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For Calliban re pressure for habitat on Mars...
In a recent post Void quoted you:
Calliban has suggested pressurization with regolith, which is not such a bad idea, as it seems that the typical Mars soil can be compacted to an almost brick like hardness.
If you have a few minutes to spare, please clarify what you might have meant.
It will require a mechanical pump to raise air pressure in a habitat on Mars. The regolith won't take part in the pressurization in an active way. My guess is that the regolith will be a passive participant in the exercise. it's role (if I understand your suggestion correctly) is to contain the pressurized gas mixture.
In PhotonByte's interesting topic about using natural pressure on Mars to eliminate the need for a pressure vessel for a habitat, we see that since the atmosphere of Mars is almost entirely CO2, we would have to add oxygen and nitrogen to the gas mixture in the habitat, until the amount of CO2 present in the mixture is tolerable to humans. The oxygen and nitrogen would have to be added and maintained using mechanical pumps, and the need would be constant, because some oxygen would be consumed by people and animals, and both nitrogen and oxygen would rise to the open sky because their molecular weights are less than that of CO2.
It seems to me that by arguing for use of the regolith as a pressure vessel, you are reinforcing the need for constant pumping activity to maintain a livable atmosphere for humans, regardless of the location of the habitat.
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For Caliban re PhotonByte's vision of an underground habitat open to the sky at 1/2 bar ....
On Earth, it is possible to excavate coal from a mine without allowing collapse of the overhead mass into the excavated space.
I'm assuming engineers must be able to predict how thick the support columns must be to hold the roof from collapse.
The scenario PhotonBytes has proposed appears to exceed human experience on Earth for withstanding pressure.
The example I found was the pressure at the bottom of the Mariana Trench, which appears to be on the order of 1,086 bar.
The Wikipedia article on the Mariana Trench reports on numerous manned and unmanned expeditions to the bottom.
I deduce that while operation at 1000 bar is difficult and dangerous, humans have learned how to do so.
On Mars, at the depth of 44 km, where (I understand) air pressure is 1/2 bar, the pressure on rock at that depth is reported to exceed 4000 bar.
My question for you is: Does material flow like molasses at that pressure? Is there any material that can withstand it?
A related question is: Can miners on Mars excavate spaces leaving columns of regolith to hold the roof at that depth?
Are there materials that can hold the walls of the vertical shaft against 4000+ bar?
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For Calliban re PhotonBytes and the deep well habitat idea...
Regarding the pressure discussed by AI, those pressures of thousands of bars are only exerienced by the rocks being compressed vertically, not by any aircavity down to that level. If you have a cavity in the crust down to that depth it can support any air pressure from 0bars to the thousands you quoted. But when you connect that air cavity to a vertical tunnel to the surface of Mars the limit drops to the weight of the air column in that tunnel all the way up to space. In fact the air preasure will then be fixed to whatever the weight of the air column would be. If you try to add more air preassure it will simply push more air out the tunnel. If you try to reduce the pressure without an airlock it will do the opposite and suck air in.
In a separate post I have noted that humans have demonstrated the ability to maintain a small volume against 1000+ bar of pressure in the ocean of Earth. On Mars, at the depth where air pressure would reach 1/2 bar, the rocks are in compression on the order of 4000 bar. If you have a moment to consider the question, is there any material in the Universe able to withstand 4000 bar of compression?
And! If there is such a material, can it serve a volume greater than a few cubic meters? This is a fascinating part of physics, and it probably deserves it's own topic, along with one on tension, since space elevators are of interest to NewMars readers.
It appears that some NewMars readers may not understand how compression works at 4000 bar. If an open shaft is drilled from the surface on Earth, the Russians have shown the depth that was achievable in the Soviet era. I expect that a greater depth is achievable on Mars, but am not sure if that depth would include 44 kilometers. At some point, the material through which the drill is searching will expert horizontal force on the drill sufficient to impede it's progress, and to fill the cavity when the drill is withdrawn.
If a lining is installed to maintain the diameter of the excavation, at some point the pressure of the material next to the excavation will exceed the strength of the lining. The question at hand is whether a hole can be drilled to 44 kilometers on Mars, and held open by any known material?
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For Calliban re justification for study of the deep habitat concept of PhotonBytes....
Ref: https://newmars.com/forums/viewtopic.ph … 87#p229387
I cannot speak to the motivation of PhotoBytes, but I ** can ** (and have) addressed the questions you raised...
** All ** habitats on Mars will be served by machinery that runs constantly, and which ** cannot ** fail to run for very long, or everyone will perish.
The habitat concept offered by PhotonBytes has the distinct advantage that the pump needed to maintain pressure can be omitted from the design. There will still be need for pumps to deliver oxygen and nitrogen to the habitat volume, but these pumps can be idle for extended periods when the gas mixture is within tolerance. My guess is that mixing fans will need to operate continuously.
For what it's worth, the habitat design/concept of PhotonBytes does NOT need an air lock. There are some who might see this as a distinct advantage, which must be weighed against the travel time by electric lift to move from the habitat to the surface.
Thanks for keeping the forum in your visit list! We are down to a very small group these days, so every visit by an active member is cause for celebration. I did a quick check of the history after your most recent observation about membership, and we have posted the daily recruiting message every day but one since May of 2021. We have accepted five folks well qualified to contribute to the forum, but none are active, except for PhotonBytes, who gifts us with updates on a space plane project, and ambitious visions for Mars.
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For Calliban re post in 55 km topic...
then going down 10km would increase air pressure to 250mbar. That pressure is breathable for human beings if it is mostly oxygen.
At first reading I was encouraged by this thought. Then I remembered GW Johnson's cautions about fire in an oxygen rich atmosphere.
Apollo 1 is remembered because the engineers used pure oxygen inside the capsule.
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For Calliban re post in 55 km topic...
then going down 10km would increase air pressure to 250mbar. That pressure is breathable for human beings if it is mostly oxygen.
At first reading I was encouraged by this thought. Then I remembered GW Johnson's cautions about fire in an oxygen rich atmosphere.
Apollo 1 is remembered because the engineers used pure oxygen inside the capsule.
(th)
Yes. But keep in mind that Apollo 1 was pure O2 at 1bar pressure.
Here we are probably talking 0.2 bar O2, with the balance being nitrogen and argon.
Last edited by Calliban (2025-01-28 04:21:24)
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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For Calliban re post in Shell world's topic...
First, thank you for providing the link to the blog where the concept of a gravity sphere is developed!
https://github.com/AlanCoding/gravitati … athematics
I deduce that someone named ? Alan Coding ? might be involved? It's hard (for me at least) to tell.
Second, I can't tell if you know this, but Analog ran a long story about exactly such an enclosed space.
As I recall, the story ran over several issues.
It was ** very ** well constructed. The rotating habitats spun in an oxygen/nitrogen atmosphere, and humans were present in large numbers. The author of the story gave responsibility for creating the environment to "aliens" and left those larger details to the imagination, so that the author could concentrate on the behavior of humans in this remarkable environment.
The primary energy source was artificial "suns" powered by fusion, but the life in the habitats was decidedly chemical and low tech.
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For Calliban re post in Shell Worlds http://newmars.com/forums/viewtopic.php … 58#p229558
In another post recently, I described a science fiction serialized novel published in Analog, that created such an environment.
The exterior wall was solid, and covered with ice, because the author imagined that the cold of space outside the wall would draw thermal energy from the interior of the volume.
The interior was heated (and lighted) by fusion "suns" that operated on a 24 hour cycle.
I doubt that the author is/was trained in engineering, but on the other hand, the work was filled with examples of machines and processes that appeared to me to reflect understanding of the physics of this scenario.
Since the interior of the sphere was maintained at 1 bar, I'm assuming that air currents between the hot "suns" and the cold wall would transport thermal energy so that a balance might be achieved.
Because the essence of the idea in the Shell Worlds topic seems to be that gas pressure is holding the wall of the habitat from collapsing, I deduce there would be gas available to transport thermal energy around the interior of the sphere, just as the novel author imagined.
If that is the case, there might not be a need for purpose built water transport, as you described?
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Possibly. Ultimately, all energy generated within the shell world needs to be radiated to space. Without forced convection, we are relying upon thermal conduction through the ice shell to remove the internal heat to the surface, where it can radiate into space. Conduction is represented by the fourier equation:
Q = kA x (T1-T2) / dx
This equation allows you to calculate the amount of heat that can be generated per square metre of shell area without exceeding the thermal limits of the shell. There is one limit in particular - the melting point of the ice. The value of T2 (outer surface temperature of the ice) will be such that the heat conducting to the surface balances the heat radiated into space. If we put some representative values into the equation, we can understand why solid conduction is quite limiting.
Say the temperature difference across the shell is 100K. It may be a bit more or less. It doesn't matter too much. Assume that the shell is 20km thick. Lets take an average thermal conductivity of 3W/m.K. How much heat can we conduct through each square metre of the shell?
Q = kA x (T1-T2) / dx = 3 x 1 x 100 / 20,000 = 0.015W/m2
When you compare that to Earth's solar flux of 1350W/m2, it illustrates the problem. A shell world that relies on solid phase conduction to lose waste heat would be capable of generating very little internal power without melting the shell. Either the civilisation within it is very frugal in its use of power of another method of losing heat must be found. The third method of heat transfer is convection. This could be forced (pumped) flow or natural convection through some sort of heat pipe. The problem with natural convection is that driving force is proportional to gravity, which will be measured in milli-g on the surface of our space balloon.
Last edited by Calliban (Yesterday 15:57:11)
"Plan and prepare for every possibility, and you will never act. It is nobler to have courage as we stumble into half the things we fear than to analyse every possible obstacle and begin nothing. Great things are achieved by embracing great dangers."
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For Calliban re #184
Thank you for taking up the question I offered, based upon a novel.
I think the basic question is pertinent for the Shell Worlds topic, and appreciate your review of the scenario.
Staying with the novel for the moment.... Let us assume the "aliens" who created this environment initialized the interior of the volume with a human breathable atmosphere of 1 bar, at STP.
Since there is no light inside the volume, the author imagined fusion "suns" that would operate on a 24 hour cycle. As a detail.... the fusion "Suns" were available for maintenance during the "off" part of the 24 hour cycle.
Those fusion "suns" would belt out a lot of energy.
In thinking about the points you have raised, I'm imagining that the air inside the volume would cool at the paltry rate you've suggested, but every square meter of the interior of the volume would be working constantly to suck thermal energy out of the interior. Meanwhile, the fusion "suns" would be belting out energy.
It might turn out that the total amount of energy being drawn out the sides would balance with the amount created by the fusion "suns".
However, since the author didn't mention heating, I'm guessing an engineer may not have been available to provide the guidance you have provided.
In a nutshell, it seems to me the designer of this structure would need to make sure the wall is able to remove thermal energy as fast as it is created, in order to maintain the STP enviroment.
Since this forum is considering "real" Shell Worlds, I assume the advice you would have given the novelist would extend to the creative minds in this forum.
With that in mind, do you have advice for the members of the team who are working on the wall?
Please keep in mind that the wall is withstanding STP while it is tasked with radiating heat to the Universe.
As I think about this, I am reminded of the work of Freeman Dyson, who I "met" at a Princeton gathering hosted by Gerard O'Neill.
Dyson has many concepts to his credit, and the "Dyson Sphere" is just one.
Following your guidance to it's logical conclusion, I understand why Dyson suggested looking for objects radiating in the infrared.
A shell around a Sun would need to radiate the equivalent energy output by the Sun as all infrared, assuming that all other wavelengths are consumed by the population inside the sphere.
For NewMars members who might be interested, here is a link to the Wikipedia article on Dr. Dyson:
https://en.wikipedia.org/wiki/Freeman_Dyson
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