The compelxities of extra-terrestrial farming

[Thor Wotansen]

One thing that has always bugged me in discussions about colonizing the moon or Mars is the casual way everyone overlooks the growing of food.  I have a fairly well rounded background in agriculture, and I have spent a lot of time learning about the complex symbioses that a lot of plants depend on to survive.  I know that NASA has been growing salad greens and some types of wheat in a very small experimental area on the ISS, but I don't think it's enough to get a good picture of what agriculture will look like on space colonies. 

First of all, any system that has colonists reliant on it for sustenance must be 99% sustainable at a minimum.  NASA's experiments have been very closely monitored with sensors giving real-time data on all sorts of parameters to a team back on Earth, and the most they've gotten out of it is a few salads.  For a serious system, it has to be somewhat robust, and able to handle some shocks and variation to conditions.  It also needs to be able to reprocess all the wastewater produced by the colonists in a safe and efficient manner.  These things are very possible to achieve, but they do present some challenges.  Growing food is maybe one of the easier ones to handle.  The most logical solution, in my mind, is aquaponics.  Aquaponics is like hydroponics, but with fish.  Turns out that fish poop has pretty much everything plants need to grow, and the plants are great at filtering the water for the fish.  This means you only have to figure out how to feed the fish.  Initially, formulating food for the fish might require some supplemental nutrients, but over time, it should be possible to stabilize the intake/output of the various micro-nutrients in the system.  Probably the best species of fish to use is Blue Nile Tilapia, a fast growing breed used around the world in commercial fish farms.

The other challenge to the system is processing the human poop.  If composted properly, human waste makes a fantastic fertilizer for plants, but it is illegal to use human waste for growing food crops in the US.  This is due to the possibility of spreading disease via unwashed vegetables.  This can be avoided in our application, since we aren't growing our plants in soil.  We can, however, reduce the possibility of spreading disease by using human waste to grow things like cereal grains and even fruit trees.  The cereal grains can be used to formulate food for the fish, as well as for things like bread or beer.

Obviously, setting up a self-sufficient system like this will require a large enough population to support it, but the advantages are many.  Fore one, you won't have to have carbon scrubbers, since the plants will easily take care of that.  Another aspect is the psychological benefits of having green things growing about the base.  One of the largest challenges, however, will be maintaining healthy populations of bacteria in the system.  Here on Earth, bacteria do a lot of the work in the treatment of wastewater, and in converting waste from both fish and humans into nutrients plants can use.  These bacteria are everywhere on Earth, and can be relied on to just show up and start growing where conditions are favorable, but on an off world base, we'll have to bring our own.  This could be extremely challenging, due to the high radiation environment in space, and any system on a moon or Mars base will have to be buried deep underground to protect it from radiation.  There is also the potential issue of symbiotic organisms that are present here on Earth, that could affect how various plants in the system grow, or don't grow.  It is also likely that we will have to introduce some species of insects into the ecosystem to pollinate plants for us.  We might also bring earthworms and other species that help decomposition, so we can compost things like food scraps, plant fibers, and solids that settle out of the various wastewater systems.  Worms would make great food for the fish, and they are excellent at breaking down fibrous materials.  As you can see, the biodiversity of a sustainable life support system is immense and complex, and certainly not possible in a sterile space station.  Sure, you could grow only certain plants and feed them with chemical fertilizer, but this would be very difficult to make self-sufficient.

Anywho, I'd love to hear other folk's thoughts on the topic, this is just what's been rattling around in my head for a few years now.  I'm currently thinking about going to school for engineering and soil science, either as a double major, or minoring in soil science with an engineering major.  I've seen little to no discussion of the actual mechanics of "just growing food in greenhouses" and I'm hoping I can kick off a bit of discussion on the topic.  I suspect that a lot of the folks into rockets and space travel aren't really into the sustainable farming movement, and vice versa, which might be why the topic is so often dismissed as a triviality or just glossed over by enthusiastic future Martians.

[Bill Phil]

Actually this is something I think about a lot for space colonization.

Interestingly some of the best literature on space farming comes from research into orbital space colonies. You should look into that. I can’t link anything right now (on mobile) but there is a lot of good stuff.

Since water is so important I’ve seen recommendations to use aeroponics whenever possible. The whole system is lighter than hydroponics (important for space colonization) and can actually have pretty great yields. 

If you’re already growing fish then aquaponics makes sense. However if we manage to mature cultured meat technology and apply it to fish then growing fish won’t be strictly necessary. Of course not every plant is great for aeroponics but it seems like it can work well.

I managed to find this link:

https://space.nss.org/colonies-in-space-chapter-9-up-on-the-farm/

This is a description of how ten thousand space colonists could be fed - though I’m not fully sure if the numbers work out. I think the proposal is to feed ten thousand people with 100 acres - might be possible with high yields, full year growing season, optimized environment, and so on. But it may be tough. Going vertical might free up more area as well.

There’s other stuff as well. I suggest giving it a good read through.

[Spacescifi]

2 hours ago, Bill Phil said:

Actually this is something I think about a lot for space colonization.

Interestingly some of the best literature on space farming comes from research into orbital space colonies. You should look into that. I can’t link anything right now (on mobile) but there is a lot of good stuff.

Since water is so important I’ve seen recommendations to use aeroponics whenever possible. The whole system is lighter than hydroponics (important for space colonization) and can actually have pretty great yields. 

If you’re already growing fish then aquaponics makes sense. However if we manage to mature cultured meat technology and apply it to fish then growing fish won’t be strictly necessary. Of course not every plant is great for aeroponics but it seems like it can work well.

I managed to find this link:

https://space.nss.org/colonies-in-space-chapter-9-up-on-the-farm/

This is a description of how ten thousand space colonists could be fed - though I’m not fully sure if the numbers work out. I think the proposal is to feed ten thousand people with 100 acres - might be possible with high yields, full year growing season, optimized environment, and so on. But it may be tough. Going vertical might free up more area as well.

There’s other stuff as well. I suggest giving it a good read through.

 

Even if we can make a lot of food, probably a deciding factor on colonization is whether or not it tastes good.

 

I just do not see people lining up to go to space habitats en mass knowing full well they will be eating the same meal for weeks/months on end. Not for fun anyway. Only for professionals.

Edited October 8, 2019 by Spacescifi

[Bill Phil]

56 minutes ago, Spacescifi said:

 

Even if we can make a lot of food, probably a deciding factor on colonization is whether or not it tastes good.

 

I just do not see people lining up to go to space habitats en mass knowing full well they will be eating the same meal for weeks/months on end. Not for fun anyway. Only for professionals.

Did you read the link?

You can get a pretty wide selection of food - probably better quality than most food on Earth too.

[Thor Wotansen]

51 minutes ago, Spacescifi said:

 

Even if we can make a lot of food, probably a deciding factor on colonization is whether or not it tastes good.

 

I just do not see people lining up to go to space habitats en mass knowing full well they will be eating the same meal for weeks/months on end. Not for fun anyway. Only for professionals.

That exactly the point of space farming.  With an aquaponics system, it is possible to grow everything from lettuce and spinach, to things like ginger and sweet potatoes, and everything in between.  You could easily incorporate things like chickens and rabbits into the system for eggs and meat (rabbits are one of the most feed efficient sources of meat, as well as having almost entirely fat free meat).  With a large enough colony, you could incorporate goats into the system for milk, and start making things like cheese and yogurt.  Any crop you can grow here on earth, you could grow in a fairly simple space farm.  In fact, I would hazard a guess that in a hundred years, life expectancy will be higher on Moon and Mars colonies simply due to a better diet and cleaner air, as well as possibly reduced radiation exposure, since we'll be building mostly under ground, and Earth has had a few nuclear accidents that have done a great job of distributing radioactive materials throughout the biosphere.

[Nothalogh]

3 hours ago, Thor Wotansen said:

One thing that has always bugged me in discussions about colonizing the moon or Mars is the casual way everyone overlooks the growing of food.  I have a fairly well rounded background in agriculture, and I have spent a lot of time learning about the complex symbioses that a lot of plants depend on to survive.  I know that NASA has been growing salad greens and some types of wheat in a very small experimental area on the ISS, but I don't think it's enough to get a good picture of what agriculture will look like on space colonies. 

First of all, any system that has colonists reliant on it for sustenance must be 99% sustainable at a minimum.  NASA's experiments have been very closely monitored with sensors giving real-time data on all sorts of parameters to a team back on Earth, and the most they've gotten out of it is a few salads.  For a serious system, it has to be somewhat robust, and able to handle some shocks and variation to conditions.  It also needs to be able to reprocess all the wastewater produced by the colonists in a safe and efficient manner.  These things are very possible to achieve, but they do present some challenges.  Growing food is maybe one of the easier ones to handle.  The most logical solution, in my mind, is aquaponics.  Aquaponics is like hydroponics, but with fish.  Turns out that fish poop has pretty much everything plants need to grow, and the plants are great at filtering the water for the fish.  This means you only have to figure out how to feed the fish.  Initially, formulating food for the fish might require some supplemental nutrients, but over time, it should be possible to stabilize the intake/output of the various micro-nutrients in the system.  Probably the best species of fish to use is Blue Nile Tilapia, a fast growing breed used around the world in commercial fish farms.

The other challenge to the system is processing the human poop.  If composted properly, human waste makes a fantastic fertilizer for plants, but it is illegal to use human waste for growing food crops in the US.  This is due to the possibility of spreading disease via unwashed vegetables.  This can be avoided in our application, since we aren't growing our plants in soil.  We can, however, reduce the possibility of spreading disease by using human waste to grow things like cereal grains and even fruit trees.  The cereal grains can be used to formulate food for the fish, as well as for things like bread or beer.

Obviously, setting up a self-sufficient system like this will require a large enough population to support it, but the advantages are many.  Fore one, you won't have to have carbon scrubbers, since the plants will easily take care of that.  Another aspect is the psychological benefits of having green things growing about the base.  One of the largest challenges, however, will be maintaining healthy populations of bacteria in the system.  Here on Earth, bacteria do a lot of the work in the treatment of wastewater, and in converting waste from both fish and humans into nutrients plants can use.  These bacteria are everywhere on Earth, and can be relied on to just show up and start growing where conditions are favorable, but on an off world base, we'll have to bring our own.  This could be extremely challenging, due to the high radiation environment in space, and any system on a moon or Mars base will have to be buried deep underground to protect it from radiation.  There is also the potential issue of symbiotic organisms that are present here on Earth, that could affect how various plants in the system grow, or don't grow.  It is also likely that we will have to introduce some species of insects into the ecosystem to pollinate plants for us.  We might also bring earthworms and other species that help decomposition, so we can compost things like food scraps, plant fibers, and solids that settle out of the various wastewater systems.  Worms would make great food for the fish, and they are excellent at breaking down fibrous materials.  As you can see, the biodiversity of a sustainable life support system is immense and complex, and certainly not possible in a sterile space station.  Sure, you could grow only certain plants and feed them with chemical fertilizer, but this would be very difficult to make self-sufficient.

Anywho, I'd love to hear other folk's thoughts on the topic, this is just what's been rattling around in my head for a few years now.  I'm currently thinking about going to school for engineering and soil science, either as a double major, or minoring in soil science with an engineering major.  I've seen little to no discussion of the actual mechanics of "just growing food in greenhouses" and I'm hoping I can kick off a bit of discussion on the topic.  I suspect that a lot of the folks into rockets and space travel aren't really into the sustainable farming movement, and vice versa, which might be why the topic is so often dismissed as a triviality or just glossed over by enthusiastic future Martians.

Raising fish is probably going to be the best resource cost to nutrient value tradeoff.

[YNM]

2 hours ago, Thor Wotansen said:

Rabbits are one of the most feed efficient sources of meat, as well as having almost entirely fat free meat.

You don't want to have protein poisoning though.

2 hours ago, Nothalogh said:

Raising fish is probably going to be the best resource cost to nutrient value tradeoff.

One of the problem with fishes is just the amount of water that they need. Plus we don't know whether they still work on reduced gravity or not.

Although it's possible to create a fish-hydro/aeroponic closed loop - there are installations on Earth that works this way already.

3 hours ago, Spacescifi said:

Even if we can make a lot of food, probably a deciding factor on colonization is whether or not it tastes good.

If ISS foods are any indication, the solution is to simply make everything more intense than usual. Seasoning helps to that. They're mostly chemicals as well, so you can produce them through other means.

Edited October 9, 2019 by YNM

[Nothalogh]

11 minutes ago, YNM said:

Seasoning helps to that

The millennia old human tradition, hide poor ingredients with overpowering seasoning.

[Thor Wotansen]

25 minutes ago, YNM said:

One of the problem with fishes is just the amount of water that they need. Plus we don't know whether they still work on reduced gravity or not.

Although it's possible to create a fish-hydro/aeroponic closed loop - there are installations on Earth that works this way already.

The cool thing about fish is that they don't care about gravity, they already live in what is effectively a 0G environment.  We know that gravity is necessary for some stages of fetal development, and I assume the same is true for fish, but for the most part, they should do fine in low G.

[YNM]

1 hour ago, Thor Wotansen said:

The cool thing about fish is that they don't care about gravity, they already live in what is effectively a 0G environment.

The water cares about gravitation, however. You don't want the water the fish lives in suddenly separates off the fish.

1 hour ago, Nothalogh said:

The millennia old human tradition, hide poor ingredients with overpowering seasoning.

Or make sure you're "indulged" enough...

Edited October 9, 2019 by YNM

[cubinator]

I want to see how well insects can be grown in space. With luck I will get back to you on that next year with some concrete information about feed mass and yield. We already know they are nutritious and efficient, but it seems no one has designed a farm unit for the task. No actual research on this application has gone further than nutrition value and "yep, insects are a good food choice for Martians."

[Spacescifi]

Just now, cubinator said:

I want to see how well insects can be grown in space. With luck I will get back to you on that next year with some concrete information about feed mass and yield. We already know they are nutritious and efficient, but it seems no one has designed a farm unit for the task. No actual research on this application has gone further than nutrition value and "yep, insects are a good food choice for Martians."

 

Yuck. Count me in on space travel the day we have the means to shorten the time scale enough that imported food will be enough.

When or if we get warp/FTL/jump drives, even intetstellar restaurant malls/stations could have imported food. Which is easier than keeping critters and beasts alive in an environment that they utterly fail to live healthy in.

[IncongruousGoat]

6 hours ago, Thor Wotansen said:

This could be extremely challenging, due to the high radiation environment in space, and any system on a moon or Mars base will have to be buried deep underground to protect it from radiation.

Is this accurate, though? I was under the impression that bacteria are A: much hardier than we are when it comes to radiation, and B: so prolific that any losses in population caused by radiation will be quickly replaced. And as for bringing them over, isn't it enough to just bring a few crates of dirt?

[cubinator]

32 minutes ago, Spacescifi said:

Yuck. 

Don't bash it until you've tried it. You don't have to eat it alive, there are countless ways to cook and prepare them into delicacies.

[Bill Phil]

4 hours ago, Thor Wotansen said:

In fact, I would hazard a guess that in a hundred years, life expectancy will be higher on Moon and Mars colonies simply due to a better diet and cleaner air, as well as possibly reduced radiation exposure, since we'll be building mostly under ground, and Earth has had a few nuclear accidents that have done a great job of distributing radioactive materials throughout the biosphere.

I don't know about better life expectancy on the Moon and Mars. Earth will remain the most developed place in the solar system for quite some time. Though this can change over time, as it always does. 

Actually the slight increase in radiation could be beneficial, if the hormesis model has any weight behind it...

I don't really think solid bodies like the Moon and Mars are suitable for settlement. Sure it could be done but we're talking about places that are far away (in the case of Mars, this is true both in terms of distance and energy, but mostly true just in the case of energy for the Moon - but it has low gravity which could be problematic). Similar to how Antarctica isn't inhabited, I doubt the Moon and Mars will be anytime soon. It will probably happen eventually (and who knows? maybe Musk's crusade to colonize Mars will actually bear fruit...) but likely after some time. Research facilities will likely be established - but orbital settlements are so advantageous that planets and moons look pretty lackluster in comparison. The biggest advantage is probably ease. If we were to do an analysis of settlements on the Moon, Mars, and in orbital space (specifically Equatorial Low Earth Orbit (or ELEO) for now, but eventually we might be able to dispel the Van Allen radiation belts - freeing up a lot more orbital real estate...) we would likely find that the mass requirements for a given population size are pretty close - this is because the Moon and Mars settlements can use local regolith as radiation protection and the radiation doses in ELEO are actually pretty mild - as well as life support mass likely scaling with population more directly than other factors. However - the energy and logistical requirements requirements would be far different. The largest object ever landed on Mars is about 1 tonne (Curiosity). The largest on the Moon is about 15 tonnes (Apollo LM). But the largest in LEO? Over 400 tonnes (ISS). Of course SpaceX might be able to change the game a bit but it seems like it'd be far easier to build a settlement in ELEO than anywhere else. Eventually the industry for building settlements can mature and extraterrestrial resources can be acquired to provide shielding (provided some kind of powered shielding method isn't developed - there are some ideas for this), expanding the locales where settlements can be built. There's an entire asteroid belt, Kuiper Belt, and Oort Cloud out there...

[kerbiloid]

First of all, we should decide, is it about zero-G farming (then the whole agriculture is unviable unless it's algae and cultured meat), or a Martian base with gravity.

***

To feed tilapia we can pet mosquitoes. They will eat the crew and drop their eggs into water.
And once per season sacrifice to them the lowest KPI labourer during the country harvest festival.

Otherwise we need some another source of food for tilapia because even organic wastes don't appear themselves.
Does a rice field with tilapias exist anywhere without other plants and animals? At least, the buffalos.

***

Rabbits are probably one of the worst choices as they are highly volatile. They appear and disappear like an eared locust.
Something more predictable is required for a semi-closed ecoloop.

***

Human feces would be the least component of the ecosystem because a food pyramid has ~10:1 ratio of biomass between stages.
So, the human biomass would be just several percent of the total biomass, and its waste is much easier to burn in oxygen converting into water, carbon dioxide, then to carbamide.
Anyway there is a lot of other wastes to cremate in such base.

***

Also we should remember that the smaller is the beast (rabbit, tilapia, hen, etc), the more it gorges relative to its mass.
The smallest of them eat more per day than they mass themselves.
So, small creatures are less effective.

***

10 hours ago, Bill Phil said:

https://space.nss.org/colonies-in-space-chapter-9-up-on-the-farm/

Spoiler

The productivity of wheat and grains can be exceeded by vegetables. The best yields for vegetables commercially grown come from greenhouses in the desert of Abu Dhabi:

vegetables	lbs. per acre per day
tomatoes	920
cucumbers	1000
cabbage	530
radishes	560
broccoli	315

No more questions to that article. NSS writers want to eat.

 

Edited October 9, 2019 by kerbiloid

[YNM]

2 hours ago, Bill Phil said:

but orbital settlements are so advantageous that planets and moons look pretty lackluster in comparison.

Complex biological life seems to not last very well in microgravity, however. True that from logistics they make sense, it's just that the payload is quite needy here.

Edited October 9, 2019 by YNM

[DDE]

9 hours ago, Spacescifi said:

Only for professionals.

As if everyone will be scrambling for all the other aspects of life in the void.

12 hours ago, Thor Wotansen said:

For a serious system, it has to be somewhat robust, and able to handle some shocks and variation to conditions.

Apparently, one serious factor is just making it big enough. The smaller systems will be a lot more vulnerable to shocks.

12 hours ago, Thor Wotansen said:

it is illegal to use human waste for growing food crops in the US.  This is due to the possibility of spreading disease via unwashed vegetables.

Given how space colonies are already ultra-conducive to the spread of all infections, this is probably a marginal factor.

12 hours ago, Thor Wotansen said:

Initially, formulating food for the fish might require some supplemental nutrients, but over time, it should be possible to stabilize the intake/output of the various micro-nutrients in the system.

From what I understand, it will be very difficult to ever take the colonists off of imported vitamin/microelement supplements. Probably true for the fish as well.

Edited October 9, 2019 by DDE

[DDE]

12 hours ago, Thor Wotansen said:

These bacteria are everywhere on Earth, and can be relied on to just show up and start growing where conditions are favorable, but on an off world base, we'll have to bring our own.  This could be extremely challenging, due to the high radiation environment in space, and any system on a moon or Mars base will have to be buried deep underground to protect it from radiation. 

Thus far, the answer has been to be prepared to purge and sterilize the entire system if a bacterium mutates significantly. This answer is primarily concerned with the tendency of natural algae to abruptly start producing nerve gas.

[kerbiloid]

Spoiler

10 minutes ago, DDE said:

This answer is primarily concerned with the tendency of natural algae to abruptly start producing nerve gas.

If those silly algae produced a psychoactive gas instead, they could spread around much faster.
That's an importance of thinking positive.

 

Edited October 9, 2019 by kerbiloid

[DDE]

2 hours ago, kerbiloid said:

If those silly algae produced a psychoactive gas instead, they could spread around much faster.

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

[kerbiloid]

7 minutes ago, DDE said:

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

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

[Thor Wotansen]

@kerbiloid and @YNM I'm assuming some gravity or facsimile thereof.

4 hours ago, kerbiloid said:

To feed tilapia we can pet mosquitoes. They will eat the crew and drop their eggs into water.

And once per season sacrifice to them the lowest KPI labourer during the country harvest festival.

Otherwise we need some another source of food for tilapia because even organic wastes don't appear themselves.
Does a rice field with tilapias exist anywhere without other plants and animals? At least, the buffalos.

***

Rabbits are probably one of the worst choices as they are highly volatile. They appear and disappear like an eared locust.
Something more predictable is required for a semi-closed ecoloop.

***

Human feces would be the least component of the ecosystem because a food pyramid has ~10:1 ratio of biomass between stages.
So, the human biomass would be just several percent of the total biomass, and its waste is much easier to burn in oxygen converting into water, carbon dioxide, then to carbamide.
Anyway there is a lot of other wastes to cremate in such base.

***

Also we should remember that the smaller is the beast (rabbit, tilapia, hen, etc), the more it gorges relative to its mass.
The smallest of them eat more per day than they mass themselves.
So, small creatures are less effective.

***

 

The entire system is a closed loop, with the only inputs and outputs being the humans traveling and whatever their digestive tracts contain, once it has fully matured. 

Growing insects to supplement the fishes diet is a good idea, but I'd be more inclined to grow something like crickets or ants, that can live off of agricultural byproducts or food scraps.  Flys are also a good option. 

Rabbits are quite dependable when kept as livestock in a controlled space.  Breeding and raising rabbits for food is already quite common in some health food circles, and it certainly isn't hard to encourage them to reproduce.  Their low individual food needs are also a plus if the system gets shocked to a point of near failure.  You could butcher all but a few breeding pairs and keep those few fed on stored feed until the crops can catch back up.

Human waste is pretty analogous to what is eaten as food, mass wise.  Burning that waste is a potential way to get rid of it, but using it as fertilizer for further crops seems like a better option in my mind.  Once a sustainable system is set up, the rate of growth of plants and animals will be fairly constant, since you'll want to be harvesting every day, and presumably pooping on a similar frequency.  There might be an eventual need to add some biomass to the system, as a population grows by having babies, but that could also be accomplished by adding raw or processed regolith, after determining it's mineral content.

Yes, smaller animals do eat more of their body mass every day, but remember, they also poop more of their body mass every day.  In general, small creatures like fish and rabbits are actually more efficient at converting a given quantity of calories into meat or milk.  They also reach harvesting age much faster, so they provide a much quicker return on the calories, and also don't tie up tons of biomass over a long growing period.  Dairy cows, for instance, require roughly ten times the food as dairy goats, but only produce four times the milk.  They also take longer to reach maturity and generally weigh around 1000lbs, making them a significant concentration of calories that you can't tap into.  For rabbits, they are happy eating mostly grass or other leafy things, and reach harvesting age in a matter of a couple months.  Fish are actually the most impressive meat animal, since they have the highest percentage of body mass usable as food, since each fish is mostly just one huge swimming muscle with some bits to keep it working.

6 hours ago, Bill Phil said:

Research facilities will likely be established - but orbital settlements are so advantageous that planets and moons look pretty lackluster in comparison. The biggest advantage is probably ease. If we were to do an analysis of settlements on the Moon, Mars, and in orbital space (specifically Equatorial Low Earth Orbit (or ELEO) for now, but eventually we might be able to dispel the Van Allen radiation belts - freeing up a lot more orbital real estate...) we would likely find that the mass requirements for a given population size are pretty close - this is because the Moon and Mars settlements can use local regolith as radiation protection and the radiation doses in ELEO are actually pretty mild - as well as life support mass likely scaling with population more directly than other factors.

I would tend to disagree.  The type of radiation we're concerned about on the moon, Mars and in LEO is the high energy galactic scale radiation.  Producing a magnetic field strong enough to repel the ionizing particles in solar radiation isn't too demanding, compared to the kind of field you'd need to protect from the galactic scale stuff.  Here on Earth, the atmosphere and it's ~100km of mass between space and us does a great job of intercepting the worst of it, but on the moon of Mars, we'd have half a sky raining radiation on us at roughly twice the level of the surface of Earth.  The only way to really stop this is with a large mass of something.  Hydrogen works the best, making water a good candidate, but on a planet or moon, you can bury your habitat under a few meters of regolith and be pretty safe.  If you're building an orbital habitat, that mass will have to come from somewhere, and there's a good chance it will come from the moon, if you're building around Earth.  Regardless, the same food requirements remain, whether you're on a planetary surface, or in an O'Neil cylinder.  I can certainly see us building massive space habitats with spin gravity and strippers and blackjack, but the first steps are undoubtedly the moon and Mars.  Figuring stuff out there, where you don't have to worry so much about structural support for your massive radiation shield is imperative to doing it for realzies on a fleet of O'Neil cylinders.

[Spacescifi]

1 hour ago, Thor Wotansen said:

@kerbiloid Fish are actually the most impressive meat animal, since they have the highest percentage of body mass usable as food, since each fish is mostly just one huge swimming muscle with some bits to keep it working.

 

 

Almost unrelated, but as a scifi writer I created a humanoid race with sharp teeth. As they enjoyed fresh (live) meat, I found fish to be an optimal choice, since it really is meal size for a humanoid. A whole cow will go to waste. They don't like the taste of cooked meat, but will ironically cook other food groups.

 

As for a space station, I would favor a massive torus. As the crew walks the glass transparent floor as it rotates, they will be amused to see an aquarium beneath them full of fish.

 

EDIT: Not sure anyone has pointed out just how lethal martian soil and lunar regolith is.

Martian soil: Has toxic compounds in it. So unless that stuff is somegow filtered out, I would not suggest eating such crops grown there.

Lunar regolith: Has what amounts to glass in it.

 

Radioactive compounds: No doubt present on the surface of both mars and the moon. Likely in the dirt.

Edited October 9, 2019 by Spacescifi

[kerbiloid]

4 hours ago, Thor Wotansen said:

Flys are also a good option. 

Any flying beast is a bad option, because it spends the food energy for flight as waste heat.

4 hours ago, Thor Wotansen said:

Human waste is pretty analogous to what is eaten as food, mass wise.  B

daily income = 800 g of dry food
daily outcome = 250..300 g of protofertilizer with 50..80% humidity.

Most part of the food mass is exhausted as carbon dioxide and carbamide.
Feces are just what's not digested, they are not a metabolic product.
You can make a food diet which leaves not solid wastes (Apollo space program liked this trick, afaik), but this is unhealthy for the intestines which stay without job.
So, it's still better to burn them into CO₂, N₂, and H₂O together with other toxic wastes, and either turn this into same carbamide, or use as is in the waterponics.

Talking about the urine, as the 1960s experiments demonstrated, it's easier to extract drinkable water from feces than from urine due to solved compounds.
And as the human dry outcome weights a negligible part of the total biomass in such biosphere, the most proper way of their utilization is to filter out the solid part of the toilet total product, evaporate as much water as it's easily possible from the liquid part, electrolyze the post-(urine+feces) water into oxygen and hydrogen (that's how they do in Soviet plant), then either pack the rest into a cylinder and drop it out, or, in case of such big base with ISRU, send to incinerator and burn into simplest compounds.

Will you toilet work without your crop field? No.
Will your crop field keep bringing harvest without your toilet? It won't even notice.
Because the top of food pyramid manages the whole pyramid by head, by decisions, not by stomach. We are smart parasites of the crop field.

4 hours ago, Thor Wotansen said:

Yes, smaller animals do eat more of their body mass every day, but remember, they also poop more of their body mass every day.

They eat more mostly because they require more energy to keep warm and to move. They spend a lot of it as waste heat.
When you are fattening a pig, you don't make it run.

4 hours ago, Thor Wotansen said:

They also reach harvesting age much faster, so they provide a much quicker return on the calories

Rabbit ~170 kcal/100 g of meat.
Pigs and cows ~250..300 kcal/100 g meat.

And now we should compare how much meat can we get from every of them per 1 kg of live meat.

4 hours ago, Thor Wotansen said:

Dairy cows, for instance, require roughly ten times the food as dairy goats, but only produce four times the milk.  They also take longer to reach maturity and generally weigh around 1000lbs, making them a significant concentration of calories that you can't tap into.

Pigs grow very fast, get the edible/killable size in a year and iirc can bring up to ~2.5 t of meat per pigyear in form of fattened piglets.
Cows and goats: females for milking, other useless stuff - for meat (cows - on next year, goats - same year).
Now we can calculate yearly calories of the milk compared to the fishes and rabbits.

Small animals are useful in hot wet climate and small family farms. A semi-looped biosphere can not be scaled down so much, it should by definition be town-sized.
So, a herd of cows beats the horde of rabbits.

Edited October 9, 2019 by kerbiloid