DESIGN I - Experiment Plan

The photosynthetic process involves the consumption of CO2 and the release of oxygen through the green leaves of a plant. However, in the dark, a plant releases CO2. Different gases are released by plants when in bloom such as the release of ethylene and acetone [1]. Based on our preliminary studies, Figure 3 reflects the requirement of an alcohol sensor to measure any VOCs released by the plant. This L-com SRAQ-G005 sensor will monitor various gases to compare ideal plant gases for a health status indicator. Using off-the-shelf devices, an array of gas and VOC sensors will be employed to make a sensor array for sensing the released chemicals from a plant being grown in a chamber (objective 1). Additionally, an array of moisture sensors will be employed for measuring the moisture in the soil near the root. Realizing that the change in the generated voltage in a zinc-air battery (Figure 4) is proportional to the change in the oxygen level. Therefore, it is planned to use an array of zinc-air batteries as the Grove MIX8410 oxygen sensor around the plant’s root. In the future, the research plan is to design fiber-shaped oxygen sensors that can be easily applied to the soil for root-zone oxygen measurement.

Setup design for Task 1 and method of conducting experiments: The effect of a closed ecological system will be studied by connecting the air and CO2 feeding pump into the chamber with the sensor array connected to the exhaust line, seen in figure #. The air pump will be regulated for the circulation of air in the chamber as it is recommended for the healthy growth of the plants however the CO2 pump will be on only during the first 16 hours of light and turned off for 8 hours of night. The flow rate of the fan will be set to a constant of .4 m/s considering red romaine lettuce needs a range of .3-.5 m/s of air velocity. Since the lettuce does not flower, there is no mechanism considered for the pollination. Utilizing the designated outlet sensor array will process the chamber’s simulated atmosphere. With each sensor response we will understand the plant’s consumption or release feedback. The humidity sensor will be in the isolation box with the coco peat while the final pH sensor will be inserted into the water chamber. 

Expected research outcomes from task 1: Critical chemicals can be identified through the alcohol sensor to assess the health status of the plant. Analyzing the sensor data and implementing the machine learning model will give more accurate information about the rate of consuming and releasing of chemicals from the plant. The data collected from the humidity and pH sensor will reveal if there is enough water provided and if it is receiving enough nutrients for growth. At the end of the experiment, the roots of the plant will be studied and compared to grown on-Earth plant roots via images for comparison.

Task 2. To design and test an irrigation system for microgravity conditions.

Since surface tension is larger than gravitational force in space, watering a plant in space is challenging. Due to this problem, conventional hydroponic irrigation is not practical for growing plants in space. Currently the International Space Station (ISS) has a vegetable production system consisting of a garden with various flowers and vegetables. The watering technique is detailed as requiring personnel tasked with an individual plant in the garden. The seeds are placed into plant pillows that contain soil consisting of a pillow garden. The tasking requires each “pillow” to be injected with water and sanitized every so often [6].  However, it is possible for soil particles to easily become viral under microgravity conditions therefore we will place a coco peat pellet in an isolation box and adapt the water-wicking system for the autonomous CubeSat.

Setup design for Task 2 and method of conducting experiments: Considering that roots grow differently in space due to the lack of gravity, the root zone of the plant needs an isolated area. For our design, the coco peat will be placed in a clear isolation box held by a tunnel big enough for the coco peat to absorb the water and expand. The seed will be tied to the coco peat pellet using a nylon thread which will ensure the seed does not dislodge during detumbling. In this method, the system can deliver water by a simple nylon thread drawing the nutritional water directly to the coco peat and then nutrition to the seed. This nylon thread provides another protective layer of antibacterial properties to avoid any possibility of degradation to the plant [7]. This design idea includes a reservoir for water storage with a connected sealed nylon thread to guide the nutritional water to the coco peat. The system is designed to fit in the bottom portion of the CubeSat which will provide enough water for the 30-day mission by this slow wicking method and absorption of water in coco peat. This experimentation will lead to further applications for growth of various plants with small adjustments to design specifications such as reservoir size and substrates.

Expected outcomes from Task 2: With this distinct water system, the top view and side view angles will be able to provide enough images if the water provided was too little, adequate, or in excess. Also, the AnyLeaf module pH sensor will relay data concerning the hydrogen ions within the water. In general, the pH sensor should indicate the water for irrigation is between the pH levels of 5 and 7 [8]. The pH sensor used will also measure temperature which should remain around 68-72 degrees F for sufficient growth of roots and maintaining dissolved oxygen. Dissolved oxygen increases the growth of the plant which reflects in the water quality. It has been correlated that the higher the water temperature, the less dissolved oxygen the water is able to hold which is why the range of 68-72 degrees is preferred. This data collection also studies the growth of pathogenic organisms, which are prevalent if not enough dissolved oxygen in the water is present [9]. The requirement of dissolved oxygen leads to using reverse osmosis water considering that dissolved oxygen can be removed during some purification methods. Using reverse osmosis water will ensure the plant retrieves the best water. The reverse osmosis process removes any harmful contaminants such as chlorine or heavy metals [10]. To ensure the water quality for successful growth, measurements from the pH sensor will provide experimental data that will benefit our current water aeration understanding. 

Task 3. To analyze the plant growth data to study the effect of stressors on the growth of a plant. It is obvious that growing plants out of Earth requires a closed ecological system. Such a system can be designed in the form of a greenhouse or small chambers in which temperature and various other conditions are controlled to grow plants. However, a critical difference between growing plants in a closed system in and out of the earth’s atmosphere is gravity. The research on the effect of gravity on agricultural crops is still an ongoing study with NASA being the pioneer in the field [11]. While solutions are offered for operational irrigation in microgravity, the effect of gravity on absorbing water and nutrients via the root system and the photosynthetic process can be different across plants species. The most notable difference is the capillary force the root system uses, for water uptake and other chemicals, which acts against gravity for plants grown on earth. At a lower gravity, the rate of transferring materials from roots to the leaves can be faster if the vascular structure in the root and stem are the same. Hence, the question is if plants grow faster at a lower gravity or if their vascular structure changes to adapt to the lower gravity. The answer can be different for different plants. This effect will be monitored via the cameras and sensors to truly understand the difference. 

Setup design for Task 3 and method of conducting experiments: For this task, the developed chamber in task 1 equipped with sensors and cameras will be used to analyze plants. The signals related to the health status of the plant, including the concentration of the verified VOCs and gases released from the plant, and humidity and pH levels will be monitored constantly as the plant grows. The growth rate and the structure of the plants will be constantly monitored through the pictures from the cameras installed. One camera will be placed vertically above the plant providing images from the leaf view. In the microgravity environment, the tumbling of the satellite may affect the distribution of oxygen and water in the root zone. The data from the sensors and images from the hyperspectral camera will be analyzed together to find the effect of the position on the growth of the plant. This data can be compared to an on-Earth growth process and even further by analyzing the correlation between the rotations and the photosynthetic activities of the plant by the measuring its biological signals and the satellite’ gyroscope data. Furthermore, the structure of the leaves, stems, and roots will be considered to fully assess the effect of gravity on the growth of the plants by the sensor array and imaging.

Expected outcomes from task 3: The results from the PHMS are expected to show the effect of gravity and air circulation on the health status of plants being grown at different angles and rotations. The images from the roots (at the end of the growth cycle) will reveal if the gravity direction changes the direction of the root’s development and its structure. The images from the leaves and stems of the plants will be used to find if the rate of growth is a function of the gravity direction and speed of the air being circulated. With the vast amount of data collected, MATLAB will be used to analyze the variation in the sensor array output that will be plotted and compared with the results from the dark and light cycles. In addition to using the image processing tool in MATLAB and machine learning (ML) algorithms, the images from the plants will be processed to find the different colors of the plant’s leaves in each chamber and correlate the sensor array data from the sensors with the size of the plant. A free hyperspectral data analysis software from the camera’s company, Resonon, is provided which has hyperspectral VIs to estimate biophysical and biochemical traits in plants. These VIs can measure the structure, biochemistry, and plant physiology/stress which is required to analyze the plant in microgravity [4].