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#26 2012-07-31 20:20:37

SpaceNut
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From: New Hampshire
Registered: 2004-07-22
Posts: 17,880

Re: Greenhouse - hydroponics vs soil

Interesting conception to put a supply of water into fish farming and hydroponics systems for growing what we need for food.
http://theaquaponicsource.com/what-is-aquaponics/

NEW.Aquaponics%20Icon.jpg


http://en.wikipedia.org/wiki/Aquaponics

Aquaponics is a sustainable food production system that combines a traditional aquaculture (raising aquatic animals such as snails, fish, crayfish or prawns in tanks) with hydroponics (cultivating plants in water) in a symbiotic environment. In the aquaculture, effluents accumulate in the water, increasing toxicity for the fish. This water is led to a hydroponic system where the by-products from the aquaculture are filtered out by the plants as vital nutrients, after which the cleansed water is recirculated back to the animals. The term aquaponics is a portmanteau of the terms aquaculture and hydroponic.

Aquaponic systems vary in size from small indoor or outdoor units to large commercial units, using the same technology. The systems usually contain fresh water, but salt water systems are plausible depending on the type of aquatic animal and which plants.

http://www.cropking.com/aqua.shtml

http://www.aces.edu/dept/fisheries/educ … ulture.pdf

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#27 2012-07-31 21:01:40

SpaceNut
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Re: Greenhouse - hydroponics vs soil

On the path of sewage and helping to create a use for the waste that will over run a crew in time why not use Algae and have the benefit of creating fuels and food from the waste recovery process....

http://www.scientificamerican.com/artic … gae-sewage

http://www.scientificamerican.com/artic … -pond-scum

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#28 2012-09-22 12:42:15

Lobster
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Re: Greenhouse - hydroponics vs soil

What about insects? Don't you need bees and alike to pollinate flowers in order to get the fruit? Or would the astronauts use brush instead? I mean even in greenhouses on Earth people hold bumblebees for that purpose.

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#29 2012-09-23 09:20:04

louis
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Re: Greenhouse - hydroponics vs soil

Lobster wrote:

What about insects? Don't you need bees and alike to pollinate flowers in order to get the fruit? Or would the astronauts use brush instead? I mean even in greenhouses on Earth people hold bumblebees for that purpose.

I understand you can use a brush. With a few people there isn't a lot of pollination to do.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#30 2012-09-30 07:20:20

Lobster
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Re: Greenhouse - hydroponics vs soil

But what kind of plants would be best to grow there for food? Because stuff like corn and wheat needs a year. I heard that NASA was growing some sort of mushrooms for that but I don't know much about it. Also in mind comes those people that grow marijuana because that also blooms every few weeks and is quite edible.

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#31 2012-09-30 09:30:05

louis
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Re: Greenhouse - hydroponics vs soil

Lobster -

Well dwarf buckwheat can be grown in about 60 days I think. Buckwheat is perfect for making breads and pancakes. 

You can grow lots of nutritious bean sprouts and water cress in a matter of days.

Also, with controlled conditions of course they receive optimal inputs of water, light and nutrients.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#32 2012-10-01 05:57:29

Glandu
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Re: Greenhouse - hydroponics vs soil

but where do you find nutrients for the plant?


"I promise not to exclude from consideration any idea based on its source, but to consider ideas across schools and heritages in order to find the ones that best suit the current situation." (Alistair Cockburn, Oath of Non-Allegiance)

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#33 2012-10-01 06:22:01

louis
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Re: Greenhouse - hydroponics vs soil

Glandu wrote:

but where do you find nutrients for the plant?

Well you can bring a lot in the form of concentrated liquid  and Mars itself can supply a lot of the basic nutrients.  It will be a mass-positive venture in the sense that the mass you need to bring from Earth will be far less than involved in bringing food from Earth. However, you do have to get started - that will involve quite a bit of infrastructure importation. But later you can create the farm habitats using Mars ISRU.


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#34 2012-10-01 18:11:09

RobertDyck
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Re: Greenhouse - hydroponics vs soil

I still argue to keep it simple. Hydroponic solutions weigh quite a bit. To create them on Mars, you have to process soil to extract the minerals. Why not just let the plants do that?

For a science mission, bring an inflatable greenhouse. That's just 2 mil thick PCTFE film with fibreglass embedded for rip-stop, and with NASA's spectrally selective coating. Inflate with oxygen, and N2/Ar harvested from Mars atmosphere. Bring plastic soil trays, fill with Mars soil. Soak with water that has had Mars atmosphere bubbled through under pressure. Add some ammonium nitrate fertilizer. That is the only fertilizer a science mission will bring from Earth. A permanent settlement will make nitrogen fertilizer: ingredients are N2, water, and electricity. Plant seeds, grow crops. Simple.

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#35 2012-10-01 18:35:43

louis
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Re: Greenhouse - hydroponics vs soil

RobertDyck wrote:

I still argue to keep it simple. Hydroponic solutions weigh quite a bit. To create them on Mars, you have to process soil to extract the minerals. Why not just let the plants do that?

For a science mission, bring an inflatable greenhouse. That's just 2 mil thick PCTFE film with fibreglass embedded for rip-stop, and with NASA's spectrally selective coating. Inflate with oxygen, and N2/Ar harvested from Mars atmosphere. Bring plastic soil trays, fill with Mars soil. Soak with water that has had Mars atmosphere bubbled through under pressure. Add some ammonium nitrate fertilizer. That is the only fertilizer a science mission will bring from Earth. A permanent settlement will make nitrogen fertilizer: ingredients are N2, water, and electricity. Plant seeds, grow crops. Simple.


As always, I think it's a question of what stage we are talking about. If we are talking about the first few missions, I think that - apart from the water - we will bring most of the growing medium with us from Planet Earth. This will be an experimental stage. We won't really rely on the farm hab - we will have enough food brought with us in various forms: energy bars, tinned food,  dried food, vaccuum packed foods, frozen foods, nuts, beans etc.

Within a few years, though, we can expand the farm hab operations to include the sort of (labour intensive) work you are talking about. Eventually, once we have a enough experience, we can conduct farming relying almost fully on natural conditions on Mars.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#36 2012-10-01 18:44:05

GW Johnson
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Re: Greenhouse - hydroponics vs soil

There's more to fertile soil than just rock dust,  water,  and ammonium nitrate (AN).  (BTW,  AN is a class 1.3 mono-propellant explosive,  even in fertilizer grade (a purity standard).  Adding fuel oil just increases the yield.  It is friction-sensitive,  shock-sensitive,  and can be induced to decompose (deflagrate) by heat;  which in large-enough piles,  can propagate into full detonation.  Try justifying the shipping of THAT in interplanetary supply.)  Any AN you use in agriculture on Mars needs to be locally produced.  We know there's perchlorate salts there;  there are probably nitrate salts as well.  These are all evaporites. 

You also need "organic matter",  which is primarily animal/human feces,  to mix with the rock dust,  which feces contains both carbon-hydrogen-oxygen-nitrogen compounds plus real,  live organisms (some microscopic,  some macroscopic-especially in the third world).  You don't have to ship the feces,  any people on Mars,  and any animals they bring,  will supply more than can be initially used.  Later on,  we'll see.  But in Asian rice culture,  it seems to balance out pretty well. 

Urine is another useful soil component,  although it might prove useful to remove some of the salt first.  The ammonia in it is fixed nitrogen,  the very thing plants need most.  Ammonia is actually better than AN in that respect,  or else the mass of AN fertilizer bags would exceed the mass of tanked ammonia at rural ag-supply places;  it does not. 

On Mars,  you are living in an environment that pressure-wise is very little different at 0.7% of an atmosphere from the vacuum of space.  It should be very easy to build a vacuum flash still rig that could separate the most of the water and nearly all of the ammonia from urine,  and so isolating the leftover brine as something to be disposed of by evaporation,  preferably not in contact with the soil.  Same thing might work in deep space travel.  Not a closed ecology,  but maximized recycling of what we can use. 

The "clean" all-hydroponic thing as most seem to conceive it may well prove to be a technological dead end.  Most of the useful plants we have are more symbiotic with the organisms in the feces than most folks want to admit.  We are not yet capable of engineering plants that do not need such symbiosis long-term. 

By the way,  although I most definitely do not claim to be an agricultural expert,  I have personally seen this process in action.  It is quite real.  I really do live on a cattle ranch in the midst of farm and ranch country.  My wife is a trained composter.  This is most definitely not theoretical knowledge from some school or some book.  It is the real McCoy. 

GW


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#37 2012-10-02 05:32:52

Glandu
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From: France
Registered: 2011-11-23
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Re: Greenhouse - hydroponics vs soil

+1 with GWJohnson, as often. a small link about the dangers of Ammonium nitrate. You don't want that in a spaceship, even in smaller amounts.


"I promise not to exclude from consideration any idea based on its source, but to consider ideas across schools and heritages in order to find the ones that best suit the current situation." (Alistair Cockburn, Oath of Non-Allegiance)

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#38 2012-10-02 14:27:55

louis
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From: UK
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Posts: 5,483

Re: Greenhouse - hydroponics vs soil

GW Johnson wrote:

There's more to fertile soil than just rock dust,  water,  and ammonium nitrate (AN).  (BTW,  AN is a class 1.3 mono-propellant explosive,  even in fertilizer grade (a purity standard).  Adding fuel oil just increases the yield.  It is friction-sensitive,  shock-sensitive,  and can be induced to decompose (deflagrate) by heat;  which in large-enough piles,  can propagate into full detonation.  Try justifying the shipping of THAT in interplanetary supply.)  Any AN you use in agriculture on Mars needs to be locally produced.  We know there's perchlorate salts there;  there are probably nitrate salts as well.  These are all evaporites. 

You also need "organic matter",  which is primarily animal/human feces,  to mix with the rock dust,  which feces contains both carbon-hydrogen-oxygen-nitrogen compounds plus real,  live organisms (some microscopic,  some macroscopic-especially in the third world).  You don't have to ship the feces,  any people on Mars,  and any animals they bring,  will supply more than can be initially used.  Later on,  we'll see.  But in Asian rice culture,  it seems to balance out pretty well. 

Urine is another useful soil component,  although it might prove useful to remove some of the salt first.  The ammonia in it is fixed nitrogen,  the very thing plants need most.  Ammonia is actually better than AN in that respect,  or else the mass of AN fertilizer bags would exceed the mass of tanked ammonia at rural ag-supply places;  it does not. 

On Mars,  you are living in an environment that pressure-wise is very little different at 0.7% of an atmosphere from the vacuum of space.  It should be very easy to build a vacuum flash still rig that could separate the most of the water and nearly all of the ammonia from urine,  and so isolating the leftover brine as something to be disposed of by evaporation,  preferably not in contact with the soil.  Same thing might work in deep space travel.  Not a closed ecology,  but maximized recycling of what we can use. 

The "clean" all-hydroponic thing as most seem to conceive it may well prove to be a technological dead end.  Most of the useful plants we have are more symbiotic with the organisms in the feces than most folks want to admit.  We are not yet capable of engineering plants that do not need such symbiosis long-term. 

By the way,  although I most definitely do not claim to be an agricultural expert,  I have personally seen this process in action.  It is quite real.  I really do live on a cattle ranch in the midst of farm and ranch country.  My wife is a trained composter.  This is most definitely not theoretical knowledge from some school or some book.  It is the real McCoy. 

GW


GW - This is an interesting study - seems to show hydroponically grown wheat is possible and - moreover, you might do it on a recirculating nutrient cycle.


http://ntrs.nasa.gov/archive/nasa/casi. … 009537.pdf


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#39 2012-10-02 19:24:13

GW Johnson
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Re: Greenhouse - hydroponics vs soil

Louis:

Very interesting study.  Hydroponics is possible,  for sure.  I did notice that the microflora were acknowledged,  but not really understood,  based on what I read in that report.  The focus of the study was obviously inorganic nutrients in the water and air.  The bacteria and fungi counts they did almost seemed like an afterthought.

That actually sort-of makes my point in my previous post.  There's a lot more to real farming than just nutrient chemistry.  It's the symbiotic stuff that's the real make-or-break item.  Always has been.  The biologists know vastly more about that issue than I do,  but I think they would agree with my assessment:  we know a lot less about symbiotic ecology than we like to admit. 

That being said,  there are millennia of accumulated human experience with growing crops here on Earth.  The bulk of it long pre-dates modern science,  and still lacks a rigorous and truly-detailed scientific basis.  The bulk of that long experience would suggest that our modern "green revolution",  which is based on the heavy use of inorganic fertilizers,  is a transient phenomenon,  that it is not sustainable over multi-century timescales.  I tend to agree,  based on what little experience I personally have out here on this little ranch. 

That's why I suggest we take the less-intensive,  demonstrably-sustainable,  "traditional" agriculture practices (that date back to the stone age) with us to Mars. 

Why screw it up twice?

GW


GW Johnson
McGregor,  Texas

"There is nothing as expensive as a dead crew,  especially one dead from a bad management decision"

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#40 2012-10-03 01:51:15

RobertDyck
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Re: Greenhouse - hydroponics vs soil

GW Johnson, Ok. We can make ammonium nitrate locally. As I said, we can make it locally, it's just a question of equipment and power. The white granules are coated to ensure they don't agglomerate. The trickiest thing making the granules is getting the granule size right, and coating them so they stay separate. I could give the step-by-step process to make it, but again I'm afraid government types would cause trouble.

I doubt they're as dangerous as you say. I have applied the granules to lawns. Until the Oklahoma bombing, they were used for lawns at home. Mono-propellant explosive? Not likely.

But one major problem with agricultural use of ammonia is that it evaporates. Granules don't. How much nitrogen fertilizer per unit weight is meaningless if it just goes up into the atmosphere. And in a contained environment, do you want astronauts breathing concentrated ammonia fumes?

As for urine, that does not actually contain ammonia. It contains urea. Ammonia is NH3, urea is CO(NH2)2. So urea is carbonyl with two ammonia molecules bonded to it. Microorganisms can break it down, but it does make your greenhouse smell like piss. Current technology filters urine to extract water, do you want to further process that to produce pure urea, without water or salt? A spacecraft could, and store urea from the interplanetary trip for use in starting a greenhouse. Again, urea will make the greenhouse smell like piss.

One mistake many people make is to repeat the rhetoric about "organic matter". Soil starts somewhere. And yes, you can grow plants in regolith with water and fertilizer. NASA already conducted an experiment growing plants in lunar regolith. The first crop grew very well.

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#41 2012-10-03 01:54:24

RobertDyck
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Re: Greenhouse - hydroponics vs soil

Louis, you appear to be stuck on the idea of hydroponics. Again I repeat, nutrient solutions are far to heavy to bring to Mars. Not for the first mission, not ever. To make them locally, you have to extract plant nutrients from Mars soil. So why not just use Mars soil directly, let plant roots extract nutrients? That completely eliminates a lot of equipment.

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#42 2012-10-03 02:00:25

bobunf
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From: Phoenix, AZ
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Posts: 223

Re: Greenhouse - hydroponics vs soil

Hydroponics just seems too complicated biologically and mechanically.  Greenhouse with soil nourished by human and, possibly later, animal waste.  Use natural light, and we have a technologically simple system with 10,000 years of experience.  It will produce food and air with very little need for energy, wiring, pumps, etc. 

Dust storms are not an issue with plants, which like defuse light, just what dust storms produce.  If the Rutherford studies point the way to near radiation free areas of Mars, that issue will also be solved.

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#43 2012-10-03 18:32:50

louis
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Re: Greenhouse - hydroponics vs soil

bobunf wrote:

Hydroponics just seems too complicated biologically and mechanically.  Greenhouse with soil nourished by human and, possibly later, animal waste.  Use natural light, and we have a technologically simple system with 10,000 years of experience.  It will produce food and air with very little need for energy, wiring, pumps, etc. 

Dust storms are not an issue with plants, which like defuse light, just what dust storms produce.  If the Rutherford studies point the way to near radiation free areas of Mars, that issue will also be solved.

If you haven't got the soil, it's more complicated: you have to make the soil.

The point about dust storms (which can continue for 90 days) is that the reduced light levels will mean the crops die. You can't build a thriving community on that basis. At the very least, whether you have soil or nutrient solution, you will need artifical light.


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#44 2012-10-03 21:43:12

RobertDyck
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Re: Greenhouse - hydroponics vs soil

louis wrote:

If you haven't got the soil, it's more complicated: you have to make the soil.

You have soil. It's just different. And making Mars soil arable is a lot simpler than making hydroponic nutrient solutions. As I said: add water, carbonated water, and nitrogen fertilizer. That's it.

The point about dust storms (which can continue for 90 days) is that the reduced light levels will mean the crops die. You can't build a thriving community on that basis. At the very least, whether you have soil or nutrient solution, you will need artificial light.

Artificial light must be a backup only. Exclusively for those dust storms. Every other life support system is dependant on power, so your power supply becomes a single point of failure. If power fails, you can't breathe. A greenhouse with ambient light is the only means of life support with power failure. Biosphere 2 found a biosystem even as large as their huge greenhouse was not stable, after a single year they had to add fresh air. But a Mars greenhouse could provide life support for weeks, or even a couple months while technicians repair the power system. Just ensure power doesn't fail at the same time as a dust storm.

Power balance: use surplus power for in-situ resource utilization, such as smelting iron, smelting aluminum, making glass, making cement, etc. During a dust storm, all power will have to go to the greenhouse, other life support systems, communications and science. Using artificial light in the greenhouse will be at the expense of ISRU.

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#45 2012-10-04 00:07:51

bobunf
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Posts: 223

Re: Greenhouse - hydroponics vs soil

Dust storms are not an insurmountable issue with plants, which like defuse light - just what dust storms produce.   Spirit and Opportunity continued to produce electricity during dust storms.  The attenuation of TOTAL light at the surface is what matters for plants. 

PV requires direct sunlight; plants don't, and can take advantage of all four sources of light: sunlight transmitted directly to the surface, sunlight reflected from the dust haze alone, sunlight scattered to the surface and reflected to the greenhouse, and sunlight reflected off the surface in all other directions, but which is subsequently scattered toward the greenhouse.   We are talking about a haze and not a blackout.

Viking, Spirit and Opportunity images taken during dust storms show a significant amount of light, although a few days do seem to be quite dark, but not black.  Plants are used to cloudy days on Earth

With or without dust storms, appropriately placed mirrors could increase the amount of light entering the greenhouse to simulate something approaching conditions on Earth. 

Heat may be an issue at night, but nighttime insulation and heating water within the greenhouse during the day could provide a considerable, perhaps sufficient, buffer.  This may be an additional problem during dust storms, but producing heat is a less demanding problem than producing light.

Last edited by bobunf (2012-10-04 00:09:55)

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#46 2012-10-04 01:29:00

Spaniard
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Re: Greenhouse - hydroponics vs soil

bobunf wrote:

PV requires direct sunlight

No. PV can work with diffuse light.

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#47 2012-10-04 02:24:46

louis
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From: UK
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Posts: 5,483

Re: Greenhouse - hydroponics vs soil

RobertDyck wrote:
louis wrote:

If you haven't got the soil, it's more complicated: you have to make the soil.

You have soil. It's just different. And making Mars soil arable is a lot simpler than making hydroponic nutrient solutions. As I said: add water, carbonated water, and nitrogen fertilizer. That's it.

The point about dust storms (which can continue for 90 days) is that the reduced light levels will mean the crops die. You can't build a thriving community on that basis. At the very least, whether you have soil or nutrient solution, you will need artificial light.

Artificial light must be a backup only. Exclusively for those dust storms. Every other life support system is dependant on power, so your power supply becomes a single point of failure. If power fails, you can't breathe. A greenhouse with ambient light is the only means of life support with power failure. Biosphere 2 found a biosystem even as large as their huge greenhouse was not stable, after a single year they had to add fresh air. But a Mars greenhouse could provide life support for weeks, or even a couple months while technicians repair the power system. Just ensure power doesn't fail at the same time as a dust storm.

Power balance: use surplus power for in-situ resource utilization, such as smelting iron, smelting aluminum, making glass, making cement, etc. During a dust storm, all power will have to go to the greenhouse, other life support systems, communications and science. Using artificial light in the greenhouse will be at the expense of ISRU.

There's never been a recorded failure of PV panels on Mars that I know of.  YOu can use the PV power to make methane which is then your stored power.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#48 2012-10-04 10:52:42

bobunf
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From: Phoenix, AZ
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Posts: 223

Re: Greenhouse - hydroponics vs soil

Spaniard wrote:
bobunf wrote:

PV requires direct sunlight

No. PV can work with diffuse light.

There is no adverse effect on photosynthesis from the loss of direct sunlight, which is most definitely not the case with PV.  Photosynthesis may actually increase.  One study (http://www.jstor.org/discover/10.2307/1 … 1280469297) reports a 37% increase in carbon gain on cloudy days.

Also, plants survive long periods of time without light.  Annual plants might survive up to 10 days with no light at all.  Perennials can last for weeks and even months without light.

But, when a cloud blocks the sun, how much does electricity generation decline?  About half if the cloud is thin and shadows are still cast on Earth.  About 80% if the cloud is thick and no shadow is cast.  About 99% for thick dark clouds covering the sky.

Obviating the need for artificial light means no need for PV panels, wiring, transformers, inverters, circuit breakers, light fixtures and bulbs; all of which requires a huge amount of on-going imports from Earth or a huge industrial base.

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#49 2012-10-04 16:18:29

louis
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From: UK
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Re: Greenhouse - hydroponics vs soil

bobunf wrote:
Spaniard wrote:
bobunf wrote:

PV requires direct sunlight

No. PV can work with diffuse light.

There is no adverse effect on photosynthesis from the loss of direct sunlight, which is most definitely not the case with PV.  Photosynthesis may actually increase.  One study (http://www.jstor.org/discover/10.2307/1 … 1280469297) reports a 37% increase in carbon gain on cloudy days.

Also, plants survive long periods of time without light.  Annual plants might survive up to 10 days with no light at all.  Perennials can last for weeks and even months without light.

But, when a cloud blocks the sun, how much does electricity generation decline?  About half if the cloud is thin and shadows are still cast on Earth.  About 80% if the cloud is thick and no shadow is cast.  About 99% for thick dark clouds covering the sky.

Obviating the need for artificial light means no need for PV panels, wiring, transformers, inverters, circuit breakers, light fixtures and bulbs; all of which requires a huge amount of on-going imports from Earth or a huge industrial base.

For clarification:

1.  Reduced insolation is not really relevant to overall power production.  Any PV based system will involve energy storage. I favour converting water and Mars air into methane as the best way of storing energy. So, take it as a given that we will have as much energy available as we need.

2.  We can manufacture solar power on Mars at an early stage. We could use solar reflectors (e.g. polished steel or aluminium) to reflect insolation on to a steam boiler to drive a turbine to produce electricity.  We can probably manufacture 90% plus of the energy system on Mars (reflectors, boilers, wiring) with a basic industrial infrastructure. Probably the connecting and gauge equipment would be imported.

3. The point is that the less insolation you get, the more your crop yield is reduced. Moreover, in the Mars context don't forget, you still have to heat your farm habs - so you are going to have to have an energy system in place.

4. With a guaranteed, controlled energy input you will maximise crop yields.

5. Hydroponics allow you to create multi-level growing systems. These are much more efficient in terms of hab space. With natural insolation systems you will need at least x3 as much space before you have to factor in your dust storm risk factor which will probably take you to X5. Building five times as much farm hab space will be incredibly resource intensive including in all those things you mention (because you still have to heat and illuminate the farm habs).


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#50 2012-10-05 22:23:55

bobunf
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From: Phoenix, AZ
Registered: 2005-11-21
Posts: 223

Re: Greenhouse - hydroponics vs soil

There is no dust storm risk factor for plants.  Most plants would survive any recorded Martian dust storm, continuing to produce oxygen, food and other products and absorb CO2 with a possible hiatus of a day or two.  Heat would be an issue at night during dust storms, but one fairly easily surmounted. 

It is possible to grow plants in multiple levels using soil and natural light with mirrors, but it would make more sense to have the plants use the space rather than trays, i.e., grow bigger plants.  It would not make sense to build a greenhouse much higher than about 2-1/2 meters.  But plants can easily use 2-1/2 meters of height and a lot more.

The height of greenhouse plants can be controlled by a number of chemical and non-chemical methods. Rye, barley, wheat, rice, and sweet potato vines have been grown to heights of 1-1/2 meters, asparagus over 2-1/2 meters.  Blueberry and huckleberry shrubs and cassava to nearly 4 meters, corn, tomatoes and grape vines to 6 meters.  Obviously 38% gravity would permit much greater heights than would be necessary to utilize the highest reasonable greenhouse, and would increase crop yields commensurately.   

No trays necessary with all their plumbing, wiring and maintenance.

Converting natural light to electricity, storing some electricity as methane and sometimes re-converting the methane to electricity, and then converting the electricity to artificial light seems extraordinary complex and unnecessary.  And it would involve a loss of energy of from 90 to 97%.  All of which seem especially unwise considering that solar electricity generation shuts down during the worst of the dust storms; but plants don't, except, possibly for a day or two at the most.

The biggest complication of using natural light is the fairly simple one of producing low quality mirrors and positioning them.

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