Author Topic: Envisioning Amazing Martian Habitats  (Read 869734 times)

Online lamontagne

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Re: Envisioning Amazing Martian Habitats
« Reply #300 on: 11/01/2016 11:21 pm »
Here is a view of safebase.  With a nice mountain just at the right place.  The landscape is from South Tunisia.
I've added a solar array field to the view.  IF you want, you can imagine an underground nuclear reactor, or not.

« Last Edit: 11/01/2016 11:22 pm by lamontagne »

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Re: Envisioning Amazing Martian Habitats
« Reply #301 on: 11/01/2016 11:29 pm »
Dome Heat

I put a bit of structure inside the dome.

Mostly platforms wit a lot of greenery.  Could be sports areas instead.  Possibly a floor of high intensity agriculture, but that might better be done in closed rooms with controlled atmosphere and lighting.  Plants are happy in conditions that people sometimes find not all that pleasant...

Again, most of the living area is actually underground, these are just entry points to the city.

The exterior wall is a form of curtain wall, in a way.  It's self supporting, mostly, and pressure driven, except for the gravity loads that are transmitted by columns to the ground.

Nice-looking structure.  btw, on winter nights your heat flux will be quite high.  For example, if panes are simple 6 cm glass, the flux would be ~100 MW.  Might give that some thought.

Why so high?  I was hoping that using a low emissivity on the glass surface would allow for the radiation to be fairly low.  I just calculated something like 100 kW.  I expected no convection or conduction.  Do you have some numbers for this?


Online lamontagne

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Re: Envisioning Amazing Martian Habitats
« Reply #302 on: 11/01/2016 11:37 pm »
LaMontage.

Can you give me the sketchup link? I might put my vizualisation skills to use and make some renderings. Finally a chance to contribute to this forum.
Best wishes,
M.
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Offline Lumina

Re: Envisioning Amazing Martian Habitats
« Reply #303 on: 11/02/2016 01:47 am »
I put a bit of structure inside the dome.
Hi lamontagne,
I don't think flattened spheres are robust pressure containers. For example in the extreme, upper and lower sides approach flat and would be worse than cubes. I think you can elongate, but not flatten. Cigars and conical points are ok.. I think?

Why not just go the full sphere? I posted a picture of a hydrogen tank in the other thread but just noticed there is a picture of it in a NSF article right now:

https://www.nasaspaceflight.com/2016/10/ksc-groundwork-sls-block-1b-upgrades/

These were the links I posted in the other thread:
these gas tanks or this big liquid hydrogen tank

EDIT:
Ok I did a search on pressure tanks and did find lots of examples that look flattened at the ends. Can anyone explain that to me? (none of them where wider than they were tall though, and when I searched for high pressure tanks, more had spherical ends.)

KelvinZero, and posters, do you think it would be a good idea to merge this thread and the geodesic glass domes thread? My thinking is that this thread went public with descriptions and pictures of glass domes and tunnels before Elon Musk mentioned them for the first time ever in his AMA. Also everything about geodesic glass domes on Mars is amazing so the entire other thread would be right at home in here. It would certainly make everyone's life easier to have one thread instead of two, we have enough worries each day to also have to worry where to post ideas about amazing glass domes in Mars Base Alpha.

Offline Robotbeat

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Re: Envisioning Amazing Martian Habitats
« Reply #304 on: 11/02/2016 02:28 am »
Dome Heat

I put a bit of structure inside the dome.

Mostly platforms wit a lot of greenery.  Could be sports areas instead.  Possibly a floor of high intensity agriculture, but that might better be done in closed rooms with controlled atmosphere and lighting.  Plants are happy in conditions that people sometimes find not all that pleasant...

Again, most of the living area is actually underground, these are just entry points to the city.

The exterior wall is a form of curtain wall, in a way.  It's self supporting, mostly, and pressure driven, except for the gravity loads that are transmitted by columns to the ground.

Nice-looking structure.  btw, on winter nights your heat flux will be quite high.  For example, if panes are simple 6 cm glass, the flux would be ~100 MW.  Might give that some thought.
Youre making the same false assumption that you made earlier when you said the polycarbonate would be brittle. You're saying the surface of the dome will be the same temperature as the incredibly thin outside air. That's simply not true.

There's not perfect thermal conductivity between the thin Martian air and the dome's surface.
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Offline LMT

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Re: Envisioning Amazing Martian Habitats
« Reply #305 on: 11/02/2016 03:46 am »
Domo Domo

KelvinZero, and posters, do you think it would be a good idea to merge this thread and the geodesic glass domes thread?

Thanks.  Could we merge, but consider keeping this thread open for non-dome structures?  There are a lot of ideas here; wouldn't want to discourage the other ideas, just because Musk tweeted "dome".

Offline TripD

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Re: Envisioning Amazing Martian Habitats
« Reply #306 on: 11/02/2016 04:00 am »
Dome Heat

I put a bit of structure inside the dome.

Mostly platforms wit a lot of greenery.  Could be sports areas instead.  Possibly a floor of high intensity agriculture, but that might better be done in closed rooms with controlled atmosphere and lighting.  Plants are happy in conditions that people sometimes find not all that pleasant...

Again, most of the living area is actually underground, these are just entry points to the city.

The exterior wall is a form of curtain wall, in a way.  It's self supporting, mostly, and pressure driven, except for the gravity loads that are transmitted by columns to the ground.

Nice-looking structure.  btw, on winter nights your heat flux will be quite high.  For example, if panes are simple 6 cm glass, the flux would be ~100 MW.  Might give that some thought.
Youre making the same false assumption that you made earlier when you said the polycarbonate would be brittle. You're saying the surface of the dome will be the same temperature as the incredibly thin outside air. That's simply not true.

There's not perfect thermal conductivity between the thin Martian air and the dome's surface.

Seems it would be straight forward to have a rollout flexible cover that could cover the glass at night or during dust storms.

Offline LMT

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Re: Envisioning Amazing Martian Habitats
« Reply #307 on: 11/02/2016 04:33 am »
Heat Loss

Dome Heat

I put a bit of structure inside the dome.

Mostly platforms wit a lot of greenery.  Could be sports areas instead.  Possibly a floor of high intensity agriculture, but that might better be done in closed rooms with controlled atmosphere and lighting.  Plants are happy in conditions that people sometimes find not all that pleasant...

Again, most of the living area is actually underground, these are just entry points to the city.

The exterior wall is a form of curtain wall, in a way.  It's self supporting, mostly, and pressure driven, except for the gravity loads that are transmitted by columns to the ground.

Nice-looking structure.  btw, on winter nights your heat flux will be quite high.  For example, if panes are simple 6 cm glass, the flux would be ~100 MW.  Might give that some thought.

Why so high?  I was hoping that using a low emissivity on the glass surface would allow for the radiation to be fairly low.  I just calculated something like 100 kW.  I expected no convection or conduction.  Do you have some numbers for this?

It would be good if I've calculated too high there, because lower heat loss would be a win for many hab schemes.

I was thinking of heat loss as it's calculated in a typical construction.  R-value (thermal resistance) for 6 cm glass works out at ~0.06 m2K/W.  Winter night temperature difference is 160 C. That gives a heat flux of 2667 W/m2

For dome surface area I used your previous scaling number of 150 m diameter, eyeballing a 75 m height, and allowing for 25% dome burial with no heat loss there.  That leaves 36,620 m2 exposed for heat loss. 

Multiply area by flux, and total heat loss is ~100 MW.

The glass panes insulate very poorly, so convection off panes should be low; but if there's a correction factor for atmospheric pressure I don't know it.  Also the dome radiates efficiently because there's no reflector outside the glass surface.

In your spreadsheet you have a smaller dome (100 m diameter), and you're using low-e film.  I think I'd seen that these films, in practice, reduce heat flux by at most 1/3.  Any thought on that?  And you're using the T4 Stefan-Boltzmann law, which is fine.  Just coming at heat loss from a different direction.
« Last Edit: 12/14/2016 07:48 pm by LMT »

Offline KelvinZero

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Re: Envisioning Amazing Martian Habitats
« Reply #308 on: 11/02/2016 04:42 am »
Domo Domo

KelvinZero, and posters, do you think it would be a good idea to merge this thread and the geodesic glass domes thread?

Thanks.  Could we merge, but consider keeping this thread open for non-dome structures?  There are a lot of ideas here; wouldn't want to discourage the other ideas, just because Musk tweeted "dome".
I would prefer them kept separate.. The domes one is about some very specific issues with domes. It is specific enough that it might actually feel answered shortly, and then that thread will fade away while this thread may continue, perhaps now focusing more on the domes and droids and tunnelling aspects.

The thing about that dome thread was specifically issues like anchoring and leaking that made the Dome statement strange to me. Someone did some math about anchoring i havent got around to yet. My expectation is that it is more time, effort and resources for a less trusty and less general result, restricting you to only certain types of ground that may or may not be near the resources you want.

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Re: Envisioning Amazing Martian Habitats
« Reply #309 on: 11/02/2016 05:02 am »
Cold Skin

Youre making the same false assumption that you made earlier when you said the polycarbonate would be brittle. You're saying the surface of the dome will be the same temperature as the incredibly thin outside air. That's simply not true.

There's not perfect thermal conductivity between the thin Martian air and the dome's surface.

?  The polycarbonate only needs to reach -60 C at one point on its surface, to become brittle there, and put the dome at risk.  On a typical night with -90 C air and ground, a -60 C cold spot on the exterior surface seems very likely to me.  Especially along the ground, where conduction produces even faster heat loss. 

And heaven forbid the dome heating system should fail even briefly, when a polycarbonate dome's integrity is so fragile at martian temperatures.  (Come to think of it, how would you ensure that the polycarbonate never reached -60 C during construction, when a dome heating system was not yet available?   Logistically, that seems a challenge in itself.)

If you wanted to make an opposite case, and give reassurance that the polycarbonate would never approach -60 C, I suppose you'd need to model 1-D polycarbonate thermal profiles, with thermal front skin depth evolution over 1 sol, both in air and on the ground.  Or is there some model already available, for polycarbonate, polyethylene or some similar sheet material?
« Last Edit: 12/14/2016 06:43 pm by LMT »

Offline Lumina

Re: Envisioning Amazing Martian Habitats
« Reply #310 on: 11/02/2016 10:03 am »
Domo Domo

KelvinZero, and posters, do you think it would be a good idea to merge this thread and the geodesic glass domes thread?

Thanks.  Could we merge, but consider keeping this thread open for non-dome structures?  There are a lot of ideas here; wouldn't want to discourage the other ideas, just because Musk tweeted "dome".

Our topic is amazing habitats of all kinds and the equipment you would take to build them. Musk mentioned domes together with "tunelling/mining droids" so there is a lot of room for envisioning either in the direction SpaceX seems to be going or in any other direction that seems amazing to you.

I would prefer them kept separate.. The domes one is about some very specific issues with domes. It is specific enough that it might actually feel answered shortly (..snip..)

The thing about that dome thread was specifically issues like anchoring and leaking that made the Dome statement strange to me. Someone did some math about anchoring i havent got around to yet. My expectation is that it is more time, effort and resources for a less trusty and less general result, restricting you to only certain types of ground that may or may not be near the resources you want.

I still think it's better to merge them but it's a step forward for our posters to have clarity on the topic of the other thread. It sounds like it's for extended discussions on glass dome issues around anchoring and leaking.
« Last Edit: 11/02/2016 10:16 am by Lumina »

Online lamontagne

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Re: Envisioning Amazing Martian Habitats
« Reply #311 on: 11/02/2016 10:27 am »
Heat Loss

Dome Heat

I put a bit of structure inside the dome.

Mostly platforms wit a lot of greenery.  Could be sports areas instead.  Possibly a floor of high intensity agriculture, but that might better be done in closed rooms with controlled atmosphere and lighting.  Plants are happy in conditions that people sometimes find not all that pleasant...

Again, most of the living area is actually underground, these are just entry points to the city.

The exterior wall is a form of curtain wall, in a way.  It's self supporting, mostly, and pressure driven, except for the gravity loads that are transmitted by columns to the ground.

Nice-looking structure.  btw, on winter nights your heat flux will be quite high.  For example, if panes are simple 6 cm glass, the flux would be ~100 MW.  Might give that some thought.

Why so high?  I was hoping that using a low emissivity on the glass surface would allow for the radiation to be fairly low.  I just calculated something like 100 kW.  I expected no convection or conduction.  Do you have some numbers for this?

It would be good if I've calculated too high there, because lower heat loss would be a win for many hab schemes.

I was thinking of heat loss as it's calculated in a typical construction.  R-value (thermal resistance) for 6 cm glass works out at ~0.06 m2K/W.  Winter night temperature difference is 160 C. That gives a heat flux of 2667 W/m2

For dome surface area I used your previous scaling number of 150 m diameter, eyeballing a 75 m height, and allowing for 25% dome burial with no heat loss there.  That leaves 36,620 m2 exposed for heat loss. 

Multiply area by flux, and total heat loss is ~100 MW.

The glass panes insulate very poorly, so convection off panes should be low; but if there's a correction factor for atmospheric pressure I don't know it.  Also the dome radiates efficiently because there's no reflector outside the glass surface.

In your spreadsheet you have a smaller dome (100 m diameter), and you're using low-e film.  I think I'd seen that these films, in practice, reduce heat flux by at most 1/3.  Any thought on that?  And you're using the T4 Stefan-Boltzmann law, which is fine.  Just coming at heat loss from a different direction.
You're missing the convective term on the outer surface of your glass.  In a typical building insulation calculation, you will have the internal film coefficient, the insulation of the building wall composition, then the outside film coefficient, usually equivalent to R 0.1.  However, if you analyse this film coefficient in detail, you will find that it is an expression of the convective conduction from the mass flow of the air on the surface of the building. Q=hAdT where h is a factor of the mass flow.  Using a slightly different equation, Q=mf*Cp*dT, power=mass flow x specific heat x temperature difference, on Mars with the atmosphere 100 times less dense than on Earth, the mass flow will be 100 times less, so the heat transfer film coefficient will be 100 times higher, or about R10 (imperial units) or 2 inches of styrofoam equivalent.  Now if you have double pane glass, you will have 2 more film coefficient, one on the inside and another on the outside of the second pane.  So the overall R will be practically 30.  Therefore the surface temperature of the outer glass pane will be near to the environment temperature, and the radiation will be very low.
And to further reduce heat low you can put the low emissivity film of the inside of the outer glass pane.  This film is an infrared mirror, so the radiation from the inner glass plane gets reflected, and the radiative heat gain on the outer glass pane is almost nil.  Summing up the very low convection and the very low radiation, you get very low heat transfer, about 1000 times less than your first order estimate, or about 100 kW.  For 12 hours of night then about 1200 kWh of heat loss.  As the heat gain is higher, the domes will tend to overheat, if the solar heat gain is not reduced.  So curtains during the day, and not during the night!

The reason low-e windows are not that effective is that they have an atmospheric pressure gas in the void.  If you had a Mars pressure gas in the void, they would insulate as well as, or better, than the walls.  Of course, they would implode first ;-)


« Last Edit: 11/02/2016 10:28 am by lamontagne »

Online lamontagne

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Re: Envisioning Amazing Martian Habitats
« Reply #312 on: 11/02/2016 10:34 am »
Cold Skin

Youre making the same false assumption that you made earlier when you said the polycarbonate would be brittle. You're saying the surface of the dome will be the same temperature as the incredibly thin outside air. That's simply not true.

There's not perfect thermal conductivity between the thin Martian air and the dome's surface.

?  The polycarbonate only needs to reach -60 C at one point on its surface, to become brittle there, and put the dome at risk.  On a typical night with -90 C air and ground, a -60 C cold spot on the exterior surface seems very likely to me.  Especially along the ground, where conduction produces even faster heat loss. 

And heaven forbid the dome heating system should fail even briefly, when a polycarbonate dome's integrity is so fragile at martian temperatures.  (Come to think of it, how would you ensure that the polycarbonate never reached -60 C during construction, when a dome heating system was not yet available?   Logistically, that seems a challenge in itself.)

If you wanted to make an opposite case, and give reassurance that the polycarbonate would never approach -60 C, I suppose you'd need to model 1-D polycarbonate thermal profiles, with thermal front skin depth evolution over 1 sol, both in air and on the ground.  Or is there some model already available, for polycarbonate, polyethylene or some similar sheet material?
Perhaps LDPE would do the trick?  It has a glass transition temperature of -125C.  I was hopping to use it for plastic algae grow tubes on the surface of Mars. 
However, plain glass is a good building material, I don't quite see why it needs to be replaced by plastic, in particular if it is produced in situ.  Shouldn't there be some obsidian flows available on Mars? Good source of glass, that, since it's already glass.

Online lamontagne

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Re: Envisioning Amazing Martian Habitats
« Reply #313 on: 11/02/2016 10:51 am »
A bit of mining.
Anyone had a look a the Hard Rock Miner's handbook I posted a while ago?
Anyway, a typical 2500 Tonne per day gold mine requires 6 MW electrical, plus about 1/2 of that at the mine itself, as fuel and explosives.  This is to crush rock into a very fine powder, to get the gold out, and to dig into very hard rock, usually with high silicate content.  If we just break the rock into gravel, we can use much less power, let's guess 1 kW/tonne.
Since rock has a density of about 3 tonnes per m3, 1 MW of solar power will extract 300 m3 of rock per day, using standard mining methods.  Over a year, we should be able to create 300x300 = 90 000 m3 of underground volume. 
If we divide this into 4.5 m floors, then we have 20 000 square m of living area, or enough for 1000 people at 20 m2 per person.  In two years, about 40m2 per person.
If someone could check this I would really appreciate it, but I guess i'll start right away on illustrating a few big caves....



Offline Robotbeat

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Re: Envisioning Amazing Martian Habitats
« Reply #314 on: 11/02/2016 11:07 am »
Very good calculations, lamontagne!
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Offline LMT

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Re: Envisioning Amazing Martian Habitats
« Reply #315 on: 11/02/2016 12:21 pm »
Dome Heat

Heat Loss

Dome Heat

I put a bit of structure inside the dome.

Mostly platforms wit a lot of greenery.  Could be sports areas instead.  Possibly a floor of high intensity agriculture, but that might better be done in closed rooms with controlled atmosphere and lighting.  Plants are happy in conditions that people sometimes find not all that pleasant...

Again, most of the living area is actually underground, these are just entry points to the city.

The exterior wall is a form of curtain wall, in a way.  It's self supporting, mostly, and pressure driven, except for the gravity loads that are transmitted by columns to the ground.

Nice-looking structure.  btw, on winter nights your heat flux will be quite high.  For example, if panes are simple 6 cm glass, the flux would be ~100 MW.  Might give that some thought.

Why so high?  I was hoping that using a low emissivity on the glass surface would allow for the radiation to be fairly low.  I just calculated something like 100 kW.  I expected no convection or conduction.  Do you have some numbers for this?

It would be good if I've calculated too high there, because lower heat loss would be a win for many hab schemes.

I was thinking of heat loss as it's calculated in a typical construction.  R-value (thermal resistance) for 6 cm glass works out at ~0.06 m2K/W.  Winter night temperature difference is 160 C. That gives a heat flux of 2667 W/m2

For dome surface area I used your previous scaling number of 150 m diameter, eyeballing a 75 m height, and allowing for 25% dome burial with no heat loss there.  That leaves 36,620 m2 exposed for heat loss. 

Multiply area by flux, and total heat loss is ~100 MW.

The glass panes insulate very poorly, so convection off panes should be low; but if there's a correction factor for atmospheric pressure I don't know it.  Also the dome radiates efficiently because there's no reflector outside the glass surface.

In your spreadsheet you have a smaller dome (100 m diameter), and you're using low-e film.  I think I'd seen that these films, in practice, reduce heat flux by at most 1/3.  Any thought on that?  And you're using the T4 Stefan-Boltzmann law, which is fine.  Just coming at heat loss from a different direction.
You're missing the convective term on the outer surface of your glass.  In a typical building insulation calculation, you will have the internal film coefficient, the insulation of the building wall composition, then the outside film coefficient, usually equivalent to R 0.1.  However, if you analyse this film coefficient in detail, you will find that it is an expression of the convective conduction from the mass flow of the air on the surface of the building. Q=hAdT where h is a factor of the mass flow.  Using a slightly different equation, Q=mf*Cp*dT, power=mass flow x specific heat x temperature difference, on Mars with the atmosphere 100 times less dense than on Earth, the mass flow will be 100 times less, so the heat transfer film coefficient will be 100 times higher, or about R10 (imperial units) or 2 inches of styrofoam equivalent.  Now if you have double pane glass, you will have 2 more film coefficient, one on the inside and another on the outside of the second pane.  So the overall R will be practically 30.  Therefore the surface temperature of the outer glass pane will be near to the environment temperature, and the radiation will be very low.
And to further reduce heat low you can put the low emissivity film of the inside of the outer glass pane.  This film is an infrared mirror, so the radiation from the inner glass plane gets reflected, and the radiative heat gain on the outer glass pane is almost nil.  Summing up the very low convection and the very low radiation, you get very low heat transfer, about 1000 times less than your first order estimate, or about 100 kW.  For 12 hours of night then about 1200 kWh of heat loss.  As the heat gain is higher, the domes will tend to overheat, if the solar heat gain is not reduced.  So curtains during the day, and not during the night!

The reason low-e windows are not that effective is that they have an atmospheric pressure gas in the void.  If you had a Mars pressure gas in the void, they would insulate as well as, or better, than the walls.  Of course, they would implode first ;-)

Thanks for the numbers there.  It looks like I was wrong in thinking that because a glass pane insulates very poorly, convection off the pane should be low even at 1 atm. 

As an apples-to-apples cross-check, can you calculate the simple 150-m dome's heat loss your way?  That is, the dome without the improvements of double-panes and low-e film.  If you could calculate that heat loss under 1 kPa atmosphere and under 100 kPa atmosphere, those would be good cross-check reference points.
« Last Edit: 12/14/2016 07:48 pm by LMT »

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Re: Envisioning Amazing Martian Habitats
« Reply #316 on: 11/02/2016 12:54 pm »
Cold Skin

Youre making the same false assumption that you made earlier when you said the polycarbonate would be brittle. You're saying the surface of the dome will be the same temperature as the incredibly thin outside air. That's simply not true.

There's not perfect thermal conductivity between the thin Martian air and the dome's surface.

?  The polycarbonate only needs to reach -60 C at one point on its surface, to become brittle there, and put the dome at risk.  On a typical night with -90 C air and ground, a -60 C cold spot on the exterior surface seems very likely to me.  Especially along the ground, where conduction produces even faster heat loss. 

And heaven forbid the dome heating system should fail even briefly, when a polycarbonate dome's integrity is so fragile at martian temperatures.  (Come to think of it, how would you ensure that the polycarbonate never reached -60 C during construction, when a dome heating system was not yet available?   Logistically, that seems a challenge in itself.)

If you wanted to make an opposite case, and give reassurance that the polycarbonate would never approach -60 C, I suppose you'd need to model 1-D polycarbonate thermal profiles, with thermal front skin depth evolution over 1 sol, both in air and on the ground.  Or is there some model already available, for polycarbonate, polyethylene or some similar sheet material?
Perhaps LDPE would do the trick?  It has a glass transition temperature of -125C.  I was hopping to use it for plastic algae grow tubes on the surface of Mars. 
However, plain glass is a good building material, I don't quite see why it needs to be replaced by plastic, in particular if it is produced in situ.  Shouldn't there be some obsidian flows available on Mars? Good source of glass, that, since it's already glass.

Isn't the brittle transition temperature more critical?  Both low- and high-density polyethylene transition at -70 C.

And how might an algae grow tube maintain the ~10 C growth temperature range, while radiating and conducting heat out on the surface? 
« Last Edit: 12/14/2016 07:47 pm by LMT »

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Re: Envisioning Amazing Martian Habitats
« Reply #317 on: 11/02/2016 01:08 pm »
Cold Skin

Youre making the same false assumption that you made earlier when you said the polycarbonate would be brittle. You're saying the surface of the dome will be the same temperature as the incredibly thin outside air. That's simply not true.

There's not perfect thermal conductivity between the thin Martian air and the dome's surface.

?  The polycarbonate only needs to reach -60 C at one point on its surface, to become brittle there, and put the dome at risk.  On a typical night with -90 C air and ground, a -60 C cold spot on the exterior surface seems very likely to me.  Especially along the ground, where conduction produces even faster heat loss. 

And heaven forbid the dome heating system should fail even briefly, when a polycarbonate dome's integrity is so fragile at martian temperatures.  (Come to think of it, how would you ensure that the polycarbonate never reached -60 C during construction, when a dome heating system was not yet available?   Logistically, that seems a challenge in itself.)

If you wanted to make an opposite case, and give reassurance that the polycarbonate would never approach -60 C, I suppose you'd need to model 1-D polycarbonate thermal profiles, with thermal front skin depth evolution over 1 sol, both in air and on the ground.  Or is there some model already available, for polycarbonate, polyethylene or some similar sheet material?
Perhaps LDPE would do the trick?  It has a glass transition temperature of -125C.  I was hopping to use it for plastic algae grow tubes on the surface of Mars. 
However, plain glass is a good building material, I don't quite see why it needs to be replaced by plastic, in particular if it is produced in situ.  Shouldn't there be some obsidian flows available on Mars? Good source of glass, that, since it's already glass.

Isn't the brittle transition temperature more critical?  Both low- and high-density polyethylene transition at -70 C.

And how might an algae grow tube maintain the ~10 C growth temperature range, while radiating and conducting heat out on the surface?
Good points, it was notional and not calculated. I'll add this to the response to your earlier question about domes, since the tubes are long skinny domes.  Regarding HDPE, I believe one of the reasons that rovers have metal wheels is that NASA has been incapable of finding a material that remains flexible at all possible temperatures.  So HDPE might fail as you mention. Certainly rubber does.  A very incomplete answer might be that colonists would deploy the algae tubes in summer, when the air is relatively warm, then use redundant heating systems for the tubes.  If the water freezes the tubes will be finished anyway.  Then they would need to store enough food for the required repair/replacement time.
If the base was nuclear powered, then there should be a lot of waste heat to keep the tubes from freezing, but that's another thread.

Offline envy887

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Re: Envisioning Amazing Martian Habitats
« Reply #318 on: 11/02/2016 01:40 pm »
Isn't the brittle transition temperature more critical?
...

Only when toughness is in question, i.e. when under impact. Brittle does not mean "weak", it simply means the material is not ductile. Concrete and granite are brittle materials.

Polycarbonate, for example, is MUCH STRONGER at 4K than it is a room temperature, even though it's not nearly as tough.

Offline KelvinZero

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Re: Envisioning Amazing Martian Habitats
« Reply #319 on: 11/02/2016 09:23 pm »
I still think it's better to merge them but it's a step forward for our posters to have clarity on the topic of the other thread. It sounds like it's for extended discussions on glass dome issues around anchoring and leaking.
There is also cross linking to other posts. I actually like threads that end. I hate threads that go on for a hundred pages where the good stuff gets buried, and then the topic gets rehashed again. Rehashing can be irritating, being told you are rehashing and this was all covered 100 pages back, and "didn't you read it??" is also irritating :)

OFF TOPIC:
I just had what I think is an AWESOME idea. Imagine if some threads were simply impossible to post to more than once? But you can reedit your post as often as you like.

These would become like thesis threads. Everyone has their thesis, whether on radiation, moon vs mars or other pet ideas. Whenever a topic starts up say on radiation again.. rather than repeating arguments over and over, you link to your thesis and just make some comment about the particular relevant part in it, and you polish your thesis in response to comments and counter arguments.

Im convinced that the quality of online discussion is largely shaped by details of forum technology. It is a very interesting topic all of it's own. Currently, it is a jungle out there. Someone could come up with the right idea and it might revolutionise how the human race manages knowledge as significantly as the scientific method did.

 

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