Beyond Earth: Aeroponics

This is a submission for the Growing beyond Earth challenge set forth by Fairchild and NASA. I came across it and thought that was a neat challenge, but a little worm in the back of my head kept making ideas and now here it is.

Notes on the figures

The first figure was the first rough sketch of the design before it eventually evolved into its current form. It is being used here in order to establish direction for the later figures as there are focused in on certain parts of the design and one could lose which way is up. Also everything is hand drawn as I don't know any CAD software, but I had a straight edge and a pencil. With the straight edge being 150mm long everything was drawn to scale at either 1:5 or 1:10 ratios.

The second figure here is a coarse overall design with the different structural components separated so they can be seen without being too crowded, but still retain a spacial relation to one another. This also has some of the finer details removed as they will be covered in later steps.

Goals of the design

The goal of this project as the title hints at is growing somewhere beyond Earth using Aeroponics. This has benefit of being an almost medium-less growing method saving space and weight. However, in a micro-gravity environment just spraying water everywhere would probably create more problems than it would solve. To try and bypass this issue I plan to try and leverage waters strong adhesion/cohesion properties. Everything will be described in greater detail as we go.

So right from the beginning I am using the back 5cm for a water reservoir to hold water for the plants. This leaves 45cm of depth to be used for growing space. (A note here would be that the design plans are done without materiel thickness being factored. A result is some spots will slightly less room that listed, but should be small enough to be negligible.) From here the next space to be taken up is another 5cm from each lateral side. This area will be taken up by the channels that will contain the roots of the plants. The center line of each channel will be where the plants are located at and each point of planting will be located approximately 15.3 cm apart in all directions. This results in 3 plants per row, which results in 24 plants per cube. This spacing was chosen based on Johnny Seed seed spacing which allowed them as close as 15cm.

Channel Placement

The location of each channel was based on the principle keeping each plant equidistant from the center of the cube. This is illustrated in figure 3. Since the left and right sides are restricted to a minimum of 20cm from the center and I aimed to have the other six channels maintain this distance. I actually was lucky at this point as it happen keep the 15cm spacing for between rows. These channels that contain the roots are currently planed to be 5cm*7.5cm*45cm in their dimensions. There will be a total of 8 channels located in a rough circle.

Leaf Space and Lighting

With the tops of the channels being about 20cm from the center of the cube, that leaves me about 10cm of empty space at the center of the cube as each plant grows to 15cm in height on average. Figure 4 summarizes the overall space usage, of this design within the growth chamber. That center 10cm is where the lights will be located on a cylinder as to ensure even coverage in all directions. The type of light I am aiming for is a full spectrum plant led light. These contain the wavelengths required for plant growth, while also containing others in order to portray colors as we would expect them. With this system, the lights will be static and so intensity control will used as the plants grow towards them.

The Open Space

The unfilled space in figure 4 is currently open for use by anything else. As of right now I plan to utilize one of the corners to house the micro-controller and the User Interface for any settings that could be adjusted. Another consideration for this space is to house a simple adapter kit for the watering system. Because this is being designed as a pseudo-aeroponics system for micro-gravity, should it be taken back into a gravity environment it could have sprayers installed creating a more traditional aeroponics system. Another corner or distributed among the corners would be valves to contro lwhich rows get water for a system that can do crop rotation. The very center of the cube (the 10cm circle) currently planned to hold the lights, but also to hold the pump for watering system. However, the pump could easily be relocated to another space if another use if the center becomes more valuable for a different component.

How to hold the seeds

This system, while based around aeroponics, still require a small bit of growth medium in order hold the seed, and later the mature plant. For that I settled on this puck design (Figure 5). It is relatively simple and hopefully reusable. The puck is 2.5cm tall by 5cm wide. The very top of the puck would be a solid material to inhibit water movement from the root channels to the growth chamber, with the rest of the puck being a mesh to allow roots to through. The inside of the puck would be filled with the same medium as the pillow packs. This is to allow water to activate the seed without drowning it, but at the roots grow outward they are free to enter the root channel.

Why the puck?

As stated above the puck will allow the seed to be watered without drowning it and prevent water from entering the growth chamber itself. There is another reason for the pucks. By having the pucks so shallow there is potential to be able to easily remove the roots from the puck by merely pulling them out. Reuse is also possible because a liquid fertilizer is planned for the feeding system instead granules. This means the pucks don't become duds after a single use.

Watering

Placed around the spot for the plant pucks within the root channel will need to be a collar and a cloth donuts, both shown in figure 7. The collar itself is shallow, only 2.5cm, and its sole purpose is to help control the water while the roots are still small. Once the roots become large enough, they can grow beyond the collar and into the main channel as needed. Injecting water into the system is the job of the cloth donut. Having a single open nozzle presents problems with being less precise and at great risk of the roots growing into the opening clogging the system. When water is pumped into the system the water should fill the donut and leak through to the root channel in a controlled matter. The idea is that the water will prefer to stick to a surface with higher surface area and the pore spaces of the plant puck should draw water in via capillary action. As the roots grow beyond the puck water should finely coat the roots, but still allow them to breathe. Testing will be needed to figure out how much water can be added before the water layer is too thick for the roots.

The Reservoir

At the very back of the cube the 5cm slot that was created will house a bladder reservoir for the watering system. With the rough dimensions of 5cm*50cm*50cm that creates a holding capacity in the ballpark 12.5 liters. This would also hold a low concentration of liquid fertilizer to give a slow controlled daily feeding to the plants. This reservoir would relay on the atmosphere of the ISS to create a positive pressure in the system in lieu of gravity performing that job.

The Pump

The pump is a simple one. It is going to be a cylinder of known volume with a linear actuator servo pumping it. Two check valves, one for drawing water from the bladder and another to inject the water into the channels. The pump would also count the number of times it drew water from the bladder and use this as a way to estimate when a refill would be needed.

From the pump the simplest method would be to send water directly to all the plants at the same time (figure 10). However, it would be better to use a manifold to be able to water different groupings that are each in different life stages. The manifold could be used within the center tube or in one of the corners.

Airflow

The last thing that would need for this system overall would be airflow. Right now I have it designed as partially closed system. The reason for that is there is still a need for air movement to prevent unwanted spore growth, but by restricting the rate air can leave I am hoping to slightly raise the humidity to reduce transpiration.

Another consideration that is unique to this system is that with the exposed roots I will install a fan moves air through the root channels. This would snake the air between the channels before expelling the air into the growth chamber.