space tree nursery

Last week I posted about building things in space like a farm, a university and factories to turn asteroids into usable products. Who knows if wood would be a valuable or useful product in space construction? Maybe it would be useful in settlements either space based or on the Moon, Mars or any other planetary body.

I picked trees that I know grow where I live, so I chose a Sugar Maple deciduous tree and an Eastern White Pine coniferous tree. Perhaps others could be added. Each can grow up to 40-45m in height. Given this height I figured to have the radius of the torus tube be 60m so as to allow for the substrate within which the trees would grow and adequate head space. Coincidentally, if we create a chord of a 60 degree arc angle we would create a 60m flat line along the bottom of the tube. Subtract 5m from each end as the depth would be too small and that leaves us with 50m width of planting area.

Using a torus that has a 350m radius and using that width of 50m of planting area we would have roughly 115000 square meters of growing space, or about 28 acres. Given a tree spacing of about 18' between trees in rows and columns this would allow for approximately 3900 trees to be grown.

In terms of construction, the Sun facing side of the torus would have solar panels to supply the needed power and would be on top of the outer layer of the torus which would be 1m of regolith bricks. Then it would be a steel structure that also acts as the proper space-inside barrier. On the inside of the steel structure, a thick impermeable layer to prevent water and tree roots from reaching the metal structure and then another 1m of regolith bricks and then 3m of imported soil from Earth only on the side of the torus where the trees will grow.

I found that 0.94, 1.05 and 1.15 RPM would provide an RCF of 0.4, 0.5 and 0.6g for a torus this size. So the whole structure would start spinning at 1 RPM to create 0.45g simulated gravity. The structure itself will be built to be able to spin at up to 0.75g and so if ever it is discovered that the trees need higher simulated gravity, it can be given.

Along the inside of the torus edge would be the atmospheric system. I envision this to be made up of a light system and a precipitation system. I would have the light mimic the diurnal/nocturnal pattern of sunlight at 45 degrees north on Earth so as to create day time, night time and seasons. Similarly I would have the lights bright like sunshine and diffuse like clouds and set and rise with appropriate hues. The precipitation system would allow for periodic rain and also snow. The air pressure within the torus would have to be at least half an Earth atmosphere and consist of roughly the same Nitrogen, Oxygen and CO2 mix as exists on Earth. Large fans would circulate the air either in concert with each other, or opposite each other to create varying wind conditions. The temperature would be controlled such that it mimics the day/night and season, such that on some summer days it peaks at 28c and on some winter days it bottoms out at -15c. The humidity would also be controlled such that at some times more humidity is released into the air and at other times humidity is drawn out, to match humid summer days and dry days too.

One tenth of the torus could be planted at the start and with each subsequent year a next tenth would be planted; this would make it so that the amount of soil that would have to come up from Earth could be spread out over the first decade. Once those first trees are planted, those trees can become the seed suppliers for future generations of trees, so somewhere within the torus would be a small nursery to start the trees to get them into seedlings. 

As imports we would need water and maybe periodic nutrients to put into the soil that would help the trees. We may need to import CO2 to provide for photosynthesis and possibly somehow capture and export O2 if the trees produce more than is optimum for the interior of the space farm.

I can imagine the monitoring and care for the trees can be mostly automated, however, there could also be built a simple barracks to house workers at any time they might be needed, for example, for the receiving of soil during that first decade, for planting the seeds for seedlings, or to plant the seedlings, or to harvest the trees and then process them into lumber.

A port and processing plant could be built inside the center of the torus in a station that can rotate with the torus in order to transfer people/material to/from the torus, or can cease rotating to be fixed to allow for easier space ship docking. The processing plant would take the cleaned trees from the tree farm and convert the lumber into standard sized lumber and processed plywood sheets and so on for the purposes of being marketed out to the space world.