space tree farm part four

I cannot guarantee that this will be my last post about the space tree farm that I will write.

To briefly summarize the idea, a mid LEO cylindrical space tree farm would only be built after an asteroid mining and processing plant is built in the mid range of LEO. It requires from that processing plant a large number of curved metal pieces that curve with a radius of 500m (and a smaller number of flat pieces for the two ends) and are in manageable sizes and will be used to construct the cylinder that has a 500m radius and a 2000m length. Similarly the processing plant will provide the oxygen for the inner atmosphere as well as both loose asteroid regolith, to be mixed with soil from Earth as well as asteroid regolith bricks to be using during the construction of the cylinder.

At the same time or after this cylinder is built, further space residences and structures would need to be built to create the market for the lumber products that the tree farm will produce.

Additional details can be found in the previous posts, what this post is about is how to create the atmosphere within the space tree farm. It turns out that getting the 20% oxygen ought to be straight forward as there are many different types of oxides that the asteroid processing plant will process. I had ChatGPT-4o help me do some calculations, I would need either 0.31 cubic km or about 12,687,037 moles of Oxygen gas to provide the ~20% of oxygen at Earth sea level pressure within the cylinder at a standard temperature.

Our Earth atmosphere is made up mostly (~79%) of Nitrogen gas, and this is not so easy to find. To have the space tree farm cylinder have the correct air pressure, after having added the oxygen gas from the previous paragraph, 1.26 cubic km or 51,530,087 moles of Nitrogen gas would be needed. I found this could be sent from Earth in 127,670 50L 200 bar pressurized gas canisters, but the weight and volume of doing this would be inordinately expensive to lift out of Earth's gravity well.

So then I went searching for how we can get Nitrogen sourced in space. There were a few ideas, like using a space ship to dip into the upper atmosphere of Earth to scoop some out, or to do the same thing at Venus which has much more Nitrogen gas. There is apparently some ammonia on the Moon and on Mars, or there are asteroids further out in the Kuiper belt that are heavy with ammonia.

I learned that 4NH3 (gas) + 3O2 (gas) -> 2N2 (gas) + 6H2O (gas) + heat. So add ammonia and oxygen gas together to get nitrogen gas, water vapour and heat. Alright, so the oxygen we can already get from our NEA asteroids, the ammonia we'll get from the Kuiper belt, but for the purposes of this large space tree farm cylinder, we'll need 876 metric tonnes of ammonia to get the correct amount of Nitrogen gas to make up our roughly 80/20 N2/O2 atmosphere at Earth sea level pressure within the cylinder.

Given the time it would take to get the ammonia from the Kuiper belt into the mid part of Earth's LEO, this would be one of the very first projects to get sent out, even before the asteroid processing plant is built. The mission would be to use gravity assists from whatever out there is useful to do so. It would be a fully automated and remote controlled space ship whose mission is to collect roughly 880 metric tonnes of ammonia and to bring it back to Earth LEO where, by the time it has returned, the space tree farm cylinder will be ready to receive it to turn the NH3 into N2.

We would create a closed system to process the ammonia and oxygen so that we simply release the N2 into the space farm, we capture the water vapour to condense it and store it for use as water, and we let the heat dissipate into the space farm as well. By feeding in the ammonia and oxygen and getting those outputs as described, we would fill our cylinder with the proper atmospheric pressure and makeup for life as we know it on Earth.

Now that there is Nitrogen in the atmosphere, I would want to create, monitor and adjust the space tree farm to have nitrogen fixing plants, and then the varieties of bacteria put into the ground that are nitrogen-fixing prokaryotes that convert N2 to NH3, then nitrifying prokaryotes to convert ammonia to nitrates and nitrites, and then finally denitrifying prokaryotes that convert nitrates back into N2 to be released back into the air of the space tree farm atmosphere.

As there are trace amounts of nitrogen in wood, when the lumber is exported out of the space tree farm this reduces the total nitrogen found in this ecosystem. Given this, the space tree farm can now import from Earth more reasonable amounts of Nitrogen gas in canisters that would be used to replenish as needed what is required for nitrogen stability.