This is a professional entry for the Growing beyond Earth Maker Contest. This system uses three sets of rotating racks that pairs each set of lettuce with another one in an earlier stage to maximize the useable area. When the seed are initially germinating they do not need as much light until they are sprouted allowing it to be partially shaded by a neighboring full grown head of lettuce. When the fully matured head lettuce is harvested, it then becomes the new seeding stage (or early growth stage if cut). The system would be able to handle 54 plants growing at one time for a continuous growing system with 9 heads of lettuce available at any given time. Lighting is provided by LED strips above each set of plants in the unit and underneath the 18 plant trays. Watering system would use a hydroponics system.

Supplies

Consumables:

Structure:

Frame made with aluminum extrusion or other building materials
Track system from curved aluminum extrusion
Water tank
Life Support system (control board, lighting controller, power supply, fans)
24X 40cm LED light strips (bright white) (These LEDs seem to be bright enough)

Software:

Fusion 360 (for 3D modeling)

Step 1: Space Station Environment Variables

Space station condition 40% humidity
22-23 deg C temperature
CO concentration 4000 parts per million
Assume astronauts have zero botany experience Extra time a week they have is zero options - harvest is ok
Automation and Volume Reservoir of water is needed. 100ml of water used per plant per day
Power supply 28 volts - 1000 watts (current uses 70 watts)
Lettuce Size 15 cm high, 15-20 cm diameter, 40 g /lettuce head
Lettuce seed pointy end down for the roots
Algae will grow on the space station so do not let the roots be exposed to light

Image courtesy of NASA https://www.nasa.gov/content/veggie-plant-growth-system-activated-on-international-space-station

Step 2: Step 1: Construct the Frame

The frame may be constructed out of whatever material is on hand. 80/20 aluminum extrusion is an easy way to quickly prototype designs as it comes in may shapes and sizes. The rear U shape tracks can also be constructed out of bend 80/20 aluminum extrusion and will be used for rotating the plants during their growing cycle. The overall size of the cube is 50x50x50 cm.

Step 3: Plant Trays X18

The system will have 18 separate trays that will contain 3 plants each. Each tray will be filled with black aquarium foam as the growing medium. This foam is intended for filtering water in aquariums but also is a great alternative to dirt for the developing root structure. The trays will include a water inlet, water sensor, and a LED light bar mounted underneath each section to light the area below.

Step 4: Adding the Electronics

The next step is to wire and plumb it all together. The blue module is the slim concentrated nutrient tank. Since there are 54 plants that would need 100ml of water a day that would require 5.4L of water / day to water all of the plants. So it is expected the system would be plumbed into the space station for the main water feed. The Red module contains the various power electronics, pump and controllers. The green module is for air circulation.

Step 5: Other Ideas or Thoughts:

Have a “filter” or solid block medium which water is diverted to recirculate a certain amount of times until the solution has the appropriate nutrient level. Other factors can be ignored since the water is distilled and there are no other sources of contamination available. Over time the plants may alter the water but should not be a critical issue since the plants uptake water and new water is added to the system regularity.
Plant chamber could have a window facing the sun similar to the solar panels. Special coatings would be needed to reduce the amount of hazardous radiation to the plants. Long panels like the solar panels could be created to create a Space greenhouse. The panels would extend out to create conveyor belt like food production in space.
Seeds compressed into a roll of foam so that it can be unrolled and implanted into the medium. So a new strip is cut and planted with the seeds distributed already in it.
Seed pills, capsule you’d normally eat contain a seed with the beginning stages of growth. The water would dissolve the outside of the capsule and start the growth of the seed.
Plants may produce more antioxidants due to UV light. Even though plants do not need UV light to grow the addition of UV light may aid in the production of micronutrients. https://www.dailymail.co.uk/sciencetech/article-2...
Switch between Daylight and Purple to mimic the natural respiration of the plants. Having just one color all the time might not be good for them but by changing the white to purple color then the plants might have the ability to “respirate” naturally promoting better growth.