Cosmos

Growing Beyond Earth

Cosmos/Cube Grower v 2.2 :)

Jaclyn Chen

High School Submission

The objective of the submission is to optimize the growing space for food production on the ISS. When plants are small, there is empty space above them. When plants grow larger, the leaves become more concentrated at the top and there is more empty space underneath the leaves. In microgravity on the ISS, objects appear to float because the ISS and the objects are free-falling at the same acceleration. Furthermore, plants do not rely on gravitropism but rather phototropisms. Water acts based on molecular adhesions and would need to be contained within the system to prevent water loss and water floating throughout the space station.

Additional parameters/information:

- 50 cm cube

- Light, water system

- ISS currently grows 6 plants in "grow pillows"

- Red Outredgeous Lettuce

- Inventive, effective :)

I first drew some rough sketches of different ideas for the system. (1-9)

8) Hexagonal Prism

- Multiple plants would grow in a row on each face towards the center of the prism

- The prism can be unfolded into its shape net. The rectangles would be able to snap on and off to allow for easier access to the plants

- Modular --> Prisms can be stacked on top of/next to each other (most efficient for space in a honeycomb pattern)

The primary designs I was deciding between were 8 and 9. Ultimately, I opted for design 9, which allows for the regulation of more variables. On the ISS, microgravity allows plants to grow in any direction, and the plant spheres “float.” One of the challenges in optimizing growing space is that “when plants are small, there will be empty space above them. As plants grow, leaf surfaces become closer to the light, creating empty space underneath.” This design uses separate pods for each plant that would break the constraints of a rigid structure (the rest of other designs e.g. (1-8). Design 9 was the only design that fulfilled the empty space requirement without a *plant rotation system* (see below). Astronauts could control the distance the plants are from a light source and the direction the plants are growing in by simply moving/tilting the sphere the plant is growing in. This way, we can move smaller plants closer to the frame, and gradually move them further away as they grow. This would also the system to grow a variety of different plants because each species has a different rate of growth and light requirements (long night, long day, red:blue ratio...etc.). Additionally, the sphere system is modular since we can add more spheres as needed to grow more plants.

*plant rotation system* With the other designs, the only way to maximize empty space when plants were small versus when they grew was to rotate the placement of small plants and large plants. In a tray system design (1 or 2), smaller plants would grow on the top tray and larger plants would grow on the lower trays. As the smaller plants grow, their tray would be moved to the lower level, the larger plants would be harvested, and the top tray could grow smaller plants again. However, in the end, I decided that the system would not be viable because plants do not grow at a linear rate. They instead grow at a Sigmoid curve Therefore, a rotation system would not work for plants of the same species (and different species of plants).

From the materials I could acquire, the frame is a 50 cm X 50 cm cube, made from 12 PVC pipes (45 cm) and 8 side outlet elbow fittings (2.5 cm additional when attached to the tube). I wrapped in the frame in transparent vinyl to contain water. The frame and vinyl are lightweight materials. The vinyl has a relatively low albedo and still allows astronauts to view the plants. Siding that is not reflective will provide more control in the direction the plants grow in (LEDs) since growth is controlled by phototropisms. If the sides were reflective, the light would bounce in all directions. On the other hand, the siding is not made an opaque black so astronauts can still enjoy them :) Growing plants is “good for [astronauts’] psychological well being” (Heiney, 2019). The vinyl was secured on the PVC with 3D-printed clips that are typically used for greenhouses.

I printed spherical containers for the plants so that the containers are symmetrical and don’t have sharp corners that can latch onto each other. They are 9.5 cm in diameter. The spheres are attached to tethers to the frame so they stay in the same position. Although there is microgravity, the spheres will still move around and it would be bothersome for astronauts to need to try to put them in a certain position. The spheres are attached to the tethers using clips or magnets. The spheres will just need to be placed onto a magnet anywhere on the tether. The tethers are attached to the frame with thinner 3D-printed clips.

Two variations:

Open sphere (has holes):

(+) Allows roots to be misted Gives more space for roots to grow Water drains/floats in the closed frame (could be a (-) )

(-) Water floats within the system (but still closed) Roots can be potentially exposed to light (depending on the type of substrate) → inhibit root growth, algae growth

Closed sphere (with a hole for watering tubing/peristaltic pump):

(+) Roots not exposed to any light Water contained within the sphere (not floating in the frame, conserve water)

(-) Limits the growth of roots → potentially choke the plant

Substrate:

Rockwool, gel, clay pebbles The sphere would be filled with a mixture of Rockwool (for initially planting the seed), plant gel (seed, water retention), and clay pebbles (for oxygen, drainage) as the substrate. I couldn’t buy any Rockwool or clay pebbles for my submission so I only tested plant gel. I boiled a mixture of cornstarch and water (1 tablespoon: 1 cup). For the open sphere, I placed the sphere in a latex glove to keep the liquid contained until it solidified in the fridge for half an hour.

In my prototype, I didn’t fill all the spheres with substrate since they dragged on the tethers. Nonetheless, in freefall, the mass would not matter.

I added led strips (24 LEDs/per strip) to each inner edge of the frame. The LEDs are not all intended to be on at once but to be programmed in segments (target direction plants grow in). For Red Outredgeous Lettuce, I used an RTC and Arduino Uno to program the lights to turn on for 14 hours each day (lettuce and spinach are long-day plants) in a 3 red light: 1 blue light ratio, and white LEDs to make the plants look natural. This timing or ratio can be changed depending on their photoperiodism or the absorption spectrum of different plant species.

The plants are watered using the substrate gel (for seeds), a water atomizer (for humidity), and peristaltic pumps. The humidity for leafy greens should be between 50-70 percent. I used a humidity sensor so that when the humidity decreases under the threshold, a relay turns on the water atomizer. A fan also circulates the air and the misted water. Peristaltic pumps with tubing to each sphere are turned on every five days or when the water sensor detects the substrate is dry. Nutrients and pH stabilizers can also be delivered to the plants from the water atomizer (aeroponics) or peristaltic pumps (added to the reservoir).

The sensors (temperature, humidity, moisture), RTC, LEDs, relays, water atomizer, fan, and peristaltic pumps are all controlled from an Arduino Uno. The LEDs are also wrapped in the vinyl to waterproof it. The “control panel” rests on the outside of the siding.

Libraries:

- FastLED

- RTC

Hardware:

I wired the LEDs similar to how it was wired in this Instructables. (https://www.instructables.com/id/Easy-Infinity-Cub...) :)

(1) I first cut a led strip reel into 12 segments of 24 LEDs. (2) I cut 24 short jumpers for each of the ground, data, and 5V nodes and (3) soldered them on each side of the led strips. This step of pre soldering the LEDs would be easier than soldering the LEDs when they are attached to the frame. (4) I attached each strip onto an edge of the frame, making sure the direction of the strips was correct. (5) I twisted the matching jumpers together and soldered the joints.

Code (attached below):

I programmed the cube to have a ratio of 3 Red: 1 Blue LEDs that turn on for 14 hours a day.

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Different RED: BLUE Ratio. (n.d.). Retrieved December 15, 2019, from https://www.led-lights.com/different-red-blue-rat...

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Heiney, A. (2019, April 9). Growing Plants in Space. Retrieved January 2, 2020, from https://www.nasa.gov/content/growing-plants-in-sp...

Instructables. (2020, January 8). "Easy" Infinity Cube. Retrieved December 22, 2019, from https://www.instructables.com/id/Easy-Infinity-Cu...

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