Author Topic: SpaceX's Martian Underground  (Read 51524 times)

Offline philw1776

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Re: SpaceX's Martian Underground
« Reply #120 on: 02/01/2017 01:49 am »
Breckenridge CO is 3 Km altitude.  Was there at age 50 in a pickup hoops game on days 1 & 2 vs 20 somethings.  Sucking wind but OK.  Then X/C skied at higher altitudes. Average people can readily adapt to lower psi.  Test colonists at Cripple Creek 10,000 ft in the Rockies for 2 weeks.  If they can't adapt, send someone else.  Enough of this concern trolling.
« Last Edit: 02/01/2017 01:50 am by philw1776 »
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Offline Oersted

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Re: SpaceX's Martian Underground
« Reply #121 on: 02/03/2017 07:55 am »
Low landers can adapt to living and working at altitude given time and patience (a few weeks)

Also remember that on Mars the colonists would be at 40% Earth gravity which - all things being equal - should place less strain on their system. Maybe less oxygen in the air will be compensated by less demand for oxygen by the organism.

Offline sghill

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Re: SpaceX's Martian Underground
« Reply #122 on: 02/03/2017 02:57 pm »
The air pressures at La Paz Bolivia (Lake Titicaca @12,500 feet) or Lhasa, Tibet (12,000 ft.) are about as low an air pressure (9 psi) as you'd want to go IMHO. 

Why that choice?  Because humans are already self-selecting.

Those two places are an interesting mix of having the world's highest population densities at that altitude combined with also having pronounced effects on humans.  Above 12,000ft there's not much of anything in terms of large populations.

The mining town of La Rinconada at 16,700ft. in Peru is a slight exception.  30,000 inhabit the town, and live at 8 psi, though much of the population actually lives in towns lower down, and I can't imagine there are many kids running around up there, as it's generally thought of as a horrible place to live.

A college student (and competitive athlete) died at Lake Titicaca from common altitude sickness in 2010, and the local populations have notably different physiology than the rest of humanity (larger lungs, shorter limbs). 

To have a population regularly living at a lower pressure invites even more drastic problems.

« Last Edit: 02/03/2017 02:59 pm by sghill »
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Online lamontagne

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Re: SpaceX's Martian Underground
« Reply #123 on: 02/03/2017 04:34 pm »
I have to admit I don't really understand why the air pressure is such an issue.  We need to design in safety factors anyway, so why not design for full pressure, and over time optimise for lower pressure if it turns out to be useful or beneficial?  Creating the atmospheres for habitats will not be a major energy drain on the colony, compared to fuel and food production.
Yes, lower pressure would allow for less massive habitats, but using in situ resources is that an issue?  What construction problems does a 30% lower pressure solve, or even 50% lower?  Isn't radiation protection more massive than whatever structural element is used anyway?


Offline RonM

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Re: SpaceX's Martian Underground
« Reply #124 on: 02/03/2017 07:24 pm »
I have to admit I don't really understand why the air pressure is such an issue.  We need to design in safety factors anyway, so why not design for full pressure, and over time optimise for lower pressure if it turns out to be useful or beneficial?  Creating the atmospheres for habitats will not be a major energy drain on the colony, compared to fuel and food production.
Yes, lower pressure would allow for less massive habitats, but using in situ resources is that an issue?  What construction problems does a 30% lower pressure solve, or even 50% lower?  Isn't radiation protection more massive than whatever structural element is used anyway?

The advantage of lower pressure is the ability to put on a spacesuit and go outside without prebreathing.

If only a small number of colonists are workers that need to don spacesuits, then there can be a work area with airlocks at lower pressure while the rest of the colony can be at full pressure.

If it turns out crops grow better in a low nitrogen and lower pressure area, then the greenhouses can also be at a different pressure to optimize crop yield.

Offline guckyfan

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Re: SpaceX's Martian Underground
« Reply #125 on: 02/03/2017 09:39 pm »
I have to admit I don't really understand why the air pressure is such an issue.  We need to design in safety factors anyway, so why not design for full pressure, and over time optimise for lower pressure if it turns out to be useful or beneficial?  Creating the atmospheres for habitats will not be a major energy drain on the colony, compared to fuel and food production.
Yes, lower pressure would allow for less massive habitats, but using in situ resources is that an issue?  What construction problems does a 30% lower pressure solve, or even 50% lower?  Isn't radiation protection more massive than whatever structural element is used anyway?

Depends. That geodesic dome would become a lot easier with low pressure. But drilled underground habitats can be any pressure desired. I tend to agree that prebreathing for space suit activities may not be a driving factor because they may be quite rare except for the very first years and they could be done from a habitat that gradually reduces its pressure over night or a number of possible arrangements.

Daily work in low pressure greenhouses may profit a lot from a lower habitat pressure.


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Re: SpaceX's Martian Underground
« Reply #126 on: 02/03/2017 09:48 pm »
what was the pressure limit for no prebreathing? I know it is up thread someplace.
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Offline guckyfan

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Re: SpaceX's Martian Underground
« Reply #127 on: 02/03/2017 10:51 pm »
what was the pressure limit for no prebreathing? I know it is up thread someplace.

I have read on diving that going to half pressure does not require prebreathing. So if the spacesuit pressure is 25% earth sea level then from a habitat at 50% no prebreathing required.

Or for diving coming up from 10m depth does not need any considerations. You can go straight up no matter how long you have been down.

Offline ThereIWas3

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Re: SpaceX's Martian Underground
« Reply #128 on: 02/04/2017 12:11 am »
There are decompression considerations for any dive over 6m.   For shallow dives this is just a limitation on ascent rate, to about 10m per minute.   How long you spend on the bottom is also a factor.

Offline nacnud

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Re: SpaceX's Martian Underground
« Reply #129 on: 02/04/2017 01:58 am »
Pressurize a large part of the base at normal earth surface pressures. As stated above sea level populations can't breed below certain pressures. Some populations can breed in lower pressures than others but they have genes that compensate for altitude, see below for info on the problems with long term exposure to low pressures.

Hypoxia, fetal growth and early origins of disease: the Andean curse on the Conquistadors

Have another area at double suit pressure where people working outside in rovers or suits can go to save time pre breathing before missions.

Treat the whole base like a diving support vessel, with it's associated pressure chambers, diving bells, and diving suits.
« Last Edit: 02/04/2017 02:02 am by nacnud »

Offline Robotbeat

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Re: SpaceX's Martian Underground
« Reply #130 on: 02/04/2017 02:25 am »
EVA prebreathing definitely isn't the only reason to operate at reduced pressures.
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Offline KelvinZero

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Re: SpaceX's Martian Underground
« Reply #131 on: 02/04/2017 02:32 am »
If you are going to design for a civilization and not an outpost, then you need to be at 9 psi or higher. 

Why? Because we literally have thousands of examples of towns and cities here on Earth where the cutoff is at 9 psi.  People just don't breed and live at lower pressures. It's ok temporarily, but not for living.
So 9psi is totally reasonable on earth? (where sealevel is 14.7)

I totally agree arguing to fine detail is not of much purpose, especially when there are all these other factors that we can't possibly really know, like the amount of EVAs required, the mass of other elements of our entire architecture. I mean, we can make reasonable guesses but there is probably at least 25% errors in all these guesses, and they all multiply together.. and it will all be sorted out by engineers in the end anyway.

But just for personal interest, if 9psi is reasonable on earth, then about what would you end up with if you kept the same partial pressure of oxygen while lowering the total pressure.. to exactly the point where the fire risk rises to again equal earth sealevel?
« Last Edit: 02/04/2017 02:33 am by KelvinZero »

Offline Paul451

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Re: SpaceX's Martian Underground
« Reply #132 on: 02/04/2017 07:04 am »
But just for personal interest, if 9psi is reasonable on earth, then about what would you end up with if you kept the same partial pressure of oxygen while lowering the total pressure.. to exactly the point where the fire risk rises to again equal earth sealevel?

If I'm interpreting your question correctly, then you could drop the total pressure to around half sea-level before the equivalent pp of 21% @ 9psi (1.89psia) becomes high enough to equal the average fire risk at ordinary sea level.

However, materials don't react uniformly to changes in percentage, partial pressure and total pressure. There's a trend, but it's not uniform across materials. Likewise, a material may have a higher burn rate, but lower ignition rate in a lower oxygen PP but higher percentage. Or vice-versa. Or some other counter-intuitive trait.

So you'd still need to test every material you use, and rewrite all fire-rating regs for equipment intended for Mars.

Online rsdavis9

Re: SpaceX's Martian Underground
« Reply #133 on: 02/04/2017 11:01 am »
So we could probably get to 6 psi with 33% O2.
2 psi partial pressure O2 with 33%.
Is this conservative enough?
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Offline Jcc

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Re: SpaceX's Martian Underground
« Reply #134 on: 02/04/2017 02:28 pm »
I wonder if a higher O2 PP will help increase tolerance of relatively high CO2. It seems to me CO2 scrubbing will be an ongoing concern, and if tolerance for it can be increased it can mitigate some risk.

Offline pobermanns

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Re: SpaceX's Martian Underground
« Reply #135 on: 02/04/2017 07:11 pm »
I wonder if a higher O2 PP will help increase tolerance of relatively high CO2. It seems to me CO2 scrubbing will be an ongoing concern, and if tolerance for it can be increased it can mitigate some risk.

That's an interesting question, with possible positive consequences for all of the reasons discussed above. However, what leads you to believe that higher O2 would combat CO2 toxicity?

Online rsdavis9

Re: SpaceX's Martian Underground
« Reply #136 on: 02/04/2017 08:45 pm »
Can't a simple cold trap get almost all the CO2 out? Like a LOX(or LN2) cooled vessel with air circulating through it.
With ELV best efficiency was the paradigm. The new paradigm is reusable, good enough, and commonality of design.
Same engines. Design once. Same vehicle. Design once. Reusable. Build once.

Offline Paul451

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Re: SpaceX's Martian Underground
« Reply #137 on: 02/04/2017 08:56 pm »
I wonder if a higher O2 PP will help increase tolerance of relatively high CO2.
[...] However, what leads you to believe that higher O2 would combat CO2 toxicity?

Blood CO₂ levels are directly related to deoxygenated hemoglobin levels, which are inversely related to blood-O₂ levels. Increase available O₂ levels and you might reduce the production of bicarb in the blood, reducing the risk of acidosis in a high-CO₂ atmosphere.

However, individual response to higher O₂ levels varies. There are two independent drivers for the breathing reflex, high CO₂ and low O₂. Some people have a reduced CO₂-trigger, and rely on the O₂-trigger; in those people increased O₂ tends to reduce their breathing rate, which allows CO₂ levels to build up to dangerous levels. This is an issue for some COPD and sleep-apnea sufferers who use supplemental oxygen at night.

[I'm sure I'll be accused of "concern trolling", but the point is that none of this stuff is linear, none of it is a uniform effect. Once you start playing with oxygen, nitrogen and carbon-dioxide levels, you will get weird interactions and side-effects. You can't isolate one aspect from the others, nor predict health effects.]

Offline Robotbeat

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Re: SpaceX's Martian Underground
« Reply #138 on: 02/05/2017 02:05 am »
I would go the opposite. By the end of this century, /outside/ CO2 levels on Earth may be around 1000ppm (or higher under a "drill, baby, drill" scenario), which is high enough to noticeably cause a sensation of stuffiness. Indoor levels would be higher, as well, of course, perhaps 1500 ppm or higher. A very stuff room.

I'd go for lower than Earth-level CO2 levels as a kind of marketing point. Bring it to 280 ppm (except in the greenhouses), just so you can say the air is clearer than on Earth, going back to pre-industrial levels.

CO2 scrubbing is a well-known technology, and you're going to need it on Mars, anyway. So scrub it down to low levels. Then you also have more margin in case of power loss or equipment breakdown.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline sanman

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Re: SpaceX's Martian Underground
« Reply #139 on: 02/05/2017 09:21 pm »
It seems increasingly likely that Musk is going with his new tunneling venture with an eye to Mars. When he first outlined his plans for Mars, he talked about people living in geodesic domes on the Martian surface. But he was probably called out on that part, by skeptics who didn't feel the dome idea could work (pressure forces, etc). So because of this, he's probably now shifting to the tunnel idea and sees the importance of getting cracking on the tunneling technology. And if there's a business case for a useful market to serve/disrupt on Earth, then all the more reason to do it.

But I don't see anything disruptive in the technology yet - it all seems off-the-shelf existing hardware. What improvements could he have in mind?

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