Introduction: 30-60 Plant Tesselatable Zero-G Grow Chamber With Accelerated Turn Around

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This is a submission in the high school category of the Growing Beyond Earth Maker Contest. This stage focuses on the innovative geometry of the project and demonstrating its effectiveness. Plant growth systems such as light, watering and ventilation will be discussed but were not implemented in this stage’s prototype pod. If this entry is chosen to advance, a more sophisticated full scale and full functionality prototype will be constructed.

Step 1: Geometric Design

After reading the contest rules, I created a few criteria for a shape that would be optimal:

  • It has to use space efficiently not only for plant growth but must account for electronics, ventilation and fluid reservoirs and distribution.
  • It must be tesselatable to allow for efficient use of space and scalability.
  • If possible, it should make use of the zero-gravity environment.
  • Should be designed with compressed volume for launch and easy assembly in space (if possible with use of waste materials via additive manufacturing).
  • Should be designed for long service life and easy replacement and servicing of electronic components.

After that, I did some research on commercial greenhouse growing trays which gave me some dimensions for space needed by the plants. I went through five or six iterations before deciding on the current model. This design assumes that the lettuce grow space is a 7.5 cm diameter hemisphere. It then slightly constrains the bottom. It grows three plants in a row, making a 45cm long growing chamber. It allows a 4cm wide by 2.25cm deep root growth space. The root space is currently not constrained in length but would likely be constrained to around 5 cm of the trough in a full scale prototype to allow for electronics and plant monitors.

It is also double sided. It does not have adequate space to accommodate two full size plants directly across from each other, but instead uses a staggered planting schedule. The lights move back and forth across the growing space on a slide powered either by a servo motor on a belt or a stepper motor with a screw drive. This plan assumes that the lettuce takes around 30 days to grow (which could be off by up to a week either direction). One lettuce plant would be planted at day 0. It would then grow for around 20 days with the light moving just above the leaves. Around day 20, the other side would be planted. At this point, both sides are growing but the plant planted first is nearing full growth. Around day 30, the first plant is harvested and the second plant, having already grown for 10 days, is already sprouted and around 5 cm tall. The cycle then repeats, allowing for harvests every 20 days 30% faster than traditional growing trays. If a plant variety that allows multiple harvests is used, the other side can grow clovers or other small legumes to allow for crop rotation. One end will open to a service area. This end will be referred to as the front, and the side against the wall will be referred to as the back.

Step 2: ​Plant Growth Systems

Light

LED grow lights will be mounted facing sideways on a bar that will move up and down the grow space. The motor and power supply will be mounted at the back. They will have a slide at the front that is built into a door that closes off the pods.

Water

The water is mixed with a soluble fertilizer mix in the reservoirs to the sides of the device. The reservoir is slightly pressurised. The water is pushed through tubing that runs through the walls of the grow pods. It is deposited to the plants and the amount received is controlled by valves at the reservoir.

Ventilation

This design allows for small fans at the back. In future versions, CO2 supplementation system could be added. This would be controlled by CO2 sensors in the pod and could use CO2 from life support fed to a ventilation space at the far back of the device. The fans could then blow it forward into the growing pods. Small ducts could be added in the front end door allowing for circulation.

Grow pillows

My initial prototype used standard potting soil. Future prototype would use something more similar to the pillows currently used in the VEGGEY system. There is also an option of switching to full hydroponic which may end up being easier.

Harvest and planting and crew time

Harvesting and planting are the only times the crew must interact with the plants. The entire plant growth trough can be slid out the front of the pod. At this point, the plants can be harvested or planted before being slid back into the pod. Each of the ten pods would need a few minutes for harvesting roughly every 30 days then separately for planting every 30 days. All pods could be kept in sync requiring around an hour of crew time for harvesting each month and another half hour for planting ten days later. I would recommend keeping the individual pods staggered in growing stage probably requiring slightly more crew time in small 5 to 10 minute blocks and producing fresh lettuce about every 3 days. The more constant availability would be good for crew morale. The way the system is designed also allows for easy integration of an automated harvesting and planting device in the future.

Servicing and maintenance

The most frequently replaced part would likely be the light bar. Replacing it is a very easy job requiring it to be removed via pulling it out the front of the device and sliding a new one in and reconnecting the power. The water valves are also simple, being mounted on the sides of the device. Plant monitors can be accessed by sliding them out on the tray as if the plants were to be harvested. The fans and light bar movement moters should not need to be serviced frequently but will require more effort to access.

Step 3: ​The Prototype

To test the basic shape of the grow pod I decided to build one. Because this is to test the shape of the grow space, materials and construction methods were done to be cheap and fast and do not represent the final proposal. It also has much different electronic components.

Step 4: Cutting Angled Supports

Step 5: Installing to Base Plate

Step 6: Installing Trough Sides

Step 7: Installing Panels and Sections of Garden Hose to Simulate Clusters of Tubing Supplying Surrounding Pods

Step 8: Sides Attached and Top Constructed

Step 9: Removable Top Installed

Step 10: A Grow Light From a Previous Project Was Used to Simulate the New Grow Light Design

Step 11: Used Standard Potting Soil to Fill the Trough

Step 12: Water Added and Seeds Planted

Step 13: Light Set and Top Installed

Step 14: Current Results

I used a syringe to water the plants. They sprouted but then died while still small, probably from over watering. Replanted and will update with results when available.

Step 15: Plans for Construction of Next Stage Prototype

The back will be constructed as one CNC machined plane with the servos and fans mounted along with slots for pre cut panels. It will be fully assembled as step 1.

There are corner slots that will be assembled to hold the panels. The front will be made up of fittings that will be 3D printed. The corner panels could also be printed with a large machine but are small and light so will probably be launched in the pack.

The pre cut plastic panels are installed along with the tubing at the same time.

Light bars along with front slides are installed and connected

Troughs are installed

Valves and reservoirs are fitted

Front doors are fitted

Systems are tested then plants are planted