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Oldfart1939

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Re: Crops

What we should be concentrating on for crops is a set of products which have very short times from planting to maturity, combined with maximum caloric and vitamin output. There are lots of books about farming for survival that indicate the most efficient crops for the colony situation. Turnips are a quick crop. Root crops can be co-planted alongside taller crops to make maximum use of the space available. Radishes, beets, and carrots are good sources of essential vitamins, in addition to providing taste variety. Swiss chard is a heavy producer, and is semi-perennial. The turnip greens are also a decent food. Look into short growing season hybrids developed for use in the northern tier of states and Canada. Vine squashes can be planted in conjunction with other crops too. Every square centimeter needs to be productive, both above ground and below ground. Add in sweet potatoes in place of white potatoes for variety and vitamin A production.

RobertDyck

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Re: Crops

I had also argued for soil agriculture instead of hydroponics. The reason is hydroponics requires liquid nutrients. Where do those come from? Yes, hydroponics can produce more from a given crop area, but what does it take to produce those liquid nutrients? My argument is to keep it simple. Use ammonium nitrate granules as nitrogen fertilizer.

That's regulated on Earth since the Oklahoma bombing, but on Mars we don't have to worry about someone going nuts who received military special forces training to make improvised explosive devices and how to make shaped charges and how to use explosives to demolish an office building. Yes, the Oklahoma bomber did receive all that specialized training from US military special forces. He was discharged from the military, and had a grudge. Mars scientists will be very smart people with excellent training, and it will include how to make fertilizer, but I don't think they will have the specialized training to make shaped charges or how to demolish an office building.

Besides, my family and neighbours used it for years to fertilize their lawn before the Oklahoma bombing. I'm told farmers often make AN/FO using farm fertilizer and diesel fuel from their tractor to blow up a tree stump. This was safely used for decades before one single individual with a grudge spoiled it for everyone. And that individual was only able to do so because of specialized military training. So we don't have to worry on Mars.

Mars soil has plenty of micronutrients. It has so little nitrogen it's below detection threshold for instruments on Sojourner. I think Curiosity found some, but it's extremely low. Mars soil does have potassium, but it's too low. We would look for potash at the bottom of the dried up ocean bed. Treat soil with soda water; that's water with CO2 dissolved under pressure. That mild acid should dissociate perchlorate, and release superoxides, and reduce soil pH. Mars soil anywhere but Meridiani Planum is alkali. Soda water has carbonic acid; when reacted with alkali soil that should start the process of adding carbon to soil.

I also argued for ambient light greenhouse. My idea is a long narrow greenhouse oriented perfectly east-west. Along both sides, mirrors. These mirrors would be flat and roughly 45°. Mirror height above ground would equal the greenhouse. A greenhouse transported from Earth would be inflatable polymer film, but a greenhouse built from in-situ materials would be glass. Width exactly twice the height. So with sunlight reflected from mirrors along the sides, reflected light would equal direct light from above. That means total light will be double Mars ambient. Since light reaching Mars is 47% that of what reaches Earth (before reduction due to ozone or clouds), that should provide roughly equal to Earth. And a long narrow greenhouse means that sunlight at dawn will reflect westward down the greenhouse, but still within the greenhouse. Sunlight at noon will reflect perfectly perpendicular. Sunlight at dusk will reflect eastward, but again still within the greenhouse. So the mirrors don't have to track the Sun. They will have to track with season, but that means 1° angle change once every 14 Mars solar days. For a small farm, you could use a notched rod to support a mirror, a settler in a spacesuit could adjust it to the next notch once every second week. Or use a motor, but that's a lot simpler than tracking through the day.

Ambient light greenhouse can produce O2 without power. And a greenhouse designed to manage sunlight for heat could avoid power for heat. Humidity would condense on cold walls, collect at a trough along all greenhouse walls. Water greenhouse crops with grey water from sewage processing. Water transpired through plant leaves will be the purest, cleanest, sweetest tasting water you could ever hope for. Far better tasting than any filtration system. So a greenhouse can provide life support during complete power failure. It's the only life support system that can.

Of course all greenhouses will have to be equipped with artificial light for use during dust storms. But if you only use it during dust storms, that leaves a lot of power for industrial use under normal conditions.

Lake Matthew Team - Cole

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Re: Crops

Max Yield

What we should be concentrating on for crops is a set of products which have very short times from planting to maturity, combined with maximum caloric and vitamin output. There are lots of books about farming for survival that indicate the most efficient crops for the colony situation. Turnips are a quick crop. Root crops can be co-planted alongside taller crops to make maximum use of the space available. Radishes, beets, and carrots are good sources of essential vitamins, in addition to providing taste variety. Swiss chard is a heavy producer, and is semi-perennial. The turnip greens are also a decent food. Look into short growing season hybrids developed for use in the northern tier of states and Canada. Vine squashes can be planted in conjunction with other crops too. Every square centimeter needs to be productive, both above ground and below ground. Add in sweet potatoes in place of white potatoes for variety and vitamin A production.

Sounds good.  Given the expense and difficulty of constructing greenhouse space, superb crops are needed, with careful co-planting for efficient use of space, and many other tweaks for max yield.

Chard is good, yes.  Turnips are yucky. 

In one exercise I roughed out an intensive garden, augmented with prawn-and-tilapia aquaculture.  Scale: 8 acres of garden, 1 acre of aquaculture.  Location: 40 South.  Lighting: 60% PPF light transmission, for 9 months of useful sunlight per Mars year, plus LEDs.  LED supplement and extended growing seasons notionally match yields to terrestrial garden yields (with exception of wheat, per above).

In this scheme the garden and aquaculture produce roughly 210 million calories per Mars year:  self-sufficiency for an initial crew of 100. 

The plots:  (link to full-res image)

I didn't attempt a Perfect Day / Thrive synthetic dairy plant in that scheme, because I can't quantify the plant's yield.  I imagine it could boost calorie production significantly.

Can you recommend some other breakout crops or methods, to make big improvements in yield?  E.g., some especially short-season (<60d) hybrids?

Last edited by Lake Matthew Team - Cole (2016-12-28 13:07:14)

RobertDyck

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Re: Crops

The turnip greens are also a decent food.

A lot of people confuse turnip with rutabaga. The root vegetables look and taste very similar. Rutabaga is a cross between turnip and cabbage. Turnip greens are not edible, they have too much cellulose. Rutabaga greens are edible. I read on Wikipedia that turnip greens are a side dish in southern US cooking, or "turnip tops" in the UK. Turnip greens have to be cooked to be edible. So turnip greens are technically edible, but I sure wouldn't eat them.

SpaceNut

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Re: Crops

I haven't been on the NasaSpaceFlight forum for quite some time but for others this is the link for the topic Scaling Agriculture on Mars

Lots of good stuff in this topic as its 50 pages long

Which reminds me landing site, payload to surface.....We will need each plot to over produce, need to time meal crops and rotate the timing for others to compliment a menu of meals for each day....

Lake Matthew Team - Cole

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Re: Crops

Fertilizer Delivery

I had also argued for soil agriculture instead of hydroponics. The reason is hydroponics requires liquid nutrients. Where do those come from? Yes, hydroponics can produce more from a given crop area, but what does it take to produce those liquid nutrients?

Well, the methods of a previous post might help.  For example, the notional plasma nitrate plant gives nitrate in solution.  It should be a very energy-efficient way to make a liquid N fertilizer, far more efficient than ammonia and/or ammonium nitrate production, to best of my knowledge.

As for delivery:

One might attempt automated "garden printing".  That is, one could install an automated pump-grid network on the ceiling, with a sprayer at each node.  Each sprayer covers a garden sector.  An IoT soil sensor is planted below each sprayer.  When a sensor detects a soil imbalance, a custom fertilizer solution is calculated, measured out, and routed through the pump-grid, to the sprayer overhead.

Conceptually it's a bit like a stationary print head.  CLICKETY-CLICKETY-PUMP-PUMP-PUMP.  Liquid fertilizer delivered.

Scaling (e.g. Ca/Mg scaling) within the grid pipes could be a problem.  One fix:  deliver that fertilizer as dry pellets, perhaps taking a page from Amazon delivery and drone-dropping it.  The drone circles the soil sensor while pouring pellets through its rotors.  BRRRRRRRRRRRRRWHUP.  Solid fertilizer delivered.

Re: substrate:

This gardening scheme assumes no appreciable nutrients in the planting substrate itself (for simplicity and safety).  Therefore it's a hydroponic scheme, where the substrate is inert and ideally pH-neutral.  One possible source of such a substrate would be rinsed sand, perhaps augmented with a little shredded compost matter for water retention.

Last edited by Lake Matthew Team - Cole (2016-12-28 11:08:50)

Oldfart1939

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Re: Crops

In other discussion threads, especially to "Chickens" discussion, many of the by-products of the root crops also serve as a major source of chicken feed. i.e.: Turnip greens, Carrot tops, Radish leaves, etc. I've raised lots of chickens on my ranch, and even grass clippings can massively reduce the need for imported/locally raised grains. In addition to being a retired chemist, I've been involved as a cattle rancher for some 20 years. I've raised chickens for both eggs and meat--for home use only. I've also been involved in hay farming, and put up 70 acres of grass & clover hay annually. Another species we need to consider introducing in each of these greenhouses is honey bees. If we're looking to grow a crop for livestock feed, Alfalfa is one such crop; Alfalfa requires pollination by bees to produce well, though. A wonderful byproduct of the bee is Honey production, as well as Beeswax. The annual yield (Earth years) of a good alfalfa is ~ 6 tons per acre. On Mars, that would go a long way in supporting chickens, swine, and cattle, or sheep for agricultural animals. Raising corn for human and animal feed is also very efficient. The entire plant is animal feed, not only the grain produced. What the Martian settler needs to do is develop agriculture for maximum symbiosis. There are some excellent short growing season corns available, many of which are "Heirloom" varieties.

By the way, Rob--my late wife was from North Carolina, and I was introduced to eating Turnip greens through her. Not. My . Favorite. As she commented, it's an "acquired taste." She also prepared Collard greens, which is an extremely useful and highly nourishing crop.

Last edited by Oldfart1939 (2016-12-28 10:36:35)

Lake Matthew Team - Cole

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Re: Crops

Milliferanauts

Another species we need to consider introducing in each of these greenhouses is honey bees.

A keystone species, surely.  And actually they adapt to spaceflight very well.  (STS-41C beehive video at 8:00.) 

In conclusion, the bees in the orbiter BEM fared quite well in outer space, managing by mission's end to adapt perfectly to microgravity. The crew noted in the log book that "...by Day 7, comb well developed, bees seemed to adapt to 0-g pretty well. No longer trying to fly against top of box. Many actually fly from place to place." This adaptation may indicate a certain "learning" capacity on the part of the bees.

Milliferanauts are ready when we are.

Last edited by Lake Matthew Team - Cole (2016-12-28 12:47:30)

Oldfart1939

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Re: Crops

Another concept here for consideration is utilization of these large greenhouses in the cycle of air renewal; we're discussing lots of photosynthesis here, given potential acres and acres of indoor crop management. A CO2 atmosphere in the greenhouses would rapidly change over to an O2 rich condition, as the plants began converting CO2 to cellulose and sugars. We then could utilize this as the source of O2 for the growing colony in a cyclic system, where the habitat air would be recirculated through the greenhouses, and re-oxygenated air provided back to the Habs.

I really like Rob's concept of long and skinny greenhouses similar in concept to Quonset Huts; these could be modular and expandable lengthwise. If given hemispherical ends, they would be structurally pretty strong. My suggestion is a "Quonset-style" greenhouse in a modular design of 100 meters in length, and a 25 meter width. Each would enclose 0.74 acres available for use. Consider the "greenhouse farm" composed of 12 of these units, or ~ 9 acres. Each could be expanded by a single unit, effectively doubling the acreage to 18. This would provides enough growing space to provide for a colony of 100 Mars pioneers, but they would be busting their buns working such a "farm."

Most of the concepts I'm presenting here are based on the "KISS" principle, keeping everything as low-tech as possible; fewer things to go wrong that way, and requiring fewer imports from Earth.

Lake Matthew Team - Cole

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Re: Crops

Most of the concepts I'm presenting here are based on the "KISS" principle...

A good principle, that. 

I really like Rob's concept of long and skinny greenhouses similar in concept to Quonset Huts...

What structural mass per m3 do you estimate for your quonset-style greenhouse?  For comparison, an LMT 300-m water-roof dome is notionally a modular titanium polygon / ETFE foil cushion structure.  That structure (including anchoring system) comes in around 0.1 kg/m3.

Last edited by Lake Matthew Team - Cole (2016-12-28 12:47:15)

Oldfart1939

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Re: Crops

What structural mass per m3 do you estimate for your quonset-style greenhouse?  For comparison, an LMT 300-m water-roof dome is notionally a modular titanium polygon / ETFE foil cushion structure.  That structure (including anchoring system) comes in around 0.1 kg/m3.

I haven't done any calculations, and am assuming the early greenhouses will be inflatables brought from Earth. Later on, they will be from locally produced Polycarbonate and/or ABS plastics.

Lake Matthew Team - Cole

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Re: Crops

What structural mass per m3 do you estimate for your quonset-style greenhouse?  For comparison, an LMT 300-m water-roof dome is notionally a modular titanium polygon / ETFE foil cushion structure.  That structure (including anchoring system) comes in around 0.1 kg/m3.

I haven't done any calculations, and am assuming the early greenhouses will be inflatables brought from Earth. Later on, they will be from locally produced Polycarbonate and/or ABS plastics.

Well, the ISS BEAM inflatable comes in around 90 kg/m3.  That is, 1000x the mass per m3.  Just for comparison.

Oldfart1939

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Re: Crops

Lake Matthew Team-Cole;

That seems to be massive overkill, and designed for deep space use. I would expect that the polymer films would be considerably lighter and thinner. The greenhouses would not need to be at 1 atm. pressure, either. We need a transparent southern exposure, if the greenhouses are optimally situated. I've calculated the area of both the hemi-cylinder and 2 hemispherical walled ends at 4907meters^2., and a heavy polymer construction at 5 kg/ meter^2. Yes, this is pretty heavy: 24,539 kg. I've estimated on the high side for the weight of the structure, and depends on the wall thickness and any Kevlar reinforcements for strips at edges of the joints.

I checked and rechecked the calculation, and have made the appropriate corrections.

Last edited by Oldfart1939 (2016-12-28 13:58:57)

Lake Matthew Team - Cole

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Re: Crops

That seems to be massive overkill, and designed for deep space use. I would expect that the polymer films would be considerably lighter and thinner. The greenhouses would not need to be at 1 atm. pressure, either. We need a transparent southern exposure, if the greenhouses are optimally situated. I've calculated the area of both the hemi-cylinder and 2 hemispherical walled ends at 4907meters^2., and a heavy polymer construction at 5 kg/ meter^2. Yes, this is pretty heavy: 24,539 kg. I've estimated on the high side for the weight of the structure, and depends on the wall thickness and any Kevlar reinforcements for strips at edges of the joints.

That's... 1 kg/m3?  Vastly superior to ISS BEAM.  How do your material properties and layerings compare with BEAM? 

The martian surface presents saltation abrasion, hard UV, electrical discharge, corrosive salts and an uncertain flux of cm-scale iron meteorite bullets.  Maybe you've accounted for these and other problems, but you'd want to be sure your greenhouse could survive them.

Last edited by Lake Matthew Team - Cole (2016-12-28 14:14:33)

Oldfart1939

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Re: Crops

I just completed another calculation, and we definitely need to include a floor. Pressurization of my structure would lift it off the deck  in a heartbeat. I'm now including an additional floor area of 6963.6 meters^2, of a substantially heavier polymer coated Kevlar fabric. I'm guessing an 12 kg per meter^2 weight. Add 83,562 kg to my initial weight of the structure; this is minus and airlocks or  support equipment (sprinklers, LED lighting, etc.). I believe there is also a discussion of the materials used on another thread? Mainly, we need a transparent south facing "window,' which can only be of a polymer film.

Oldfart1939

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Re: Crops

My proposed greenhouse system will undoubtedly be only temporary; I would prefer the construction to be more resistant to the postulated micrometeorite hits, tears, and more suitable for enclosing livestock (?).Long term solution? Build of regolith bricks and polycarbonate windows. That, or glass , locally produced. RobertDyck has proposed a much smaller greenhouse in the Materials thread. I'm approaching this problem as one who has actually produced crops and livestock; anything as small as proposed elsewhere will ultimately fail in the purpose of feeding the anticipated numbers. The smaller versions will undoubtedly be useful in augmentation of the food supplies brought from Earth, but nowhere close to generating sustainability.

RobertDyck

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Re: Crops

Note: micrometeorites don't reach Mars surface. Regular meteorites will, but micrometeoroids burn up in Mars atmosphere. The burn up about 30km above the surface. On Earth they burn up about 100km above the surface. How deep into the atmosphere depends how large the meteoroid. So an inflatable habitat on Mars doesn't need the micrometeoroid shield of BEAM. It will need something to protect against astronauts scuffing the outside, or more importantly sand storms or dust storms. I recommend a single layer of Tennara architectural fabric. That's the same material as the outermost layer of Orthofabric, which is the outer fabric used for white spacesuits. But Tennara is just PTFE fibres, no Kevlar or Nomex, and Tennara has a twill weave instead of double layer plain weave. But that's an inflatable hab, not a greenhouse. A greenhouse must be transparent. I suggest PCTFE film, sold under the brand name Clarus, made by Honneywell. It's a fluoropolymer film.

Oldfart1939

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Re: Crops

Has anyone here contemplated Elon Musk's proposal of bringing settlers to mars 100 at a batch, and the impact that has on supply side of things? Calorie counting aside, a normal person has a 2 % body weight daily food intake for weight maintenance, and 2.5 % to 4 % or more with heavy activity; i.e. doing farming or construction. Running some rough numbers, supplies from Earth will be a major source of food for the first 3 years after new arrivals  begin consuming supplies. Taking the FAA guideline for the average passenger weight on an airliner, 170 pounds, that calculates to a minimum of 340 pounds per day for sedentary activity, or double that if they are all going to be engaged in construction or say an average of 500 pounds per day for an average set of activity levels. Before they arrive, I would expect there to be a 3 year supply of food on hand, which calculates to 547,500 pounds of food. Add in the base building advance party of maybe 20 to 50 workers, there's another supply/logistics problem of having 273,750 more pounds stockpiled. His interplanetary transport system is going to be busy bringing food, much more so than additional colonists. Some SERIOUS WORK  needs to be accomplished before massive colonization begins. There's a distinct need for a serious agriculture base before overloading the system with more mouths.

As I mentioned in another post--an initial exploration party of 7 is ideal; enough hands to get something done, and not just wandering around doing science. Need to begin the agricultural experiments with a wide variety of test crops in a smallish greenhouse, and get some serious structures capable of shielding from Solar flares. Finding and developing a reliable water supply; bringing a small Nuclear reactor on line, etc. Other suggestions of using artificial light for agriculture are nicely discussed in Robert Zubrin's "Entering Space." Too high a power requirement!

Lake Matthew Team - Cole

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Re: Crops

Bullet Time

A greenhouse must be transparent. I suggest PCTFE film, sold under the brand name Clarus, made by Honneywell. It's a fluoropolymer film.

Cool.  Clarus is a great cryogenic polymer. 

I see that PCTFE is used in coatings and containers, but I haven't seen it used as a suspended architectural fabric.  Can you help locate examples?  Or is there some limitation of PCTFE that makes ETFE preferable for greenhouse architecture?

Note: micrometeorites don't reach Mars surface. Regular meteorites will, but micrometeoroids burn up in Mars atmosphere. The burn up about 30km above the surface. On Earth they burn up about 100km above the surface. How deep into the atmosphere depends how large the meteoroid. So an inflatable habitat on Mars doesn't need the micrometeoroid shield of BEAM.

Right, but micrometeorites scale only to 2 mm.  I was focused on the cm-scale iron meteorites, which do penetrate the atmosphere and impact at the speed of... well, of bullets.  That flux is uncertain at present.  Greenhouse "bullet protection" is needed unless/until the bullet flux is found to be too slight to worry about.

Last edited by Lake Matthew Team - Cole (2016-12-28 19:27:21)

Lake Matthew Team - Cole

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Re: Crops

Has anyone here contemplated Elon Musk's proposal of bringing settlers to mars 100 at a batch...?  I would expect there to be a 3 year supply of food on hand, which calculates to 547,500 pounds of food. Add in the base building advance party of maybe 20 to 50 workers, there's another supply/logistics problem of having 273,750 more pounds stockpiled. His interplanetary transport system is going to be busy bringing food...

Well, 30 tons of MREs can get a 100-man crew through 500 days of greenhouse construction, assuming robotics/telerobotics do most of the heavy lifting.  The boring menu would motivate the crew to get the greenhouse ice cream factory up and running asap.

RobertDyck

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Re: Crops

Cool.  Clarus is a great cryogenic polymer. 

I see that PCTFE is used in coatings and containers, but I haven't seen it used as a suspended architectural fabric.  Can you help locate examples?  Or is there some limitation of PCTFE that makes ETFE preferable for greenhouse architecture?

I look at primary material specifications. Tensile strength, bursting strength, etc. It's significantly more expensive than ETFE, but actually strong. PCTFE is also highly UV resistant, primarily because it's transparent to UV. The UV just goes right through without reacting. Its the most impermeable to water of any polymer known to man, and highly impermeable to oxygen. There are other polymer films more impermeable to oxygen, but they won't survive cold of Mars night. You can make film even more impermeable with a metal coating applied through vapour deposition. NASA uses gold, nickel, and silver oxide as coatings on windows of spacecraft and the space station to block UV and control IR. You can buy commercially polymer film with silver oxide applied using NASA's technique. For Mars we would want the entire coating, with gold and nickel to control UV. That metal coating, literally so thin you can see through it, clogs pours in the polymer film making it more impermeable. So it basically doesn't leak air.

It controls IR because it's spectrally selective. For a cold environment such as Mars, you want the film to keep heat in. That's done by reflecting more long-wave IR which comes from warm objects such as the floor, or furniture, or plant beds. It reflects less short-wave IR which comes from extremely hot things such as the surface of the Sun.

I had intended to set up a material exposure experiment at MDRS in Utah. I have 8.5"x11" samples of PCTFE, ETFE, and Teflon FEP, in 2 mil and 5 mil thicknesses. I intended to put them in picture frames, set them up outdoors at an angle so rain can run off but it will be exposed to sunlight. Had financial trouble and vehicle trouble, haven't been able to make it out. However, I have the polymer film samples on a shelf behind me as a type this.

Right, but micrometeorites scale only to 2 mm.  I was focused on the cm-scale iron meteorites, which do penetrate the atmosphere and impact at the speed of... well, of bullets.  That flux is uncertain at present.  Greenhouse "bullet protection" is needed unless/until the bullet flux is found to be too slight to worry about.

Sprit, Opportunity, and Curiosity have found a total of 1 meteorite sitting on the surface of Mars. They didn't see it fall, it was already there. That doesn't sound like a shooting gallery to me.

SpaceNut

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Re: Crops

I did a quick search on Greenhouse and ended up with 15 pages of topics where we meantion them... but here are some of those links.

As you can see we do drift quite a bit and some of the time I can get us back on topic and other times not so much...

We seem to be crossing some of the same old ground for some of the last few posts, so here are some of the topics which discuss these items.

Material Choices for Mars

Mars Needs Nitrogen

starving on five acres

Pyramid Greenhouse

Greenhouse

Growing Plants on Mars

Food! - Marsians=vegetarians?

Designing the best greenhouse demonstrator for Mars

Aerogel - don't build - your greenhouse w/o it

Greenhouse - hydroponics vs soil

Lake Matthew Team - Cole

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Re: Crops

Sprit, Opportunity, and Curiosity have found a total of 1 meteorite sitting on the surface of Mars. They didn't see it fall, it was already there. That doesn't sound like a shooting gallery to me.

? Oh, they found more than that. 

Besides, it's not easy to find a cm iron meteorite in a pebble field.  Just looking at the photos, how can we tell which pebble is a bullet in disguise? 

But surely I'm OT at this point.  Can we talk about greenhouse cheese, chard and calcium again?  I'd like to integrate NMF improvements into our notional LMT greenhouse; and scale it not merely for self-sufficiency, but even for a stockpile of excess production.  Stockpiling allows us to consider "local food provisioning", or delivery, to all expeditions planet-wide.

Last edited by Lake Matthew Team - Cole (2016-12-28 23:40:59)

SpaceNut

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Re: Crops

Another topic suggestion area for soil type and conditioning for agriculture:

Soil Manufacture on Mars
Sewage treatment
Building Soil with Salt Marshes
Building soil
Mars regolith analog

Lake Matthew Team - Cole

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Re: Crops

Known Unknowns, Etc.

Another topic suggestion area for soil type and conditioning for agriculture:

Soil Manufacture on Mars
Sewage treatment
Building Soil with Salt Marshes
Building soil
Mars regolith analog

There are some very creative ideas in those threads.  Focusing on soil, I find that many of the creative ideas for soil manufacture seem to introduce more unknowns than they remove.  For example, the idea of blending waste streams into the soil could introduce unpredictable fluctuations in toxins, microbes, pH and nutrient loads.  On Earth, soil microbes are diverse and abundant, and their metabolisms help the soil manage fluctuations.  But on Mars, most of the beneficial soil microbes would be absent unless explicitly cultivated.  Perhaps fluctuations could be managed by the greenhouse crew, but it would seem to be a worrisome job.  It's just more unknowns.

Hydroponics removes unknowns by simplifying the soil down to an inert substrate, such as pH-neutral rinsed sand.  In a greenhouse with ISRU fertilizer, sterile nutrients are added in a controlled manner, again removing unknowns.  A microbiome isn't required and can be suppressed, to remove even more unknowns.  For example, a plasma nitrate plant makes hydrogen peroxide as a byproduct.  That hydrogen peroxide is added to the liquid nitrate fertilizer to kill off soil pathogens without harming the plants.   (Conceivably this treatment could remove a further unknown:  hypothetical Mars exo-pathogens.  Microbes evolved under martian anoxic conditions really shouldn't like sudden peroxide oxygen baths.)

To my mind the removal of unknowns is a main reason to aim for a hydroponic greenhouse, one having no more organic matter in the substrate than may be necessary for water retention.  A little cellulose could be adequate.

But am I missing something?  Is there good reason to convert sand substrate into a soil that's rich in organics, microbes, worms, etc., in this unique circumstance?

Last edited by Lake Matthew Team - Cole (2016-12-29 18:52:23)