Author Topic: Skepticism about space colonization  (Read 77778 times)

Online spacenut

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Re: Skepticism about space colonization
« Reply #280 on: 09/24/2017 06:15 pm »
All of the information on greenhouses is no the "Scaling Agriculture on Mars" thread.  Two to three feet of water is a very good insulator for radiation.  Water could be placed in tanks above greenhouses that open to the outside with side windows.  Sunlight would be indirect, but grow lights could be placed above the plants.  Believe me, I have used grow lights, it is amazing how fast plants can grow with these things.  Anyway, read the thread.  Agriculture will start small, and grow from there as greenhouses, above or below ground, are built to provide food and green ambiance for the closed in colonists.  A lot of water will be needed for human and plant consumption, as well as fish and small animals.  Most will be recycled, but much will still need to be added to a growing colony, and to provide fuel for spacecraft returning to earth. 

Offline Coastal Ron

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Re: Skepticism about space colonization
« Reply #281 on: 09/24/2017 07:33 pm »
Two to three feet of water is a very good insulator for radiation.  Water could be placed in tanks above greenhouses that open to the outside with side windows.  Sunlight would be indirect, but grow lights could be placed above the plants.

Once colonists have the ability to produce acrylic glass, one way of doing what you suggest is to build a giant aquarium as the roof for part of a underground habitat. That would maximize the amount of natural sunlight (which could be a psychological benefit), and it could be used for growing fish as a human food and nutrient source for plants (i.e. aquaculture).

Of course such a design is likely not realist for the 1st or 2nd generation Mars habitats, so it's not going to help the initial colonists survive - both physically and psychologically.
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

Offline Robotbeat

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Re: Skepticism about space colonization
« Reply #282 on: 09/24/2017 07:44 pm »
People are tougher than we often give them credit for, especially if they're pushing for something better.

NASA has been working on that IceHouse concept, and they've improved it.
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Offline high road

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Re: Skepticism about space colonization
« Reply #283 on: 09/24/2017 09:09 pm »
Greenhouses don't need to be underground. That's sort of a misconception. It's okay to be above-ground for a few hours per day (up to ~30-35 hours per week if the rest of the time is well-shielded) without exceeding annual dose limits for Earthbound radiation workers (which most people on Mars basically will be), just like it's okay from a skin cancer perspective to be outside like 15-30 minutes per day without protection on a sunny day on Earth.

How long can the plants stay in those greenhouses without suffering adverse effects from the radiation? Or how much protection is required to lower Martian radiation levels to the point they are no longer harmful to plant or animal life?
At Mars levels, the radiation has basically no effects on plants and almost none on animals. It matters a little for humans because we have long lifespans. But as long we limit the length of time to about 30-35 hours a week, it's no worse than radiation worker limits on Earth.

The Chernobyl exclusion zone is incredibly lush because the humans are gone. The radiation has essentially zero effect on the wildlife.

oh, humans are far worse for habitability than radiation, no doubt. But genetic damage in seeds might build up quickly for plants with short generaions. I wouldn't want my sole food source to depend on steadily mutating crops. Their nutrient production might change unexpectedly.

Offline high road

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Re: Skepticism about space colonization
« Reply #284 on: 09/24/2017 09:15 pm »
All of the information on greenhouses is no the "Scaling Agriculture on Mars" thread.  Two to three feet of water is a very good insulator for radiation.  Water could be placed in tanks above greenhouses that open to the outside with side windows.  Sunlight would be indirect, but grow lights could be placed above the plants.  Believe me, I have used grow lights, it is amazing how fast plants can grow with these things.  Anyway, read the thread.  Agriculture will start small, and grow from there as greenhouses, above or below ground, are built to provide food and green ambiance for the closed in colonists.  A lot of water will be needed for human and plant consumption, as well as fish and small animals.  Most will be recycled, but much will still need to be added to a growing colony, and to provide fuel for spacecraft returning to earth.

either you use several feet of water for radiation protection and it dwarfs all other hydrogen needs other than fuel, or hydrogen is used to grow the colony and radiation protection is done by going underground. One or the other.

Online spacenut

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Re: Skepticism about space colonization
« Reply #285 on: 09/24/2017 09:24 pm »
I've read that only one foot of water screens out most radiation, on this forum somewhere.  I didn't realize how little it took.  Not several feet. 

Online spacenut

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Re: Skepticism about space colonization
« Reply #286 on: 09/24/2017 10:06 pm »
http://forum.nasaspaceflight.com/index.php?topic=35877.0


Tried to make a link for this.  58 pages of information.  This is on "Scaling Agriculture on Mars"  It is under Missions to Mars.

Offline Robotbeat

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Re: Skepticism about space colonization
« Reply #287 on: 09/25/2017 01:58 am »
All of the information on greenhouses is no the "Scaling Agriculture on Mars" thread.  Two to three feet of water is a very good insulator for radiation.  Water could be placed in tanks above greenhouses that open to the outside with side windows.  Sunlight would be indirect, but grow lights could be placed above the plants.  Believe me, I have used grow lights, it is amazing how fast plants can grow with these things.  Anyway, read the thread.  Agriculture will start small, and grow from there as greenhouses, above or below ground, are built to provide food and green ambiance for the closed in colonists.  A lot of water will be needed for human and plant consumption, as well as fish and small animals.  Most will be recycled, but much will still need to be added to a growing colony, and to provide fuel for spacecraft returning to earth.

either you use several feet of water for radiation protection and it dwarfs all other hydrogen needs other than fuel, or hydrogen is used to grow the colony and radiation protection is done by going underground. One or the other.
Mars isn't hydrogen-starved like the Moon.
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Online spacenut

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Re: Skepticism about space colonization
« Reply #288 on: 09/25/2017 02:05 am »
Yes, Mars has a lot of frozen water.  More than enough to sustain a few million colonists.

Offline AncientU

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Re: Skepticism about space colonization
« Reply #289 on: 09/25/2017 12:47 pm »
Greenhouses don't need to be underground. That's sort of a misconception. It's okay to be above-ground for a few hours per day (up to ~30-35 hours per week if the rest of the time is well-shielded) without exceeding annual dose limits for Earthbound radiation workers (which most people on Mars basically will be), just like it's okay from a skin cancer perspective to be outside like 15-30 minutes per day without protection on a sunny day on Earth.

How long can the plants stay in those greenhouses without suffering adverse effects from the radiation? Or how much protection is required to lower Martian radiation levels to the point they are no longer harmful to plant or animal life?

Mean lifetime of a plant is a few months; for 'livestock' a year at most.
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Online spacenut

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Re: Skepticism about space colonization
« Reply #290 on: 09/25/2017 01:27 pm »
Yes even a beef cow is only about 18 months.

Offline john smith 19

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Re: Skepticism about space colonization
« Reply #291 on: 09/25/2017 05:44 pm »
oh, humans are far worse for habitability than radiation, no doubt. But genetic damage in seeds might build up quickly for plants with short generaions. I wouldn't want my sole food source to depend on steadily mutating crops. Their nutrient production might change unexpectedly.
A fair question but one which is also faced on Earth by any long term seed bank to maintain genetic diversity.

They take precautions to maintain the seeds in sealed, stable containers, usually underground. Modern techniques can allow a small amount of seed to be massively replicated before transplant into fields.
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Offline tdperk

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Re: Skepticism about space colonization
« Reply #292 on: 09/26/2017 12:36 am »

oh, humans are far worse for habitability than radiation, no doubt. But genetic damage in seeds might build up quickly for plants with short generaions. I wouldn't want my sole food source to depend on steadily mutating crops. Their nutrient production might change unexpectedly.

I think the occasional good mutation would be deliberately propagated while cuttings and seeds from far deeper nurseries used to plant most gardens

Offline AncientU

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Re: Skepticism about space colonization
« Reply #293 on: 09/26/2017 03:59 pm »

oh, humans are far worse for habitability than radiation, no doubt. But genetic damage in seeds might build up quickly for plants with short generaions. I wouldn't want my sole food source to depend on steadily mutating crops. Their nutrient production might change unexpectedly.

I think the occasional good mutation would be deliberately propagated while cuttings and seeds from far deeper nurseries used to plant most gardens

There would be need to develop seed lines that were optimized for growing conditions on Mars.  Genetic variation, including spontaneous mutation, and cross-breeding are parts of this research effort.  Areogronomy...
« Last Edit: 09/26/2017 04:02 pm by AncientU »
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Offline DarkenedOne

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Re: Skepticism about space colonization
« Reply #294 on: 09/26/2017 08:36 pm »
I've read that only one foot of water screens out most radiation, on this forum somewhere.  I didn't realize how little it took.  Not several feet.
The halving thickness of water is about 7.2 inches.  One foot of water will absorb 70% of the radiation.  Two feet will absorb 90%.

NASA estimates a deep space cruise of 253 days would deliver a dose of .66 sieverts based on the data from Curiosity's trip to Mars.  That comes out to ~2.608 millisieverts daily.  For comparison exposure at Earth's surface is 10 microsieverts daily.  Now if you are on the surface of Mars than Mars will block out half of the sky, thus half of the radiation so that leaves you with ~1.304 millisieverts daily.  NASA says that a dose of 1 sievert is associated with a 5.5% increase in fatal cancer.  Assuming you want to stay under 1 sievert than you could not stay on Mars unprotected for more than 476 days.  Sounds ok for an exploration mission. 

Now when it comes to a settlement a foot of water is not nearly good enough.  A 70% decrease will increases the time it takes to reach the 1 sievert dose from 476 days to 1586 days, which is only a little over 4 years.  Two feet of water will increase the time to about 13 years.  You really need about 40 inches before the time to reach 1 sievert comes out to 100 years. 
« Last Edit: 09/26/2017 08:38 pm by DarkenedOne »

Offline KelvinZero

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Re: Skepticism about space colonization
« Reply #295 on: 09/26/2017 11:47 pm »
Or go my favourite option: at least two meters and have a nice rooftop swimming pool :)

That is interesting though. I hadn't heard it expressed that way before. Any discussion can be diverted to one of the threads on radiation. There is a big debate there on whether cancer risk scales linearly etc. We will never resolve that here.. or there. It does not sound like a show stopper.

Offline Robotbeat

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Re: Skepticism about space colonization
« Reply #296 on: 09/27/2017 12:26 am »
DarkenedOne: You're off by a factor of 2. You forgot the significant shielding due to Mars' atmosphere (people often wrongly neglect this). Mars Curiosity measures 0.64 mSv/day on the surface.

Also, that's 5.5% incident of cancer, not cancer /deaths/. And that's a pretty conservative estimate based on extrapolations from extremely high dose rates. Mars' dose rates will be far less, giving time for our DNA/cellular repair and protection mechanisms to respond.

To give a comparison, your odds of getting cancer if you smoke are about 20-25% higher, and also huge cardiovascular risks (which is even more likely than cancer to kill you). So, say, 4 to 5 Sievert. That's about 21 years  (233mSv/yr) completely unshielded.

But any large colony is going to end up highly shielded just due to the structure of the colony. Everything about 50 ft in from the exterior (i.e. 5 stories down) of a typical building will be shielded enough to get you down to 10 mSv/year (radiation worker limit is 50 mSv/year). Alternately, you can just use a couple meters of water (which, if pure gives a nice, blue-tinted view outside) or regolith on the top floor and shield nearly everything below.

So a combination of exterior shielding on the city (probably built as a huge building) and limiting your time on the surface to about 30 hours per work week should do ya. Yeah, our current models mean your cancer risk is higher, but on the other hand, almost no chance of sun-caused skin cancer.
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Offline john smith 19

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Re: Skepticism about space colonization
« Reply #297 on: 09/27/2017 07:09 am »
The halving thickness of water is about 7.2 inches.  One foot of water will absorb 70% of the radiation.  Two feet will absorb 90%.
And 1 cubic foot of water weighs about 62lb on Earth but 20 and 2/3s lb on Mars.

That's useful to know.

It suggests naturally lit greenhouses could have adequate radiation shielding for crops, provided they are regularly renewed before serious radiation damage occurs to the crops.

So in answer to "What will they eat on Mars" we can say "A variety of plants and fish and birds, all of which can be grown in a variety of different ways from naturally lit greenhouses to artificially lit underground locations."
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Offline guckyfan

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Re: Skepticism about space colonization
« Reply #298 on: 09/27/2017 07:51 am »
There is no need whatsoever to radiation shield greenhouses or pens for animals.

Online TrevorMonty

Re: Skepticism about space colonization
« Reply #299 on: 09/27/2017 08:42 am »
I've read that only one foot of water screens out most radiation, on this forum somewhere.  I didn't realize how little it took.  Not several feet.
The halving thickness of water is about 7.2 inches.  One foot of water will absorb 70% of the radiation.  Two feet will absorb 90%.

NASA estimates a deep space cruise of 253 days would deliver a dose of .66 sieverts based on the data from Curiosity's trip to Mars.  That comes out to ~2.608 millisieverts daily.  For comparison exposure at Earth's surface is 10 microsieverts daily.  Now if you are on the surface of Mars than Mars will block out half of the sky, thus half of the radiation so that leaves you with ~1.304 millisieverts daily.  NASA says that a dose of 1 sievert is associated with a 5.5% increase in fatal cancer.  Assuming you want to stay under 1 sievert than you could not stay on Mars unprotected for more than 476 days.  Sounds ok for an exploration mission. 

Now when it comes to a settlement a foot of water is not nearly good enough.  A 70% decrease will increases the time it takes to reach the 1 sievert dose from 476 days to 1586 days, which is only a little over 4 years.  Two feet of water will increase the time to about 13 years.  You really need about 40 inches before the time to reach 1 sievert comes out to 100 years.
Great post. So for deep space habitat even few inches would be enough for upto year.

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