One of the current scenarios for growing plants on Mars is the development of autonomous greenhouses capable of transmitting information on the plants to Earth, via telemetry. This article follows M-PHIS: A New Imaging System to Grow Plants on Mars, and presents the experiments performed on this multispectral system, which includes several new features.
This article is part of a series on research and technological developments intended for the colonization of other planets.
Short Duration Low Pressure Experiments
The imager was installed in a hypobaric chamber at the University of Guelph‘s (Ontario, Canada) Controlled Environment Systems Research Facility (CESRF). The objective was to evaluate its ability to capture images of induced green fluorescent protein (GFP), natural red and near-infrared fluorescence and simulate plant health studies in a hypobaric environment. The testing was also designed to shed light on the operational constraints that a fully automated plant health imaging system may face on-orbit or other spaceflight scenarios.
Although the imager hardware and software went through several weeks of operational testing prior to deployment at CESRF, it was still unknown if the imager would operate at the low atmospheric pressures planned for the experiment. Such extreme operational conditions are far from standard, and as such no data was available regarding low pressure operation of each individual imager component. To address this question a preliminary test was performed without biological samples in the imager. On February 16 2012, the imager was installed in the hypobaric chamber and set to capture a Full sequence (GFP, Red, Infrared, Black and White) every 20 minutes under low pressure conditions (see Figure 1). A calibration plate designed and fabricated by the University of Florida was installed in the imager for the tests. The plate was engineered to fluoresce similar to GFP and chlorophyll.
The chamber pressure was initially decreased from ambient to 25 kPa over a 30 minute period. A full imaging sequence was subsequently captured and verified in real-time. After confirmation of imager functionality at 25 kPa, the chamber pressure was further decreased to 5 kPa over 10 minutes, where it was maintained for 30 minutes and a full sequence of images captured. The images obtained at low pressure (25 kPa and 5 kPa) were directly compared to those collected at ambient pressure. They confirmed that the low pressures did not affect or alter the camera or liquid crystal tunable filter (LCTF) optics in any significant way. These tests also confirmed that the imager was capable of operating at low atmospheric pressures.
Long Duration Low Pressure Experiments
Following the general confirmation of the M-PHIS functionality in low-pressure environments, a long duration low pressure run utilizing actual biological samples was conducted. After the chamber was closed for the first 5 kPa run, M-PHIS was set to capture a sequence of images (GFP, Red, Infrared, Black, and White) at the start and every four hours thereafter for a period of forty-eight hours. This meant that the first capture sequence was taken when the chamber pressure was still at ambient. The chamber reached 5 kPa 84-min following initiation of pressure draw-down. The second series of images, taken four hours from the start, was taken with the plants growing at 5 kPa. Figure 2 shows a comparison between the first two sequences. Two small rectangular markers are positioned on the top left of the sample tray and act as the LCTF calibration indicator. These reference indicators should nominally remain at the same intensity for each specific image capture type. For example, Figure 2 demonstrates that the intensity of the indicators were essentially the same for the image capture at atmospheric pressure and at 5 kPa.
Heat Removal Issues
During the long duration experiment, the internal temperature of M-PHIS rose beyond the tolerance limits of the biological samples contained within. After further investigation, several potential causes where discovered:
- Although the hypobaric chamber was temperature controlled, its lighting system composed of high-pressure sodium bulbs radiates heat on to the imager’s metal casing. During the initial operability trial, the chamber lights were off (no biological samples in the chamber). During the plant imaging experiments however, the chamber lights were on to support control samples outside of M-PHIS.
- The imager cooling fans were insufficient in the hypobaric environment, as there was not enough air to carry away all the heat being generated. The preliminary operability tests were too short to allow the team to observe this heat management problem, which was further enhanced with the chamber lights turned on.
- Since the imager system was sealed to prevent light contamination, waste heat and energy from the grow lights accumulated overtime. To overcome or minimize the heat issue, the system was covered with a heat-reflecting blanket, the grow lights were kept off and the test durations were reduced. In the future it is likely that the fan located behind the sample tray will be replaced by a Peltier cooling system. In addition, as the CESRF hypobaric chambers are equipped with crop irrigation lines, liquid-cooling loops could also be incorporated either individually or in combination with the thermoelectric cooler to further increase cooling capacity.
The following videos were captures in the ground unit (Run 3A Ground) and in the flight unit on the International Space Station (Run 3A Flight) in the GFP Imaging System (GIS) housed in the ABRS (Advanced Biology Research System) and developed by Kennedy Space Center Engineers.
A plant health imaging system capable of capturing biological gene activities and translating these signals into plant stress measurements would be an indispensable diagnostic device in bioregenerative life support systems. In this study, we discussed the research and development of an autonomous multispectral imaging system designed to evaluate plant health in situ, in regular greenhouses or in plant production facilities located in hostile or space analogue environments. With its LCTF, the imager could be set to capture a series of images including, but not limited to GFP and natural chlorophyll fluorescence. In addition, its custom designed LED circuit board, composed of independently controllable LEDs with seven distinct central wavelengths as well as independent control of the upper / lower half of the board, meant the lighting system could be employed in a wide array of scenarios and studies.
The Multispectral Plant Health Imaging System was deployed in a hypobaric chamber and successfully captured images at several wavelengths, including those for GFP and red/near-IR for chlorophyll. In addition, M-PHIS was the first fluorescent imager to run autonomously in a low-pressure plant growth chamber. Its deployment and operations have demonstrated the feasibility of plant diagnostic systems that will allow for monitoring and control of space biology experiments and bioregenerative life support systems. Multispectral plant imaging systems are powerful tools for plant health monitoring; they represent a significant step towards securing the technical capacity for sending plant heath information in a telemetric fashion from an extra-terrestrial location. Results from this work, combined with past and future experiments will be used to evaluate remote sensing plant response to low pressure environments.
For more information, see the following research article:
Abboud, Talal; Berinstain, Alain; Bamsey, Matthew; Ferl, Robert; Paul, Anna-Lisa; Graham, Thomas; Dixon, Mike; Leonardos, Demos; Stasiak, Michael; Noumeir, Rita. 2013. Multispectral Plant Health Imaging System for Space Biology and Hypobaric Plant Growth Studies. Insciences Journal –Sensors, 3(2), p. 24-44.
Or the following master’s thesis: Abboud, Talal (2013). Systèmes d’imagerie pour l’étude de la santé des plantes et la biologie spatiale. Mémoire de maîtrise électronique, Montréal, École de technologie supérieure. 90 p.
Talal Abboud holds a Bachelor and a Master of Engineering from the Department of Electrical Engineering of the École de technologie supérieure (ÉTS). He is currently an electronics designer at Kongsberg Automotive centre of excellence (CoE) department.
Alain Berinstain spent 17 years at the CSA where he was Director of Planetary Exploration and Space Astronomy. Since 2013, with the creation of his own company, Psyence, he now devotes himself to the communication of science and technology.
Matthew Bamsey is a Research Associate at Institute of Space Systems DLR in Germany. He is also part of the EDEN ISS project team. He worked on research projects at the University of Florida, University of Guelph and the CSA.
Robert Ferl is a Professor at University of Florida and Director of the Interdisciplinary Center for Biotechnology Research (ICBR) His research interests are space biology, examination of 14-3-3 proteins and of chromatin structure.
Anna-Lisa Paul is a Research Professor in Horticultural Sciences,University of Florida. Her research interests focus on the regulation of plant gene expression in response to abiotic stress and extreme environments.
Thomas Graham is a Research and Development Manager at the University of Guelph’s CESRF. His research interest focuses on improving volume utilization efficiency in bioregenerative life-support systems.
Mike Dixon has been a Professor at the University of Guelph since 1985. He is the Director of the CESRF and lead a team of researchers investigating the contributions of plants to human life support in space.
Demos Leonardos is a Research Associate of the Controlled Environment Systems Research Facility (CESRF) at the University of Guelph.
Michael Stasiak is a Senior Research Associate and the Technical Operations Manager of the Controlled Environment Systems Research Facility (CESRF) at the University of Guelph.
Rita Noumeir is a professor in the Electrical Engineering Department at ÉTS. Her research includes applying artificial intelligence methods to create decision support systems as well as video and image processing.
Program : Electrical Engineering