Assuming I have 16 goats and each acre of land can support 2-4 goats, any advice for making my dream of a lunar goat farm come true? (2-4 goats per acre is the suggested number of goats for poor quality soil, which I'm assuming Moon soil is when it comes to goat upkeep.)

This is just the sort of question I like to receive!

Sadly, I think even poor quality soil may be overselling lunar regolith.

I’m not fully sure what determines soil quality insofar as it pertains to goat farming. There seem to be dozens of soil classification schemes that relate to all kinds of properties of the soil, from its strength and engineering properties to its material composition. We’re specifically interested in agricultural soil science but even that seems really complicated.

There is a portion of the lunar regolith referred to as lunar soil. Wikipedia has this to say of it:

The physical properties of lunar soil are primarily the result of mechanical disintegration of basaltic and anorthositic rock, caused by continuous meteoric impact and bombardment by interstellar charged atomic particles over billions of years. The process is largely one of mechanical weathering in which the particles are ground to finer and finer size over time.

This situation contrasts fundamentally to terrestrial soil formation, mediated by the presence of molecular oxygen (O2), humidity, atmospheric wind, and a robust array of contributing biological processes.

Some have argued that the term “soil” is not correct in reference to the Moon because on the Earth, soil is defined as having organic content, whereas the Moon has none. However, standard usage among lunar scientists is to ignore that distinction.

So it’s pretty unlike Earth soil. Here’s another comparison:

There are two profound differences in the chemistry of lunar regolith and soil from terrestrial materials.

The first is that the Moon is very dry. As a result, those minerals with water as part of their structure such as clay, mica, and amphiboles are totally absent from the Moon.

The second difference is that lunar regolith and crust are chemically reduced, rather than being significantly oxidized like the Earth’s crust. In the case of the regolith, this is due in part to the constant bombardment of the lunar surface with protons (i.e. hydrogen (H) nuclei) from the solar wind. One consequence is that iron on the Moon is found in the metallic 0 and +2 oxidation state, whereas on Earth iron is found primarily in the +2 and +3 oxidation state.

In terms of its practical consequences for creating goat pastures on the moon, I’m guessing lunar soil is going to be totally unsuitable for growing Earth plants. Crucially, it has almost no nitrogen at all.

Hopefully it’s possible to create fertilisers that can be mixed with lunar regolith to make something more suitable (taking care to mind the health risks of lunar dust) but if not, you’ll need to bring enough soil with you to cover your full 4-8 acres of land to a suitable depth. You will also need to bring significant amounts of water.

Wikipedia gives another long passage (sorry) on lunar agriculture:

Growing crops on the Moon faces many difficult challenges due to the long lunar night (354 hours), extreme variation in surface temperature, exposure to solar flares, nitrogen-poor soil, and lack of insects for pollination.

Due to the lack of any atmosphere on the Moon, plants would need to be grown in sealed chambers, though experiments have shown that plants can thrive at pressures much lower than those on Earth.[54]

The use of electric lighting to compensate for the 354-hour night might be difficult: a single acre of plants on Earth enjoys a peak 4 megawatts of sunlight power at noon. Experiments conducted by the Soviet space program in the 1970s suggest it is possible to grow conventional crops with the 354-hour light, 354-hour dark cycle.[55]

A variety of concepts for lunar agriculture have been proposed,[56] including the use of minimal artificial light to maintain plants during the night and the use of fast growing crops that might be started as seedlings with artificial light and be harvestable at the end of one Lunar day.[57]

OK, so, supposing you can create an area with an adequate soil quality. Let’s think about other considerations for goat farming on the moon.

There are a number of potential problems with constructing a lunar goat farm (or any moon colony). They’re discussed in a fair bit of detail in this wiki article. The main issues:

• The moon is tidally locked to the Earth, meaning the lunar ‘day’ takes about a month. This leads to extreme temperature swings each month, and of course any attempt to grow crops would have them in darkness for half of each month. A potential solution to some of these problems is to place a lunar colony at one of the poles, since the moon’s rotation is very close to being perpendicular to the eclipltic.
• Lacking a protective magnetic field and atmosphere, the moon’s surface is constantly bombarded with solar wind, UV radiation, and meteorite impacts of many sizes. For this reason, it’s often suggested to build a colony underground, perhaps in a lava tube.

All the same, this means we need to take care to keep the moon colony warm during the night and cool during the day, and it means we need to provide and store significant electrical power to keep the pastures illuminated for the half-a-month-long night.

It’s going to be very inefficient! Electrical power is inefficiently generated from sunlight or nuclear power, and is inefficiently re-radiated over the crops, is inefficiently used to produce carbohydrates in the grass by photosynthesis, is inefficiently digested by goats…

Living organisms are generally adapted to light and other environmental cues cycling over 24 hours (many biological processes display circadian rhythms). I expect we’d need to reproduce that in order to keep the goats happy and healthy. If our pastures are exposed to sunlight, we’d need to shield them; otherwise we’d need to turn the lights off at night.

Although the stereotypical sci-fi image is of a dome-shaped lunar colony, I think this wouldn’t be ideal. Domes, while good pressure vessels with no weak points, have a lot of air in them that’s too high off the ground to be useful (unless they’re very flat, in which case there’s a lot of inaccessible ground) that you still need to control the temperature of. Plus it would be difficult to cover up a dome with a shade to create artificial ‘night’. Instead, the above-ground habitat units would probably want to be as small as possible.

I feel inclined towards the underground moon colony concept instead. Our goat pastures would be arranged along a lava tube, or built in artifical caves.

Lunar lava tubes can be as wide as 500 metres before they collapse. Assuming we can cover about 80% of the circumference half of the lava tube with pasture before it gets too steep for the goats, the area of pastures of length $$L$$ is $$0.8\times \pi \times 250 \mathrm{m} \times L$$. For four acres of land, $$L$$ comes out to only $$13\mathrm{m}$$, which is very promising! The tube very likely wouldn’t be that big, and our pastures would extend further along it; all the same, this is a good sign.

More of an issue is the power of providing artificial light. Wikipedia’s above figure of peak 4 megawatts per acre would probably be an overestimate of what’s needed (also where on Earth is that calculated? Crops at the equator get much more energy than crops close to the poles!). Still, we’ll probably need a few megawatts of power to illuminate our crops. That would require a lot of solar panels, or else lifting a nuclear reactor to the moon.

While multi-megawatt reactors have not yet been launched into space, they have been thought about. In this earlier discussion of a drawing of a Soviet nuclear-powered airship, I found this report which discusses the possibility of 15MW reactors for use in space, which would more or less cover our goat farm. So nuclear power wouldn’t be out of the question.

So here’s my proposal for your lunar goat farm: we find a lunar lava tube. We place inside it some inflatable pressure vessels, containing enough soil to sustain a lunar goat farm (this will probably require quite a few lunar launches to place it all up there). Additionally we add areas to grow crops for ourselves? All water and waste is recycled back into the soil, but we may need to rebalance it with external inputs from time to time.

Keeping the ecosystem stable might prove difficult, however. So far, no-one has yet managed to create a stable enclosed ecosystem that can be mantained for a indefinite period.

We power it with a 15MW nuclear reactor weighing about 100 metric tonnes (this exceeds the trans lunar injection capacity of the Saturn V by a factor of two, but we might be able to reduce its mass by reducing shielding [since it will not be activated until it’s on the moon and we’re safely underground] and lifting it in parts), which will provide artificial light to the goats and the grass they’re eating.

The underground location provides protection from solar wind and other forms of radiation. The electric lights give us full control over the light in the enclosed environment, so we can keep our goats (and ourselves) in more or less Earth-like conditions.