Design Ideation

Summary of Initial Design Ideas

Initially, we had various ideas for the project. The types of designs in consideration were hydroponics, aeroponics, and a permeable tube method, however, with further research and discussions with advisors, we discovered that each had their flaws due to microgravity. The hydroponic system had the inability to support the flow of water and nutrients in the system as expected, while the aeroponics system had an improved movement of water and nutrients but was more difficult to manage. After consideration of the two previous ideas, we decided to take the permeable tube method and improve upon it. Originally, this model used sown seed packets wrapped around the permeable tube and as a team we came up with three different models that are built upon this concept.

All these designs consist of a grow area (3 x 2 x 1.5 feet) that would provide a fully controlled optimal growing climate. Since different plants require different climates to optimally grow in, our team focused on allowing total control over the system. Our light system can be controlled down to the frequency of the light emitted, the amount of water distributed to the plants, the heat, humidity and airflow through this system.

Modular Autonomous System (MAS)

The modular system was designed with growing microgreens in mind. The design was a self-contained unit that would grow microgreens in the contained units that would be able to stack and all the sensor code be monitored by the same board. The Figure A below is how we planned to stack and interconnect with each module. We designed this system with the thought of adding automation because one of our main stakeholder requirements was to reduce the crew time needed. Therefore, with each unit of this system there's a harvesting arm/blade and dispenser that replaces the seeds packets.

Figure A: Modular Autonomous System

Figure B: Cooling Centered System

Cooling Centered System (CCS)

This design came about when we started to consider the heat transfer issues we may encounter due to the heat generated by the LED. The idea behind this design was to isolate the heat source (LEDs) and to cool it using a HVAC system as shown in figure B. This design also includes automation by having a harvesting arm/blade but unlike the Modular Autonomous system it needs manual replacement of the seed packet.

Idea Elimination and Down Selection

Variable Height System (VAS)

The advantages of this system allowed for a greater variety of plants. This system would contain its power systems (Lights, circuits, cooling). The base plate that would contain the irrigation system would move further away from the led matrix roof as the ultrasonic sensors report plant growth to the microcontroller.

The issues with this design involved the power system that we needed to raise and lower the system in microgravity. The system also uses a billowing clear sheet to allow for optimal visibility. However, this also does not allow for optimal climate retention.

Autonomous System (AS)

The Autonomous system represents a time effective way to grow smaller plants in small spaces. This allows for the possibility for a crew to set up multiple systems for different plants. Creating specific environments for specific plants. with this possibility you would not need to design a dual climate regulation system. These systems can be implemented when needed.

Cooling Centered System (CCS)

This system focuses on dissipating heat with the least amount of energy possible. It takes the cooling system for the chamber and utilizes its flow to cool the back sides of the led system and pump. This is done by creating an extra chamber that is also connected to the cooling duct.

Through our simulations, we have determined that the heat generated by the system is not sufficient enough for it to be worth the extra material to dissipate the heat.

Automation

Adding automation to the MicroTerra reduces crew involvement time and adds a level of distinction between the past NASA plant growing systems. An Arduino microcontroller is the brain that reads the input from the sensors and controls the environment within the container. Such as, when to turn the lights on and off, initiate the fans to cool the internal temperature down, and when to water the microgreens. The system will also have moveable automated parts. Microterra will have an auto-harvesting arm that will cut ready to eat microgreens from the roots and deliver them to a side port for collection. There will also be an auto-feeder that replaces the old coconut fiber seeded sheet with a new one to start the whole process again. This level of automation will allow the system to be fully functioning on its own and would only need human intervention when it comes time for collection and when it needs a new roll of seeded coco mats.

Harvesting Arm vs Blade

Initially we had the idea to create a harvesting arm that would be fixed in one axis and be able to move about the harvesting chamber and use a vacuum tube to collect the microgreens after they are cut. We ran through some complications with the coding and could not implement it through the system. So instead we implemented a blade motor assembly. To the right we have an example of the 3D printed motor assembly that we used to convert the rotational motion to linear motion. We use that to rock the blade back and forth to cut the greens. This was much simpler to integrate into the model.

Mat Roller vs Seeded Mat Feeder

We initially had a roller with mats on a spool that would be fed into the system, however, finding mats that would roll with ease turned out to be difficult. As the material we are using has too much friction and is not pliable enough to roll. Instead, we went with a seeded mat feeder that has an assembly of linear rods and motor with bearings that push an acrylic sheet upwards. The mats rest on the sheet as the motors push the acrylic sheet up. Then a roller at the top of the feed then pulls the mat into the next chamber. This design looks nice and runs smoother than our previous one.

Design Matrix

From the ideas generated the design that changed the most was the modular autonomous system because we realized that being modular was not a stakeholder requirement and in practicality, it was not the best way to scale up the system because of all the added complexity that would have to make it modular. So we decided to focus more on harvesting automation and now call the design Autonomous System. We then evaluated the three designs and down-selected them using the following metrics: cost, level of autonomy, crew time required and Maintenance. The cost was evaluated between the designs by adding up the cost of each individual component in each design and comparing the total cost. Level of Autonomy was evaluated by comparing the amount of automation of each design. The crew time was the evaluation of how much time the crew would have spent per month harvesting and replacing the seed packets, these values were calculated based on approximately how long it took us to harvest and replace the seeds. Lastly, maintenance was evaluated by how often individual components may need to be serviced and how much servicing may be needed for the whole system. The design matrix below shows that the Autonomous system best fits our stakeholders needs.

Proposed Design for Further Investigation

The proposed design for further investigation is the Autonomous system. We will continue to look into how to optimize and further develop the harvesting arm and seed packet dispenser.

Assessment Plan

Our team has decided to build our system around the autonomous system model. The first step to our testing was to build an inexpensive small-scale model of our system to test our code/ sensor effectivity. We decided to use a .45 scale model so that the parts can be printed on a household 3d printer (255mmx255mm). We were able to test the 2 different types of LED strips for the system. This helped determine the amount of light, power, and heat that is acceptable by the system for an optimal climate. Using this small-scale model of our contained system allowed us to build our circuit and helped narrow down the optimal sensors for the system.

After receiving materials and beginning the manufacturing of our final prototype, we were able to test the Irrigation system with a pump and water reservoir and test Its automation with our system's codes. We also tested the Integration of the code that controlled all of our sensors, motors, and other moving components.

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