Introduction: Zero Gravity Gardening Concept for Deep Space Travel
Hey Instructables, this is my submission in the collegiate level to NASA's Growing Beyond Earth Contest. My micro gravity garden is codenamed G.R.E.E.N.S, which stands for Growing Romaine in Extraterrestrial Environments for Nutritional Supplement. If you guys like my design, please give it a vote and let’s see if we can get some G.R.E.E.N.S. up to our astronauts on the ISS.
Phase I of NASA's Growing Beyond Earth contest focuses on the creative use of 3D space to maximize the amount of fresh vegetables they can grow in the limited volume within the ISS. My design uses three key principles to optimize 3D space:
- It uses "Phase Crop Production" by splitting the plants into 4 different growth stages to minimize the issue with wasted headroom above young plants
- It uses a mathematical concept called “circle packing” to maximize the volume of open space taken up by the plants
- It capitalizes on the microgravity environment on the ISS by growing plants on back to back trays
This design will produce 12 lettuce plants every 7 days. This is a 800% increase from the current VEGGIE system which only produces 6 plants every 28 days. Imagine our astronauts on the ISS having a fresh salad every single day for lunch… That exciting idea is a made possible by my design. Follow along, and let's see how to make that happen!
Step 1: Growth Stages
The first volume-optimizing strategy I will explain is splitting the plants up into growth stages. Splitting the plants into 4 different growth stages with 4 drastically different size constraints allows us to make much more efficient use of 3D space. This is because it allows us to design a growing system which has different compartments for the different sized plants. This maximizes 3D space because it eliminates the extra “headroom” plants would need as they grow.
The 4 phases would be as follows:
- Stage 1: 0-7 days
- Stage 2: 7-14 days
- Stage 3: 14-21 days
- Stage 4: 21-28 days
Stage 1 is comprised of germinating seeds in the first 7 days of the growth cycle. They will be covered with germination caps to increase the humidity and encourage germination. This is a strategy currently used on the ISS, and definitely worth continuing. The maximum dimensions of the seedlings in this stage will be 2cm tall by 2cm in diameter.
Stage 2 is comprised of seedlings from Day 7 to Day 14 of the growth cycle. The germination caps will be removed in this stage. The mass of the plant will not increase much during this stage. The maximum dimensions of the seedlings in this stage will be 4cm tall by 4cm in diameter.
Stage 3 is comprised of maturing lettuce plants from Day 14 to Day 21 of the growth cycle. At this stage the lettuce will begin growing at an exponential rate (or at least their mass will be increasing at an increasing rate). The maximum dimensions of the plants in this stage will be 9cm tall by 12cm in diameter.
Stage 4 is comprised of maturing lettuce plants from Day 21 to Day 28 of the growth cycle. This stage is the final growth stage, and the lettuce will be growing to maturity for harvest on Day 28. The maximum dimensions of the plants in this stage will be 15cm tall by 15cm in diameter.
*Note that the above dimensions had been gathered from data published by high schools participating in research along side Fairchild Tropical Botanical Garden.
Stages 1 and 2 will be when the Outredgeous Lettuce is still in its "Lag Stage" of growth during its first 14 days. This lag stage occurs because the plants grow very slowly while the seed germinates. Accordingly, the growing tray for the first two stages is significantly smaller than the growing trays for the second two stages. In Stages 3 and 4, the lettuce will grow in what the botanists at Fairchilds Botanical Garden were calling "Logarithmic Growth". During the second 14 days of their growing cycle, the lettuce adds a new leaf roughly every day, and the water usage increases exponentially. Accordingly, Stages 3 and 4 take up substantially more room, and it is why they comprise two full size (50cm by 50cm) growing trays whereas Stages 1 and 2 take up less than even half a growing tray (only 20cm by 50cm).
The growing trays also have drawer slides on the tops and bottoms of them so that they can slide out of the growing chamber and allow for easier access for when the astronauts need to harvest and tend to the plants.
Step 2: Circle Packing
Circle packing is a field of mathematics dedicated to optimizing the amount of circles one could pack into a given shape. In this project, I used circle packing to maximize the area of circles that can fit into the 50cm by 50cm growing trays. (The “circles” I'm referring to in this case are actually the diameters of the lettuce plants at their respective stages).
Two variables which made designing the circle packing for this project even more complicated were that: 1) I had to pack circles with different diameters since I combined two growth stages onto each growing tray, and 2) I also had to consider 3D space, not just two dimensional circles. In other words, I needed to consider that the lettuce will be growing roughly in half-sphere shapes, so I must also consider height as well while I was arranging the circle packing. My creative solution to optimize the amount of half-spheres I could fit into the design, was that I slanted the growing tray.This allows me to combine Stage 3 and Stage 4 plants (which are different heights) without sacrificing valuable head space above the plants. The reason it was so crucial to combine two growth stages into each growing tray was due to the fact that Stage 3 and Stage 4 had drastically different lettuce diameters. This meant that I could only pack 9 total Stage 4 plants into a 50cm by 50cm tray, but I could pack 16 total Stage 3 plants into a 50cm by 50cm tray. However, by combining the two growth stages, I could fit 6 plants from each Stage 3 and Stage 4 plants into a 50cm by 50cm tray. Multiply those six plants by two 50cm by 50cm growing trays and you get 12 plants from each Stage 3 and Stage 4. That is a 33% increase in lettuce plants maturing every 7 days (12 plants vs 9 plants).
The two innovations I used to arrange the heads of lettuce drastically increased the efficiency of the "phase crop production" methods many others have considered. There two innovations are: 1) circle packing and 2) combining different growth stages into the same growing trays. As you can see in the graph above, the area of the growing trays covered by lettuce leaves was increased from a mere 35% ratio, to nearly 70% of the area of the growing trays being covered by lettuce leaves. These two methods featured in this design doubled the efficiency of the "phase crop production" designs many others have considered, and it is why I think this design is a true contender for being the most efficient design out there.
Another space-saving element I could utilize through circle packing was combining the growing medias for both sides of the tray into a single plane (one layer of aquaponics thick, not two layers like many designs). This saved another 4 centimeters width-wise across the entire height of the 50cm by 50cm growing chamber. To see how this was achieved, please see the last three pictures included above.
Step 3: Consideration of Microgravity
My design utilizes the unique conditions of microgravity experienced on the ISS by having two growing planes on opposite sides of the same growing tray. In other words, there will be plants growing 180 degrees from each other. This layout is possible because in microgravity, plants rely on phototropism (their innate ability to growing towards light) to orient their direction of growth.
Step 4: Irrigation & Aquaponics
My design uses drip aquaponics with nutrient rich water (also called nutritive water) to feed the plants. Nutrients will be dissolved in the water reservoir (the highlighted white box in the image above) once per week, and steadily distributed with the water to the plants over the next 7 days. The reservoir encompasses an impressive volume of 30cm by 40cm by 10cm, which is a total of 12 liters. Due to the large size of the internal reservoir, this system only needs to be refilled with water every 5 days, which is a drastic decrease from the daily monitoring required by the current VEGGIE system. The plants are also watered autonomously, meaning astronauts are no longer required to water plants manually every single day (more details below).
For my prototype the plants will be growing in Rockwool Macro plugs. These 1 inch by 1.5 inch plugs have earned a reputation as being a phenomenal growing media for lettuce in aquaponics, and this proven track record is one of the reasons I selected them for my design. Their mass is also less than 5 grams per plug, and although you need to add in the weight of the dissolved nutrient to make it a fair comparison, that is still a far cry from the current 200 gram Arcilite pillows currently being used on the ISS.
There would effectively be two "loops" of irrigation with two individual peristaltic hose pumps each dispensing different amounts of water. One loop would serve the largest growing tray housing the Stage 3 & 4 plants, and this loop would dispense 100mL per plant per day. The second loop would serve the smaller growing tray housing Stage 1 & 2 plants, and dispense substantially less than 100mL per plant per day. This lesser amount would be discovered through further testing.
Although the livestreams that Fairchild Tropical Botanical Gardens hosted emphasized our designs do not yet need to take into account the effects of microgravity on water, the drip irrigation system my design uses along with peristaltic pumps to accurately dispense small volumes of water accurately would presumably function in a microgravity environment. One extra consideration yet to be made would be that the reservoir must be made of a flexible material (such as a bag) so that one the pumps begin removing water from the reservoirs, it creates a small vacuum within and the reservoirs slowly deflate as their with water is drained. This is an important consideration because otherwise the pumps may be sucking up air, since in microgravity water would not be pulled down into the pumps.
Step 5: Lighting
In the photos above, the LED lights are highlighted in red, and other components are removed to better show the LEDs. All of the growing trays span across the entire 50cm depth of the growing chamber, and LED lights likewise span across the entire depth of the chamber.
One way which this design shines is in the lighting category, due to the fact that it splits the plants up into growth stages. This is because by splitting up plants into the growth stages, it removes extraneous headroom above the plants (For example, if there is a 3cm tall seedling in a growing chamber designed to house a 15cm tall fully mature plant, there may be 12cm of extra headroom above the plant). This extra headroom is detrimental to rapid plant growth as the intensity of light decreases exponentially as a function of its distance from the source. (To help augment my explanation I've included a diagram from this nasa.gov website in the photos above). Without getting bogged down by the science in the Instructable, this design maximizes the amount of light that is absorbed by the lettuce leaves by placing them in very close proximity to the source of the light. This thereby increases the rate at which the lettuce grows, as well as saves energy as there is very little excess light that is not absorbed and ends up escaping the growing chamber.
Step 6: Final Thoughts
Overall, I would like to take a quick moment to review the features of this design, and explain why it is a contender for the most space-efficient design out there, and how it is able to produce 48 fully developed 15cm by 15cm heads of Outredgeous lettuce in the same 28 days it would take VEGGIE to produce 6 heads.
This design uses several different innovative techniques to increase to production of romaine lettuce 8-fold from the current VEGGIE system. These innovations include:
- "Phase growth production" to eliminate wasted headroom above young plants
- Circle packing to maximize the area of the growing trays that are covered by lettuce leaves
- A slanted growing tray to allow for two different growing stages to be combined into one growing tray without sacrificing volume to wasted headroom
Another unique element of this design is not only can it produce 12 fully grown lettuce plants every 7 days, but with the increased size of its interior water reservoir and inclusion of an autonomous watering system, it also only needs to be tended to once a week (This weekly maintenance would include harvesting crops, rotating the growth stages, refilling the water reservoir with dissolved nutrients, and refilling water reservoir with water). Overall this design satisfies the three main issues presented in Phase I of the Growing Beyond Earth Challenge. These issues were:
- Creative & efficient use of 3D space to optimize the volume of plants that could be grown
- Autonomous watering of the plants & increased size of the water reservoir to decrease the time astronauts would have to spend tending to plants
- Moving away from the heavy and nonreusable Arcillite Clay growing media in favor for a lighter (and thereby more efficient and sustainable) method of growing plants in space for long term space travel
Before I close, I would like to thank NASA, Fairchild Tropical Botanical Gardens, and Instructables, along with the countless people working for these organizations who have helped to make this Growing Beyond Earth challenge a possibility. It was a blast conceptualizing and designing this growing chamber over the last few months, and I think it is wonderful NASA turned to the citizens to crowdsource ideas for their future missions to deep space. Thank you so much for this wonderful opportunity!
Brandon Spellman (Author and Designer of G.R.E.E.N.S.)
Runner Up in the
Growing Beyond Earth Maker Contest