Introduction: Disco Ball GBE Design
Hyperholics is a two-student team entering into the High School Division of the GBE competition.
We discovered this project while searching for a stimulating science topic to further research. Our team is inspired by the prospect of applying knowledge learned from our courses to a very much real world problem. GBE provides a breeding grounds for solving the problem of sustaining plant life outside of the livable environment that Earth provides as well as a gravitational force. Without gravitational constraints, we could come up with creative solutions to maximizing plant growth within a limited space.
We designed the apparatus with three considerations in mind:
1. Maximizing use of the 3D space in microgravity.
2. Efficient usage of resources (energy, water, and air).
3. The different sizes of plants that can potentially grow with the apparatus.
We have listed them elsewhere.
For the water reservoir system, we were thinking 3D Printed.
Step 1: Considerations
Selected plant: We decided to use lettuce as our standard plant as it is has been successfully grown on the ISS. Our apparatus also allows for the growth of other plants, and depending on the plant size can actually fit more (smaller ones can fit more) with consideration of necessary growth space.
Our design also assumes that only one type of plant will be grown within it, as it minimizes the extra complications of adjustments in water level, temperature, light intensity and coloration, humidity, etc.
Based on the average spreads and heights of plants that have been grown in space, we took in consideration to the amount of volume an "average" plant unit would occupy, and used a spread of 18 cm and a height of 22 cm for our calculations.
Step 2: Overall Structure: Maximizing 3D Space
We had come up with many designs but ended up with our current design structure through considering several variables: volume, surface area, and energy efficiency.
We've linked a github repository that stores all of our prospective designs including: a conical structure jutting from one wall, tube(s) that would have plants growing from the circular surface, aisles of rectangular walls, and an inverted sphere, it looks like a cone with a hyperbolic surface.
The code provided us with the maximum capacity of plants that can fit into the volume of the cube after building a structure that could "hold" the plants. We calculated for the volume of each plant, with the half ellipsoid formula and ran the program to see how many plants the leftover volume could fit. This was all before we had the idea of having a sort of floating light source in the middle of the apparatus. Originally, we were going to have a light source from the corner of the apparatus and for structures that potentially blocked the light from one side, we would install mirrors to deflect light so that every plant in the design would have access to light.
One fault with the code is that it didn't take into consideration that the plants needed to be on a surface, so the resulting numbers are not completely accurate-- the simulation assumes plants can be grown while floating in the space not already occupied by other plants. Though this may actually be a good thing as it potentially allows for more space to grow into. Without the limits of gravity, it seems plants can actually grow taller in comparison to their counterparts growing on Earth.
https://github.com/kateosipovav/Disco_Ball.git This link is to all the previous designs.
https://github.com/kateosipovav/FourShapesSimulat... This links to our current design.
Step 3: Watering System: "Hydrophilic Foam"
The idea behind hydrophilic foam is ridding the apparatus of a watering system which would only take up space that can be instead be used for plant growth. Due to the constraints of a 50 by 50 by 50 cm cube, we minimized the amount of space a watering system would take up while ensuring sustainability for plants.
- Hydrophilic: The reasoning behind this property is to
- keep the water in one place (so it doesn’t float off and formulate into droplets due to its highly cohesive properties),
- Due to the hydrophilic properties of the material, water would be attracted to it, preventing water from floating off into the air space within the cube
- allow for water to uniformly spread throughout the apparatus without any external force,
- Ideally, the hydrophilic properties of the foam material would allow for extremely efficient wicking that would completely dampen the entire material. However in the case that this doesn’t happen, we have incorporated multiple reservoirs for multiple points of contact on the foam to achieve dampness across the entirety of the foam. In microgravity, water tends to stay in the middle of the medium used for wicking it, through capillary forces, as there is little gravity to pull it in any other direction.
- which runs off of the second point, it eliminates the need for separate growing units for each plant (which takes up more space)
- With materials like rockwool, they are manufactured in blocks and many of the designs for hydroponic agriculture, is by individual units. However with the lack of gravity, the cohesive properties of water as well as the hydrophilic material of the foam should rid the need for these individual potting units. Our design completely rids of an individual potting structure to hold each plant. It also eases up the potting process, we can simply plot seedlings wherever on the foam material without having to account for how many pots needed.
- rids the need of human/constant maintenance.
- Originally we were going to use a drip system that could go to each individual unit, however from previous experience with hydroponics using a drip irrigation system, we wanted to minimize non-uniform irrigation which usually occurred as a result of clogging. There’s a variety of issues that can result from a drip system that can easily go faulty: overpressurization, under-pressurization, inadequate flow rates, etc. making it relatively higher maintenance than the material my team proposes to use-- a hydrophilic foam.
- keep the water in one place (so it doesn’t float off and formulate into droplets due to its highly cohesive properties),
- allow for aeration of the roots, as well as
- Roots need air to grow, which soil allows for, and this porous foam would also allow for. But the aeration of the roots should also prevent dampness and condensation which are potential breeding grounds for fungal spores. Fungi are not helpful for plants to say the least. Even so, with this precaution, the damp material may still spawn unwanted growth, a problem which we attempted to address with further air movement in a following section.
- growth room for roots (The relatively porous material encourages root growth, much like rockwool)
- can easily adhere to a shape that is decidedly optimal, but still maintain a solid form.
- The foam can be manipulated into the ideal shape meaning it can bend at sharp angles to form a hollow cubical tube, or a hollow cylinder whichever is most optimal in providing the most surface area. Because of its flexibility, there is no need to use stiff, rigid, material that is hard to manipulate to create the optimal shape for growing the most amount of plants. While being easily manipulatable, foam is still relatively stiff and would not warp too much even with the “absorption” of water. The material itself doesn’t absorb water, rather it attracts water
Conclusion: Capu-cell is a “hydrophilic polyurethane foam” that comes quite close to the requirements for this specific purpose of utilization. The company that manufactures this foam allows for customization of the materials used for the foam to best fit the purpose of the product. Below is a link to their products.
Step 4: Air Ventilation System
Air Ventilation: a moving air flow is necessary to prevent condensation which can promote the germination of fungal spores (which then damage the plant). Some possible options we went through:
Not Necessary At All
Plants can produce their own oxygen for consumption. In closed terrariums plants can thrive, but due to a lack of air movement, there is high humidity which not all plants are suited for, some examples are water spinach and arugula, to list a couple. As it has not been tested yet, we don’t know if the humidity would be too high without an air ventilation system even for the plants that thrive under high humidity. Without experimental data, we were unable to calculate it. Based on the requirements of the plants the design may not need any air ventilation, allowing for even more space in the apparatus for plant growth. For example, the basics of this design will be the same across cultivation of different types of plants, however for specific plant species, an air ventilation system may not exist for that individual apparatus, while for others it would be necessary.
Access the ISS's Air
Basically leave the apparatus open, able to access the air from the station. My team was thinking of a simple air ventilation system, a fan that can draw in air and push out air (avoid pressurizing the apparatus too much) complete with a humidity filter on the other side so we don’t turn the ISS into a swamp. In addition to accessing the air from the station, the plants can also provide “extra” oxygen for the crew! A truly symbiotic relationship. We decided to go for this option.
For individual fan units, we decided to use DC motors for rotating the fan blades. By hooking it up to an arduino, we can “change the direction” of airflow, allowing for air to be expelled and taken into the apparatus. The units will be a part of a dehumidifier unit explained in a later step.
The fan we'll be using is installed with the climate control portion of this design.
Note: We did consider creating oxygen and perhaps even carbon dioxide, but it was overly complicated an unnecessary when we have such a wonderful and bountiful supply of both from the ISS.
Step 5: Lighting System
With the lighting system, we wanted to achieve the best results with high energy usage, lighting coloration that would encourage the most growth, lighting intensity, and also low heat emission. Plants have been found to flourish under red and blue lighting, and can do just as well under white light as they can also use other colored lights towards photosynthesis, just in smaller amounts. We considered efficiency, heat emission, and life expectancy as light coloration doesn’t matter as much (there isn’t a significant difference in overall growth rate with pinkish lights compared to white lights).
HPS Lighting in combination with Metal Halide Lamps
- HPS Lights tend towards an amber orange-ish glow, which veers towards the redder colors of the visible light spectrum, whereas Metal Halide lamps tend towards whiter, blue-ish light. HPS lights emit more “usable” light than MH lights, relatively 142,500 lumens per standard 1,000 watt bulb and 95,000~ lumens. With a combination of these lighting fixtures, we can produce the optimal color to encourage a faster photosynthetic rate. These are also highly efficient in terms of lumens. Low pressure sodium lights can range from 50 to 160 lumens/watt.
LED Lighting (Adjustable Color Spectrum-- simply hook it up to an arduino and programming it to adjust lighting based on type of crop)
- Instead, we decided to go with LED lighting as they are highly efficient (they usually score above 50 lumens/watt). We are using LED light strips, that can also deliver UV and infrared light so as to allow for usage across a wide spectrum of plants (in case ISS wanted to have more variety with their plants). My team chose to use strips so we could suspend a lighting fixture that is able to emit light in all directions, in the middle of the apparatus. The point is to essentially have a sort of disco ball that emits light. Without gravity, the plants can grow towards the middle allowing for energy efficiency by only having one lighting fixture that’s “accessible” for all plants. Having a light source fixed to one of the walls of the cube eliminates one entire wall of space for growth. We decided to just wrap the light strips around a cube shaped foam piece (the material can be changed, we just thought foam was easier to shape and easier to feed twines into, to attach to the sides of the apparatus to keep the light fixture from floating around).
Step 6: Climate Control
A higher humidity climate is preferable as it has a wealth of benefits: reduces the need for evaporation (more efficient usage of water), higher photosynthesis rates as it keeps the stomata open to uptake more carbon dioxide, to list a few. Most crops generally operate best at around a 75%-85% humidity rate and can thrive well outside of the range. However, one concern is that too high of a humidity might render the plants unable to evaporate water as a way of cooling down due to the high moisture content in the air, and rot. So we installed a simple dehumidifier that is connected through an arduino to humidity sensors. Should humidity levels reach too high, it will trigger the dehumidifier to turn on. The dehumidifier also doubles as a temperature regulator.
Building the Dehumidifier: Video on how to construct this.
Computer Fan (DC), Arduino unit, two-way rotation with two relays, and sufficient wires.
This is how to construct it.:
Large and small heat sink
Thermoelectric cooler or peltier chip (one side increases temperature and other side decreases temperature, essentially creating an environment that allows for condensation)
heat sink compound,
Switch along with a connector and some screws.
Battery (12 V).
Capu-Cell (absorb the condensation so it doesn’t float)
Note this unit is connected to an arduino connected to a humidity sensor
Step 7: Citations
Country Fresh Herbs “Mizuna Leaves.” Https://Www.specialtyproduce.com/Produce/Mizuna_Lettuce_2027.Php, 2018, portalvhds26k4f5tktj3ck.blob.core.windows.net/spotpics/sp43804.jpg.
Chidiac, Joseph. (2016). Photosynthesis in Lettuce: A Review.. 10.13140/RG.2.1.3640.3605.
Link for dehumidifier: Credit to Owner, RcLifeOn
Step 8: Potential Improvements
Our water supply will likely be depleted relatively quickly with the watering system we have in mind. As there are no individual potting units, the sheet of hydrophilic foam material is a huge surface area that does not efficiently retain water as a drip system with its limited access. However a suggestion for addressing this problem is a unit that can collect condensation and perhaps reuse it. My team is still working on how to best implement this with our current design constraints.
My team became aware of this contest recently, so we didn’t have the time to experiment with certain plants. One of the possibilities with the air system was that we would not need one at all, depending on the plant having a high photosynthesis rate and ability to thrive in high humidity-- one that would be present in a 50 cm cube with the number of individual plant units it would grow. With more time, we would’ve been able to provide data and ensure whether our design truly required an air ventilation system as without it, we would have more room for plant growth or other necessary machinery that could further automate the cultivation and harvesting process.
The twines holding the lighting fixture in place shouldn’t interfere with plant growth too much, but the most ideal situation is having a rigid wire that won’t conduct electricity holding the cube in place. Also, Ideally, we make a LED sort of bulb that’s still a sufficient grow-light, and not just LED strips wrapped around a foam cube.
If we could somehow make the water reservoir system more flexible and not as rigid, we could simply unfold the cube for easier harvestation.
Participated in the
Growing Beyond Earth Maker Contest