Design II course Assignments

Investigate autonomous plant development in the LEO microgravity environment to enhance our knowledge of space agriculture and contribute to the long-term sustainability of human habitation beyond Earth.

The proposed CubeSat mission will autonomously grow the candidate plant Red Romaine Lettuce and expose it to the stressors in LEO such as microgravity and radiation. As the driving requirements are derived by the respective candidate plant, it is imperative to monitor all aspects of the growth chamber. Therefore, a series of sensors such as temperature/ humidity sensors along with hyperspectral and optical cameras will be used to capture the impact the stressors impart on the plant and communicate it back to Earth. The resulting data can then be compared to previously collected control data from earth and the ISS. The investigation of autonomous plant development in the LEO microgravity environment to enhance our knowledge of space agriculture and contribute to the longterm sustainability of human habitation beyond Earth. 

Astronaut freeze-dried foods lose a significant amount of their nutritional vitamin/mineral value within the first six months of storage. Therefore, producing food in near space in the form of edible crops for space exploration is a necessity. Conducting experiments is incredibly expensive, time consuming, and requires daily human interaction. The need for autonomous growth chambers for the study of plant growth in LEO would greatly contribute to this research area. While the concept of sending plant life to space is not inconceivable, developing a satellite with a growth chamber large enough to support such a large produce plant is quite a challenge. Previous designs have centered around microgreens but are still limited in study. The uniqueness of this problem results in custom builds and even pricier customized components. Furthermore, our team is embarking on the groundbreaking mission to develop the small satellite, BIOSat (Botany In Orbit Satellite). 

Currently, food within space is limited to freeze-dried food which can lose nutritional value over time. The ISS is growing nutritional plants however this requires human tasking such as watering and cleaning. Along with human interaction, space and time is involved, leading to high expenses. BIOSat’s mission is to autonomously grow red romaine lettuce for NASA to further investigate candidate plants for nutritional diversity. This closed loop system will allow for optimal tunability to develop a healthy growing plant while exposing it to microgravity in the LEO environment. The results will expand NASA’s understanding of plant stressors in space and further nutritional variety for astronauts in deep space exploration while minimizing overall cost and size/space requirements.  

Monitoring these parameters is mandatory, as the simulation of red lettuce’s ideal natural environment negates variables either due to limitation of physical resources or overlooking one of its nuanced requirements. Accounting and supplying fundamental necessities through this system contributes to the study and can refine future experiments. To account for the condensed spacing, a specialized chamber, made of acrylic to isolate the red romaine lettuce from the environment and fitting within the dimensions of a 3U CubeSat was used. Table 1 presents solutions for the regulation of internal environmental factors by sensor data collection and a simplified control system. Air circulation will be maintained by a fan, with a velocity between 0.3 and 0.5 meters per second, ensuring evenly transmitted heat regulation and gas exchange needed for photosynthesis and transpiration at the leaf’s surface. LED strips placed above the chamber will provide blue (~450 nm) and red (~700nm) light to mimic natural light cycles, optimizing vegetation growth. The chamber features external outputs for air and CO2, with sensors placed in a printed bus for monitoring CO2, alcohol, O2, temperature, and humidity levels. The setup includes two fisheye cameras for imaging of the roots and leaf growth, which are also used as hyperspectral cameras. Imaging allows for assessing growth patterns and heath for observations in developmental changes over time. Chamber temperature must stay between 18–22 °C when external temperatures become severe in near space.

To address the objectives of the project, three main tasks are planned for our study: 

1. To design and implement the sensor system for studying the critical parameters representing the plant’s health status. 
2. To design and test an irrigation system for microgravity conditions. 
3. To analyze the plant growth data to study the effect of stressors on the growth of a plant. 

These three tasks investigate the plant’s growth in a closed-loop ecological system completely isolated from the surrounding environment. This study will analyze the effect of limited supplies and isolation have on the health status of the plant. The amount of oxygen, CO2, air, and water in the chamber will be derived by the needs of the specific candidate plant under study while the heater, fan, and insulation will maintain the minimum necessities of plant life. This is the mission of BIOSat, which requires further on-Earth testing to compare to the in-space testing environment. 

Our preliminary studies were focused on red romaine lettuce as one of the recommended plants for growing plants in space by NASA [1]. We understand that in addition to lettuce, there are a few other plants such as Chinese cabbage, banana pepper, and cherry tomatoes that are identified by NASA as candidate plants for space missions [1,2]. Furthermore, we intend to test growing lettuce in a 3U area, displayed in Figure 2, however since our proposed plant health monitoring system (PHMS) can be used for any plant, we plan to test other candidate plants in the future.

Lettuce Seed not germinating 

• The most significant risk in our project is the possibility of our seed not germinating. We plan to avoid this risk by planting multiple seeds, hoping that at least one sprouts. We will also evaluate growing our lettuce in the CubeSat on the ground to allow us to practice and adjust to maximize our chances of successful sprouting.

All Lettuce seeds germinating 

• In the case that multiple seeds sprout in our CubeSat, we have researched to learn the behavior of plants under extreme resource stress and have come to find out that plants would release hormones that’ll kill off surrounding plants as a defense mechanism thus allowing us to guarantee that we will only have to worry about a singular plant. Additionally, we plan only to plant three seeds to control the number of possible plants that could sprout. 

Renewable resources for growing plant 

• The next issue in the case of being successful in plant germination is creating an environment where a plant can grow autonomously, meaning we must be extremely conservative with our resources. We plan to track the utilization of our resources through sensors and control systems to minimize the resources we must use to ensure the plant can grow.

CubeSat solar panels deployment system 

• Due to our CubeSat being in space, it is essential that the CubeSat has a way of generating renewable energy. We plan to use solar panels and have a deployment system to ensure the solar panels are open to the most optimal position to generate power. We also plan to have a system that will guarantee that the solar panels open correctly. 

Lack of electricity to power CubeSat's systems 

• If our solar panels do not generate enough power for all our systems, we plan to have a program to allocate power towards essential components to keep the plant alive. We can also track what is being powered through our communication line with CubeSat via satellite comms. 

Establishing communication with CubeSat 

• Establishing communication with our CubeSat is vital to keeping track of our plant systems and locating where our CubeSat is. Regarding this, we plan to use a strong enough antenna that can send and receive signals from space. On the day we send off our CubeSat, we will also have a program that will restart the microcontroller repeatedly until a communication line has been established. 

If our CubeSat is successful and becomes a product. We plan for it to serve as the pathway towards sustainable living in space. This will significantly impact the world's space excursions as we can now generate a nutritious and autonomous way of making food in space. We plan to achieve this by ethically: 

Reducing Harmful Materials

• Part of creating a safe and sustainable system must be to minimize using harmful materials in our CubeSat. Our CubeSat was designed to utilize environmentally friendly materials and components that would follow all industry standards and regulations. 

Recyclability and Reusability

• Due to our mission of creating a sustainable environment for plants to grow, we also planned to include that idea in our CubeSat design. We plan to use as many materials as possible and devices that could be reused or recycled at the end of its life cycle. 

Educational Initiatives 

• In engaging with this project, we also aim to bring awareness towards our responsibility as a species to create a sustainable environment, meaning it is our responsibility to ensure we create and use materials and devices that are capable of being correctly disposable or recycled. 

Long-Term Sustainability

• Our goal for this project is to create a long-term sustainable system to allow plants to grow autonomously. Additionally, we should incorporate that ideology of creating sustainable systems within our lives and future generations by managing our resources in space and on Earth.