Author Topic: SpaceX's Martian Underground  (Read 16628 times)

Offline CuddlyRocket

Re: SpaceX's Martian Underground
« Reply #160 on: 03/05/2017 01:29 AM »
Just a reminder.

To give the equivalent protection that Earth's atmosphere provides people at Sea Level takes about 3m of Martian Regolith.

But how much of Earth's atmosphere is needed for adequate radiation shielding? After all, people live quite happily in Nepal and Tibet, which have approximately only 30% of the atmospheric pressure at sea level (ref).

Also, Mars does have an atmosphere, which provides some shielding, and the Solar radiation flux is less.

Offline Paul451

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Re: SpaceX's Martian Underground
« Reply #161 on: 03/05/2017 02:56 AM »
Thinking of my adolescent son, playing in front of his computer, I don't think he sees natural light more than a few minutes every week

You should hope so. Current research on near-sightedness suggests that a major part is the lack of exposure to bright lights while growing up. It doesn't take much, a few minutes a day. You don't have to drag them outside for hours. Even wearing sunglasses (under full sun) is sufficient, or through cloud cover without sunglasses. (The sun, hidden behind tinted lenses or clouds, is still much brighter than indoor lights directly.)

(Likewise, childhood sun exposure may be a significant factor in adult depression and other mental illness.)

Online Robotbeat

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Re: SpaceX's Martian Underground
« Reply #162 on: 03/05/2017 03:17 AM »
Literacy in general is a risk factor in nearsightedness. Reading books.
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Offline Paul451

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Re: SpaceX's Martian Underground
« Reply #163 on: 03/05/2017 03:45 AM »
Literacy in general is a risk factor in nearsightedness. Reading books.

No, that's what the new research tested. It's not books or TV or video-games. (Or close work in general.) It's that kids who preferred those activities tended to spend less time in the sun. Once you correct for that, the link with reading/education, or other activities is eliminated.

(The Sydney Myopia Study tracked 4000 school-age children from 55 schools. The only statistically significant link was time spent outdoors. Follow-up animal studies showed the that light levels alone can alter eye elongation (the cause of myopia.) It seems to be related to dopamine levels in the eye, which is related to switching between rod and cone dominated vision. Block the dopamine pathway (yet further follow-up research) and you not only induce 100% myopia in the animals, but eliminate the protective effect of light exposure. In a school trial in Sydney, they added 50 minutes of additional sun exposure to the school day, and saw a 25% reduction in myopia. In Taiwan, researchers were able to convince authorities to add 100 minutes of extra sun exposure to school days, and saw a 50% reduction in myopia.)

[Aside: I said "a few minutes a day". I was wrong. Actually for the full protective effect, it's about 3hrs/day at 40,000 lux, which is about mid-winter sun or mid-summer under cloud. A typical "bright" indoor room gets about 1000 lux. So you do need to drag them outside for hours. Sorry Michel.]



This was originally and off-topic aside but this may be an issue for Mars. If colonists are essentially living underground, what is their typical light exposure? Can you afford to illuminate entire habitats to 40,000 lux?

Offline Adaptation

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Re: SpaceX's Martian Underground
« Reply #164 on: 03/05/2017 06:08 AM »
Most materials are actually more flammable at martian gravity than than earth gravity.  Lunar is even worse.  By more flammable I do not mean that it burns faster or more vigorously but rather things which would self extinguish do so slower or not at all under these lower gravities.  There is still adequate convection to deliver fresh oxygen to keep the flame fed meanwhile the total amount of convection is lower providing less cooling which is aids in self extinguishing. 

For me these were counter intuitive results.  I correctly anticipated the weaker convection to deliver less oxygen, causing a lower rate of combustion.  I had assumed this would scale proportionally with the decrease in convective cooling.  When adding in the fact that radiative cooling would not be effected by gravity I had expected the total flammability to be lower.

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20130010991.pdf

Offline Oersted

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Re: SpaceX's Martian Underground
« Reply #165 on: 03/05/2017 07:19 AM »
So, what you are saying is that the Mars colonists living in tunnels and caves for the first couple of generations will become a race of blind moles?  :-O

Offline Paul451

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Re: SpaceX's Martian Underground
« Reply #166 on: 03/05/2017 04:50 PM »
So, what you are saying is that the Mars colonists living in tunnels and caves for the first couple of generations will become a race of blind moles?

Depressed, schizophrenic, myopic, gangly, pasty moles.

Offline gospacex

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Re: SpaceX's Martian Underground
« Reply #167 on: 03/05/2017 05:15 PM »
Literacy in general is a risk factor in nearsightedness. Reading books.

No, that's what the new research tested. It's not books or TV or video-games. (Or close work in general.) It's that kids who preferred those activities tended to spend less time in the sun. Once you correct for that, the link with reading/education, or other activities is eliminated.

My personal data point does not support this theory.
I was 7 many years before computers became widely available, and I did play outside a lot. Yet, I also started reading a lot. A LOT. Like, two books a day. That's when myopia started for me.
« Last Edit: 03/05/2017 05:16 PM by gospacex »

Offline john smith 19

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Re: SpaceX's Martian Underground
« Reply #168 on: 03/07/2017 09:47 AM »

But how much of Earth's atmosphere is needed for adequate radiation shielding? After all, people live quite happily in Nepal and Tibet, which have approximately only 30% of the atmospheric pressure at sea level (ref).

Also, Mars does have an atmosphere, which provides some shielding, and the Solar radiation flux is less.
Just a reminder.

Mars surface pressure is 1/160 that of Earth at SL.

(The Sydney Myopia Study tracked 4000 school-age children from 55 schools. The only statistically significant link was time spent outdoors. Follow-up animal studies showed the that light levels alone can alter eye elongation (the cause of myopia.) It seems to be related to dopamine levels in the eye, which is related to switching between rod and cone dominated vision. Block the dopamine pathway (yet further follow-up research) and you not only induce 100% myopia in the animals, but eliminate the protective effect of light exposure. In a school trial in Sydney, they added 50 minutes of additional sun exposure to the school day, and saw a 25% reduction in myopia. In Taiwan, researchers were able to convince authorities to add 100 minutes of extra sun exposure to school days, and saw a 50% reduction in myopia.)
This is very exciting, suggesting myopia can be radically reduced in developed countries.

But it is a concern for Mars and future generations of Mars.

Given Mars is so much farther away from the Sun it already starts out with a lower solar level than Earth. Multiply by lack of regular exposure and the long term effects could be severe.

Unless people are prepared to look at "anti-myopia" pills.
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline gospacex

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Re: SpaceX's Martian Underground
« Reply #169 on: 03/07/2017 02:32 PM »
Given Mars is so much farther away from the Sun it already starts out with a lower solar level than Earth. Multiply by lack of regular exposure and the long term effects could be severe.

Unless people are prepared to look at "anti-myopia" pills.

Or have brighter indoor lighting?

Offline Paul451

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Re: SpaceX's Martian Underground
« Reply #170 on: 03/07/2017 09:39 PM »
The Sydney Myopia Study tracked 4000 school-age children from 55 schools. The only statistically significant link was time spent outdoors. Follow-up animal studies showed the that light levels alone can alter eye elongation (the cause of myopia.) It seems to be related to dopamine levels in the eye, which is related to switching between rod and cone dominated vision. [...]
This is very exciting, suggesting myopia can be radically reduced in developed countries.

I found it interesting when I first heard of it a year or so back, which I why it stuck in my memory. It subverts the obvious and expected causes.

Given Mars is so much farther away from the Sun it already starts out with a lower solar level than Earth.

That doesn't concern me. The sun is so frickin' bright that even on Mars you're looking at 50,000 lux for a typical day, and probably averaging over 30,000 during the year. And dust matters less than water-clouds on Earth (it scatters the light, reducing direct sun brightness drastically, but the overall sky-illumination remains higher than an equivalent reduction via water-clouds.)

People being trapped inside may be the issue.

Or have brighter indoor lighting?

If you are currently in a brightly lit room, the lighting level will be around 1000 lux. We need 30-40,000 lux. So multiply the number of lights in your room by 40-fold over the same area. Then, even allowing for LED efficiencies, think about the power consumed, the heat released, and the annoyance of working on anything with a screen. It seems unlikely anywhere outside a grow-chamber (indoor greenhouse).

The cheat would be to exploit the inverse-square law and have lights right in front of your eyes. IIRC, the photosensors in the eyes for secondary effects (body-clock, dopamine, etc) are clustered in the peripheral vision. That means you can wear glasses with bright LED's around the edges of your cone-of-vision. (You can still do normal work through the centre.) It shouldn't take much experimenting with animals to prove whether that's sufficient to offset the heightened myopia risk.

As a bonus, if you time it right, it will also reset your body-clock each morning, helping deal with the slightly longer day.

Offline gospacex

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Re: SpaceX's Martian Underground
« Reply #171 on: 03/07/2017 10:41 PM »
Or have brighter indoor lighting?

If you are currently in a brightly lit room, the lighting level will be around 1000 lux. We need 30-40,000 lux. So multiply the number of lights in your room by 40-fold over the same area. Then, even allowing for LED efficiencies, think about the power consumed, the heat released, and the annoyance of working on anything with a screen. It seems unlikely anywhere outside a grow-chamber (indoor greenhouse).

It's not necessary to have 30K lux all the time, right? How about this: (if the theory about myopia caused by dim lighting is proved with much more research,) Mars health regulations might mandate that spaces such as corridors, shops, other similar public places should be lighted not lower than below $BIGNUM lux.

(Thankfully, higher power consumption on Mars is less of a problem than on Earth: with outside temps of around -60 C average, even underground bases likely will need heating.)
« Last Edit: 03/07/2017 10:41 PM by gospacex »

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