Author Topic: Envisioning Amazing Martian Habitats  (Read 869747 times)

Online lamontagne

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Re: Envisioning Amazing Martian Habitats
« Reply #500 on: 11/28/2016 03:16 am »
A final point about thermodynamics of underground bases.  Conduction equation is Q=AdT/R.
dT is the temperature difference between the interior of the base and the soil.  R in the insulation value of the materials.
Now, as your soil heats up, the thickness of the warm soil around the base and the original cold soil gets thicker and thicker.  Eventually, you will have a few meters of warm soil, and it will now serve as insulation.

Any underground base that is sufficiently deep will reach an equilibrium where the heat loss becomes negligible, and eventually overheat.  The only exception is if the heat reaches the surface and starts radiating away.

The Earth is a perfect example of this. 12-20 km of Rock, with  an overall R value of many thousands, has been keeping the core hot for billions of years... (plus the radioactive materials in the core, of course). 

Online lamontagne

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Re: Envisioning Amazing Martian Habitats
« Reply #501 on: 11/28/2016 03:19 am »
So the colonists need 3 MW of photosynthesis, i.e light.  But since plants are not 100% food, you will probably need 5 to 10 times more.  So now your base is overheating because of the lights required for plant growth...

?  But where to get 15 MW

in winter

at night

on Mars?


Insulate your base with the patented 'Lamontagne Tiles'.  No more heat loss ;-)  Produce twice the food you need in summer, as reasonable people do.  Eat the surplus in winter.  Since you are not producing food in winter, you are adding much less heat to your base.  Win-win.



Online lamontagne

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Re: Envisioning Amazing Martian Habitats
« Reply #502 on: 11/28/2016 03:22 am »
You can also get a nuclear reactor.  They always solve everything. 
But solar only is so much more Fun!

Offline Robotbeat

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Re: Envisioning Amazing Martian Habitats
« Reply #503 on: 11/28/2016 03:32 am »
So the colonists need 3 MW of photosynthesis, i.e light.  But since plants are not 100% food, you will probably need 5 to 10 times more.  So now your base is overheating because of the lights required for plant growth...

?  But where to get 30 MW

in winter

at night

on Mars?


Build near the equator, as I suggest. Melas Chasma in Valles Marineris is a good spot, nice and low with a great view and available water. Don't need 30MW at night because you'll have daytime and a lot of thermal inertia. And you'll have a lot of batteries.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

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Online lamontagne

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Re: Envisioning Amazing Martian Habitats
« Reply #504 on: 11/28/2016 03:35 am »
So the colonists need 3 MW of photosynthesis, i.e light.  But since plants are not 100% food, you will probably need 5 to 10 times more.  So now your base is overheating because of the lights required for plant growth...

?  But where to get 30 MW

in winter

at night

on Mars?

Build near the equator, as I suggest. Melas Chasma in Valles Marineris is a good spot, nice and low with a great view and available water. Don't need 30MW at night because you'll have daytime and a lot of thermal inertia. And you'll have a lot of batteries.
And don't grow the food at night, never a good idea!
Robot is right, build the base with a lot of heavy walls, and a lot of water tanks.  It'll be both nicer, less noisy and have plenty of thermal inertia.  The surface swings up and down depending on the sun, underground, it's all smooth and calm...
« Last Edit: 11/28/2016 03:37 am by lamontagne »

Offline Robotbeat

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Re: Envisioning Amazing Martian Habitats
« Reply #505 on: 11/28/2016 03:48 am »
Oh, and also, each refueling of a BFS requires approximately 0.5-1MW of power on average. Some of that power is lost as waste heat in the exothermic Sabatier reaction or inefficiencies of electrolysis. Because I'm too lazy to calculate, I'd bet it's around half of the power ends up as low quality waste heat that could be used for heating the colony space, just like waste heat from generators at the South Pole is used for heating, too. So 250-500kW per BFS

So if you have 100 BFS refueling every year, that's about 30MW of heat on average, plus the solar gain you get on that huge glass dome, etc. And with 1000BFSes, that's 300MW of heat. With 10,000 BFSes, 3GW of heat.

I think waste heat will be largely sufficient for base operations. In a pinch, you could burn some ISRU fuel, but it'd have to be an emergency.

Waste heat from ISRU, waste heat from photosynthesis (good call on the factor of 50, so about 5kW per colonist just in waste heat from inefficient photosynthesis), plus solar thermal gain from glass dome, insulation, and thermal inertia. I agree that rejected heat may end up being the more annoying problem long-term as the base grows.
« Last Edit: 11/28/2016 03:55 am by Robotbeat »
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Offline LMT

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Re: Envisioning Amazing Martian Habitats
« Reply #506 on: 11/28/2016 04:02 am »
A final point about thermodynamics of underground bases.  Conduction equation is Q=AdT/R.
dT is the temperature difference between the interior of the base and the soil.  R in the insulation value of the materials.
Now, as your soil heats up, the thickness of the warm soil around the base and the original cold soil gets thicker and thicker.  Eventually, you will have a few meters of warm soil, and it will now serve as insulation.

Any underground base that is sufficiently deep will reach an equilibrium where the heat loss becomes negligible, and eventually overheat.  The only exception is if the heat reaches the surface and starts radiating away.

The Earth is a perfect example of this. 12-20 km of Rock, with  an overall R value of many thousands, has been keeping the core hot for billions of years... (plus the radioactive materials in the core, of course).

Right, ultimately you want the rock to stop being a heat sink, and start insulating.  Problem is, each m3 of rock soaks up ~ 200 million Joules on its way to room temperature.   Long road, deep mountain.  But it would be very interesting to see how the 1-D thermal profile under the hab room evolves over time, with various heat inputs.  Starting point is of course a stubborn -60 C.

Speaking of thermal profiles, maybe it's worth noting that the martian crust has a profile rather more cruel than Earth's.  Even an extremely deep hab, at 2 km depth, would be surrounded by rock at ~ -40 C, which is not very helpful.  A hab at equilibrium (in room temperature bedrock) would have to hit a sick depth of ~ 8 km.  A very diligent Sandvik MR620, running 6 hours per sol on a 10 degree cut, would need about 40 years to reach the front door. 

If it doesn't hit basalt.  :o
« Last Edit: 12/14/2016 06:32 pm by LMT »

Offline Robotbeat

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Re: Envisioning Amazing Martian Habitats
« Reply #507 on: 11/28/2016 04:05 am »
Let's say we have 100 tons of material per colonist that is heated to room temperature. Assume it has a heat capacity of 1J/(gram*degreeC) (water has 4J/(g*C)). So that's 1E8J per degree C. So let's say we allow up to 20degreesC temperature change. That's 2E9J per colonist. Even if all power is cut, the whole thing is plunged into utter darkness and everyone's metabolism stops, that means if we have 1kW of heat loss per colonist, it'd take over 20 days to eat through all that thermal inertia.

Triple that if you also had 10 tons of water (or 40 tons of rock/sand) heated to near boiling by Sabatier waste heat (which is optimally 300-400C).
« Last Edit: 11/28/2016 04:19 am by Robotbeat »
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Offline LMT

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Re: Envisioning Amazing Martian Habitats
« Reply #508 on: 11/28/2016 04:41 am »
So the colonists need 3 MW of photosynthesis, i.e light.  But since plants are not 100% food, you will probably need 5 to 10 times more.  So now your base is overheating because of the lights required for plant growth...

?  But where to get 30 MW

in winter

at night

on Mars?


Build near the equator, as I suggest. Melas Chasma in Valles Marineris is a good spot, nice and low with a great view and available water. Don't need 30MW at night because you'll have daytime and a lot of thermal inertia. And you'll have a lot of batteries.

Thermal inertia from sunshine doesn't warm the winter tunnel.  We couldn't even manage solar heating of an insulated winter greenhouse, as I recall, which is why we had to abandon lamontagne's dome for the season.  But you might try heating water with winter flux, to see what you get.

As for batteries, flow batteries are presently state-of-the-art at this scale.  A 100 ton flow battery can deliver, I think, maybe 70 billion J of electrical heating.  At a 30 MW burn rate, that lasts half an hour.

How to survive the winter?
« Last Edit: 12/14/2016 07:49 pm by LMT »

Offline guckyfan

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Re: Envisioning Amazing Martian Habitats
« Reply #509 on: 11/28/2016 08:37 am »
And don't grow the food at night, never a good idea!

Unless you have that nuclear reactor that wants to produce power day and night. You would probably want a set of greenhouses that are lighted in turns.

But why do I argue this? I am much in favor of greenhouses using mostly ambient light and maybe some added light for peak biomass production for some crops during part of their growth cycle.

Offline LMT

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Re: Envisioning Amazing Martian Habitats
« Reply #510 on: 11/28/2016 11:54 am »
Sabatier waste heat (which is optimally 300-400C)

Sabatier reaction is exothermic, but it can't run at a scale to heat Hew Thermopylae in winter because the energy input required to maintain the reaction is far too high, as I think you know.  It's more efficient to heat electrically, from PV, and skip intermediary processes.  But in winter the PV for tunnel heating just isn't there.
« Last Edit: 12/14/2016 06:30 pm by LMT »

Offline guckyfan

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Re: Envisioning Amazing Martian Habitats
« Reply #511 on: 11/28/2016 12:04 pm »
Sabatier waste heat (which is optimally 300-400C)

Sabatier reaction is exothermic, but it can't run at a scale to heat Hew Thermopylae in winter because the energy input required to maintain the reaction is far too high, as I think you know.  It's more efficient to heat electrically, from PV, and skip intermediary processes.  But in winter the PV for tunnel heating just isn't there.

As you stated the Sabatier reaction is exothermic. It does not need any energy input to run except the initial energy to get it to operating temperature.

Needeed is hydrogen from water electrolysis, this indeed needs a lot of energy. You can produce the hydrogen during the day and keep the Sabatier reaction going all night.

Offline LMT

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Re: Envisioning Amazing Martian Habitats
« Reply #512 on: 11/28/2016 12:38 pm »
Sabatier waste heat (which is optimally 300-400C)

Sabatier reaction is exothermic, but it can't run at a scale to heat Hew Thermopylae in winter because the energy input required to maintain the reaction is far too high, as I think you know.  It's more efficient to heat electrically, from PV, and skip intermediary processes.  But in winter the PV for tunnel heating just isn't there.

As you stated the Sabatier reaction is exothermic. It does not need any energy input to run except the initial energy to get it to operating temperature.

Needeed is hydrogen from water electrolysis, this indeed needs a lot of energy. You can produce the hydrogen during the day and keep the Sabatier reaction going all night.

The reaction needs hydrogen, heat and pressure, yes, and exothermy doesn't get us there, unfortunately.  As example, Zubrin's unit is predicted to output 1 kg/hr, while requiring 700 W electrical, continuous.

And his hydrogen comes from a bottle, gratis.
« Last Edit: 12/14/2016 07:49 pm by LMT »

Offline LMT

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Re: Envisioning Amazing Martian Habitats
« Reply #513 on: 11/28/2016 02:39 pm »
PV or not PV?

Just to quantify the winter PV problem at Hew Thermopylae:

1 ton of state-of-the-art PV produces ~ 100 kW, summer high-noon max.

Hew Thermopylae is at 34° N, where winter sunlight intensity drops to ~ 15% of summer max.

So in winter, that's 15 kW max, maybe 160 million Joules / sol. [corrected]

If that energy were stored and released on-demand with 80% efficiency, that's 130 million Joules/sol of heat energy.

And with a hypothetical 8 MW conductive heat loss, the uninsulated tunnels would need 700 billion Joules / sol.

So 5400 tons of PV, just for heat. 



And assuming no winter storms:o
« Last Edit: 12/14/2016 06:30 pm by LMT »

Offline JasonAW3

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Re: Envisioning Amazing Martian Habitats
« Reply #514 on: 11/28/2016 02:55 pm »
Perchlorates are both an energy and oxygen source.

This is not a microbial astrobiology thread, Senior Member Robotbeat.
I'm not talking about astrobiology.

The equivalent of Martian Coal?
My God!  It's full of universes!

Offline RonM

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Re: Envisioning Amazing Martian Habitats
« Reply #515 on: 11/28/2016 03:06 pm »
How to survive the winter?

Good old fashioned engineering and planning.

Once you have a Mars base with ISRU that produces breathable air, drinkable water, and food you are in pretty good shape. If a habitat design can't maintain a livable temperature, then it's time to design a different habitat. If a location can't produce enough solar power during winter, you need to pick a better location.

Offline guckyfan

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Re: Envisioning Amazing Martian Habitats
« Reply #516 on: 11/28/2016 03:20 pm »
And his hydrogen comes from a bottle, gratis.

No it doesn't. Half of the hydrogen goes into water and needs to be recovered by electrolysis.

Edit: Some power is needed for controlling gas flow and pumping the process products but that is miniscule in comparison to the amounts produced.
« Last Edit: 11/28/2016 03:29 pm by guckyfan »

Offline Robotbeat

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Re: Envisioning Amazing Martian Habitats
« Reply #517 on: 11/28/2016 03:31 pm »
Sabatier waste heat (which is optimally 300-400C)

Sabatier reaction is exothermic, but it can't run at a scale to heat Hew Thermopylae in winter because the energy input required to maintain the reaction is far too high, as I think you know.  It's more efficient to heat electrically, from PV, and skip intermediary processes.  But in winter the PV for tunnel heating just isn't there.

As you stated the Sabatier reaction is exothermic. It does not need any energy input to run except the initial energy to get it to operating temperature.

Needeed is hydrogen from water electrolysis, this indeed needs a lot of energy. You can produce the hydrogen during the day and keep the Sabatier reaction going all night.

The reaction needs hydrogen, heat and pressure, yes, and exothermy doesn't get us there, unfortunately.  As example, Zubrin's unit is predicted to output 1 kg/hr, while requiring 700 W electrical, continuous.

And his hydrogen comes from a bottle, gratis.
You are ignoring scale which is why Zubrin needed input power for a very exothermic reaction. If you're doing megawatts of Sabatier youll need to dump heat to keep your reactor from melting
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Offline LMT

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Re: Envisioning Amazing Martian Habitats
« Reply #518 on: 11/28/2016 04:58 pm »
And his hydrogen comes from a bottle, gratis.

No it doesn't. Half of the hydrogen goes into water and needs to be recovered by electrolysis.

Edit: Some power is needed for controlling gas flow and pumping the process products but that is miniscule in comparison to the amounts produced.

His hydrogen comes from a bottle.  In his shop.  Obviously electrolysis is required on Mars, pulling even more electrical power.  Point:  even the exothermic Sabatier reactor requires electrical power, continuously, by itself.
« Last Edit: 12/14/2016 07:49 pm by LMT »

Online lamontagne

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Re: Envisioning Amazing Martian Habitats
« Reply #519 on: 11/28/2016 05:18 pm »
PV or not PV?

Just to quantify the winter PV problem at Hew Thermopylae:

1 ton of state-of-the-art PV produces ~ 100 kW, summer high-noon max.

Hew Thermopylae is at 34° N, where winter sunlight intensity drops to ~ 15% of summer max.

So in winter, that's 15 kW max, maybe 22 million Joules / sol.

If that energy were stored and released on-demand with 80% efficiency, that's 18 million Joules/sol of heat energy.

And with a hypothetical 8 MW conductive heat loss, the uninsulated tunnels would need 700 billion Joules / sol.

So 40,000 tons of PV, just for heat.


Isn't 15 kW x 3600s x 6 hrs = 324 million joules?  so 2000 tonnes rather than 40 000 tonnes?
If you stop food production and fuel production during winter, and insulate the base to a heat loss of 2 MW, then 500 tonnes of solar cells would be enough to keep you warm.  No reason you couldn't go bellow 2 MW with a well insulated base, and keep some production capacity going.

In summer, the cells would produce 6.6 times more energy, so 13.2 MW, enough for basic food production, then another 500 tonnes would produce 25 MW, enough food to pass the winter, and fuel for the ships.

If you had sun tracking solar panels, you could probably do better than these numbers; less mass or more energy.

And some of these powers are used twice, once for Sabatier fuel production, then, the lower grade losses can be used to heat the base, or again, 95%+ of the plant light turns into heat, that can also be used to heat the base.  So most of the time no heating load.
« Last Edit: 11/28/2016 05:30 pm by lamontagne »

 

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