usually used to keep the sun out, so it's not good for a greenhouse, but I think it would do fine for a park/common area dome.

Multilayer film seems to actually be overkill, since it can essentially reduce thermal losses to 0, when used in space with a large number of layers.
I join a standard manufacturer's flyer, plus a NASA spec for multilayer insulation.  Interestingly, it can also be created as a type of foam, so I see it used as a thermal barrier on underground installations as well, rather than what we usually think of as insulation.
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 01/27/2019 05:36 am
I don't really think we need 5 layers of windows. [safety film]

You should remember that the windows will have a large pressure difference. Even with 5 layers, you're looking at 20kPa against each layer, or 2 tonnes of force per square metre. That's a substantial increase on the next layer if a layer breaks.

With two layers, that's 5 tonnes per square metre on each layer. Break one layer and you are slamming an extra 5 tonnes of force per square metre on the next (and only) layer.

As for thermal, I note that triple-glazing is becoming increasingly common for temperate-climate homes, where you have maybe 20℃ difference between inside and outside. Having 100℃ difference is a little bit worse.

By putting a low-e film on the inside of the exterior glass, radiation can be reduced by a very large value,  97% if I understand the product literature correctly. Meaning that a single layer of film will reduce heat loss to practically nothing,

No quite. There's two components to thermal radiation: the IR being generated from the surfaces inside the room (or from sunlight outside) and passing through the window, and then there's the IR generated by the window itself. By adding an IR reflecting film, you can reduce the amount of IR passing through the window (that's where the 97% figure comes from), but you can't stop the window pane itself emitting black-body radiation proportionate to its own temperature. The marketing dept likes to quote the big impressive figure.
Title: Re: Elon Musk: glass geodesic domes
Post by: Dalhousie on 01/27/2019 06:34 am
Window glass needs a minimum purity of 99.5%.  The highest purity found on Mars to date, at Home Plate in Gusev Crater, is still substandard. https://www.verdantminerals.com.au/projects/dingo-hole-silica-project-nt/silica-high-purity-quartz-information

Silica rich deposits on Mars appear rare, and Home plate is an exception. Martian sand is not silica rich, unlike that on Earth, and martian sandstone is lithic in character.  Mars has not had, as far as we can tell, the type of tectonic-magmatic processes that produce silica rich rocks, nor the multiple cycles of erosion and deposition that produce highly purity quartz sands and sandstones.
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 01/27/2019 01:30 pm
Ok, I give in.  We will not fine sufficiently pure sand on Mars.  We need to treat it. 

Now, how do we do that?   Metallurgirst 911 to the rescue (I kid you not):

https://www.911metallurgist.com/blog/silica-sand-processing-sand-washing-plant-equipment

The key terms seem to be flotation and classification.  Floatation should work fine, classification is a type of gravity separation so it will require experiment in situ before it can be used.  You just can't do reduced gravity experiments.  So it is basically impossible to completely design a production line at this point.

So i'll concentrate on acids and regents, as possible choke points for production.

By the way, joined is an image of sand production plant from Fledspar in Brazil. It even has the geodesic dome!  Joined the original pdf description of the installation. 


Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 01/27/2019 01:43 pm
A first suggested path for sulfuric acid production:
Wash pretty much any martian sand.  6 to 22% concentration of SO3!! Instant acid. 
SO3 + H2O=H2SO4.   
That was simple  ;-)

Title: Re: Elon Musk: glass geodesic domes
Post by: Slarty1080 on 01/27/2019 01:56 pm
A first suggested path for sulfuric acid production:
Wash pretty much any martian sand.  6 to 22% concentration of SO3!! Instant acid. 
SO3 + H2O=H2SO4.   
That was simple  ;-)

And where does the SO3 come from?
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 01/27/2019 02:02 pm
The second item we need as a reagent seems to be a frothing agent.  Pine oil or bunker oil.  More modern references send us to glycols, for example CH3OCH2CH2OH.  C and O and H. Ethylene glycol ethers.
Joined is a process diagram of that.
So alcool production, that comes from biomass and biological reactors.
Then a catalyst.  That should come from Earth as part of the equipment.
Then ethylene oxyde.  That needs further research.

BTW, if frothing agents are 1% of the mass of production, then for 500 tonnes per year of glass we can simply ship 5 tonnes of Ethylene glycol ethers from Earth.  But the 1% is just a guess.  Might be anything at this point.

Amazing what can be done with bubbles and sticky stuff!  We'll need them for most separation processes anyway.
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 01/27/2019 02:04 pm
A first suggested path for sulfuric acid production:
Wash pretty much any martian sand.  6 to 22% concentration of SO3!! Instant acid. 
SO3 + H2O=H2SO4.   
That was simple  ;-)

And where does the SO3 come from?

Please read the joined paper.  Mars seems oversupplied with the stuff.  My guess is that it washes out by simple immersion, but perhaps we need a crushing step first.
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 01/27/2019 02:28 pm
So Ethylene oxyde production.  Almost there.

Silver catalyst from Earth.  Check.
Oxygen. Check.
Ethylene. That's a harder one to crack.

Option 1- Oxidative coupling of methane.  Hum, theoretical but not effective because there is no good catalyst.  Perhaps if we find nothing better.  Probably beats shipping from Earth even at low yields. 
Option 2- Ship ethylene from Earth.  Doesn't seem to be much of a mass gain over shipping the finished product.
Option 3- Ship ethane from Earth.  Same as option 2.
Option 4- Steam cracking of larger hydrocarbons.  That would be a by product of the plastics industry, based on biological sources oils.  Perhaps our best bet?
Wonder what the ethane fraction is in steam cracking.

So options 1 or 4, at worst 3 if the reagent requirements are low.  Am I allowed to say that that should be solvable and use In situ produced glass for geodesic domes now?   :)

Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 01/27/2019 02:50 pm
Ahha!  The Fischer–Tropsch process

Perfect!  The CO2 and H2 are fed into a Fischer Tropsch process, just like the Sabatier process but it makes more fun stuff, and the ethylene fraction is used to produce Ethylene oxyde, then Ethylene glycol ethers.

https://en.wikipedia.org/wiki/Fischer%E2%80%93Tropsch_process

Now can I use in-situ glass production?  : ;)

Title: Re: Elon Musk: glass geodesic domes
Post by: Lar on 01/27/2019 03:28 pm
That's some impressive synthesis of synthesis paths, Lamontagne... nice work. Ethylene oxide is an important precursor to a lot of things. I was surprised about the sulfuric acid just falling out from cleaning things... looks like it's even easier than HCl ...

I think we still missed the part about getting pure silica though. Are we sure that if we grind martian rock fine enough we get quartz grains, not some other mineral that has impurities like iron alloyed in?
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 01/27/2019 03:58 pm
An updated process diagram. 
Although the processing box remains the same, it now feeds water treatment, and, although I ran out of place to show the entire pertrochemical process, it gets reagents from the hydrocarbons box at the bottom.

Adic H2SO4 tank from heating and washing rock,

Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 01/27/2019 04:38 pm
That's some impressive synthesis of synthesis paths, Lamontagne... nice work. Ethylene oxide is an important precursor to a lot of things. I was surprised about the sulfuric acid just falling out from cleaning things... looks like it's even easier than HCl ...

I think we still missed the part about getting pure silica though. Are we sure that if we grind martian rock fine enough we get quartz grains, not some other mineral that has impurities like iron alloyed in?

Thanks!  Good thing I've talked a lot over the years with my geologist brother :-)  because I'm far from my real expertise here.

This is my understanding of the process:

As liquid magma solidifies, or as solutions in water precipitate when water evaporates, crystals form.  These crystals naturally exclude other minerals from their structure and produce small, or sometimes larger, nuggets of pure minerals, mixed with other minerals that have also produced crystals.  So you get rock.  Crushing and milling breaks the different types of mixtures naturally along their contact lines.  With sufficient crushing in the presence of water, you will eventually produce a sludge of mixed minerals, some of which are the ones you want, the ore. The stuff you don't want is the gangue.

https://en.wikipedia.org/wiki/Gangue
https://en.wikipedia.org/wiki/Mineral_processing

Separating the sludge into the various batches of crystals is done by various means, as Wikipedia nicely describes.
It would seem that separating out SiO2 crystals is not one of the most complex processes, at least from what I found in my little research. 
Title: Re: Elon Musk: glass geodesic domes
Post by: Dalhousie on 01/27/2019 05:05 pm
Ok, I give in.  We will not fine sufficiently pure sand on Mars.  We need to treat it. 

Now, how do we do that?   Metallurgirst 911 to the rescue (I kid you not):

https://www.911metallurgist.com/blog/silica-sand-processing-sand-washing-plant-equipment

The key terms seem to be flotation and classification.  Floatation should work fine, classification is a type of gravity separation so it will require experiment in situ before it can be used.  You just can't do reduced gravity experiments.  So it is basically impossible to completely design a production line at this point.

So i'll concentrate on acids and regents, as possible choke points for production.


By the way, joined is an image of sand production plant from Fledspar in Brazil. It even has the geodesic dome!  Joined the original pdf description of the installation.

Washing only removes easily separated contaminants, such as clays. 

It can't create the high purity silica you need in the first place. Which does not appear to occur on Mars in any quality.
Title: Re: Elon Musk: glass geodesic domes
Post by: Lar on 01/27/2019 05:09 pm
Also, Fischer-Tropf has methane as an "unwanted" side product. I bet we can find a use for it...

Title: Re: Elon Musk: glass geodesic domes
Post by: Lar on 01/27/2019 05:14 pm
Washing only removes easily separated contaminants, such as clays. 

It can't create the high purity silica you need in the first place. Which does not appear to occur on Mars in any quality.

Silicon is one of the most common elements. Are you saying
- Mars has no silicon? I'm dubious of that one
- Or that all silicon is bound up in other compounds than SiO2? If so which ones?
- Or that the SiO2 is mixed (alloyed) with other compounds in a  way that  no amount of crushing to get finer and finer grains will allow it to be mechanically separated? (that's the one I was afraid of, but see above, lamontagne is saying that the melts form pure crystals of various things. The crystals may be intermingled, but they are pure if you just crush fine enough and then separate)

Did I miss any possibilities?

Title: Re: Elon Musk: glass geodesic domes
Post by: Slarty1080 on 01/27/2019 05:17 pm
A first suggested path for sulfuric acid production:
Wash pretty much any martian sand.  6 to 22% concentration of SO3!! Instant acid. 
SO3 + H2O=H2SO4.   
That was simple  ;-)

And where does the SO3 come from?

Please read the joined paper.  Mars seems oversupplied with the stuff.  My guess is that it washes out by simple immersion, but perhaps we need a crushing step first.

The quoted SO3 percentages are for a variety of sulphides and sulphates all expressed in terms of SO3 equivalent for comparative purposes. In the same way if you look at fertilizers you will see them quotes as N-P-K but they do not contain Nitrogen, phosphorous or Potassium in elemental form. Alternatively you might see Phosphorous and Potassium quoted as their oxide equivalents P2O5 and K2O.

You can see the same idea in use for Martian soil samples here:

https://en.wikipedia.org/wiki/Martian_soil#/media/File:PIA16572-MarsCuriosityRover-RoverSoils-20121203.jpg

Note Martian soil does not contain any Na2O as it reacts with Carbon dioxide to form the carbonate. The Soil sodium content is merely expressed as Na2O for comparative purposes. Similarly with “Cl” most of that is probably mostly in the form of perchlorate rather than chloride.

That said I’m sure that sulphuric acid can be produced given a source of sulphur or sulphate.

Concerning the ethylene oxide
Ethylene oxide is one of the most important organic molecules synthesised industrially (in the top 20). It can be produced by controlled oxidation of ethylene (which itself can be synthesised from carbon dioxide and hydrogen as noted up thread). Ethylene will be a key material for plastics and ethylene oxide can be used to make ethyl alcohol, ethylene glycol and a wide range of other organic chemicals.
Title: Re: Elon Musk: glass geodesic domes
Post by: blasphemer on 01/27/2019 05:19 pm
That diagram really shows a nice overview of the whole thing. Great work, lamontagne!  :)
Title: Re: Elon Musk: glass geodesic domes
Post by: blasphemer on 01/27/2019 05:29 pm
Someone correct me if I am wrong, but didnt Zubrin mention in his Case for Mars book that he worked on experiments synthetizing methane from Martian atmosphere analog and then various hydrocarbons/plastics from it? Could be useful to find those papers..
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 01/27/2019 05:30 pm
A first suggested path for sulfuric acid production:
Wash pretty much any martian sand.  6 to 22% concentration of SO3!! Instant acid. 
SO3 + H2O=H2SO4.   
That was simple  ;-)

And where does the SO3 come from?

Please read the joined paper.  Mars seems oversupplied with the stuff.  My guess is that it washes out by simple immersion, but perhaps we need a crushing step first.

The quoted SO3 percentages are for a variety of sulphides and sulphates all expressed in terms of SO3 equivalent for comparative purposes. In the same way if you look at fertilizers you will see them quotes as N-P-K but they do not contain Nitrogen, phosphorous or Potassium in elemental form. Alternatively you might see Phosphorous and Potassium quoted as their oxide equivalents P2O5 and K2O.

You can see the same idea in use for Martian soil samples here:

https://en.wikipedia.org/wiki/Martian_soil#/media/File:PIA16572-MarsCuriosityRover-RoverSoils-20121203.jpg

Note Martian soil does not contain any Na2O as it reacts with Carbon dioxide to form the carbonate. The Soil sodium content is merely expressed as Na2O for comparative purposes. Similarly with “Cl” most of that is probably mostly in the form of perchlorate rather than chloride.

That said I’m sure that sulphuric acid can be produced given a source of sulphur or sulphate.

Concerning the ethylene oxide
Ethylene oxide is one of the most important organic molecules synthesised industrially (in the top 20). It can be produced by controlled oxidation of ethylene (which itself can be synthesised from carbon dioxide and hydrogen as noted up thread). Ethylene will be a key material for plastics and ethylene oxide can be used to make ethyl alcohol, ethylene glycol and a wide range of other organic chemicals.
Ah that makes more sense!  I was wondering how such an energetic substance could have survived so long.
So are these sulfides and sulphates easily transformable into sulfuric acid?  I'm guessing it's no.
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 01/27/2019 05:31 pm
That diagram really shows a nice overview of the whole thing. Great work, lamontagne!  :)
Thanks!  However, it's already out of date as my sulfuric acid production method was based on ignorance rather than actual facts,  :-)
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 01/27/2019 05:33 pm
Someone correct me if I am wrong, but didnt Zubrin mention in his Case for Mars book that he worked on experiments synthetizing methane from Martian atmosphere analog and then various hydrocarbons/plastics from it? Could be useful to find those papers..
Many of Zubrin's papers are in the publicly accessible archives of the MArs Society web site.
Perhaps I should go have a look myself, rather than inventing square wheels  :D. 

Anyway, here is another version that produces the sulfuric acid from gypsum, calcium sulfate, inside the magic processing box.  Hope this one works.
Title: Re: Elon Musk: glass geodesic domes
Post by: Slarty1080 on 01/27/2019 06:36 pm
Washing only removes easily separated contaminants, such as clays. 

It can't create the high purity silica you need in the first place. Which does not appear to occur on Mars in any quality.

Silicon is one of the most common elements. Are you saying
- Mars has no silicon? I'm dubious of that one
- Or that all silicon is bound up in other compounds than SiO2? If so which ones?
- Or that the SiO2 is mixed (alloyed) with other compounds in a  way that  no amount of crushing to get finer and finer grains will allow it to be mechanically separated? (that's the one I was afraid of, but see above, lamontagne is saying that the melts form pure crystals of various things. The crystals may be intermingled, but they are pure if you just crush fine enough and then separate)

Did I miss any possibilities?
Mars has plenty of Silicon chemically bound up in both silica and silicates both of which occur physically mixed with a variety of other minerals and impurities. But in at least one (and probably many) places on Mars relatively pure silica SiO2 does exist. Unfortunately the one example we have to go on it is contaminated with small amounts of Chromium which even in said small quantities will produce a very green coloured glass. IMO it is unlikely that glass grade silica will be found on the surface of Mars and some degree of processing will be required.

The nature of the processing will depend upon the nature of the impurities and the crystal structure of the starting material. A lot of research and development will be required on both Mars and Earth to produce a viable process. First decide where you are going to land. Then see if there is a viable source of silica nearby. Then determine what impurities it contains and what its crystal structure is. Then consider what physical and chemical separation and purification methods might be appropriate bearing in mind that Mars has a reduced gravity and a near vacuum. And everything used must be recycled in order to make the process viable. Then try it out on Mars refine the process and scale it up. Might take quite a while.

It’s too soon to say which processes will be used, but in many cases they may not resemble the processes used on Earth due to the very different conditions. For example froth floatation may not work as anticipated under reduced gravity and things like acid washing to “waste” will be out.
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 01/27/2019 07:14 pm
Washing only removes easily separated contaminants, such as clays. 

It can't create the high purity silica you need in the first place. Which does not appear to occur on Mars in any quality.

Silicon is one of the most common elements. Are you saying
- Mars has no silicon? I'm dubious of that one
- Or that all silicon is bound up in other compounds than SiO2? If so which ones?
- Or that the SiO2 is mixed (alloyed) with other compounds in a  way that  no amount of crushing to get finer and finer grains will allow it to be mechanically separated? (that's the one I was afraid of, but see above, lamontagne is saying that the melts form pure crystals of various things. The crystals may be intermingled, but they are pure if you just crush fine enough and then separate)

Did I miss any possibilities?
Mars has plenty of Silicon chemically bound up in both silica and silicates both of which occur physically mixed with a variety of other minerals and impurities. But in at least one (and probably many) places on Mars relatively pure silica SiO2 does exist. Unfortunately the one example we have to go on it is contaminated with small amounts of Chromium which even in said small quantities will produce a very green coloured glass. IMO it is unlikely that glass grade silica will be found on the surface of Mars and some degree of processing will be required.

The nature of the processing will depend upon the nature of the impurities and the crystal structure of the starting material. A lot of research and development will be required on both Mars and Earth to produce a viable process. First decide where you are going to land. Then see if there is a viable source of silica nearby. Then determine what impurities it contains and what its crystal structure is. Then consider what physical and chemical separation and purification methods might be appropriate bearing in mind that Mars has a reduced gravity and a near vacuum. And everything used must be recycled in order to make the process viable. Then try it out on Mars refine the process and scale it up. Might take quite a while.

It’s too soon to say which processes will be used, but in many cases they may not resemble the processes used on Earth due to the very different conditions. For example froth floatation may not work as anticipated under reduced gravity and things like acid washing to “waste” will be out.
Absolutely.  It's all very speculative.  There will be separation, and processing but their exact nature can only be guessed at.  I do think that there are no obvious show stoppers to producing glass, but there may be un-obvious ones.  The very question of what might be a viable Mars base/colony is open to debate, and there are many, many people that feel the whole idea is absurd.

Exploration will give the answers.  And for that we need in situ fuel, but hardly in situ glass. However, this is the glass geodesic dome thread, so we need to talk about glass  :) I think we have gone over all the required elements of what might be needed to make glass, but if there is anything else major, i'll be glad to add it to the process.
Title: Re: Elon Musk: glass geodesic domes
Post by: Lampyridae on 01/27/2019 07:19 pm
I think the floatation will work just fine under Martian gravity. Might take a while longer, but we can do testing with reduced gravity parabola flights.. But you can always just supply extra gravity with centrifugal force. There are a lot of things we don't bother with on Earth due to the relative low value of the materials involved, so I reckon there is plenty of room for ISRU innovation.

I like the idea of plastics from the atmosphere and ice. Cuts out the heavy business of mining entirely.

Re: no quartz on Mars. Quartz has been positively identified in Martian meteorites.

And at the end of the day, if the colonists are really really desperate they can grab some olivine (everywhere on Mars, just like the Moon) and run CO2 over it at high pressure. Result: silicon dioxide, magnesium carbonate and some iron oxides. The reaction is slow but somewhat exothermic; it's been studied for carbon sequestration on Earth.
Title: Re: Elon Musk: glass geodesic domes
Post by: Slarty1080 on 01/27/2019 07:49 pm
I think the floatation will work just fine under Martian gravity. Might take a while longer, but we can do testing with reduced gravity parabola flights.. But you can always just supply extra gravity with centrifugal force. There are a lot of things we don't bother with on Earth due to the relative low value of the materials involved, so I reckon there is plenty of room for ISRU innovation.

I like the idea of plastics from the atmosphere and ice. Cuts out the heavy business of mining entirely.

Re: no quartz on Mars. Quartz has been positively identified in Martian meteorites.

And at the end of the day, if the colonists are really really desperate they can grab some olivine (everywhere on Mars, just like the Moon) and run CO2 over it at high pressure. Result: silicon dioxide, magnesium carbonate and some iron oxides. The reaction is slow but somewhat exothermic; it's been studied for carbon sequestration on Earth.

Yes, these is certainly no shortage of silica on Mars, just a variety of impurities and a variety of possibilities for purification.
Title: Re: Elon Musk: glass geodesic domes
Post by: Lar on 01/28/2019 02:21 pm
I think the floatation will work just fine under Martian gravity. Might take a while longer, but we can do testing with reduced gravity parabola flights.. But you can always just supply extra gravity with centrifugal force. There are a lot of things we don't bother with on Earth due to the relative low value of the materials involved, so I reckon there is plenty of room for ISRU innovation.

I like the idea of plastics from the atmosphere and ice. Cuts out the heavy business of mining entirely.

Re: no quartz on Mars. Quartz has been positively identified in Martian meteorites.

And at the end of the day, if the colonists are really really desperate they can grab some olivine (everywhere on Mars, just like the Moon) and run CO2 over it at high pressure. Result: silicon dioxide, magnesium carbonate and some iron oxides. The reaction is slow but somewhat exothermic; it's been studied for carbon sequestration on Earth.

Yes, these is certainly no shortage of silica on Mars, just a variety of impurities and a variety of possibilities for purification.

The chromium contaminants you referred to... are those alloyed with the crystals of SiO2 ??? because I think the point being made is that if you grind fine enough, you'll get some particles that are pure crystals of each thing (and some that still, even being very small, have grain boundaries and have some of each thing.... those you discard or (if you have the energy budget) melt and recrystalise)

If you refer to the gold thread that Lake Matthew Team posted a lot of good resources to, there seems to be a lot of work done  in the industry on mechanically and chemically separating things, even at trace levels
Title: Re: Elon Musk: glass geodesic domes
Post by: Slarty1080 on 01/28/2019 05:22 pm
I think the floatation will work just fine under Martian gravity. Might take a while longer, but we can do testing with reduced gravity parabola flights.. But you can always just supply extra gravity with centrifugal force. There are a lot of things we don't bother with on Earth due to the relative low value of the materials involved, so I reckon there is plenty of room for ISRU innovation.

I like the idea of plastics from the atmosphere and ice. Cuts out the heavy business of mining entirely.

Re: no quartz on Mars. Quartz has been positively identified in Martian meteorites.

And at the end of the day, if the colonists are really really desperate they can grab some olivine (everywhere on Mars, just like the Moon) and run CO2 over it at high pressure. Result: silicon dioxide, magnesium carbonate and some iron oxides. The reaction is slow but somewhat exothermic; it's been studied for carbon sequestration on Earth.

Yes, these is certainly no shortage of silica on Mars, just a variety of impurities and a variety of possibilities for purification.

The chromium contaminants you referred to... are those alloyed with the crystals of SiO2 ??? because I think the point being made is that if you grind fine enough, you'll get some particles that are pure crystals of each thing (and some that still, even being very small, have grain boundaries and have some of each thing.... those you discard or (if you have the energy budget) melt and recrystalise)

If you refer to the gold thread that Lake Matthew Team posted a lot of good resources to, there seems to be a lot of work done  in the industry on mechanically and chemically separating things, even at trace levels
IMO it’s likely that a lot of the impurities are present as separate grains, although there will presumably still be some level of “alloyed” impurities. Whether the best method of purification is physical, chemical or a combination remains to be seen and will depend on the nature of the impurities. There are many options for both types of processing and it will take a fair amount of research to determine the best method.
Title: Re: Elon Musk: glass geodesic domes
Post by: rsdavis9 on 01/28/2019 06:00 pm
In general a good half of all plutonic rocks will probably have quartz grains in them.
Here are some sources showing you the element contents and the resulting mineral composition.
https://en.wikipedia.org/wiki/QAPF_diagram
https://en.wikipedia.org/wiki/TAS_classification

Basically it all boils down to the ratio of alkali elements (Na K) to Si.
So I am not too worried about finding large deposits of granites or the likes.
The other source of very pure quartz is hydrothermal deposits. Basically hot, high pressure water on cracks that deposits its dissolve SiO2 when cooled.
Where I live in NH there is huge mountains made of quartzite. A white rock formed of mostly pure quartz in a very fine grain form. These deposits are hydrothermal.
And mars did have water at one point.
And it did have molten rock at one point. Olympus Mons tallest volcano in the Solar System.

Title: Re: Elon Musk: glass geodesic domes
Post by: Slarty1080 on 01/28/2019 06:16 pm
In general a good half of all plutonic rocks will probably have quartz grains in them.
Here are some sources showing you the element contents and the resulting mineral composition.
https://en.wikipedia.org/wiki/QAPF_diagram
https://en.wikipedia.org/wiki/TAS_classification

Basically it all boils down to the ratio of alkali elements (Na K) to Si.
So I am not too worried about finding large deposits of granites or the likes.
The other source of very pure quartz is hydrothermal deposits. Basically hot, high pressure water on cracks that deposits its dissolve SiO2 when cooled.
Where I live in NH there is huge mountains made of quartzite. A white rock formed of mostly pure quartz in a very fine grain form. These deposits are hydrothermal.
And mars did have water at one point.
And it did have molten rock at one point. Olympus Mons tallest volcano in the Solar System.
True Mars did have water and molten rock at some early point, but that was a long time ago and in all ikelyhood there have been billions of years with very little water and a lot of very fine dust blowing all over the planet.
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 01/30/2019 02:03 am
In general a good half of all plutonic rocks will probably have quartz grains in them.
Here are some sources showing you the element contents and the resulting mineral composition.
https://en.wikipedia.org/wiki/QAPF_diagram
https://en.wikipedia.org/wiki/TAS_classification

Basically it all boils down to the ratio of alkali elements (Na K) to Si.
So I am not too worried about finding large deposits of granites or the likes.
The other source of very pure quartz is hydrothermal deposits. Basically hot, high pressure water on cracks that deposits its dissolve SiO2 when cooled.
Where I live in NH there is huge mountains made of quartzite. A white rock formed of mostly pure quartz in a very fine grain form. These deposits are hydrothermal.
And mars did have water at one point.
And it did have molten rock at one point. Olympus Mons tallest volcano in the Solar System.
True Mars did have water and molten rock at some early point, but that was a long time ago and in all ikelyhood there have been billions of years with very little water and a lot of very fine dust blowing all over the planet.
In my little research on glass, I came across the information that most wind blown dunes, such as the ones in Michigan where in fact too coarse for glass making and needed to be ground finer.  So who knows, really what we will find?  Wind separation, or centrifugal separation, is often used to differentiate out materials with different densities, so there may be spots where this happened on Mars.
Anyway, on the first ships to Mars, I expect we will include a complete process lab, with miny grinders, mini cyclones, mesh separator, reagents and all that good stuff to actually measure the conditions and determine what can be done.  Then they will then have a synod or so to react before they send the next ships, with appropriate process equipment.  I expect you can do quite a bit with 100 tonnes.
Title: Re: Elon Musk: glass geodesic domes
Post by: Lar on 01/30/2019 02:06 am
If the cyclones, grinders, separators, etc are made to be adjustable, they can get pilot production going with the first human shipload... this isn't something robots can handle though.
Title: Re: Elon Musk: glass geodesic domes
Post by: Slarty1080 on 01/30/2019 07:16 pm
In general a good half of all plutonic rocks will probably have quartz grains in them.
Here are some sources showing you the element contents and the resulting mineral composition.
https://en.wikipedia.org/wiki/QAPF_diagram
https://en.wikipedia.org/wiki/TAS_classification

Basically it all boils down to the ratio of alkali elements (Na K) to Si.
So I am not too worried about finding large deposits of granites or the likes.
The other source of very pure quartz is hydrothermal deposits. Basically hot, high pressure water on cracks that deposits its dissolve SiO2 when cooled.
Where I live in NH there is huge mountains made of quartzite. A white rock formed of mostly pure quartz in a very fine grain form. These deposits are hydrothermal.
And mars did have water at one point.
And it did have molten rock at one point. Olympus Mons tallest volcano in the Solar System.
True Mars did have water and molten rock at some early point, but that was a long time ago and in all ikelyhood there have been billions of years with very little water and a lot of very fine dust blowing all over the planet.
In my little research on glass, I came across the information that most wind blown dunes, such as the ones in Michigan where in fact too coarse for glass making and needed to be ground finer.  So who knows, really what we will find?  Wind separation, or centrifugal separation, is often used to differentiate out materials with different densities, so there may be spots where this happened on Mars.
Anyway, on the first ships to Mars, I expect we will include a complete process lab, with miny grinders, mini cyclones, mesh separator, reagents and all that good stuff to actually measure the conditions and determine what can be done.  Then they will then have a synod or so to react before they send the next ships, with appropriate process equipment.  I expect you can do quite a bit with 100 tonnes.

I look forward to it. I would have thought that our understanding will be able to improve quickly in multiple directions once boots are on the ground.

But note although a hundred tons sounds like a large amount bear in mind that there will be a lot of competition for this mass, including the fittings, floors, chairs, rovers, solar power, scientific kit, food, water, radiation protection, etc etc etc. So first mission kit may be modest.
Title: Re: Elon Musk: glass geodesic domes
Post by: Lar on 01/31/2019 01:24 am
This is a good point. What's a reasonable mass budget for this out of the first 100 tonnes?  500kg? that's actually respectable, a pilot plant is not out the question... 50kg? still can do some investigation.
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 01/31/2019 04:43 am
Dome and airlock.
My guess is 60 to 70 tonnes for a 30m diameter dome.
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 01/31/2019 06:29 am
Dome and airlock.
My guess is 60 to 70 tonnes for a 30m diameter dome.
(https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=41526.0;attach=1541959;image) (https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=41526.0;attach=1541959;image)

What keeps the ~14,000 tonnes of pressure in. (Half of it straight up. About 75 tonnes of force per linear metre around the rim.)
Title: Re: Elon Musk: glass geodesic domes
Post by: Rocket Surgeon on 01/31/2019 06:42 am
Dome and airlock.
My guess is 60 to 70 tonnes for a 30m diameter dome.
(https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=41526.0;attach=1541959;image) (https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=41526.0;attach=1541959;image)

What keeps the ~14,000 tonnes of pressure in. (Half of it straight up. About 75 tonnes of force per linear metre around the rim.)

If you don't mind me asking, how did you get that number? If you've got a link and/or equation, that would be awesome!
Title: Re: Elon Musk: glass geodesic domes
Post by: Lampyridae on 01/31/2019 06:43 am
I've been thinking about this for a while now, but I believe we're going about glass domes all wrong. Glass is good in compression, as Paul451 has mentioned several times, but not good in tension. And domes are good for compression under passive Earth weight, but are fiddly when you try and pressurise them (they want to be spheres).

So, perhaps domes should be inverted.

(http://www.leisureopportunities.co.uk/images/849287_152032.jpg)

You sacrifice some volume, but all domes really are on Mars is a way to gawk at the open sky. By sacrificing some volume, you also further lower the pressure on the panes. Build a large cylinder and stick the inverted dome in as a roof.
Title: Re: Elon Musk: glass geodesic domes
Post by: guckyfan on 01/31/2019 08:57 am
The dome is IMO not for being a skylight to look at the sky or let light in from above. It is to allow a free view to the landscape around it. An inverted dome would not serve this purpose. The forces will not be contained by the glass but by the structure that holds the glass panes. Those would be metal or carbon composite which are very good at tension forces.
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 01/31/2019 09:29 am
I've been thinking about this for a while now, but I believe we're going about glass domes all wrong. Glass is good in compression, as Paul451 has mentioned several times, but not good in tension. And domes are good for compression under passive Earth weight, but are fiddly when you try and pressurise them (they want to be spheres). So, perhaps domes should be inverted.
(http://www.leisureopportunities.co.uk/images/849287_152032.jpg)

This doesn't solve either issue. The glass is still under the exact same tension in the frame. The frame is under compression, but making a tensile frame was never my objection. And you still have 75 tonnes of force per linear metre of rim, trying to rip the rest of that roof off.

If you have a structure capable of holding that force, and the glass can handle the air-pressure, then the structure in that image can also have an upward dome.

I just like to remind people of the forces involved whenever they plonk a dome on the surface, with no apparent sub-structure. I don't think it's an unsolvable problem, I just think people either don't know or really want to forget that it even exists as a problem. It's not a little house. It's a pressure vessel.



a 30m diameter dome.
What keeps the ~14,000 tonnes of pressure in. (Half of it straight up. About 75 tonnes of force per linear metre around the rim.)
If you don't mind me asking, how did you get that number?

It's just air pressure. At approximately sea-level pressure, you've got 100,000 Pa pushing outwards on the dome. That's creates a force equivalent to 10 tonnes per square metre. Force = Pressure X Area. (Using equivalent-mass-on-Earth as a pseudo-unit for force to make it easier to visualise. Since Force = Mass X Acceleration, we let Acc=1g.)

All of the force that isn't vertically aligned is taken up by the frame. So as long as the frame is strong enough... But the vertical component is unopposed, it's trying to lift the dome off the ground. Thankfully, working that out is simply the cross-sectional area of the dome (a circle radius 15m). The dome is, presumably, only attached at the rim (otherwise why bother with a dome shape), and so you divide the total unopposed force by the circumference (circle radius 15m) to work out the upward force pushing on every linear metre of rim.

(You can try to drop the pressure, but that opens up other issue.)
Title: Re: Elon Musk: glass geodesic domes
Post by: Dalhousie on 01/31/2019 09:37 am
Washing only removes easily separated contaminants, such as clays. 

It can't create the high purity silica you need in the first place. Which does not appear to occur on Mars in any quality.

Silicon is one of the most common elements. Are you saying
- Mars has no silicon? I'm dubious of that one
- Or that all silicon is bound up in other compounds than SiO2? If so which ones?
- Or that the SiO2 is mixed (alloyed) with other compounds in a  way that  no amount of crushing to get finer and finer grains will allow it to be mechanically separated? (that's the one I was afraid of, but see above, lamontagne is saying that the melts form pure crystals of various things. The crystals may be intermingled, but they are pure if you just crush fine enough and then separate)

Did I miss any possibilities?

Of course Mars has silicon as silicates. 

The martian crust is mostly mafic in composition - basalts, dolerites, gabbros, and the like.  This means that while they are up to 44% SiO2 by analysis, that is largely tied up in other silicates, olivine, pyroxenes, amphiboles, feldspars, etc. mafic rocks would generally at most contain only 5% free SiO2 (quartz, and usually none.

Felsic rocks - granites and their volcanic equivalents rhyolites and dacites - contain anywhere from 20 to 60% quartz.  But these rocks, as far as we know, are very rare on Mars.  Mostly due to the absence of plate tectonics.

Quartz is liberated by weathering of host rocks - hydration, carbonation, and oxidation.  Other minerals are transformed to clays.  As far as we know weathering on Mars is weak, and has been for 3.5 billion years. Without the weathering the quartz won't be liberated and the sedimentary sorting that allows pure deposits to form on rivers to beaches can't happen.  Martian sedimentary rocks appear lithic for the most part, composed of unweathered rock fragments.  Some forms of hydrothermal silica are also pure.  Homeplate is a good example, but it is only 98% SiO2.  Quartz veins and siliceous alteration is a possibility, but generally are associated with felsic rocks, which appear rare.

To make clear glass you need extremely pure silica, about 99.5% pure SiO2, AKA quartz.  I am not saying that such deposits are absent on Mars, but they are certainly rare, we have not seen them yet.  so let's not be too too quick to construct industries based on deposits that are not known and are probably quite rare.

Note that if we do find deposits of such purity they will be in demand for making metallic silicon for solar cells and computers. Assuming we can find enough strong reductants (on Earth coal, wood, or methane) to reduce SiO2 to Si.
Title: Re: Elon Musk: glass geodesic domes
Post by: Lampyridae on 01/31/2019 10:14 am
The dome is IMO not for being a skylight to look at the sky or let light in from above. It is to allow a free view to the landscape around it. An inverted dome would not serve this purpose. The forces will not be contained by the glass but by the structure that holds the glass panes. Those would be metal or carbon composite which are very good at tension forces.

You're thinking of the frame taking the weight of the glass. Pressure is distributed evenly across a pressure vessel. If you cut the dome into panels, the panels themselves still are subject to tension across them. The tension is proportional to radius: the larger the radius, the larger the tension. But there is a way to reduce the tension.

Parachutes don't tear because they use lobes to reduce the pressure across the fabric and instead the tension is transferred to the cords between them. Lobing reduces the radius and therefore the tension on the material. High-altitude balloons take advantage of this. But, I'm not sure how transferrable this is to rigid structures.

(note: for future reference in our discussions please assume that we account for the dome bottom somehow, making it a sphere and burying the bottom etc)
Title: Re: Elon Musk: glass geodesic domes
Post by: guckyfan on 01/31/2019 10:37 am
The dome is IMO not for being a skylight to look at the sky or let light in from above. It is to allow a free view to the landscape around it. An inverted dome would not serve this purpose. The forces will not be contained by the glass but by the structure that holds the glass panes. Those would be metal or carbon composite which are very good at tension forces.

You're thinking of the frame taking the weight of the glass.

Not at all. I am thinking of the atmospheric pressure that puts the frame into tension. The single glass pane only transfers the pressure on it to that frame. Only while the dome is not pressurized the structure needs to hold the weight of the glass under compression which is miniscule compared to the pressure forces causing tension.

BTW I regularly have argued that any structure would need to be stable both under pressure and without pressure. That's why using mass to counter pressure is problematic and needs to be designed carefully.
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 01/31/2019 11:20 am
Dome and airlock.
My guess is 60 to 70 tonnes for a 30m diameter dome.
(https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=41526.0;attach=1541959;image) (https://forum.nasaspaceflight.com/index.php?action=dlattach;topic=41526.0;attach=1541959;image)

What keeps the ~14,000 tonnes of pressure in. (Half of it straight up. About 75 tonnes of force per linear metre around the rim.)

Steel rods going through the foundation walls and into a fairly thick bottom slab.
I'm presuming reasonable amounts of calcium  or magnesium carbonates are found, to be able to pour concrete in place.

The calculations for the dome, including the anchoring question, are in the joined spreadsheet.  The steel structure has to represent about 3% of the dome area to provide an adequate factor of safety.

The hoop stress is entirely taken up by the steel structure.  I have serious doubts that at this scale the geodesic shape is the best one.  My guess is that circular sections terminating at anchor points would be better.

The glass in the dome in under bending stress, so the panes need to be kept relatively small in order to reduce this to a reasonable amount.  It's also better to keep them small so when they fail, the depressurisation is not too severe.  You want to have time for your crack intervention team (a second job for the fire brigade) to bring in the patch!  The image shows panes about 1m accross, but perhaps 500mm would be better.

Steel is strong stuff.  Standard construction steel at 40 000 psi strength is 20 tonnes per square inch.  So you need a section of about 3 inches square for the tension, plus a safety factor of three would give us 10 square inches of steel per meter.    So a 1 inch section rod every 10 cm.  Sorry for the mixed units  :-)  my structural design days were imperial. 

A real design would  finish with some kind of tension spreader beam at the base of the dome, before the foundation wall, to conduct the forces from the steel hoops in the dome to the steel rods in the concrete/compressed regolith blocks.

Title: Re: Elon Musk: glass geodesic domes
Post by: guckyfan on 01/31/2019 11:48 am
I would love to be able to do good design pictures. My idea of a dome:

Build a central cylindrical building that can hold pressure if needed. Give it a massive thick roof that extends quite a lot beyond the perimeter of the building, heavy enough to hold the pressure. Build the geodesic dome around it. That would give some radiation shielding and would reduce the pressure force that needs to be anchored to the ground by a lot, depending on how big that mushroom hat is.
Title: Re: Elon Musk: glass geodesic domes
Post by: Lampyridae on 01/31/2019 11:58 am
The dome is IMO not for being a skylight to look at the sky or let light in from above. It is to allow a free view to the landscape around it. An inverted dome would not serve this purpose. The forces will not be contained by the glass but by the structure that holds the glass panes. Those would be metal or carbon composite which are very good at tension forces.

You're thinking of the frame taking the weight of the glass.

Not at all. I am thinking of the atmospheric pressure that puts the frame into tension. The single glass pane only transfers the pressure on it to that frame. Only while the dome is not pressurized the structure needs to hold the weight of the glass under compression which is miniscule compared to the pressure forces causing tension.

BTW I regularly have argued that any structure would need to be stable both under pressure and without pressure. That's why using mass to counter pressure is problematic and needs to be designed carefully.

Tension in a pressurised vessel doesn't work like that. It doesn't matter whether your truss structure is made of unobtanium. The pane must be able to withstand the pressure placed upon it: the outward component.

To use your example, you could replace the 60cm thick acrylic aquarium window at the Churaumi Aquarium in Okinawa with a titanium frame (because hey that's helluva strong)... and insert single sheets of 6mm window glass to hold back 7 500 tonnes of water. Water doesn't somehow see the frame and choose to push there and avoid the window glass, nor does the window glass teleport the 10 tonnes per square metre pressure to the frame. The truss does help, but not all that much.

Glass is weak. This is why the cupola windows on the ISS are 2x25mm thick, and the ISS modules are 2.5mm thick aluminium. To make the dome bigger, the glass must be thicker. But if you're producing Victorian-era quality glass, then you have a real problem. I kind of think acrylic will be easier in terms of ISRU.
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 01/31/2019 01:06 pm
So I made a little test for the glass, spreadsheet joined.  Turns out that for a span of 500mm you would need glass about 50mm thick (2 inches).  So glass slabs, not glass sheets.

This is for a glass beam.  Continuously supported plates would be under considerably less strain, but nevertheless, that's thick glass.
Polycarbonate is twice as strong as soda glass, so it would be about 35 mm thick.

There are formula for supported plates
https://en.wikipedia.org/wiki/Bending_of_plates#Simply-supported_plate_with_uniformly-distributed_load

Too much work for me but if someone want to tackle it would love to see the results!

So although the mass of steel remains the same the mass of glass goes up to 140 tonnes, so an overall mass of 170 tonnes.
I guess we should include the anchor mass,that should be at least as much as the dome, so the mass requirements for a dome are about 200 tonnes, plus the concrete for the slab.

Really need to want to look outside  :-)
Title: Re: Elon Musk: glass geodesic domes
Post by: guckyfan on 01/31/2019 03:23 pm
Tension in a pressurised vessel doesn't work like that. It doesn't matter whether your truss structure is made of unobtanium. The pane must be able to withstand the pressure placed upon it: the outward component.

Yes, of course the pane needs to withstand the pressure. So it can not be too big as a single pane. I have built fish tanks and I am very much aware of this. But it is solely the structure that needs to take the whole load determined by the size of the dome.
Title: Re: Elon Musk: glass geodesic domes
Post by: IncongruousGoat on 01/31/2019 03:25 pm
Washing only removes easily separated contaminants, such as clays. 

It can't create the high purity silica you need in the first place. Which does not appear to occur on Mars in any quality.

Silicon is one of the most common elements. Are you saying
- Mars has no silicon? I'm dubious of that one
- Or that all silicon is bound up in other compounds than SiO2? If so which ones?
- Or that the SiO2 is mixed (alloyed) with other compounds in a  way that  no amount of crushing to get finer and finer grains will allow it to be mechanically separated? (that's the one I was afraid of, but see above, lamontagne is saying that the melts form pure crystals of various things. The crystals may be intermingled, but they are pure if you just crush fine enough and then separate)

Did I miss any possibilities?

Of course Mars has silicon as silicates. 

The martian crust is mostly mafic in composition - basalts, dolerites, gabbros, and the like.  This means that while they are up to 44% SiO2 by analysis, that is largely tied up in other silicates, olivine, pyroxenes, amphiboles, feldspars, etc. mafic rocks would generally at most contain only 5% free SiO2 (quartz, and usually none.

Felsic rocks - granites and their volcanic equivalents rhyolites and dacites - contain anywhere from 20 to 60% quartz.  But these rocks, as far as we know, are very rare on Mars.  Mostly due to the absence of plate tectonics.

Quartz is liberated by weathering of host rocks - hydration, carbonation, and oxidation.  Other minerals are transformed to clays.  As far as we know weathering on Mars is weak, and has been for 3.5 billion years. Without the weathering the quartz won't be liberated and the sedimentary sorting that allows pure deposits to form on rivers to beaches can't happen.  Martian sedimentary rocks appear lithic for the most part, composed of unweathered rock fragments.  Some forms of hydrothermal silica are also pure.  Homeplate is a good example, but it is only 98% SiO2.  Quartz veins and siliceous alteration is a possibility, but generally are associated with felsic rocks, which appear rare.

To make clear glass you need extremely pure silica, about 99.5% pure SiO2, AKA quartz.  I am not saying that such deposits are absent on Mars, but they are certainly rare, we have not seen them yet.  so let's not be too too quick to construct industries based on deposits that are not known and are probably quite rare.

Note that if we do find deposits of such purity they will be in demand for making metallic silicon for solar cells and computers. Assuming we can find enough strong reductants (on Earth coal, wood, or methane) to reduce SiO2 to Si.
And I take it that there aren't any practical processes for getting SiO2 out of silicates?
Title: Re: Elon Musk: glass geodesic domes
Post by: rsdavis9 on 01/31/2019 04:31 pm
And I take it that there aren't any practical processes for getting SiO2 out of silicates?

Its more like nobody bothers because there is ample SiO2 in the wild. We have already seen hydrothermal SiO2 on mars. We will probably find the felsic minerals (granites etc). Probably need to dig a little. Mechanical separation is easier if these sources exist.
Title: Re: Elon Musk: glass geodesic domes
Post by: Lar on 01/31/2019 04:46 pm
And I take it that there aren't any practical processes for getting SiO2 out of silicates?

Its more like nobody bothers because there is ample SiO2 in the wild. We have already seen hydrothermal SiO2 on mars. We will probably find the felsic minerals (granites etc). Probably need to dig a little. Mechanical separation is easier if these sources exist.

There appears to be a significant dispute about this. I want to believe. But Dalhousie is convinced that SiO2 that isn't contaminated with impurities (alloyed in) is very low abundance on Mars.

Ground truth is needed I think.
Title: Re: Elon Musk: glass geodesic domes
Post by: Slarty1080 on 01/31/2019 05:31 pm
I've been thinking about this for a while now, but I believe we're going about glass domes all wrong. Glass is good in compression, as Paul451 has mentioned several times, but not good in tension. And domes are good for compression under passive Earth weight, but are fiddly when you try and pressurise them (they want to be spheres). So, perhaps domes should be inverted.
(http://www.leisureopportunities.co.uk/images/849287_152032.jpg)

This doesn't solve either issue. The glass is still under the exact same tension in the frame. The frame is under compression, but making a tensile frame was never my objection. And you still have 75 tonnes of force per linear metre of rim, trying to rip the rest of that roof off.

If you have a structure capable of holding that force, and the glass can handle the air-pressure, then the structure in that image can also have an upward dome.

I just like to remind people of the forces involved whenever they plonk a dome on the surface, with no apparent sub-structure. I don't think it's an unsolvable problem, I just think people either don't know or really want to forget that it even exists as a problem. It's not a little house. It's a pressure vessel.



a 30m diameter dome.
What keeps the ~14,000 tonnes of pressure in. (Half of it straight up. About 75 tonnes of force per linear metre around the rim.)
If you don't mind me asking, how did you get that number?

It's just air pressure. At approximately sea-level pressure, you've got 100,000 Pa pushing outwards on the dome. That's creates a force equivalent to 10 tonnes per square metre. Force = Pressure X Area. (Using equivalent-mass-on-Earth as a pseudo-unit for force to make it easier to visualise. Since Force = Mass X Acceleration, we let Acc=1g.)

All of the force that isn't vertically aligned is taken up by the frame. So as long as the frame is strong enough... But the vertical component is unopposed, it's trying to lift the dome off the ground. Thankfully, working that out is simply the cross-sectional area of the dome (a circle radius 15m). The dome is, presumably, only attached at the rim (otherwise why bother with a dome shape), and so you divide the total unopposed force by the circumference (circle radius 15m) to work out the upward force pushing on every linear metre of rim.

(You can try to drop the pressure, but that opens up other issue.)
Imagine the dome has 10m of water in it (Olympic diving pool depth x2) and you have to secure it upside down to some sort of huge ceiling. Not quite the right analogy but it conveys the magnitude of the forces involved. That will take some major engineering - hard but doable.
Title: Re: Elon Musk: glass geodesic domes
Post by: Oersted on 01/31/2019 08:20 pm
In "envisioning amazing habitats" we already went through the dome discussion around 60 pages and three years back. Yup, glass domes are actually no good on Mars.

For those who are new to this forum and to discussing bases on Mars that thread is a good long read.

It will also explain to you why so many oldtimers in here seem to fancy tunnels (as does Musk).
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 01/31/2019 10:04 pm
Divide and conquer.  If glass is too weak for wide spans, make smaller spans.  And add steel.

With the smaller glass panes, I'm pretty confident 2 cm thick would be OK

But when does it become too much steel?
Title: Re: Elon Musk: glass geodesic domes
Post by: Cinder on 01/31/2019 10:53 pm
What about additional layers ? D&C'ing further.  It's been mentioned upthread but I'm not sure I understand if it's ruled out for this specific case too.
Title: Re: Elon Musk: glass geodesic domes
Post by: Jcc on 01/31/2019 11:09 pm
I am thinking geodesic domes are not really a good idea on Mars. Arched glass roof over a rectangular building would work, and be easier to design to hold in the pressure.
Title: Re: Elon Musk: glass geodesic domes
Post by: Robotbeat on 01/31/2019 11:53 pm
In "envisioning amazing habitats" we already went through the dome discussion around 60 pages and three years back. Yup, glass domes are actually no good on Mars.

For those who are new to this forum and to discussing bases on Mars that thread is a good long read.

It will also explain to you why so many oldtimers in here seem to fancy tunnels (as does Musk).
That wasn’t actually a consensus opinion.
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 02/01/2019 04:19 am
I just like to remind people of the forces involved whenever they plonk a dome on the surface, with no apparent sub-structure.
Imagine the dome has 10m of water in it (Olympic diving pool depth x2) and you have to secure it upside down to some sort of huge ceiling. Not quite the right analogy but it conveys the magnitude of the forces involved.

(Or 26m of water on Mars.) Not sure the analogy helps, I don't think people actually have a good grasp of how much water weighs. It's a common building cock-up you hear about, where people add hot-tubs, waterbeds, aquariums, and don't realise how much weight they are adding to the floor, frame, deck, etc.
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 02/01/2019 04:23 am
So I made a little test for the glass, spreadsheet joined.

I haven't gone through all of it, I was looking at the anchoring part. (Spot the obsessive.) And there's some oddities there.

Eg, you calculate the weight (MxA) of the dome (row 32), you have the cross-sectional force from air-pressure (row 29),
then at row 34 you have the anchoring force required, which is calculated by row 29 minus row 32. Okay. But then you calculate the "Mars regolith required to keep the dome down", where you subtract the dome weight again, before converting to kg-equivalent. The latter seems wrong, unless I'm missing another assumption in another formula.

Similarly, the formulas for depth of anchoring seem... weird. Eg, you seem to be treating the entire volume under the dome as one anchor. But there's something else going on, given that the first three cases (5m, 15m, 30m) all end up with an identical 56m anchor depth.
Title: Re: Elon Musk: glass geodesic domes
Post by: Lampyridae on 02/01/2019 10:21 am
So I made a little test for the glass, spreadsheet joined.

I haven't gone through all of it, I was looking at the anchoring part. (Spot the obsessive.) And there's some oddities there.

Eg, you calculate the weight (MxA) of the dome (row 32), you have the cross-sectional force from air-pressure (row 29),
-snip-

I also had a look at it, and here's what I think.

Looking at the bending moment, this is true if you have to actually place a load on the surface, like 1.5 fully grown African elephants or 10m of water. But this isn't really representative of hoop stress.

The ability to resist the African elephant's weight comes from the tangent of the curvature of the pressure vessel, which is where the stress is carried. Which is part of the reason why we like curved pressure vessels. You can only resist the outward pressure with the outward component of the tension "vector."

(http://hyperphysics.phy-astr.gsu.edu/hbase/imgmec/lapl2.gif)

Pressure vessels are less walls holding back force and more like strings holding up a weight. The longer your string has to be, the more you have to pull on the string to bring the weight upwards.
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 02/01/2019 01:43 pm
So I made a little test for the glass, spreadsheet joined.

I haven't gone through all of it, I was looking at the anchoring part. (Spot the obsessive.) And there's some oddities there.

Eg, you calculate the weight (MxA) of the dome (row 32), you have the cross-sectional force from air-pressure (row 29),
then at row 34 you have the anchoring force required, which is calculated by row 29 minus row 32. Okay. But then you calculate the "Mars regolith required to keep the dome down", where you subtract the dome weight again, before converting to kg-equivalent. The latter seems wrong, unless I'm missing another assumption in another formula.

Similarly, the formulas for depth of anchoring seem... weird. Eg, you seem to be treating the entire volume under the dome as one anchor. But there's something else going on, given that the first three cases (5m, 15m, 30m) all end up with an identical 56m anchor depth.
Really appreciate your checking the spreadsheet!
Yes there were mistakes at the end.  Corrected, I hope. 
Reduced the strength of the steel to common construction steel.
I also clarified the mass of the dome by putting in a glass thickness parameter.
The final column is for a plastic bag used as a aquarium for algae, as it is continuous, it doesn't need to be anchored.
It's clear that the larger the dome, the deeper the anchors, since the force from the pressure goes up to the square of the radius, while the anchoring circumference goes up linearly.   Eventually, the mass of the dome starts playing a significant part and you end up getting negative forces, i.e the dome keeps itself in place.
Anchoring requirements are sever in all cases.  I think it is more practical to build a continuous pressure vessel, i.e. have a spherical dome or have a structural floor.

Anyway, it's clear to me that you have to really really want a dome to bother building one of significant size.


Title: Re: Elon Musk: glass geodesic domes
Post by: Rocket Surgeon on 02/04/2019 12:04 am
So I made a little test for the glass, spreadsheet joined.

I haven't gone through all of it, I was looking at the anchoring part. (Spot the obsessive.) And there's some oddities there.

Eg, you calculate the weight (MxA) of the dome (row 32), you have the cross-sectional force from air-pressure (row 29),
then at row 34 you have the anchoring force required, which is calculated by row 29 minus row 32. Okay. But then you calculate the "Mars regolith required to keep the dome down", where you subtract the dome weight again, before converting to kg-equivalent. The latter seems wrong, unless I'm missing another assumption in another formula.

Similarly, the formulas for depth of anchoring seem... weird. Eg, you seem to be treating the entire volume under the dome as one anchor. But there's something else going on, given that the first three cases (5m, 15m, 30m) all end up with an identical 56m anchor depth.
Really appreciate your checking the spreadsheet!
Yes there were mistakes at the end.  Corrected, I hope. 
Reduced the strength of the steel to common construction steel.
I also clarified the mass of the dome by putting in a glass thickness parameter.
The final column is for a plastic bag used as a aquarium for algae, as it is continuous, it doesn't need to be anchored.
It's clear that the larger the dome, the deeper the anchors, since the force from the pressure goes up to the square of the radius, while the anchoring circumference goes up linearly.   Eventually, the mass of the dome starts playing a significant part and you end up getting negative forces, i.e the dome keeps itself in place.
Anchoring requirements are sever in all cases.  I think it is more practical to build a continuous pressure vessel, i.e. have a spherical dome or have a structural floor.

Anyway, it's clear to me that you have to really really want a dome to bother building one of significant size.

Has there been any discussion about building a sphere instead of a dome? I know the general consensus is that burying half a sphere would involve moving too much dirty, but what if you build it above ground?
 
Support it at the "South Pole" and have Support struts running from the ground up to the Equator. Could make it mostly out of steel with small windows at various locations.
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 02/04/2019 02:56 am
So I made a little test for the glass, spreadsheet joined.

I haven't gone through all of it, I was looking at the anchoring part. (Spot the obsessive.) And there's some oddities there.

Eg, you calculate the weight (MxA) of the dome (row 32), you have the cross-sectional force from air-pressure (row 29),
then at row 34 you have the anchoring force required, which is calculated by row 29 minus row 32. Okay. But then you calculate the "Mars regolith required to keep the dome down", where you subtract the dome weight again, before converting to kg-equivalent. The latter seems wrong, unless I'm missing another assumption in another formula.

Similarly, the formulas for depth of anchoring seem... weird. Eg, you seem to be treating the entire volume under the dome as one anchor. But there's something else going on, given that the first three cases (5m, 15m, 30m) all end up with an identical 56m anchor depth.
Really appreciate your checking the spreadsheet!
Yes there were mistakes at the end.  Corrected, I hope. 
Reduced the strength of the steel to common construction steel.
I also clarified the mass of the dome by putting in a glass thickness parameter.
The final column is for a plastic bag used as a aquarium for algae, as it is continuous, it doesn't need to be anchored.
It's clear that the larger the dome, the deeper the anchors, since the force from the pressure goes up to the square of the radius, while the anchoring circumference goes up linearly.   Eventually, the mass of the dome starts playing a significant part and you end up getting negative forces, i.e the dome keeps itself in place.
Anchoring requirements are sever in all cases.  I think it is more practical to build a continuous pressure vessel, i.e. have a spherical dome or have a structural floor.

Anyway, it's clear to me that you have to really really want a dome to bother building one of significant size.

Has there been any discussion about building a sphere instead of a dome? I know the general consensus is that burying half a sphere would involve moving too much dirty, but what if you build it above ground?
 
Support it at the "South Pole" and have Support struts running from the ground up to the Equator. Could make it mostly out of steel with small windows at various locations.
I have a few variations done.  It's a fun idea.  What's your favorite of the three?
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 02/04/2019 05:36 am
Has there been any discussion about building a sphere instead of a dome? I know the general consensus is that burying half a sphere would involve moving too much dirty, but what if you build it above ground?

Bunch of variations in the Envisioning Amazing Habitats (https://forum.nasaspaceflight.com/index.php?topic=41427.0) thread.

It doesn't have to be a sphere, per se, it just needs to be a complete pressure vessel. The further you go from an ideal shape, the higher the forces at the sharpest angles/curves.

In the case of half-burial to create a "dome", it particularly doesn't have to have a sphere because the pressure of the regolith will be countering the side-pressure of the atmosphere. As long as it has a foundation sufficient to anchor the dome. It's just that the forces are substantial enough that by the time you've anchored it down, and sealed the floor against air loss, IMO you might as well have built the "anchor" as part of the floor foundation and just fully enclosed the structure.
Title: Re: Elon Musk: glass geodesic domes
Post by: Rocket Surgeon on 02/05/2019 12:38 am
So I made a little test for the glass, spreadsheet joined.  Turns out that for a span of 500mm you would need glass about 50mm thick (2 inches).  So glass slabs, not glass sheets.

This is for a glass beam.  Continuously supported plates would be under considerably less strain, but nevertheless, that's thick glass.
Polycarbonate is twice as strong as soda glass, so it would be about 35 mm thick.

There are formula for supported plates
https://en.wikipedia.org/wiki/Bending_of_plates#Simply-supported_plate_with_uniformly-distributed_load

Too much work for me but if someone want to tackle it would love to see the results!

So although the mass of steel remains the same the mass of glass goes up to 140 tonnes, so an overall mass of 170 tonnes.
I guess we should include the anchor mass,that should be at least as much as the dome, so the mass requirements for a dome are about 200 tonnes, plus the concrete for the slab.

Really need to want to look outside  :-)

So I didn't do the support plate calculations...I just went straight to FEMAP ;)

The below images are of glass with a Young's Modulus of 50 GPa, of varying thicknesses (10mm, 30mm and 50mm) and different net pressures (50 kPa and 25 kPa). Modelled as a plate, 1000mm long each side.

https://www.engineeringtoolbox.com/young-modulus-d_417.html

50 kPa may be doable with higher oxygen content (somthing like 8psi, 32% Oxygen...or 8/32), 25 kPa would have to be done by having a second layer, pressurised with atmospheric CO2 to partially counteract the internal pressure.

Results are:
- 50 kPa, 10mm, the highest stress is 49.25 MPa
- 50 kPa, 30mm, the highest stress is 5.448 MPa
- 50 kPa, 50mm, the highest stress is 1.943 MPa

- 25 kPa, 10mm, the highest stress is 24.62 MPa
- 25 kPa, 30mm, the highest stress is 2.724 MPa
- 25 kPa, 50mm, the highest stress is 0.971 MPa

With all cases, the peak stress is half way along the edges. Tensile yield stress of basic glass is 7 MPa, so 10mm of glass fails under both situations. Thickening rapidly makes it stronger. Bare in mind that these results are actually an over estimate as the plates are Constrained by fixing along their edges, which is an over estimation, increasing the stress.

https://en.wikipedia.org/wiki/Strength_of_glass

Lamontage, what where you using as your Yield Stress for the Glass? and what would be an advisable Safety Factor?
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 02/05/2019 03:15 am
So I made a little test for the glass, spreadsheet joined.  Turns out that for a span of 500mm you would need glass about 50mm thick (2 inches).  So glass slabs, not glass sheets.

This is for a glass beam.  Continuously supported plates would be under considerably less strain, but nevertheless, that's thick glass.
Polycarbonate is twice as strong as soda glass, so it would be about 35 mm thick.

There are formula for supported plates
https://en.wikipedia.org/wiki/Bending_of_plates#Simply-supported_plate_with_uniformly-distributed_load

Too much work for me but if someone want to tackle it would love to see the results!

So although the mass of steel remains the same the mass of glass goes up to 140 tonnes, so an overall mass of 170 tonnes.
I guess we should include the anchor mass,that should be at least as much as the dome, so the mass requirements for a dome are about 200 tonnes, plus the concrete for the slab.

Really need to want to look outside  :-)

So I didn't do the support plate calculations...I just went straight to FEMAP ;)

The below images are of glass with a Young's Modulus of 50 GPa, of varying thicknesses (10mm, 30mm and 50mm) and different net pressures (50 kPa and 25 kPa). Modelled as a plate, 1000mm long each side.

https://www.engineeringtoolbox.com/young-modulus-d_417.html

50 kPa may be doable with higher oxygen content (somthing like 8psi, 32% Oxygen...or 8/32), 25 kPa would have to be done by having a second layer, pressurised with atmospheric CO2 to partially counteract the internal pressure.

Results are:
- 50 kPa, 10mm, the highest stress is 49.25 MPa
- 50 kPa, 30mm, the highest stress is 5.448 MPa
- 50 kPa, 50mm, the highest stress is 1.943 MPa

- 25 kPa, 10mm, the highest stress is 24.62 MPa
- 25 kPa, 30mm, the highest stress is 2.724 MPa
- 25 kPa, 50mm, the highest stress is 0.971 MPa

With all cases, the peak stress is half way along the edges. Tensile yield stress of basic glass is 7 MPa, so 10mm of glass fails under both situations. Thickening rapidly makes it stronger. Bare in mind that these results are actually an over estimate as the plates are Constrained by fixing along their edges, which is an over estimation, increasing the stress.

https://en.wikipedia.org/wiki/Strength_of_glass

Lamontagne, what where you using as your Yield Stress for the Glass? and what would be an advisable Safety Factor?
Wow, great to see up to date tools being used. Thanks a lot!
I used 30 MPa yield for the glass with a factor of safety of 2, that comes out to about 15 MPa.  So likely optimistic.
I think the 7 MPa may be for a limit state design, so you wouldn't really add much of a factor of safety?  Musn't mix two methods :-)

I expect the most likely means of breaking the glass is a sharp punch that breaks the glass no matter what the safety factor is. That might be countered with a safety film, although I'm not certain the film could survive the tension once the glass was broken.

Yeah, fixing the edges would be a recipe for disaster.  Dome explodes on the first morning/night cycle!  I do wonder of the high strain at the edges might be a calculation artifact, due to the constraints.  Would have thought that the highest stress would have been in the center.  Ah, unless it's shear along the supports. That would work.

I think the best solution is to use smaller glass panes.  You could fit much smaller glass panes into a larger triangular frame and still have a lot of light.  More steel required, but much thinner glass.  The steel is so much safer than the glass!

The problem with the small glass panes is that the total length of joints to seal go up tremendously, so all that many more leak possibilities.  We need a long lasting sealant that can survive low temperatures. 

We also need to design a glass arrangement that keeps the sealant as warm as possible, that's why I think a second, or even third non structural glass layer will be required to carry low e film, so the interior glass surface temperature doesn't get too low.  We'll need something of the kind to prevent condensation anyway, as that seems to be bad structurally for Soda glass.  Plus it rusts the steel.  And you can't see out, defeating the initial purpose!

Joined is a nice little text on glass structural properties.  Too bad we can't make perfect glass!

Thanks again!  If you can find the time to do some tests with smaller glass panes would love to see the results.


Title: Re: Elon Musk: glass geodesic domes
Post by: Semmel on 02/05/2019 06:17 am
There are plenty different glass types that have all kinds of expansion coefficients. ZERODUR for example has a zero expansion coefficient, hence the name. You also might  find some with the same coefficient as steel. Not sure about the price though. And these glasses are usually made for optical elements, they probably are not easily available in planes.
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 02/05/2019 06:57 am
50 kPa may be doable with higher oxygen content (somthing like 8psi, 32% Oxygen...or 8/32),

That would drastically increase your fire risk.

[Nice FEA though. I'm curious how much difference it would make if the glass wasn't flat but was domed. For eg, doming it inwards (towards the pressure) would put some of the force in compression. AIUI, glass has a compressive strength better than two orders of magnitude higher than its tensile strength.]
Title: Re: Elon Musk: glass geodesic domes
Post by: Rocket Surgeon on 02/05/2019 08:42 am
50 kPa may be doable with higher oxygen content (somthing like 8psi, 32% Oxygen...or 8/32),

That would drastically increase your fire risk.

[Nice FEA though. I'm curious how much difference it would make if the glass wasn't flat but was domed. For eg, doming it inwards (towards the pressure) would put some of the force in compression. AIUI, glass has a compressive strength better than two orders of magnitude higher than its tensile strength.]

Will look into, the above was REALLY easy to run as it's a basic static load. I'll do a few extra Sims tomorrow. I also need to reconsider my constraints. WAY too over constrained right now.

As for atmosphere, I'll check my source but my understanding was 8/32 had the right balance of increase percentage and decreased pressure to maintain a similar flammability.

I know it's much more dependant on concerntration than pressure, but I thought the above mix walked that line. I'll double check.
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 02/05/2019 11:19 am
50 kPa may be doable with higher oxygen content (somthing like 8psi, 32% Oxygen...or 8/32),
That would drastically increase your fire risk.
As for atmosphere, I'll check my source but my understanding was 8/32 had the right balance of increase percentage and decreased pressure to maintain a similar flammability.

Looking at what I have at hand, something which is on the just self-extinguishing at 14.7psi & 21% Oxygen will self-extinguish at 12/23 and 7/28. Therefore 8/32 is well over the line.

That's at 1g. At Mars gravity, flammability is even higher.
Title: Re: Elon Musk: glass geodesic domes
Post by: Lampyridae on 02/05/2019 12:45 pm
50 kPa may be doable with higher oxygen content (somthing like 8psi, 32% Oxygen...or 8/32),
That would drastically increase your fire risk.
As for atmosphere, I'll check my source but my understanding was 8/32 had the right balance of increase percentage and decreased pressure to maintain a similar flammability.

Looking at what I have at hand, something which is on the just self-extinguishing at 14.7psi & 21% Oxygen will self-extinguish at 12/23 and 7/28. Therefore 8/32 is well over the line.

That's at 1g. At Mars gravity, flammability is even higher.

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20130010991.pdf

In general, higher oxygen concentrations are bad news at low g. I didn't know this before. But 12-13psi / 0.8bar with the same oxygen concentration? That's fine. I'm breathing that right now.

MOC is the minimum oxygen concentration to continue burning (basically like 1% chance of sustained fire). ULOI is a concentration where there 50% chance that the material continues to burn.
Title: Re: Elon Musk: glass geodesic domes
Post by: Lampyridae on 02/05/2019 01:09 pm
50 kPa may be doable with higher oxygen content (somthing like 8psi, 32% Oxygen...or 8/32),

That would drastically increase your fire risk.

[Nice FEA though. I'm curious how much difference it would make if the glass wasn't flat but was domed. For eg, doming it inwards (towards the pressure) would put some of the force in compression. AIUI, glass has a compressive strength better than two orders of magnitude higher than its tensile strength.]

Doming it in would reduce the radius of curvature and decrease the loading. An example from an ILC Dover expandable habitat:

http://www.simulia.com/download/scc-papers/Aerospace/structural-design-analysis-testing-lunar-habitat-2009-F.pdf

I had a better link which modelled all the elements, including the habitat window. The habitat window meanwhile was flat (ostensibly for viewing) and the principal load was along the long edges.

Pretty much all heavy-duty inflatables have this kind of lobing to reduce stress.

http://adsabs.harvard.edu/full/2005ESASP.581E.101L

A geodesic dome would ideally have hexagonal/pentagonal panels which would be better domed. The principle stress is usually along the longest, straightest edge of a panel.
Title: Re: Elon Musk: glass geodesic domes
Post by: guckyfan on 02/05/2019 01:15 pm
On another thread, I think in the Mars section, a while back there was a video showing a room at sea level pressure with the air inside at somewhat lower oxygen partial pressure. Comfortable for humans to breathe but at that oxygen level open fire seemed impossible. Matches or lighters would not ignite. A candle or torch brought in from the outside extinguished quickly. In an enclosed habitat where fire is extremely dangerous this would be a good condition.

Assuming that most pressurized volume is made by tunneling with only few exceptions on the surface, like a geodesic dome for psychologic reasons, having full pressure would not be a major problem. Maybe for safety reasons this would be the way to go. I am coming from the position that half SL pressure with increased partial oxygen is desireable but I have changed my position. Fire is something that should be avoided at almost any cost.
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 02/05/2019 01:41 pm
On another thread, I think in the Mars section, a while back there was a video showing a room at sea level pressure with the air inside at somewhat lower oxygen partial pressure. Comfortable for humans to breathe but at that oxygen level open fire seemed impossible. Matches or lighters would not ignite. A candle or torch brought in from the outside extinguished quickly. In an enclosed habitat where fire is extremely dangerous this would be a good condition.

Assuming that most pressurized volume is made by tunneling with only few exceptions on the surface, like a geodesic dome for psychologic reasons, having full pressure would not be a major problem. Maybe for safety reasons this would be the way to go. I am coming from the position that half SL pressure with increased partial oxygen is desireable but I have changed my position. Fire is something that should be avoided at almost any cost.
I just happen to be working on underground subway stations these days.  Fire risk and exit is one of the driving forces in the design.  Fire codes requires that the station can be evacuated within 6 minutes.  During that time the ventilation system must clear out the smoke to prevent the passengers from being blinded, asphyxiated and cooked.  A minor trash can fire can reach a few MW in power, and a large vehicle fire 15 MW or more.  A tanker truck in 100 to 200 MW of power.
The fire can also damage the concrete of the tunnel and create spalling, weakening it to the point of structural failure.
The classic approach to fire protection is the joined triangle: Oxygen, combustible, heat.  Increasing the oxygen content is a bad idea, from this point of view.  Reducing the use of organic materials is a good idea, to eliminate combustible.  Paint is a big problem in this regard.  Ceramic coverings might be favored for this reason. 
To reduce heat, the classic approach is to add sprinklers to construction.  A fairly recent advance it to use high pressure misters rather than sprinklers when the equipment is water sensitive.  The mist cools the air and displaces some oxygen, attacking the fire on two fronts.
This has been replacing CO2 protection, that is pretty much phased out everywhere now, as it does the same job, displace oxygen, without the risk of asphyxiation.  Plus the cooling.
I expect any permanent colony would be entirely protected by sprinklers, including all the corridors, the domes, if any, and all the technical spaces as well.
BTW some authorities, such as Australia, have decided to install sprinklers in all road tunnels.  It's a growing trend.
I would also expect a high level of partitioning, for smoke control and to create safe spaces for egress.
I wonder if breathing masks with small 10min breathing bottle might be available, and if these could serve in case of pressure loss as well.  On the other hand it would be difficult to have a few hundred of these available quickly in a large dome, a cafeteria full of people, for example, that suddenly lot a section of windows.


Title: Re: Elon Musk: glass geodesic domes
Post by: Lampyridae on 02/05/2019 02:09 pm
I wonder if breathing masks with small 10min breathing bottle might be available, and if these could serve in case of pressure loss as well.  On the other hand it would be difficult to have a few hundred of these available quickly in a large dome, a cafeteria full of people, for example, that suddenly lot a section of windows.


However, a colony can voluntarily vent atmosphere to contain a fire. But I wouldn't go with increased O2 concentration at all, given the fire hazards in Martian g.

Multi-lobed fuel tanks are an actual thing, and have lighter skins than would otherwise be the case. However, the connections (nodes) weigh more because the load has to go somewhere.

(http://www.izumi-steel.co.jp/english/contents/business/images/ship_tank-d/contents_format_ship_tank_d_v1_29.jpg)

And althought the noded composite tanks for the X-33 were a debacle (and an excuse to kill the program), the Al-Li tanks were just fine for the purpose.

(https://www.nasaspaceflight.com/wp-content/uploads/2006/01/2016-07-11-123002-350x256.jpg)

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.450.4264&rep=rep1&type=pdf
Title: Re: Elon Musk: glass geodesic domes
Post by: Rocket Surgeon on 02/06/2019 12:16 am
50 kPa may be doable with higher oxygen content (somthing like 8psi, 32% Oxygen...or 8/32),
That would drastically increase your fire risk.
As for atmosphere, I'll check my source but my understanding was 8/32 had the right balance of increase percentage and decreased pressure to maintain a similar flammability.

Looking at what I have at hand, something which is on the just self-extinguishing at 14.7psi & 21% Oxygen will self-extinguish at 12/23 and 7/28. Therefore 8/32 is well over the line.

That's at 1g. At Mars gravity, flammability is even higher.

Thanks! Do you mind if I ask what your source is for the above numbers? I'd like to read more into this and have a better knowledge of what prior work has been done.
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 02/06/2019 01:52 am
Do you mind if I ask what your source is for the above numbers? I'd like to read more into this and have a better knowledge of what prior work has been done.

I generally quote numbers from:- Hirsch, Williams, Beeson, "Pressure Effects on Oxygen Concentration Flammability Thresholds of Polymeric Materials for Aerospace Applications," Journal of Testing and Evaluation, Vol. 36, No. 1, 2008, pp. 69-72; because I've snipped out some of the tables/graphs.

The reduced gravity flammability comes from:- Olson & Ferkul, Evaluating Material Flammability in Microgravity and Martian Gravity Compared to the NASA Standard Normal Gravity Test. 42nd International Conference on Environmental Systems 2012, ICES 2012. Again, I've snipped some figures, so it's handy.
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 02/06/2019 02:24 am
However, a colony can voluntarily vent atmosphere to contain a fire.

That might be required just to deal with the thermal expansion anyway. Fire, hot. Using misters will also increase internal pressure, rule of thumb is 1600 times volume expansion. So your fire system will already have venting built in.

If the vented air (and misted water) smothers the fire, the remaining air will cool rapidly and the pressure will start to drop. Pump in stored nitrogen (cool from expansion) to keep pressure constant. Constant pressure lets the rescuers more easily enter the area (with portable oxygen), without much air-mixing at the hatches, reducing re-ignition/backdraft/flashover risks. Once the fire is definitely positively absolutely out and cold, you can use the same vents to flush the smoke while reintroducing breathable air. (Or just seal and vent to external pressure if you are writing it off or need to do a full rebuild.)

Even with a large fire, venting to Mars pressure might be unnecessary. Most fires might be dealt with by venting to a higher-than-Mars-pressure. Not sure how low you'd need to go to guarantee extinguishing, but it might be that the pressure can be kept high enough that any trapped humans can still breath (even if they are really, really unhappy) and self-evacuate.

But I wouldn't go with increased O2 concentration at all, given the fire hazards in Martian g.

Because of the issues of fire in a closed system, I've mentioned before that I'd rather spend the engineering costs and design to a higher pressure, with lower oxygen percentage. Reduce the flammability of materials below Earth normal.

But if venting (partial or fully) is effective enough, it might mean that fire isn't really such a great risk. (Lowering building pressure in response to a fire is not an option on Earth, so isn't part of our mind-set.)
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 02/06/2019 03:28 am
However, a colony can voluntarily vent atmosphere to contain a fire.

That might be required just to deal with the thermal expansion anyway. Fire, hot. Using misters will also increase internal pressure, rule of thumb is 1600 times volume expansion. So your fire system will already have venting built in.

If the vented air (and misted water) smothers the fire, the remaining air will cool rapidly and the pressure will start to drop. Pump in stored nitrogen (cool from expansion) to keep pressure constant. Constant pressure lets the rescuers more easily enter the area (with portable oxygen), without much air-mixing at the hatches, reducing re-ignition/backdraft/flashover risks. Once the fire is definitely positively absolutely out and cold, you can use the same vents to flush the smoke while reintroducing breathable air. (Or just seal and vent to external pressure if you are writing it off or need to do a full rebuild.)

Even with a large fire, venting to Mars pressure might be unnecessary. Most fires might be dealt with by venting to a higher-than-Mars-pressure. Not sure how low you'd need to go to guarantee extinguishing, but it might be that the pressure can be kept high enough that any trapped humans can still breath (even if they are really, really unhappy) and self-evacuate.

But I wouldn't go with increased O2 concentration at all, given the fire hazards in Martian g.

Because of the issues of fire in a closed system, I've mentioned before that I'd rather spend the engineering costs and design to a higher pressure, with lower oxygen percentage. Reduce the flammability of materials below Earth normal.

But if venting (partial or fully) is effective enough, it might mean that fire isn't really such a great risk. (Lowering building pressure in response to a fire is not an option on Earth, so isn't part of our mind-set.)
You're not injecting a lot of mist though, so that's not so bad.  And water condenses out fast, so it's less of a problem than other gases.  The expanse in volume of the hot air from a fire is quite high, so you would want to stop it fast to prevent overpressure, that's a good point.  Doubling or tripling the pressure in a glass dome is not a good idea.  I agree that standard air pressure is probably, best.  There will be so many other things to deal with, let's try to keep at least one parameter constant in the experiment that a Mars colony would be.

Once you get everybody out, the simplest may indeed be to just vent the dome.  Save the people, then save the building.  Basic fire fighting.  The sprinklers are really there for the first few critical minutes, to ensure you don't get to the latter catastrophic situation.
Wonder what type of pressure/fire door would be best?  Hopefully, not a gigantic door, with big locking crenelations, that slams down and that your hero just barely manages to slip under.  And not the other door, where the sidekick gets caught on the wrong side and the hero watches helplessly as his best friend dies right in front of the tiny little window.
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 02/06/2019 05:13 am
Wonder what type of pressure/fire door would be best?  Hopefully, not a gigantic door, with big locking crenelations, that slams down and that your hero just barely manages to slip under.  And not the other door, where the sidekick gets caught on the wrong side and the hero watches helplessly as his best friend dies right in front of the tiny little window.

As long as the life support system counts oxygen levels in seconds-remaining, I'm happy.
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 02/06/2019 05:59 am
I'm curious how much difference it would make if the glass wasn't flat but was domed. For eg, doming it inwards (towards the pressure) would put some of the force in compression. AIUI, glass has a compressive strength better than two orders of magnitude higher than its tensile strength.

Just to be clear, by "dome inward", I didn't mean the entire structure is inverted, a la

(http://www.leisureopportunities.co.uk/images/849287_152032.jpg)

I still mean a mundane outward curving shape, but the individual glass panes would curve inwards, to convert tensile forces on the glass into compressive force. (The frame is still tensile.) I'm curious if it would make glass more viable.

For eg,
Title: Re: Elon Musk: glass geodesic domes
Post by: Lampyridae on 02/06/2019 11:23 am
I'm curious how much difference it would make if the glass wasn't flat but was domed. For eg, doming it inwards (towards the pressure) would put some of the force in compression. AIUI, glass has a compressive strength better than two orders of magnitude higher than its tensile strength.

Just to be clear, by "dome inward", I didn't mean the entire structure is inverted, a la

(http://www.leisureopportunities.co.uk/images/849287_152032.jpg)

I still mean a mundane outward curving shape, but the individual glass panes would curve inwards, to convert tensile forces on the glass into compressive force. (The frame is still tensile.) I'm curious if it would make glass more viable.

For eg,

Well, these would function as a set of (the tops of) vacuum bell jars. For 18" / 45cm you have up to 8mm glass thickness. Bell jars are designed for cylindical stresses, not spherical ones - the dome is therefore overdesigned.

Light bulbs are about .6mm in thickness, and they are crushed at depth as a low-energy seismic source.

http://saund.stanford.edu/saund1/Light_bulbs.pdf

Following the link we have a handy dandy selection of light bulbs, thicknesses, volume and their crush pressures.

Generally, the average (E27) 60mm diameter light bulb 0.6mm thick can take up to 1000kPa (yes 10 bar) of extra pressure before it implodes (neglecting internal pressure, some 80kPa). Since thickness is proportional to pressure and radius, we can easily scale these values up. Some implode at 200KPa so we'll keep this diameter-to-thickness ratio, and call it a safety factor of 2 as glass is a treacherous beast.

Using the above information, assuming the large size poses no manufacturing issues, we can confidently make a 6 metre diameter inverted dome section that is 6cm thick with a lightbulb-glass safety factor of 2. Or, a 60cm window 6mm thick that has a safety factor of 2.

https://ecatalog.corning.com/life-sciences/b2c/US/en/Glassware/Jars/PYREX%C2%AE-Bell-Jars-with-Top-Knob/p/6885-222

Taking a different method, a Pyrex bell jar from Corning's catalogue is 225mm in diameter and 4.5mm thick. It's meant to be pretty tough and withstand all sorts of experimental nasties. Make it 2.25m in diameter and the glass will be 45mm thick.

http://www.hyvac.com/Products/Systems/Bell_jar_specs.htm

This website lists an 18" (45mm) bell jar that's 8mm thick. So again, scaling up would give us something 40mm thick.

The fact that bell jars have a cylindrical component is what requires them to be thicker, as well as handle little explosions inside, rapid pressurisation etc.

Tempering improves the strength of glass by "freezing in" compressive forces that cancel tensile forces before the glass yields. This is energy intensive and time consuming.
Title: Re: Elon Musk: glass geodesic domes
Post by: Rocket Surgeon on 02/07/2019 04:36 am
Ask and ye shall receive!

So just quickly...I believe fixing the edges IS an accurate model, as the edges of the glass would be set into a frame, probably locally made steel, with a very tight fit to provide a seal. This would "stop" the glass from moving in a specific direction, or rotating at the edge, effectively fixing it.

For a more accurate simulation, I'd have to make the glass a Solid and "weld*" steel Plate to the edge of it. Doable, just a little more time consuming.

Again, I assuming yield strength is 7 MPa.

Results for a 500mm Equilateral:
- 50 kPa, 10mm, the highest stress is 11.47 MPa
- 50 kPa, 30mm, the highest stress is 1.252 MPa
- 50 kPa, 50mm, the highest stress is 0.438 MPa

- 25 kPa, 10mm, the highest stress is 5.736 MPa
- 25 kPa, 30mm, the highest stress is 0.626 MPa
- 25 kPa, 50mm, the highest stress is 0.219 MPa

As a comparison, the 1000mm Equilateral:
- 50 kPa, 10mm, the highest stress is 49.25 MPa
- 50 kPa, 30mm, the highest stress is 5.448 MPa
- 50 kPa, 50mm, the highest stress is 1.943 MPa

- 25 kPa, 10mm, the highest stress is 24.62 MPa
- 25 kPa, 30mm, the highest stress is 2.724 MPa
- 25 kPa, 50mm, the highest stress is 0.971 MPa

So the shorter, the better, and the thicker, the better. In fact, even at 50 kPa, a 30mm thick panel is more than sufficient structurally, depending on your safety factor.  Such a panel would only be 9 kg, excluding the framework.


*This is just a FEMAP use term, not actually welding in real life.
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 02/07/2019 07:02 am
I believe fixing the edges IS an accurate model, as the edges of the glass would be set into a frame, probably locally made steel, with a very tight fit to provide a seal. This would "stop" the glass from moving in a specific direction, or rotating at the edge, effectively fixing it.

Since it's under outwards pressure, the alternative is to let it self-seal against the inner face of the frame. (A few light clips to hold it in place when the dome is unpressurised.) That way it can expand and shrink at a different rate than the frame (within reason) and the seal is tight regardless.

Eg... (flat panes because I forgot about domed panes until I'd finished)


Title: Re: Elon Musk: glass geodesic domes
Post by: Lampyridae on 02/07/2019 08:53 am
I believe fixing the edges IS an accurate model, as the edges of the glass would be set into a frame, probably locally made steel, with a very tight fit to provide a seal. This would "stop" the glass from moving in a specific direction, or rotating at the edge, effectively fixing it.

Since it's under outwards pressure, the alternative is to let it self-seal against the inner face of the frame. (A few light clips to hold it in place when the dome is unpressurised.) That way it can expand and shrink at a different rate than the frame (within reason) and the seal is tight regardless.

Eg... (flat panes because I forgot about domed panes until I'd finished)




An example from real life, the LEM windows were mounted on sprung metal inside a teflon seal and were thus "floating," taking only the force of cabin pressure.

Aircraft cabin windows are designed as cutouts, so the stress can go around them. The principle is the Kirsch hole-in-an-infinite-plate. Stress distribution is independent of the size of the hole, always triple right at the edge and then dropping off one diameter away. /notanengineer

(http://www.fracturemechanics.org/images/hole/holestress_9.svg)

SpaceShip Two has windows spaced somewhat over one diameter apart, and Burt Rutan gave a sharp welding hammer to the SpaceShip One pilots and told them to try and break the polycarbonate windows during a pressure test.

(https://robbreportedit.files.wordpress.com/2018/04/captive_carry_vc01.jpg?w=1000)

New Shepard windows are huge, and seem to keep this one diameter spacing.

(https://s.newsweek.com/sites/www.newsweek.com/files/styles/embed_tablet/public/2018/04/30/rtx34axk.jpg)

SpaceShip One, Two and New Shepard all have curvature in their windows for streamlining but may also help distribute stress.

I don't know at what point the assumption becomes that the windows can no longer be treated as simple structural cutouts.

Article on Apollo program windows: https://www.lpi.usra.edu/lunar/documents/apolloSpacecraftWindows.pdf
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 02/07/2019 10:46 am
Colour version of that Apollo LM window.

(https://4.bp.blogspot.com/-2GXSZkY0MWM/UAl97kwoM2I/AAAAAAAAA-I/tbWjKn9s1vU/s1600/LM_FW.png) (https://4.bp.blogspot.com/-2GXSZkY0MWM/UAl97kwoM2I/AAAAAAAAA-I/tbWjKn9s1vU/s1600/LM_FW.png)

[edit: Just to be clear, found it on the interwebz, I didn't colour it.]
Title: Re: Elon Musk: glass geodesic domes
Post by: Rocket Surgeon on 02/07/2019 10:57 am
Hmmm... those configuration would still constrain the glass in T(x,y,z) but would allow rotation, possibly reducing stress... AND still allow the model to solve!
Title: Re: Elon Musk: glass geodesic domes
Post by: Oersted on 02/07/2019 08:31 pm
In "envisioning amazing habitats" we already went through the dome discussion around 60 pages and three years back. Yup, glass domes are actually no good on Mars.

For those who are new to this forum and to discussing bases on Mars that thread is a good long read.

It will also explain to you why so many oldtimers in here seem to fancy tunnels (as does Musk).
That wasn’t actually a consensus opinion.

I agree and I didn't say it was.
Title: Re: Elon Musk: glass geodesic domes
Post by: rarchimedes on 02/09/2019 05:24 am
I'm just catching up on all this after a week in the hospital from foot surgery, so let me take a few shots. I agree with the initial comments that I have seen on domed windows, but the one thing that I do not understand is the references to glass thicknesses as directly proportionate to radius when every other thing in this world that I know is proportional to the square of the change in radius.

Moving on, truly hemispherical segments make the most sense because they transfer all lift forces perpendicular to the base plane and therefore to the frames. The hemisphere is the strongest possible form to present to both forces from within and dangers from without. If you were flying these, the weight of hemispheres as opposed to almost any other glass form might be prohibitive.

I renew my objection to any "window" exposed directly to a line of sight leading to the atmosphere on Mars. That atmosphere will hardly slow or filter or burn up incoming rocks or radiation of any kind, leaving a necessity for complex support and emergency repair systems as well as thicker and more complexly produced glass, itself. Mirrors can be used to bring light and images (properly erected) to properly protected windows, but I have seen no evidence that lack of external lines of sight is the kind of psychological problem that has been evinced in theses parts. Some of the sunniest states in our union have some of the highest suicide rates. I might not find it ideal, but I might prefer it to exposure to unmediated Mars. Explosive decompression is also not much fun and can be difficult to remediate. Referring to the ISS or to the LEM isn't of much help as both of those are horrendously expensive and not easily translatable to hectare size exposures. Plastics can easily be formed into hemispheres of any particular thickness with actually better optical clarity than glass, especially at the greater thicknesses. The hydrogen content of most plastics make them better radiation filters than most glass and at much lower densities.

As noted elsewhere, the process to produce rocket fuel can easily be tied to a process to produce plastics and without heavy duty mining, crushing, separating and possible extended chemical processes necessary to make glass of any useful quality. The only mining operation necessary early on, on Mars would be for the production of water which would then feed almost all other processes.

Elsewhere in these posts there have been discussions ad nauseum about production of various metals and silicon, none of which seem likely to be done with the equipment available to the early cycles to Mars. Pure heat separation may possibly produce small amounts of the lower temp metals, but the closest nearly pure metals are allegedly to be found in metallic asteroids. If that is so, bringing metals from asteroids might be far cheaper than from Earth or through production on Mars. Unlike on Earth, where an elevator to geosynchronous orbit is just marginally physically possible, putting in an elevator to areosynchronous orbit has no technical issues, it will be fairly easy to establish a Mars elevator to bring down such riches to the Mars surface while making the safety of access to and egress from the surface magnitudes of order safer and easier than at present. That is how we get our windows and almost everything else.
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 02/11/2019 04:59 pm
If small glass panes are advantageous as far as mass goes, since they are under less strain and can be thinner, then we might want to forget about float glass and perhaps go with another forming process?  Perhaps even molds, rather than a continuous process?  Not that is matters much if we have waste glass, as it seems typical to re-melt part of the production.  I think it would be nice to have rounded corners in the glass panes, as per the LEM.

Or perhaps go with a very narrow production line, perhaps 200mm wide?  Would certainly save on mass and complexity.

Might be interesting, if the parts are small enough, to do some of the treatment for toughness that Corning uses for it's glass?  Potassium should be available, or can come from Earth if need be.  Anyway it'll be required for other things so might as well produce it locally.

https://www.corning.com/au/en/innovation/the-glass-age/science-of-glass/the-secret-of-tough-glass-ion-exchange.html

We only need a tiny production line, after all, a few tonnes per day will already be quite a success.

A small industrial installation here on Earth seems to be 400 tonnes per day.
Title: Re: Elon Musk: glass geodesic domes
Post by: Lar on 02/13/2019 06:39 am
Space Elevator discussion was off topic. Several posts were moved to the Space Elevator thread:

https://forum.nasaspaceflight.com/index.php?topic=41971.0

Please continue any discussion there.

A special thanks to  Lampyridae who saved me the bother of finding the right thread. When you report off topic stuff (via report to mod) giving the place you suggest that we move things to? Really helps a lot and is really appreciated.


 
Title: Re: Elon Musk: glass geodesic domes
Post by: Vultur on 02/13/2019 09:33 am
If the primary purpose of the domes are access to natural sunlight/outside view without a spacesuit, with plants in it for primarily psychological/aesthetic benefits (even if they are also edible plants), then they probably don't have to be all that large.

More, smaller domes might be better - less structurally demanding, and if the smaller domes have a higher glass-to-framework ratio, they might *feel* just as open if not more so.

If the domes are a primary food production area, though, you'd probably want them larger.
I renew my objection to any "window" exposed directly to a line of sight leading to the atmosphere on Mars. That atmosphere will hardly slow or filter or burn up incoming rocks or radiation of any kind, leaving a necessity for complex support and emergency repair systems as well as thicker and more complexly produced glass, itself.

I think the Mars atmosphere would stop micrometeorites. Larger meteorites probably are not common enough to worry about; even if the rate is 1000x what it is on Earth, what percentage of buildings on Earth have ever been damaged by meteorites?

Especially since the concept here seems to be domes as a fairly small portion of a mostly subterranean Mars colony ... they will not be very large targets.

Quote
Mirrors can be used to bring light and images (properly erected) to properly protected windows, but I have seen no evidence that lack of external lines of sight is the kind of psychological problem that has been evinced in theses parts.

I don't think there would be any way to get that evidence... You really don't have situations on Earth where people have no access to natural light/outdoor views for longer than, say, a nuclear sub tour of duty - except maybe some prisons with poor conditions, and that's not even close to a representative psychological sample.

Quote
Referring to the ISS or to the LEM isn't of much help as both of those are horrendously expensive and not easily translatable to hectare size exposures.

I really, really doubt these are going to be hectare size domes... at least in the early decades of a colony. If the domes are a relatively small part of a mostly subterranean settlement...

I do think plastics are likely to be the way to go... I wouldn't be surprised if bioplastics end up being an extremely important tool for a Mars colony (since you could skip most of the complex industrial infrastructure). By the time we get to manufacturing structural elements on Mars, bioplastics and genetic engineering technology will likely be a lot more advanced.

While it's not near term, at some point you might even get to engineering the organisms to grow in the open, unpressurized... Mars atmosphere has enough CO2 to support photosynthesis, and the thermal environment isn't beyond what some lichens can handle (lichens living at Mars pressure/temperature has actually been demonstrated).
Title: Re: Elon Musk: glass geodesic domes
Post by: Slarty1080 on 02/13/2019 04:22 pm
I'm curious how much difference it would make if the glass wasn't flat but was domed. For eg, doming it inwards (towards the pressure) would put some of the force in compression. AIUI, glass has a compressive strength better than two orders of magnitude higher than its tensile strength.

Just to be clear, by "dome inward", I didn't mean the entire structure is inverted, a la

(http://www.leisureopportunities.co.uk/images/849287_152032.jpg)

I still mean a mundane outward curving shape, but the individual glass panes would curve inwards, to convert tensile forces on the glass into compressive force. (The frame is still tensile.) I'm curious if it would make glass more viable.

For eg,
Might be a bit of a dust trap
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 02/13/2019 04:39 pm
outward curving shape, but the individual glass panes would curve inwards, to convert tensile forces on the glass into compressive force.
Might be a bit of a dust trap

Good point. But you could have an outermost pane that's unpressurised and flat.
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 02/13/2019 08:47 pm
Would look like one of the walls made from beer bottles :-)  Perhaps no much good for looking out but ok for light.

Glass both inside and out may need a protective coating from dust and scratches.
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 02/13/2019 11:41 pm
The Montreal geodesic dome. Acrylic panes.  And why plastic might not be such a good idea...

The dome did survive the fire, that happened in 1976, and is still used today, but with an open structure.  I want to stay away from exaggerated concern so there are certainly ways to mitigate this.  But glass doesn't burn :-) so that's solving the problem at the source. 

It does make for some lovely symmetries from the interior.

I wonder if using small batch processes we might be able to mass produce glass that was tougher than classic soda glass.  I'm thinking small panes less than 1 foot across.  These would not be safe from sabotage but should survive most likely accidents.  Smaller panes would make the result of the break like the one shown less dramatic.
Title: Re: Elon Musk: glass geodesic domes
Post by: Rocket Surgeon on 02/14/2019 01:18 am
The Montreal geodesic dome. Acrylic panes.  And why plastic might not be such a good idea...

The dome did survive the fire, that happened in 1976, and is still used today, but with an open structure.  I want to stay away from exaggerated concern so there are certainly ways to mitigate this.  But glass doesn't burn :-) so that's solving the problem at the source. 

It does make for some lovely symmetries from the interior.

I wonder if using small batch processes we might be able to mass produce glass that was tougher than classic soda glass.  I'm thinking small panes less than 1 foot across.  These would not be safe from sabotage but should survive most likely accidents.  Smaller panes would make the result of the break like the one shown less dramatic.

Is there any way to make the laminate for Laminated Glass?

My understanding is polyvinyl butyral (PVB) or ethylene-vinyl acetate (EVA) are primarily used on Earth, and you can produce Polyethylene relatively easily on Mars.

Could that be used? or would you need more.
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 02/14/2019 01:46 am
The Montreal geodesic dome. Acrylic panes.  And why plastic might not be such a good idea...

The dome did survive the fire, that happened in 1976, and is still used today, but with an open structure.  I want to stay away from exaggerated concern so there are certainly ways to mitigate this.  But glass doesn't burn :-) so that's solving the problem at the source. 

It does make for some lovely symmetries from the interior.

I wonder if using small batch processes we might be able to mass produce glass that was tougher than classic soda glass.  I'm thinking small panes less than 1 foot across.  These would not be safe from sabotage but should survive most likely accidents.  Smaller panes would make the result of the break like the one shown less dramatic.

Is there any way to make the laminate for Laminated Glass?

My understanding is polyvinyl butyral (PVB) or ethylene-vinyl acetate (EVA) are primarily used on Earth, and you can produce Polyethylene relatively easily on Mars.

Could that be used? or would you need more.
I suggested glass safety film a few pages ago. Surprisingly thin, just a few mills, and it is very tough.  Simply stuck to the glass.  It could come from Earth at first, then be produced locally.
Title: Re: Elon Musk: glass geodesic domes
Post by: Lampyridae on 02/14/2019 07:33 am
Assuming you're building a glass dome that has buildings in it like we usually see in SF, one way to reduce the amount of glass required is to make the buildings tall enough that they reach the roof. Those sections where they are effectively part of the roof are made of opaque materials, steel, concrete. You could cut down on the glass requirements by 50% or more. With walkways and such you can make more use of the "open to sky" volume. Alternatively you could make more use of the roof space if you have buildings. Real estate development being what it is, I guess you'd see a bit of both.
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 02/14/2019 07:56 am
We've also previously suggested (in the Envisioning Amazing Habs thread, I suspect) hanging buildings from the frame. The weight of the buildings is much less than the outward force from the atmosphere, but reduces the load on the frame a little. Similarly, to run tensile structures from the frame to the foundation, to warp the pressure vessel into a more useful shape, then hang buildings off those tensile "pillars".
Title: Re: Elon Musk: glass geodesic domes
Post by: Hominans Kosmos on 02/14/2019 01:18 pm
to run tensile structures from the frame to the foundation, to warp the pressure vessel into a more useful shape,

Maintenance safety hazards aside, isn't a tall dome useful in itself? Isn't a a high air mass and distance from particle impacts beneficial towards radiation protection?
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 02/14/2019 10:33 pm
to run tensile structures from the frame to the foundation, to warp the pressure vessel into a more useful shape,
Maintenance safety hazards aside, isn't a tall dome useful in itself?

Except you aren't starting with a dome. A dome isn't a natural shape for a pressurised volume. So if you want to distort your pressure-vessel into more of a dome-like shape, you are going to need tricksy engineering voodoo.
Title: Re: Elon Musk: glass geodesic domes
Post by: Lampyridae on 02/17/2019 07:20 pm
to run tensile structures from the frame to the foundation, to warp the pressure vessel into a more useful shape,
Maintenance safety hazards aside, isn't a tall dome useful in itself?

Except you aren't starting with a dome. A dome isn't a natural shape for a pressurised volume. So if you want to distort your pressure-vessel into more of a dome-like shape, you are going to need tricksy engineering voodoo.

Not really voodoo:

(http://www.americaspace.com/wp-content/uploads/2012/09/STS-49-cabin.jpg)
Title: Re: Elon Musk: glass geodesic domes
Post by: Paul451 on 02/17/2019 10:48 pm
Not really voodoo:

You don't think the shuttle involved engineering witchcraft? You were not paying attention.
Title: Re: Elon Musk: glass geodesic domes
Post by: lamontagne on 02/19/2019 11:26 am
Geodesic dome with small panes.
Small panes undergo much lower stress, and the breakage of a pane is much less important.
Lots of joints though.

Nodes further away are covered by a concrete dome with a window line.  Ground is removed.

This is the industrial area of the colony, and the dome houses the cafeteria.

Title: Re: Elon Musk: glass geodesic domes
Post by: Lampyridae on 02/19/2019 02:04 pm
Geodesic dome with small panes.
Small panes undergo much lower stress, and the breakage of a pane is much less important.
Lots of joints though.

Nodes further away are covered by a concrete dome with a window line.  Ground is removed.

This is the industrial area of the colony, and the dome houses the cafeteria.



Looking good!

Given the updated radiation transport models with pion dose contribution, I think we're going to need at least 6m of regolith cover to achieve satisfactory radiation protection. Once the effect of atmosphere is taken into account 1m or so may do nothing or maybe even make things worse. I haven't found any papers testing the updated HZTERN models with regolith, but anything more than 20g/cm^2 of aluminium starts counteracting the shielding and 70g/cm^2 makes things worse than if there were no shielding at all.

Currently we use comparisons between atmosphere to simulate regolith depth, but pions have a short decay path and would probably not show up at kilometres of very low density shielding like they would for a metre or so of shielding.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1002/2016SW001418
Title: Re: Elon Musk: glass geodesic domes
Post by: RoboGoofers on 02/20/2019 04:28 pm
This might be a half baked idea, or one that's been discussed already, but what about building a dome within a soil retaining dam filled with a heavy gas like sulfur hexaflouride or a suitably dense easily in-situ produced gas. Gas phase might be easier than liquid phase at these pressures, though it wouldn't provide anywhere near the same counter-pressure.

it would make suited excursions a bit easier in the immediate area outside the hab within the dam for construction or repairs.