Introduction: Harvest Drawers - NASA Growing Beyond Earth Contest Entry

Summary:

Aboard the international space station, astronauts don't have much room for growing food. This hydroponic garden is designed to operate efficiently using the minimum amount of space to harvest 30 plants on a rotating schedule in a zero-gravity environment. This is an entry for the NASA Growing Beyond Earth Contest Entry in the professional category.

Design:
This design accommodates 30 plants with 13cm separation on a 3-tier growing cycle in an enclosed 50cm cube. The cube contains three drawers that reflect different points of maturity. The bottom shelf is new plants up 0-13 days old sprouts. The second shelf contains maturing plants 13-26 days old. The top shelf contains plants that are ready for leaf harvest or fully mature at 26-38 days.

Built into each drawer are the lights, electronics, hoses, and security elements for each row of plants. The power supply, water source, and pumps are placed on the rear of the unit.

Scaling:

This design would scale exceptionally well because the drawers can be positioned at any height on the track. Each drawer contains the components to keep the row below functioning, and could be stacked infinitely.

Supplies

  • 12 pieces of extruded aluminum (or similar)
  • 3 x drawer hardware sets
  • 40 x extruded metal fasteners (cards and nuts)
  • 3x plastic trays and drawer bases
  • 3x hydroponics foam sheets
  • 10x pieces of corrugated polypropylene sheet (or similar insulating material)
  • 1x Spray Adhesive
  • 60 ft of Plant-friendly LED Light strips
  • 12 volt 360 watt power supply
  • Automatic watering kit (see https://www.instructables.com/id/Easiest-Arduino-...
  • Mylar sheets
  • Soldering equipment
  • Exacto knife or box cutter
  • Zip ties
  • Tweezers
  • Gallon Jug
  • Seeds
  • Hydroponic Plant Nutrients

Step 1: Build the Box

  1. Cut and drill your 12 pieces of aluminum extrusion:
    1. Piece A: 4x pieces of 2.5cm x 2.5cm x 50cm length
    2. Piece B: 4x pieces of 2.5cm x 2.5cm x 47.5cm length (with fastener holes on the ends)
    3. Piece C: 4x pieces of 2.5cm x 5cm x 47.5cm length (with fastener holes on the ends)
  2. Cut corrugated plastic pieces to fit the sides of the box.
    1. Piece D: 2x pieces of 46cm x 46cm
    2. Piece E: 2x pieces of 40cm x 46cm
      *Optionally, you can adhere mylar sheet to one side of the plastic using spray adhesive. This will help with heat and moisture retention.
  3. Create the base:
    The aluminum frame base will be "A" on the base front and back, with "B" on the base sides using fasteners. Insert 1 corrugated plastic piece "D" before applying the last aluminum piece on the base. Before adding the next layer, add 6 extra fasteners to the back aluminum track facing up.
  4. Attach the vertical sides:
    The aluminum frame sides will be "C", lined up to the corners pointing upward and attached to the base using fasteners. Before adding the top, add some 4 fasteners on each corner facing inward for the drawer hardware. Insert 2 corrugated plastic pieces "E" to each side.
  5. Attach the front door:
    Using a tinted acrylic plastic, attach a bifold door (or similar) to the front of the unit. This protects the caretaker from the bright lights when the unit is running, but allows the caretaker to observe and maintain the plants. *The door should have a small vent at the lower bottom to allow for airflow.

Step 2: Add the Drawers

The drawers support plant at different growth points during a 30 day life cycle.

  1. Attach the drawer slides
    On the sides of the aluminum frame, attach the drawer hardware using the fasteners that were previously added to the track. They should be staggered to allow for different growth cycle stages.
    1. Lowest: 2cm
    2. Middle: 9cm
    3. Highest: 23cm
  2. Attach the drawer base
    Using the drawer hardware, attach a drawer base. This needs to be small enough to easily fit into the cube, but sturdy enough to support the plants, water, hose, and electronics. A drawer base can be corrugated plastic or acrylic attached directly to the drawer hardware, so something more specialized. The drawer needs to be flat and slide in and out smoothly.
  3. Add the plastic trays
    Attach a plastic tray to the drawer base, which can be removed during maintenance. We used a 5cm deep plastic tray attached with velcro to allow enough room for the 4 cm hydroponic foam.

Step 3: Wire the Drawers

The drawer is the foundation for all of the support systems of the plant; each drawer supports the drawer below.

  1. Attach the Lights
    Oriented in the same direction, adhere 5+ led strips to the bottom of each corrugated drawer base and the top of the cube. The wires should be accessible from the back of the drawer box. Use zip ties to fasten the wires to the drawer base as necessary, allowing enough slack so the drawer can fully extend in and out of the cube without disrupting upper and lower drawers.
  2. Connect Power
    Solder the wires from each drawer to connect to a 12 volt 360 watt power supply. Attach the power supply to the back of the unit. Ensure that the fan has adequate ventilation.
  3. Connect the fan
    Using a small microwave fan (or similar), wire the fan into the power supply to provide ventilation for the plants. The fan should be placed at the upper back of the unit. The vent in the front door assists in airflow circulation.
  4. Wire the Watering System
    Attach the automated watering system pump, sensors, and arduino to the power supply, using the instructions from the kit of your choice. We are using an arduino kit: https://www.amazon.com/Elecrow-Watering-Moisture-G...
  5. Apply the hose
    To each valve on the watering system connect a hose segment. In each drawer, secure a watering hose with enough slack so the drawer can fully extend in and out of the cube without disrupting upper and lower drawers.
  6. Connect the water
    Fill the water tank with water. Attach the primary hose to a central water pump, and attach the pump to the water tank at the back of the unit using a hose segment. The water tank will be attached outside of the cube, easily accessible for refill, nutrients and maintenance.
  7. Secure the hoses and wire
    Using a cable carrier, fix the hoses and wires to the side of the unit and to each drawer to they can move in and out with the drawer without disturbing the layers below.

Step 4: Add Your Plants!

Once the support systems are in place, you can add the hydroponic foam and start growing your plants.

  1. Cut the foam
    Using a template, cut the foam to the size of the removable plastic growth tray. It should comfortably sit in the tray, avoiding a gap between the sides of the tray and the foam material.
  2. Mark the plant locations
    Using a ruler or measuring device, mark where the plants will be located on the foam in rows of 3,2,3,2 —10 plants total on each tray. The plants will appear staggered. Measure diagonally with 13-15cm between plants to confirm spacing.
  3. Cut an "X"
    At each plant location, cut a 1cm "X" (two slits) into the foam using an exacto knife or box cutter at a 5mm depth (or whatever the seed suggested depth is).
  4. Place the seeds
    With a tweezers, carefully place two seeds in each slit just below the surface of the foam. The seeds will be hard to see, but be diligent to place them at the right depth.
  5. Attach the removable tray
    Now that the seeds are in place, attach your tray to the lowest drawer base.

  6. Attach the hoses and sensors
    Cut a slit in the plant growth material (foam) big enough for one sensor to slip in. On the side of the drawer opposite the sensor, insert the hose. This drawer is ready for automatic watering. Turn on the unit, and ensure the drawer is saturated with water. The seeds must be fully saturated with water in order to sprout.

Step 5: Watch Them Grow

Maintaining the garden requires a few tasks:

  1. Hook it up
    Ensure the cube always has adequate power and water.
  2. Water the plants
    To water the plants, use distilled water combined with hydroponic nutrient concentrate. When the seeds are first placed, the foam should be completed saturated in nutrient rich water. After that, the foam should always be moist, but not drowning. A moisture sensor should automatically water plants as needed, but manual watering is a fallback.
  3. Transplanting
    The goal is to have one plant in each position. Sometimes, a sprout won't come up. Luckily, 2 seeds were placed in each location to create redundancy. If neither plant doesn't sprout in a specific location, transplant a doubled-up sprout from another location to complete a full 10 plant tray.
  4. Rotate the trays
    Place the new tray at the bottom location until the plants reach 12 days (or halfway to maturity).
    1. At 13 days, move the lowest tray up to the next level and plant a new tray with 10 plants.
    2. At 26 days, move all trays up to continue growing, and the top tray is ready to be harvested.
    3. Select the most mature plants to harvest first, and proceed to harvest all 10 plants over the following 12 days. When mature lettuce reaches the top row, enjoy your harvest!