Tetrahedron Growth Chamber

This entry is for the High School competition.

A Little About Me

I am a high school Junior who had completed the Fairchild Tropical Botanical Garden Summer Internship in the summer of 2019. In said internship, I was working with microgreens to test and see whether they would be viable food source for space travel. While I was in the internship, I had heard of NASA's interest in designing a new growth chamber, which sparked my interest and prompted me to begin this adventure.

The Challenge and Other Issues NASA Faces

NASA plans on heading to Mars and deep space on future missions. A critical component of these future space exploration missions is food. Astronauts need a sustainable and efficient source of food that can be grown in the space station. As the amount of space for crop growth is limited and confined, it is paramount to use every inch of the space effectively.

Since microgravity conditions are so drastically different from our 1 g environment, the plant does not have to adhere to the standard growing set-up (placing a plant on a flat surface with a light over it so that it grows upwards in one direction, plant pillow set-up at NASA). This prompted me to attempt to fill every space of the growth chamber with leafy greens by strategically placing each plant around a central regular shape, which I will go in depth with later on in the Instructable.

Another issue NASA faces when growing plants in space, aside from the inefficient growing methods, is the media used to facilitate root growth. Media is crucial in plant growth, since it is what fosters healthy root systems which intake nutrients. However, the clay-based soil used currently in NASA's plant pillows cause and face several problems. The soil is relatively heavy compared to other media's that could be used, such as memory foam or hydroponics, so the cost of shipping it up in a payload is increased because of that. The soil also does not properly disperse and spread the water throughout the pillow, even with the use of paper wicks that attempt to draw in the water towards the seed, meaning that some areas of the pillow are drowning while others are in drought. Finally, the soil is also non-renewable, meaning that it currently can not be reused for multiple growth cycles. This is the biggest issue with this kind of media, among others, because you must have a sustainable and closed system for long term space travel. There is no way to dispose and replace the soil in space without simply putting it to waste, which is also the issue with other forms of media such as foam or silica beads. This issue brought me to design a 3D printed matrix as the "media" for the plant which would, in theory, facilitate plant root growth, be reusable, and have the ability to be taken apart in order to extract root mass from prior plants.

My Proposed Solution

In order to fill in the most amount of space, plants would be grown on the vertexes of a tetrahedron inspired plant pillow that would hold in the roots at the center of the shape in a small confined area, potentially solving the watering issue which I will explain later, grow plants outwards in the 360 degrees around the planting site, and be reusable because of the 3D matrix replacement for media.

Step 1: Step 1: the Brainstorm

I wanted to tackle the issue of "inefficient use of three dimensional space" first, as it was where much of the innovation could be centered around. I flew through a plethora of ideas, from modular designs to automatic harvesters, which I scrapped because they were unreasonable, until I found what I believed to be a sound tactic. Choose a point in space and use the 360 degrees of space around it to grow plants. The center of the space would be used to contain the roots while the rest of it would be for leafy greens. This led me to look at regular polyhedrons, which were three dimensional shapes that would evenly spread out the plants throughout the 360 degrees of rotation. Depending on what polyhedron you chose, you would have a different amount of plants being grown around it, assuming you planted each plant at the vertex of said shape, as seen on the figures above. After playing around with several different shapes in a variety of different sizes, I settled on two shapes, the tetrahedron and the cube. The tetrahedron of side lengths 8.5 cm could hold four plants in just 72.38 cm^3, while the cube of the same length could hold 8 plants in 614 cm^3.

Root Space

This led me to the realization that my plants would be sharing root space, so I wouldn't know if they were going to grow in harmony and assist each other or simply choke each other out. This also led me to the fact that the bonsai effect could be present in my plants because of their restricted root systems, which would lead to dwarf sized plants. However, I couldn't be sure that either of those factors would destroy my design without testing it first, so I stayed on task and kept designing with those things in mind. The small root space also brings up the idea that because the root space is so minimal, the water will have an easier time spreading throughout the shape, theoretically fixing the watering issue.

The plants would ideally shoot their roots down into the center of the shape, draw up and use the water, and continue to develop their root mass throughout the remainder of the shape.

Tetrahedron Over Cube

I was discouraged from using the cube design because it was a lot of plants being grown in extremely close proximity, which I knew would lead to some plants becoming overshadowed by others. This led me to use the tetrahedron as the main polyhedron for the design, because it used less space for the roots per plant and had each plant at such an angle that their growth would not overshadow the others.

Lights

I also planned out where each tetrahedron would go in the 50 cm cube in order to maximize space, which allowed me to fit 8 tetrahedrons in the growth chamber, 32 plants, while also giving them enough space to grow. The lights would be strategically placed in order to grow certain plants in certain directions, since plants use light to determine which way to grow.

Watering/Harvesting

The tetrahedron was a framework, which would allow for the plant pillow material to be wrapped around it, with the media inside, and sealed. There is a hole for the water pipe at one of the bases and would be used to hold the shape in microgravity. The water pipe is also a quick release seal, meaning that astronauts could detach the tetrahedron from the growth chamber and pull it out for easy 360 degree harvesting.

Step 2: Step 2: the Design

The growth chamber was designed in Fusion 360.

The growth chamber is a 50 cm cube that has the capabilities to facilitate the growth of up to 32 plants. In the first image, the water pipes, shown in blue, run along the sides of the box and then branch off to hold the tetrahedrons, in black. The six lights, shown in yellow run from the back of the box to the front and are held by suspensions at the opening. The green is meant to represent the plants, assisting in the visualization of the idea that the plants will grow in 360 degrees, and where they will grow. The red boxes are fans, 6, which will circulate air throughout the box.

The box cover is a hinged door that has a glass cover so that you may see into the box and a screen at the bottom where you can see the temperature and humidity readings, among other statistics, of the box. The cover of the box is hollow so that it may incorporate Raspberry pi's, which could ideally adjust the watering amount, fan speeds, and the lights RGB intesity, water reservoirs, and temperature/ humidity sensors.

The box would ideally be made out of a solid material such as acrylic or steel and contain reflective material on the inside walls in order to maximize the amount of light reaching the plants. The water pipes are going to be PVC and will be connected to the automatic watering system which would use pressure and capillary action to shoot the water into the tetrahedrons.

Variation in Tetrahedron Sizes

Because it is difficult to predict how the 8.5 cm length tetrahedron will perform without testing it, I decided to have bigger tetrahedrons, increased side length in 1 cm intervals, in case the original does not have enough room to support plants.

Step 3: Step 3: the 3D Matrix

Ideally, the plants would grow without media, in order to stay reusable and sustainable. In order to do this I have designed a three dimensional matrix that would, in theory, hold water in its holes and allow for the plants roots to grow around it. The idea is that there are two pieces to the matrix, an X and a Y matrix, that interconnect in order to form a 3D matrix, as shown in the first figure. After the plants have developed their roots, the plant pillow would be opened, the matrix would be removed and then taken apart in order to remove all of the root mass, then put back together, ready for another growth cycle. The design I have made is currently made for the cube design, however I can easily adjust it to fit into the tetrahedron. The matrix would be three d printed.

Step 4: Step 4: Benefits of My Design/Future Prospects

My tetrahedron design offers a variety of solutions to the current issues faced by NASA's VEGGIE system and plant pillows. I allows for a productive use of 3D space, potentially fixes the watering issue by confining the root space, allows for reusability, no use of media, and, most important of all, is simple. The design was made to be simple so that it could be easily adjusted and flexible. None of the components are set in stone and it all needs to be tested in order to be proven valid or failure. In this design, the placement of the lights, orientation of the tetrahedron, use of different polyhedronic shapes, staggered growth cycles, use of different media and much more could be tested/changed in response to how the initial test goes.

I hope to begin testing all of these designs once I have access to an efficient way of simulating microgravity, such as a homemade 3D clinostat. I would be able to then determine the appropriate amount of root space needed, whether or not the 3D matrix works, and how nutritious my plants would be, which would be done by testing for phenolic compound concentrations and comparing them to those grown by NASA's VEGGIE pillows.

Step 5: Acknowledgements

I want to thank Dr. Salazar and Jordan Dewitt for assisting me and being there to answer my questions when I needed it the most. If it were not for them, I would be much more lost, so I am thankful for their contributions.