Scaling Agriculture on Mars

[Twark_Main]

Can we situate greenhouses underground for better temperature insulation and pressurization, and just pipe in the light from the surface above? What's wrong with that?

Oh, this is a cool one!

Nothing wrong with it, but we're limited by something called Conservation of Etendue.

https://en.wikipedia.org/wiki/Etendue

https://what-if.xkcd.com/145/

It says, essentially, that you can't use optics to "funnel down" light brighter than the surface it came from (minus any atmospheric/optics loss). This isn't a huge problem for the beam sunlight itself, but it means you can't shrink down the diffuse "sky glow" and pipe it through a small window. Since Mars averages 50% diffuse sunlight, this means you're losing a lot of potential sunlight.

Also the high concentration systems use solar trackers, so for a huge sunlight collection area that means a huge added cost. Since you're going to need a lot of area, I expect a simple transparent cylinder combined with modest (2-3x) fixed concentration is the way to go.  YMMV

Mushrooms already grow in caves, and we could perhaps start out with these on Mars too. Later, we'd just figure out how to bring in light from above, for other crops.

Sure. You don't need intense sunlight for mushrooms (regular indoor office lighting is fine), so that doesn't need a greenhouse or an LED grow room. But mushrooms don't create new biomass from CO2 or create breathable oxygen (like plants), they "only" convert inedible biomass like wood chips into edible biomass.

This is super useful, and we should expect literal tons of mushroom farming on Mars actually. Just bear in mind it isn't functionally substitutable for photosynthetic plants.

[spacenut]

As mentioned, insulating underground is fine with LED grow lights.  Solar panels on the surface to make power. 

There are greenhouses today on the surface that use the sun, but LED grow lights at night.  Growing time is almost cut in half, so more crops can be produced than normal once a year farming. 

Also, as a side note, many egg producing chicken houses turn lights on about mid-night and he chickens lay another egg.  They turn the lights off around 2am.  So the egg layers sometime lay two eggs a day. 

Lots of ways to grow food on Mars until Mars in terraformed.  Greenhouses above ground an underground will be the norm. 

[Twark_Main]

As mentioned, insulating underground is fine with LED grow lights.  Solar panels on the surface to make power.

As mentioned...

If you do have natural light greenhouses (vs if LED indoor farms "win"), I expect that for economic reasons they would ...

... I'm not sure if natural light greenhouses can "win" engineering-wise and economically.  Personally I consider it to be still an open question. But if it can be done, that's (roughly) what it's going to look like IMO.

Fairly answering the question involves doing your best job to design the best natural-light greenhouse, and the best LED solar photovoltaic indoor farm, and then see which option is cheaper/faster/better. If you just throw up your arms and say "I see a problem so it must be that B is better," then you never really know which option was actually better. I think it's important to try just as hard on both designs, at least for such major top-level decisions.

There are greenhouses today on the surface that use the sun, but LED grow lights at night.  Growing time is almost cut in half, so more crops can be produced than normal once a year farming. 

If it's so economical why don't all greenhouses do it?   


One of the problems with doing this on Mars is that you don't have solar power at night. One of the major economies of using LED grow lights on Mars is that you don't really need to supply batteries to smooth out the day/night demand curve. This is nice because grow rooms take a lot of power, so this saves you a lot of batteries.

Greenhouses above ground an underground will be the norm.

Could be!  I won't be assigning high confidence to either solution.

Note that technically "greenhouses" use natural lighting and "indoor farms" use LED lighting.

[Twark_Main]

One other major design variable (almost "too obvious to think about") is the diameter of your transparent greenhouse tubes.

We may picture large tubes big enough for a man to walk through, but what if you instead use small ("polytunnel" size) tubes just big enough for the plants?

A 2-liter bottle (made of an inexpensive PET polymer that naturally resists UV) can hold 12 atmospheres, so if we reduce that safety factor down to 2.5x then we can expand the diameter to over 12" without increasing the wall thickness. This becomes a good rule-of-thumb: every 12" in diameter you need one additional thickness of a 2-liter bottle. Naturally you wouldn't actually use the exact same plastic composition, but this gives us a rough estimate.

Obviously if we minimize the thickness of the transparent wall, this also minimizes the resources required per unit of natural light collected. Air handlers (the same equipment you'd use in any other design) feed air in on one end of the long tube and pick it up on the other end. Robot tele-handlers can easily ride along inside the tube for maintenance and harvesting, and you'd almost certainly use robots in any other design too because human labor is so expensive to maintain on Mars.

[guckyfan]

I was thinking, have the tubes filled partly with water and the plant trays swim in them. That way they can float by a processing station with little effort.

[Solarsail]

If a 12" thin plastic tube really is a viable Mars pressure vessel for plant growth, then I am impressed & inspired into a few ideas:

1)   A lot of my technological speculation for the last year (off this site) has leveraged mini-trains rolling on very small track gauges.  Perhaps, instead of keeping soil still inside a pipe and trying to fit a harvesting robot in the remaining space...  We could move the potted soil on mini-trains!  A little bit alike hydroponic trays.  Any time you want to touch the plants, you pull them out of their sun-lit tube and into a space where humans or large robots can work around them.  Having the plants on either tiny trains or floating trays also means that all infrastructure needed to work with individual plants can stay fixed, relative to the moveable plants.  An issue here, is that many common crop plants appear to be quite a bit taller than the diameter of a 12" pipe.

2)   While a lot of online sources seem to be negative about the early-thread prospects of growing Spirulina in outdoor pipes, and feeding that to (specifically) Tilapia...  Many eucaryotic algae species appear to be edible to the Silver Carp.  Eucaryotic algae can flow around in a pipe of water about as easily as cyanobacteria.  I'm not sure if any single-celled eucaryotic algae would be more edible as a staple crop than Spirulina is for us, but at least that is a plausible pairing for feeding fish tanks on sunlit water pipes.

3)   Mars could use Diazotrophic organisms for the nitrogen fixation task, to produce (what I think works as) bio-fertilizer.  Some cyanobacteria might be able to handle Mars-air bubbled directly through water as a source of dissolved CO2 and N2.  Or an organism that fixes nitrogen without producing O2 as a metabolite (anoxygenic photosynthesis)  could grow without being predated on by oxygen-consuming microbes...  I think.

So uh, a question for people more familiar with either biology or agriculture than me:  How compatibly could these work together?  Composting as a way to recover (most) nutrients to the soil, cyanobacteria (or similar) added to the soil for the nitrogen, and moving the soil and plant around in a low-height tray?

[Fake edit] 4)   Could we get anywhere interesting trying to grow macroscopic underwater plants / algae in under water trays, and pulling those through sunlit pipes of water?  Wikipedia thinks that most macro-algae is very high dietary iodine, so we may need to be careful with that.  To disclose a train of thought, A year back I was looking through the animal kingdom for (sedentary, brainless) animals that might preferentially eat phytoplankton....  Apparently ascidiacea ("sea squirts") have very high amounts of iodine in their tissues.  (As well as being a normal filter feeder, eating more zooplankton than phytoplankton.)

[Real edit]  I've also been surprised to read that ascetic acid, found in vinegar, can not only be digested by humans efor useful calories (and only food energy...), it can also be manufactured via industrial processes.  Only example I know of, of non-biological manufacture of useful food molecules.  Maybe that's a useful start to figuring out how to make more complex / useful food molecules?

[Vultur]

[Real edit]  I've also been surprised to read that ascetic acid, found in vinegar, can not only be digested by humans efor useful calories (and only food energy...), it can also be manufactured via industrial processes.  Only example I know of, of non-biological manufacture of useful food molecules.  Maybe that's a useful start to figuring out how to make more complex / useful food molecules?

Acetic acid is far from the only molecule with calorie value that can be produced artificially. Here's one for ethanol
https://www.nature.com/articles/srep34670
Indeed very complex food molecules have been lab synthesized. But these processes are often really complex and not terribly efficient (if there are many steps and each step is even a little less than 100%...) The total synthesis of vitamin B12 is pretty crazy for example. Even apparently very simple things, like glucose + fructose = sucrose, can be tricky and unimpressive in efficiency: https://pubs.acs.org/doi/10.1021/cen-v078n039.p052

So there's no way it would make sense to separately, artificially synthesize all of the many complex components of food.

However, on Mars there might be some role for artificial production of a few much more chemically simple components using solar power and CO2/H2O/CH4. But it'd be a supplement, not a primary source.

[Robotbeat]

Synthesize glucose. Synthesize ammonia. The rest can be done biologically

[sghill]

Synthesize glucose. Synthesize ammonia. The rest can be done biologically

I can't believe my favorite thread is still alive! I was away from NSF for about a year while I worked on my fertilizer company.

We recently delivered a Plasma Activated Water synthesis device to a hydroponics facility for testing. We have learned some lessons and are integrating a pH raising system. Depending on the results, an unfunded NASA cooperative agreement is next on the punch list.

Here are some photos.

[Robotbeat]

Cool!