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.