Introduction: SeedShuttle - Growing Beyond Earth
Hello! This is a collegiate submission by GroTech @ Berkeley, a student research organization dedicated to the design and innovation of agricultural technologies. We have designed a plant growth chamber for Phase I of the Growing Beyond Earth (GBE) Maker Contest. The objective is to “design a plant growth chamber for use in space that makes effective and inventive use of the available volume on spacecraft (a cube 50cm of a side), while also incorporating the necessary features for plant growth (sufficient lighting, irrigation, and air circulation).” - GBE Maker Contest Overview Page
To start, we identify design constraints:
- International Space Station (ISS) conditions: 50cmx50cmx50cm space and microgravity
- Required features for plant growth: light, nutrients, water, space, air, temperature
- Plant of interest: Johnny’s Seeds’ ‘Outredgeous’ Red Romaine lettuce
- Leaf head grows to approximately 15cm in height and 15cm in diameter at full maturity after about 28 days of growth
- Roots require minimum 216cm³ volume with 6cm of depth
- Seeds sowed at 1/8" depth for germination
- Requires approximately 100mL daily
- Grows best at temperatures of 16-18°C (60–65°F)
With these design constraints in mind, we now proceed to the fun part: design! We primarily base the spatial arrangement of our plants on ‘Outredgeous’ Red Romaine Lettuce geometry:
- Mature lettuce is shaped like an upside-down cone. By arranging plants to grow outwards radially rather than grow upwards linearly, we minimize unused volume between adjacent plants. [See lettuce image 1 above.]
- When we arrange eight columns of plants radially inside a cube, there are two different volumes for growth (towards side of cube and towards edge of cube) so we stagger planting. [See lettuce image 2 above.]
- When plants at the latter growth phase are mature, we harvest. New plants are inserted and the eight column arrangement is rotated 45° so plants at the earlier growth phase now occupy the volume of the harvested plants. [See lettuce image 3 above.]
We arrive at a radial design for our plant growth chamber, which we affectionately name SeedShuttle. SeedShuttle has three layers with eight plants each (with alternating growth phases). SeedShuttle houses a total of 24 plants and yields 12 mature heads of lettuce every 2 weeks, a four-fold increase in production compared to NASA’s Veggie, which houses a total of 6 plants and yields 6 mature heads of lettuce every 4 weeks.
The following steps address additional design choices based on ISS conditions/plant growth requirements and detail the construction of our prototype in sequential format:
- Medium density fibreboard (MDF)
- Aluminum L channels
- Transparent acrylic
- Hinge (x2)
- Bolt Lock
- LED light strips
- Reflective tape
- 3D-printing PLA
- Guar gum (as glue)
- Calcined clay substrate
- Slow-release fertilizer
- Foam gaskets
- Irrigation tubing
- Syringe (for manual water injection)
- Water pump (for automatic irrigation)
- 3D-printing PLA
Lazy Susan bearing (x2)
- Small fan
- 3D-printing PLA
- Stepper motor
- Central reservoir
- 360° rotation solenoid
- Arduino microcontroller
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Step 1: Enclosure | Building a Transparent Box
The plant growth chamber will be placed in a NASA EXPRESS Rack, which is accessible only at one side.
We choose transparent material for the enclosure walls so that astronauts can visualize and monitor the growth of the plants.
- Construct a 50cmx50cmx50cm box with medium density fibreboard (MDF) sheets for the top and bottom, connected by four aluminum L channels as edges.
- Attach transparent acrylic sheets to three of the four open sides.
- For the remaining side, attach another transparent acrylic sheet to an L channel via a hinge, allowing the sheet to swing out like a door. (This side, the access point, will be known as the front.)
- Secure the door with a bolt lock.
- Position an additional acrylic sheet 5cm above the bottom MDF as a partition: electronics will be housed below while plants will be placed above.
- Since a portion of the acrylic partition obstructs insertion/removal of pots in the lower layer, cut that portion and mount it to the door. When the door is opened, this portion swings out along with the door.
Step 2: Lights | Attaching LEDs
Under microgravity conditions, lights dictate the directionality of plant growth.
We decide to use red-blue LED strips because plants primarily absorb red and blue light; LED strips are relatively slim, allowing more space for plants.
Between LED strips and plants, there must be a minimum clearance of approximately 5cm so that light can reach each leaf; this also prevents plant stress due to heat emitted from LEDs.
- Position three LED light strips on each wall (including the door) such that each light strip is aligned with one layer of plants.
- To ensure that the plants at the top and bottom layer receive a similar amount of light as the plants in the middle layer, coat the top MDF sheet and the acrylic partition with reflective tape.
Step 3: Soil | Assembling Pots
Roots require water and oxygen, so we choose an absorbent yet porous soil substrate: calcined clay (we choose solid growth media because liquid growth media cannot easily retain a homogenous mixture of both water and oxygen in microgravity).
An alternative substrate that may satisfy water and oxygen requirements while trending away from solid media is polyurethane foam; this foam has high porosity and consequently low density, making it more cost effective than calcined clay to send to space. We choose calcined clay for now because its use has been validated on the ISS.
To mitigate microbial growth, we build our pots with light-blocking material (to ward off photosynthetic invaders!) and use slow-release fertilizer as our method of nutrient delivery.
We isolate plants by growing one plant per pot, in order to prevent competition and cross-contamination.
Sowing millimeter-sized seeds at a precise germination depth under microgravity conditions is difficult; thus seeds must be secured on Earth so that they maintain the desired depth while in space.
- 3D-print trapezoidal pots so that eight pots fit together in an octagon. In this arrangement, lettuce heads can grow up to 7.5cm in height/diameter (growth towards the enclosure sides) or 15cm in height/diameter (growth towards the enclosure edges); the height measurements account for the 5cm lighting clearance.
- Each pot is 6cm in height and 15cm in length and has two compartments for the following: substrate (216cm³ volume for roots) and reservoir. These compartments are separated by a reservoir barrier.
- Cut rectangular wicks from felt and insert wicks through the slit in the reservoir barrier.
- Glue the seed to the wick with guar gum to ensure it maintains the desired 1/8" germination depth.
- Measure slow-release fertilizer and calcined clay substrate in the ratio of 7.5g fertilizer to 1000cm³ dry substrate.
- Mix fertilizer and substrate evenly and then pour the mixture into the substrate compartment without burying the wick.
- Attach a lid to the pot and sandwich the wick between a foam gasket such that it protrudes from the substrate compartment.
Step 4: Water | Initiating Plant Growth
A passive irrigation method, such as wicking, saves valuable astronaut time and energy on the ISS. For each pot, a wick conveys water from the reservoir to the substrate via capillary action.
- Install irrigation ports to each reservoir compartment.
- Initiate plant growth by pumping water through the irrigation port via a manual syringe or a water pump and tubing system.
- Each plant requires approximately 100mL of water daily during each of the 24 days of growth. Since pot reservoirs at full capacity hold approximately 450cm³ volume of water, water must be pumped into the reservoir at least five times within 24 days.
Step 5: Space Scaffold | Installing a Rotating Barrel
A central scaffold secures pots in place; this rotating barrel enables accessibility for maintenance and accounts for the staggered growth phases.
- Construct a hardwood scaffold consisting of four panels connected perpendicularly to a vertical octogonal tube. The four panels create three layers of space that accommodate eight pots per layer.
- 3D-print clips and mount them to the panels; pots are secured by snapping into the clips.
- Mount Lazy Susan bearings on the top and bottom of the scaffold for rotation. Then install the scaffold in the center of the enclosure.
- Since plant growth phases are staggered by 14 days, the barrel is rotated every 14 days.
Step 6: Air | Installing a Fan
Under microgravity conditions, air stagnates so plants can suffocate. A fan displaces air so that carbon dioxide circulates in and oxygen out. Air circulation also helps regulate humidity and temperature.
On the ISS, air (carbon dioxide and oxygen levels), humidity, and temperature are regulated, so we choose to have an open system.
- Cut a circular hole through the center of the top MDF sheet and mount a small fan inside to allow for air intake.
- Mount a 3D-printed spacer between the bottom of the scaffold and the bottom MDF sheet so that air can move from the scaffold interior to the plants.
- Create several slits in the top MDF sheet for air to escape.
- When the fan is turned on, air enters through the top of the enclosure, passes through the interior of the scaffold, exits through the bottom of the scaffold, circulates around the plants, and escapes through the top of the enclosure.
Step 7: Automation | Incorporating Electronics
Our design should scale such that maintaining multiple growth chambers at once is easy. Who wouldn’t want that! In this section, we describe electronics and propose automation.
- House electronics in the 50cmx50cmx5cm space below the acrylic partition. (Excess space may hold maintenance tools for measurement and harvesting.)
- Install a stepper motor that rotates the barrel via a belt connected to the bottom Lazy Susan bearing.
- Install a central reservoir and a water pump that connects to each pot via tubes. (Irrigation tubes will be loosely coiled inside the interior of the barrel and/or attached to a 360° rotation solenoid such that the barrel retains rotational functionality.)
- Connect the LEDs, water pump, stepper motor, and fan to an Arduino microcontroller for automation.
- Interface the plant growth chamber with the NASA EXPRESS Rack cooling loops because they can maintain a moderate temperature of 16.1°C to 18.3°C, the perfect growth temperature for our plant of interest.
Growing Beyond Earth is a three-phase contest, with this submission being Phase I. We propose some future directions regarding automation for Phase II and Phase III:
Phase II | Automate maintenance by coding the following:
- A 12-hour light cycle photoperiod.
- A 14-day planting/harvesting cycle notification along with barrel rotation.
- Timed irrigation and central reservoir refill notification.
Phase III | Automate planting and harvesting:
- Planting: Insert pre-seeded pots and initiate growth with automatic injections of water
- Harvesting: Chop mature lettuce with an automatic vertical blade positioned in the front; remove pot after harvesting.
Step 8: Prototype | Areas for Improvement
Although not required for this submission, we built a prototype to demonstrate that our design can be realistically built. (Side note: our prototype is still in progress, so it features some differences such as cost-effective materials alternative to those outlined in supplies.)
We reflect on lessons we learned, which we aim to apply to our next iteration of design/prototyping:
- We grew several plants with non-reusable pots and produced tremendous waste. On the ISS, pots should be reusable. If the pot and substrate can be autoclaved safely and without drastically altering properties, they can be sterilized and reused. Our substrate, calcined clay, is autoclave compatible.
- When the substrate is dry, wicking requires a longer time. Priming the substrate for wicking by irrigating the substrate at initiation will speed up the process; the substrate may be primed by injecting water through the foam gasket.
- Lastly, an automatic irrigation system is more complex than manual irrigation in that it requires more components: a central reservoir, a water pump, and additional tubing. Given the complexity of our proposed automatic irrigation system, we should mitigate potential areas of failure. For instance, we can prevent entanglement of irrigation tubes by installing a 360° rotation solenoid. Additionally, we could design the system with both automatic and manual irrigation such that if the former fails, watering is still possible.
Nevertheless, our design SeedShuttle has successfully addressed Phase I of the design challenge by increasing plant production capacity four-fold relative to the baseline, NASA's Veggie.
We would like to conclude this submission by thanking NASA, Fairchild Tropical Botanic Garden, and of course all the contest partners. Thank you for giving us college students an opportunity to learn and collaborate through a truly awesome design challenge. We hope to return for Phase II… until then, stay tuned!
Anthony Neil Tan (primary author)
Second Prize in the
Growing Beyond Earth Maker Contest