Author Topic: Elon Musk: glass geodesic domes  (Read 98967 times)

Offline Robotbeat

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Re: Glass geodesic domes
« Reply #40 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.
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Offline docmordrid

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Re: Glass geodesic domes
« Reply #41 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.
« Last Edit: 10/29/2016 08:23 pm by docmordrid »
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Offline KelvinZero

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Re: Glass geodesic domes
« Reply #42 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.

Online launchwatcher

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Re: Glass geodesic domes
« Reply #43 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. 


Offline Vultur

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Re: Glass geodesic domes
« Reply #44 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.

Online MickQ

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Re: Glass geodesic domes
« Reply #45 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.

Offline Robotbeat

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Re: Glass geodesic domes
« Reply #46 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.
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Offline lamontagne

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Re: Glass geodesic domes
« Reply #47 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.

« Last Edit: 10/30/2016 01:00 am by lamontagne »

Offline LMT

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Re: Glass geodesic domes
« Reply #48 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:

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 ironAguayo et al. 2011, Fig. 38

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



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. 

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

Offline gospacex

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Re: Glass geodesic domes
« Reply #49 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?

Online guckyfan

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Re: Glass geodesic domes
« Reply #50 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.

Online guckyfan

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Re: Glass geodesic domes
« Reply #51 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.

Offline docmordrid

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Re: Glass geodesic domes
« Reply #52 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
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Offline KelvinZero

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Re: Glass geodesic domes
« Reply #53 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.

Offline Oli

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Re: Glass geodesic domes
« Reply #54 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.

Offline gospacex

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Re: Glass geodesic domes
« Reply #55 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.
« Last Edit: 10/30/2016 12:28 pm by gospacex »

Offline Robotbeat

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Re: Glass geodesic domes
« Reply #56 on: 10/30/2016 12:38 pm »
Because the new building is specifically designed to withstand moving ice and blown snow.
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Offline Robotbeat

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Re: Glass geodesic domes
« Reply #57 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.
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Offline gospacex

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Re: Glass geodesic domes
« Reply #58 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.

Offline LMT

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Re: Glass geodesic domes
« Reply #59 on: 10/30/2016 02:21 pm »
GCRs are not X-rays or gammas. They're high energy particles.

100+ MeV, 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, for example.  Which is the better shield against high-energy protons?
« Last Edit: 12/14/2016 06:48 pm by LMT »