The issue of Agri-Worlds

Emperor Tippy

Merchant of Death
Super Moderator
Staff Member
Founder
They work a lot better in fantasy than in Sci-Fi actually. Being fantasy you can throw on all kinds of mystical reasons for agri-worlds. Sci-Fi you just run headlong into the inconvenient fact that O'Neill cylinders in close orbit around the local star are basically better in every way. Well accepting the 40k reason; better political control by the central government over hive worlds.
 

VicSage

Carpenter, Cobbler, Chirugeon, Dataminer.
The O'Niell cylinder concept is good, but for 40k it has the problem of all the metal that would be used is being put into war materiel production. Something like the Quarian liveships might work. The tricky part ironically for doing ship or station borne production is an ironic inversion of the problem I noted with soil depletion. It's the question of "Where are we going to get enough CO2 in order to grow the food in this closed system that we keep removing carbon materials from?"

If you thought your stool was dark before...
I'm told a charcoal cleanse is healthy for you.
 

Captain X

Well-known member
Osaul
Why wouldn't cyber-limbs just be able to draw power from the nervous system since they'd have to be hooked up to it anyway to receive movement commands? Is there not enough power there?
 

VicSage

Carpenter, Cobbler, Chirugeon, Dataminer.
Oh HELL no there's not enough. The nervous system does use some electrical channels, the stimulus is converted into signals that pass along specific neurons to the brain and vice versa. BUT, this is in the millivolt range, and the amperage is even less. The electrical potential of the human nervous system is less than that of a AA cell.
 

Marduk

Well-known member
Moderator
Staff Member
They work a lot better in fantasy than in Sci-Fi actually. Being fantasy you can throw on all kinds of mystical reasons for agri-worlds. Sci-Fi you just run headlong into the inconvenient fact that O'Neill cylinders in close orbit around the local star are basically better in every way. Well accepting the 40k reason; better political control by the central government over hive worlds.
Depends on the economics of it. Just because its doable, doesn't make it the most economically feasible option. Just like we can grow most of crops in a fully controlled greenhouse environment right now, even in parts of Earth that are completely unsuitable for agriculture, we generally don't, because the products are bound to be at several times more expensive than extensive agriculture on open fields.

Putting the fully controlled environment on the orbit doesn't help the costs at all, while already adding half the logistics shared by transporting them from an agri-world. The only thing it helps with is energy for growing crops, which in the grand scheme of things, for a sci-fi civilization with this kind of capabilities is already either cheap (well engineered fusion/fission reactors) or free (the traditional way) on planet surface.

As i said, for sci-fi civilizations the agri-world question is simple - is the cost of growing food on an agri-world plus transporting bulk quantities of food from an agri-world to where it is needed lower than the cost of maintaining artificial environments and infrastructure sufficient for growing the same food where it is needed? If yes, then the option is worth considering (still may or may not get nixed by security considerations and such though).
As such, they are at least potentially feasible for any civilizations who already have a large and functional network of interstellar commercial bulk transport.
 
Last edited:

bintananth

behind a desk
Oh HELL no there's not enough. The nervous system does use some electrical channels, the stimulus is converted into signals that pass along specific neurons to the brain and vice versa. BUT, this is in the millivolt range, and the amperage is even less. The electrical potential of the human nervous system is less than that of a AA cell.
Volts and amps isn't the right way to think of this. Watts are.

Our brains operate at about 12W and are the most metabolically expensive part of our anatomy.* They're also very energy efficient because 12W is about what an LED lightbulb needs.

* Our brains weigh about 3lbs and consume about 12% of our basal metabolic power output when we're just lounging around doing nothing.
 

Bear Ribs

Well-known member
Why wouldn't cyber-limbs just be able to draw power from the nervous system since they'd have to be hooked up to it anyway to receive movement commands? Is there not enough power there?
The body really isn't all that fond of electricity and doesn't use it for power, just to send messages. Energy is generated by the cells individually from sugar, mostly. The body can generate more than sufficient amounts of energy but not electrical energy in the nerves.

Basically like taking a car and needing to drive it. But instead of using the engine for power, you hook up a solar cell to the dashboard lights and then try to run an electric motor off that.
 

Navarro

Well-known member
The O'Niell cylinder concept is good, but for 40k it has the problem of all the metal that would be used is being put into war materiel production.

O'Neill cylinders are only really valuable in a setting without artificial gravity, which the IoM has. Now a decent percentage of its population do live on various ships and space habitats, so many that it was a background in Dark Heresy.
 

Aaron Fox

Well-known member
O'Neill cylinders are only really valuable in a setting without artificial gravity, which the IoM has. Now a decent percentage of its population do live on various ships and space habitats, so many that it was a background in Dark Heresy.
Actually... not really if you go into the nitty-gritty. An ArtGrav station might be considered less efficient in terms of material used than a CentGrav station. It really relies on the technological assumptions of the setting. Hell in my A New World setting has ArtGrav the domain of planet/moon/asteroid-side facilities due to just how inefficient ArtGrav is. Sure the setting has inertia dampening out the wazoo, but like in B5, that's the byproduct in trying to make viable ArtGrav systems. In addition, planets that make good agricultural centers also have free debris defense called the atmosphere. A thick enough atmosphere means you are immune to most space debris and most impactors (at 15km/s or more, your projectile has a tendency to explode right then and there due to atmo-friction).
 

The Unicorn

Well-known member
How long can they be sustained?
Indefinitely.
If it's economic to send billions of tons of food off planet, then they can also import billions of tons of fertilizer then they can ship back billions of tons of natural fertilizer (or a fraction of that if it's desiccated). IIRC Asimov's Tarantor even had that explicitly stated with ships coming to Tarantor laden with food, and leaving fool of fertilizer.

For that matter, asteroid mining for fertilizer would (assuming our system is typical) provide more than 1e15 tons of fertilizer. Even at a billion tons/year that will last for more than 100,000 years before needing to look for other sources.

The problem with Agri-worlds is not that they'd get depleted over time, it's that settings which have them pretty much never have the transport and other economic incentives to justify shipping billions of tons of food to other star systems (for example - StarTrek has the needed transport, but Replicators mean they have no reason to actually transport things like that).

I see Agri-worlds and pretty much any other single-industry world as the sign of a lazy writer. Planets are big and one populated enough to have large scale industry will be largely self-sufficient in terms of basic goods because space travel is neither cheap nor easy.
This, very much this.
There will be some food exported off-world. It'll mostly be part of the regular supply runs to places which don't have sufficient local agriculture (nearby space stations, small outposts, new colonies, &c), expensive luxury items, or disaster relief.
Not really, I'd think mostly it would be luxuries, basically the equivalent of Cavier, Safron(or other spices), cuban cigars, and expensive Champagne or other intoxicants.

It depends on the planetoid.

For example, Jupiter's moon, Titan, receives only 1% of the sunlight the Earth does, so using the surface area of the planet to grow crops would be a waste
Not really. In almost all SF settings the energy to transport food to somewhere like Titan would be less than the energy cost of growing it there (using artificial lighting of course, possibly hydrophonic or vertical farming).
(also the gravity weak enough it can't keep an atmosphere anyway).
Say what? Titan's atmospheric pressure is ~50% higher than earth's.
Agricultural worlds might also make sense if there is interstellar war going on.
Nope. Other way around. They make less sense in war because the last thing you want when you're fighting a war is critical supplies that need to be transported long distances.

Smelting enough steel to produce any given room will in turn release more oxygen than could ever reasonably fill that space.
THis is true on earth because pretty much all iron ore contains oxygen absorbed from the atmosphere. It is not true in most metalic asteroids and I would not assume it's true on [random planetoid]

You also have to look at energy concerns. A major problem with IRL urban farming is how much grow-lights can add to the electric bill, it turns out it's surprisingly hard to compete with sunlight for cost.
THat's when you don't have transport costs. If the urban farming had no, or very low transport costs(i.e if they didn't need to pack things and ship them to the store), and the sunlight based farm had high transport costs (for example if they needed to fly their produce in) the artificial lighting is much more economical.
Now maybe you're thinking "Oh, but they have superpower plants, energy won't be a problem, which is fair, but not the actual issue. It's heat.
That's not an issue on any planetoid or large asteroid, and not much of one on a large station. The amount of energy we're talking about is insignificant.
Human manure needs to be composted for at least a year, to kill off the harmful bacteria inside, same for manure of other omnivores like pigs and chicken.
Or it can be sterilized and processed much faster.
 

Atarlost

Well-known member
They work a lot better in fantasy than in Sci-Fi actually. Being fantasy you can throw on all kinds of mystical reasons for agri-worlds. Sci-Fi you just run headlong into the inconvenient fact that O'Neill cylinders in close orbit around the local star are basically better in every way. Well accepting the 40k reason; better political control by the central government over hive worlds.
Congratulations, you've just re-invented the Agri-world.

Except remember the heat problem? Solar agriculture is cool. It's easier to get rid of heat from orbital habs because they have no atmosphere to complicate mounting radiators. This means that if you're using cylinder habs it's more efficient to move as much of your industry and population as possible to the habs and turn the planet into an agri-world.
 

bintananth

behind a desk
Congratulations, you've just re-invented the Agri-world.

Except remember the heat problem? Solar agriculture is cool. It's easier to get rid of heat from orbital habs because they have no atmosphere to complicate mounting radiators. This means that if you're using cylinder habs it's more efficient to move as much of your industry and population as possible to the habs and turn the planet into an agri-world.
You're wrong on the heat issue.

Dumping waste heat in space is hard because you're limited to black body radiation and not much else. The Apollo 13 astronauts started to get cold after things went wrong because the spaceship they were in was designed to dissipate heat they weren't generating with the power off.
 

Abhorsen

Local Degenerate
Moderator
Staff Member
Comrade
Osaul
Agriworlds get both dumber and smarter when it comes to a possible future food source: lab created produce and meat. When it comes down to it, this will be cheaper, less space intensive, and not require sun. I expect that agriworlds would instead be places that export rare and difficult to produce foodstuffs that's 'authentic'.
 

The Unicorn

Well-known member
Dumping waste heat in space is hard because you're limited to black body radiation and not much else. The Apollo 13 astronauts started to get cold after things went wrong because the spaceship they were in was designed to dissipate heat they weren't generating with the power off.
While this is true, the black body temperature of Earth is ~4 degrees below freezing. As long as you're not too close to the sun (as in mercury's orbit or such like) disposing of heat from a space station is only a problem if you don't have the ability to get large quantities of material into orbit.

The space program IRL does not have problems with heat generation and dissipation because doing that in space is hard, they have problems because all the easy ways require too much mass.
 

Atarlost

Well-known member
You're wrong on the heat issue.

Dumping waste heat in space is hard because you're limited to black body radiation and not much else. The Apollo 13 astronauts started to get cold after things went wrong because the spaceship they were in was designed to dissipate heat they weren't generating with the power off.

You're ultimately limited to black body radiation and nothing else on planets too. That's why ecumenopoleis don't work.
 

The Unicorn

Well-known member
You're ultimately limited to black body radiation and nothing else on planets too. That's why ecumenopoleis don't work.
I don't follow the logic there. How does a planet's black body radiation relate to weather or not an ecumenopoleis would work?
It's not as if an ecumenopoleis would produce enough heat to matter on the scale of a planet. Not when compared to how much more is shed by increasing the planet's albedo.
Currently, Earth's albedo is ~0.3, that means 1.218e18 W are absorbed by earth from the Sun, since a world covered with a city would easily have an albedo of ~0.95 that means you'd need to be producing ~1.13e18 W just to maintain it's current black body temperature(That's enough for ~120 trillion people at the current US energy consumption rate), then since you completely destroyed the greenhouse effect you'd need a few quintillion more Watts to get things warmed up to their current temperature.

There are reasons ecumenopoleis might not make sense, depending on various assumptions, but the planet's black body temperature is not one of them.
 

Captain X

Well-known member
Osaul
From what I got told by a NASA engineer, it's actually hard to get rid of heat because the ways we typically have of dealing with it is to exchange heat with another medium, and there is not medium for the heat to go into in space. This is why having a nuclear reactor in space would actually be very difficult apparently.
 

PsihoKekec

Swashbuckling Accountant
I saw a design for nuclear powered spaceship some time ago, heat dissipation system took most of the volume.
 

The Unicorn

Well-known member
From what I got told by a NASA engineer, it's actually hard to get rid of heat because the ways we typically have of dealing with it is to exchange heat with another medium, and there is not medium for the heat to go into in space. This is why having a nuclear reactor in space would actually be very difficult apparently.
That's...not quite accurate (although for current technology and space transport capabilities a reasonable explanation).
Heat is exchanged by Radiation, Convection and Conduction. On Earth we use all three, in space only Radiation works so it's a lot less efficent, however while in an atmosphere radiators do have some heat transfer by conectionand conduction, their primary method of heat transfer is radiation, so you could in theory put a nuclear steam-turbine reactor in space with only difference being larger radiators to account for the lower efficiency.
The problem is we're talking about designs massing multiple tons, and with our current technology we count grams (Getting something to Geosync . orbit costs over 30$/gram) so we look for alternate methods of distributing heat that don't require giant radiators and pumps to move heat transfer fluid throughout the station.
In a SF setting where you have large space infrastructure this is not an issue.
 

Users who are viewing this thread

Top