O7 - Optimized 7 Day Lettuce Supply Cycle

Introduction: O7 - Optimized 7 Day Lettuce Supply Cycle

About: A dedicated architectural design professional, preparing for the future of space architecture.

The O7 - Optimized 7 Day Lettuce Supply Cycle is a submission for the "Growing Beyond Earth" challenge in the professional category. The contest asks that we optimize the use of a 50 cm x 50 cm x 50 cm volume, to grow a minimum of 6 red lettuce plants (that grow to a 15 cm height, with a 15 cm diameter at the top of the head.) Time is suggested as a factor for consideration. Currently, the Veggie system on-board the International Space Station (ISS) has a 6 plant maximum capacity. It is the goal of this contest, and myself to help astronauts and cosmonauts get their much needed veggies.

O7, designed by Brainstorm District: Lead Designer Bonnie Jean Dominguez, with feedback from Mathematician Stephen Jacob Harris




The O7 is a lettuce grow box that can hold 40 lettuce plants at one time, supplying 10 full grown lettuce heads per 7 days (after the first planting cycle gets going.) The lettuce are divided into 4 stages of their growth: Stage 1 Seedling/Sprout, Stage 2 Immature Small, Stage 3 Immature Medium, and Stage 4 Mature Full Grown (15 cm). (SEE image above.) Each stage has 10 plants.

Plants are further divided into pairs (SEE image for Configurations below), on Tubular Growth Vessels (TGV).(SEE image below, under Preliminary Automation for more in depth information on Tubular Growth Vessels, a.k.a "metal pipe reservoirs"). Pairs share nutrient/water flow and cleanings. Cleanings are an idea I am playing with, where the TGV gets flushed to get rid of any harmful growths of non-symbiotic life forms. The lack of interconnection between each TGV further reduces the possibility of contamination at the root level.

After every plant growth stage, the TGVs holding each stage are moved up-- Stage 1 to Stage 2, Stage 2 to stage 3, etc. After the Stage 4 growth and harvesting is completed, the TGVs are re-seeded and moved to the Stage 1 position.

Note 1: More research is needed, but this might be a candidate for the nutrient film method.

Note 2: The TGVs will be further developed for automation, if selected to move onto contest 2.

Design Reasoning:

In past studies of human factors I learned that in space, creating a local up and down is helpful to astronauts. This design follows this idea. In O7, all plants are oriented with a single, local up and down. (SEEexample of Sunita "Suni" WIlliams orienting herself in this video.)

By observing YouTube videos uploaded by NASA astronauts, I also previously learned that it is important to keep the O7 walls transparent to allow astronauts to see the plants. Again, "Suni" Williams told a story about astronauts tying green trash bag ties around a garbage container to create the appearance of seaweed in the ocean. This story made it clear that astronauts miss the green of the Earth, and that this design needs to secure visibility of the plants to the astronauts.

To determine the yield and the mouths the O7 grow box can feed, I did some research. According to Space.com, in 2009 the ISS housed a record of 13 people. In 2019, between September and October, the ISS housed 9 people. For this project, the assumption will be that we will need to feed an average of 11 people. According to Better Homes & Gardens(BH&G), 1 lettuce equals 10 cups of torn lettuce. BH&G states that a side or first course of salad is 1 to 1.5 cups of lettuce per person. A salad as a main dish is 2 cups of salad per person. This project can provide 10 mature red lettuce plants every seven days. This means that O7 can provide 11 astronauts, 1 serving of lettuce a day (2 lettuce heads), for 5 days out of the 7 day cycle.

You may have noticed that Stage 3 and 4 are not on horizontal planes, but are at an angle. The angle allows plants to continue to grow up to 1 extra inch than the minimum height required by the contest. (SEE the image above called Minimum Height for Mature Plant.)

Step 1: Configurations

After a lot of ideas, this was the final design. I settled on this pattern because this pattern reduced contact between the plants. This allows them to grow out and away from each other. This pattern maximizes airflow between the plants.

Step 2: Ventilation

One fan at the top brings air in, and the other fan at the bottom pulls it out. The top fan ensures that the air around the Stage 4 plants stays clear of gas bubble build up and reduces the possibility of mold growth. The Stage 1 and 2 plants are more delicate than the Stage 4 plants and so are furthest away from the air intake. It is assumed that the speed of the air exhaust fan can be optimized to not harm the Stage 1 and 2 plants, and yet still pull out enough air to be effective.

Step 3: Lighting

The lighting is LED tape inside of housing. Depending on the level of light required at each stage, LEDs can be programmed to output more or less light.

Step 4: Preliminary Automation

This contest mentions automation as part of the following contest (finals) and suggests we talk about any ideas we may have, though it is not required that the idea be fully fleshed out.

(See image.) The idea to use one tube inside of another, with a blade, would make fast work of cutting many plants at once. I imagine that once the plants are cut, a vacuum can draw out the harvested plants to some receptacle. The seed baskets (see image) would then be emptied and the Tubular Growth Vessels would be flushed for cleanliness. The TGVs that completed Stage 4 would then need to be re-seeded and re-positioned at Stage 1.

I hope you find this useful and can make something out of it. =) Please leave questions, comments or recommendations below, and I will try my best to reply.

Step 5: Assumptions:

  • It is assumed that gas bubbles will collect around plants, without proper ventilation.It is also assumed that more mature plants can handle more air flow and not dry out, as compared to smaller plants.
  • If there is chlorophyll on the underside of a leaf, photosynthesis will happen.

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