Passive & Sustainable Agriculture System

The optimization of plant growth is an interesting challenge to try and tackle, especially doing so in Outer Space. The astronauts aboard the International Space Station have limited time and patience for the upkeep of a typical plant system. Therefore a new design is being suggested that reduces human interaction to nearly zero and allows for the most plants to grow at the same time. Other than harvesting and perhaps occasionally refilling the water supply this design is self-sufficient and can be used repeatedly with limited to no maintenance in between each growing session. This system was designed with red lettuce in mind, which when fully grown can be up to 15x15 centimeters in size. With this information in mind, the layout was spaced accordingly, but it could also be adjusted to better suit other plants as well.

It is my hope that although my artistic skills may be lacking, the concept shines through and the details below assist in the explanation of how a device like this might work.This entry is for the college level.

The system as a whole will be contained in a case that measures 50cm x 50cm, as specified in the contest rules. The walls are to be made out of carbon fiber, with acrylic windows on all sides. The left hand side would need to have 6 equally spaced squares (12cm x 12cm) cut to allow for the fans to pull in and push out air, as described later on in the airflow section. A handle would be placed on the front panel to allow for easy access. The plants would be visible at all times in order for easy viewing of their progress. These materials were chosen due to their durability and low weight.

The inside will be explained in more detail but will consist of 3 tiers of plants. The 1st tier is located at the bottom of the container and has 9, 15cm x 15cm squares designated for one plant each. The second tier will be 17 centimeters above the 1st tier with another 9 designated spaces. The 3rd tier will be 34cm above the 1st tier and have 9 spots as well, for a total capacity of 27 plants. Each tier has a tray underneath it with a thickness of 1cm or less. This helps to separate each tier and allows for the attachment of light strips to the bottom side of the trays.

The lighting will consist of 3, 50cm x 1cm 12V LED light strips attached to the ceiling of each tier. This results in a total of 9 light strips. Adhesive will be used to attach the first and second tier (closest to bottom) lights to the bottom of the plant tray above it. The 3rd tier lighting will be attached to the top of the container. The light strips are to be waterproof and alternate blue/white, with a combined power draw of 5 amps. They shall be powered by 5 Amp Enclosed LED Driver Power Supply with PFC & Dimming from Jameco and controlled with a dimmer switch.

In order to give the plants appropriate airflow, there will be 2 fans designated for each tier of plants, for a total of 6 fans. They are to be 12cm x 12cm x 2.5cm AC Infinity fans, centered on the left hand side of the container, equally spaced per tier. They shall be connected to the same power supply and dimmer switch as the lighting. One of the fans will be designated to provide outside air, bringing fresh air into the system to give to the plants, while the other will act as an exhaust fan pushing air out of the system. This will encourage the circulation of air throughout each tier and allow for an even balance of air makeup, and natural adjustment of CO2 levels.

The success of this system depends almost entirely upon the ability to properly hydrate the seeds and foster an environment where they will thrive. A test tube like structure will be filled with nutrient rich water at the start of each growing cycle. Through capillary action, the water will move from the large test tube into the designated seed holders, which will have a cup like shape and be made of plastic. Inside, these cups will be filled with silica gel beads which will help to suck up and trap the water, keeping it in place. In the middle of the beads will rest the seed, which will have the opportunity to absorb the water and nutrients from the seeds in a safe and friendly environment. As the seed begins to germinate it can lay its roots, continuing to suck up water which is being continuously (but passively) filled. The expectation is for the base of the plant to stay in these cups but for it to be able to grow and expand above them over time.

Here we shall attempt to bring the system back into its full picture, with all sub-components more properly explained. The container shall have three layers, or tiers, of plants with 9, 15cm x 15cm plots to grow heads of lettuce for a total of 27 possible plants at a single time. The system shall be filled with nutrient rich water; each tier will have 3 passive irrigation lines, and each of those serves 3 plants. Through capillary action, the water continuously flows to the plants as needed. The plants will be held in small containers which will be filled with silica gel beads to trap the moisture and allow for a sustainable growing environment. The plants will have plenty of room to grow upwards towards the light located directly above. The 2 fans for each tier will run continuously; 1 will bring fresh outside air into the container and the other will exhaust back outside the system. Occasionally, water may need to be added, but this should be on an infrequent basis. Once the plants are fully grown they will manually need to be harvested, and new seeds shall be placed. The system will then be ready to start the cycle again.