Last year at the Nation of Makers Conference a design challenge was announced by NASA and the Fairchild Botanical Gardens. A three stage competition to design a farm for the international space station. Apparently even astronauts need to eat, I know shocking. Turns out that sending every pound of food to orbit at a cost of $2,500 per pound on a SpaceX Falcon 9 is cost prohibitive. Not to mention that most of the food they eat up there is not exactly fresh. The answer LETTUCE! Stage one will be to design a chamber for growing plants, specifically Red Romaine Lettuce. Later stage two would be building and stage three automating its operation. As someone who can't keep a house plant alive this sounded like something I was not qualified to do. So naturally as a maker I got started right away.

Step 1: Research....i.e. Googleing Stuff

Going into this project I had no idea how to grow a plant. I'm from Wisconsin so I've seen a plant before, even been on a farm but had no idea what a plant needs to grow. Dirt I guess? Maybe I should go get a shovel and start digging in the back yard?

There are so many ways to grow a plant. Turns out dirt is optional. The 5 things you need to germinate a seed and grow a plant are:

1. Grow Medium

Something has to nest the seed and allow the first roots of the plant to sprout and find the path to water and nutrients. Here on plant earth we can just put a seed in the ground and let the dirt hold the seed but you can also use lots of different sponge like materials to keep your seed wet while its sprouting. The ISS is a fairly clean environment, except for that cool zero gravity toilet, and we should try to keep it that way. Maybe dirt is not the best option.

2. Nutrients (plant food)

Plants got to eat too yo. The circle of life we eat plants, plants eat minerals and glasses, minerals eat tiny vibrating strings in the 4th dimension? Not really but you do need things like:

Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca), Sulfur (S), Magnesium (Mg), Carbon (C), Oxygen (O), Hydrogen (H)

Lots of these items are already in dirt in various amounts and also in the air here on plant earth. On the ISS there are some challenges here and some advantages. For example in zero gravity there is no natural convection of lighter or hotter gasses and heavy or colder gasses. Fans are super important on the ISS. For example with out them carbon dioxide would build up in a bubble around the astronauts as they sleep choking them. The same goes for our plants. Without a fan the plants would not get the gasses they need to survive. SPACE! Why are you trying to kill us so much?!

3. Light

You know the sun. We all remember from 5th grade that plants use some sort of which craft called photosynthesis. For the purpose of keeping this short plants use light to convert the previously mentioned chemicals Nutrients into energy. It's frickin cool and ya'll should look it up. Science is real people! Here on earth the sun is a great light source it rises everyday and provides hours of light before setting again day after day. The ISS is whipping around the earth at 17,100 miles per hour. That means it sees a sunrise every 90 minutes! Which is basically like a strobe light for a plant.

4. Water

The earth is mostly water. Salty water. This is not the kind we need to grow a plant. We need the fresh kind that falls from the sky and runs down a mountain side into a river or lake. The kind of water we put feces in and flush down the toilet in the western world. It's actually a moderately rare commodity that many people in the world don't have access to. This is a google rabbit hole all in it's self and I'm not going to touch it. All we need to know for this project is water is what carries those nutrients into the roots of the plant.

Wow! Nature is neat. You should really click this link...

Step 2: Building Knowledge.

Ok don't be a victim of the Dunning–Kruger effect. Lets do some experimenting, put what we know to the test, and add to it buy building a thing. Specifically lets try to make something that will grow plants in my apartment.

Warning: DO NOT google growing plants hydroponically in your apartment.

Lots of not safe for work images that might be ok in California or Illinois. A little searching led me to the Kratky method. This can be as simple as a mason jar filled with water and nutrients with a seed suspended in your grow medium place in a window. I wanted to do some testing on parts we would need to use on the ISS so I went with a slightly more complected set up.

I chose to build with commonly available items and no custom parts. Most of the parts can be found at your local home improvement store. That plus amazon and I was good to go. The structure is made from 10x10mm aluminum extrusion and the water tank is two sizes of PVC pipe. To take the place of the sun I found some 10W led lights that I am running with a raspberry pi to turn on and off for a day cycle. I am sure I could run them with a Arduino Nano but I just like python better.

For the competition I need to grow Red Romaine Lettuce but I needed to walk before I could run on this one. I went with a pre-made solution by AeroGarden. They make a small container with seeds suspended in a growing medium ready to go. They even supply the chemicals to add to your water. I just needed to try and grow something to prove that I could.

https://www.amazon.com/AeroGarden-Salad-Greens-Seed-6-Pod/dp/B01614SRAS/ref=sr_1_7?keywords=hydroponic+plant+pods&qid=1579456288&sr=8-7

Step 3: Designing the Zero G Hydroponic System

WHOO HOO! My seeds sprouted! And that's about all they did... My theory is not enough light but I think we can move on to a design with some of what we learned. This time we will apply the inverse square law as it applies to light brightness over distance into account. I always like to start with a sketch something basic to get the idea across. Here are some of the design thoughts.

1. The light should start closer to the plant and move further away as it grows.

2. You should be able to get lettuce weekly if not daily

3. Water needs to circulate with nutrients in zero gravity, but remain contained.

Part of challenge was this system would need to fit inside a 500x500x500mm cube so I started with a square. I knew if I designed around an off center axis I could rotate the plants to change their distance from the light source as they grew. It would also allow me to have lettuce at all stages of growth from seed to ready to eat. Buy having rows of plants potentially you could have several heads of lettuce ready to eat every week after getting through one grow cycle. In the past I have worked with peristaltic pumps to move water and in this case we can also use one to add nutrients as needed.

ISS Grow Cube.tif
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Step 4: So...Much...Modeling...

Strangely this is one of my favorite parts of the design process. There is something relaxing about drawing every little part to see how they will fit together. I teach a weekly class at my local makerspace in Fusion 360 so I got to modeling. After drawing the lighting, heat sinks, motor, pump, Raspberry Pi, pulley, and lots of aluminum extrusion I was able to assemble them all into one component. This is how it will work.

The central tube contains 6 rows of 5 plants for a total of 30 heads of lettuce. I really liked using those pods from AeroGarden so I found some similar grow medium that I can place seeds in and designed a 3d printed cage to hold them. A peristaltic pump moves water from the back of the tube to the front pushing it over the roots and grow medium along the way. As there is no gravity to move the water I will use 3 fans mounted in the front section to help push the water from front to back. This pump is powered across a slip ring that allows the entire central tube to rotate on bearings as the plants grow. Every week one row of plant pods will be placed. Right now this will be done by a person but I am hoping to automate that process in the future. Once a row is planted in the tube for germination the tube will rotate to the first position where lights are the closest. One week later after planting the second row the tube will rotate again. Lighting is progressively further away from the plants giving them a bit more room to grow each time the tube rotates. After doing this for 5 weeks on the 6th week in addition to planting one row there will also be one row ready to harvest. This means that after one full growing cycle of 6 weeks astronauts will be able to harvest 5 heads of lettuce ever week for the duration of the gardens use.

Step 5: Time to Make Stuff.

This is a design challenge so no making is required but making stuff is fun. Also there is lots to learn about how to better design something by building it. I wanted to put into testing some of my design modifications from the first tests which feel like so long ago now. It's so amazing to me that so many towns have access to a great makerspace. It just so happens that ours in Milwaukee is among the best. Although I am more than a little bias, because I have been a member for 8 years, I have been to space in Tokyo, Chicago, Los Angles, New York, and London just to name a few and the Milwaukee Makerspace is second to none for it's community of interesting makers and what they can do. Without the brain picking that is an everyday occurrence on a project like this it would not be possible to build this. If your in the Midwest make a trip and you will not be disappointed.

Enough about my makerspace From this testing platform I plan to do experiments on light distance, brightness, and color as well as water life span. I'll also be able to run some of the hardware and software that I plan to use in the prototype.

Step 6: The Final Design to Begin Testing

It's not the end it's the begin...again. Leonardo da Vinci said "Art is never finished, only abandoned". While I am not at the point of abandoneing the project it is time to call it designed and move on to the next stage of the process. Testing! There is so much to test and then take what I learn and iterate on the design.

Step 7: Thinking About the Next Steps

The next two stages of the challenge will be building/testing and then automation. I wanted to start thinking about these things right from the start. I have some rudimentary ideas how this will get implemented. Here are the questions I hope to answer during testing on both the prototype and my small single row unit.

How far away the lighting will be at each of the 6 stages inside the cube?

What is the best wavelength of light to use at each stage of growth knowing white will be used in the final stage to show off the green of the plants.?

How often will water need to be changed out?

How often will nutrients need to be added?

What is a good frequency to pump the water?

Do the Fans blowing on the roots effect them?

Different duration of light at each of the 6 growth stages?

Will roots in the chamber get tangled making plants hard to remove?

Possible design additions might include a water tank so fresh water can be added or exchanged with the water in the grow tube and a gray water tank for expired water. Finally automation, the more this cube can be self sufficient the better. I have some ideas how to move a simple rotating arm on an axis to remove fully grown plants and add new pods for germination but those ideas will need to be further examined. From here I will be continuing my development on the GitHub page below so feel free to follow and contribute if you would like. There I have photos, Fusion 360 files, wiring diagrams, and some python for your enjoyment. I will also finish work on the prototype that is already in the works. Once I gather some data from the small test platform I built.

https://github.com/donuts4life/0G-Grow-Cube