Compact and automated sensing systems are needed to monitor plant health for NASA's controlled-environment space crop production. A new hyperspectral system was designed for early detection of plant stresses using both reflectance and fluorescence imaging in visible and near-infrared (VNIR) wavelength range (400-1000 nm). The prototype system mainly includes two LED line lights providing VNIR broadband and UV-A (365 nm) light for reflectance and fluorescence measurement, respectively, a line-scan hyperspectral camera, and a linear motorized stage with a travel range of 80 cm. In an overhead sensor-to-sample arrangement, the stage translates the lights and camera over the plants to acquire reflectance and fluorescence images in sequence during one cycle of line-scan imaging. System software was developed using LabVIEW to realize hardware parameterization, data transfer, and automated imaging functions. The imaging unit was installed in a plant growth chamber at NASA Kennedy Space Center for health monitoring studies for pick-and-eat salad crops. A preliminary experiment was conducted to detect plant drought stress for twelve Dragoon lettuce samples, of which half were well-watered and half were under-watered while growing. A machine learning method using an optimized discriminant classifier based on VNIR reflectance spectra generated classification accuracies over 90% for the first four days of the stress treatment, showing great potential for early detection of the drought stress on lettuce leaves before any visible symptoms and size differences were evident. The system is promising to provide useful information for optimization of growth environment and early mitigation of stresses in space crop production.
Polydimethylsiloxanes (PDMS) degrade into dimethylsilanediol (DMSD), a soluble compound that affects the performance of several life support systems on the International Space Station (ISS). In industry, PDMS are typically removed using gas purification equipment using commercial sorbents. A bench scale test bed was developed at KSC for evaluating candidate commercial sorbents for the removal of gas phase PDMS using environmental conditions found on ISS (i.e., RH 40% and 23 oC). The test bed consists of four subsystems: 1) a Kin-Tek gas generator to supply a humid gas stream with the desired concentration of siloxanes and volatile organic compounds (VOCs); 2) a sorbent assay tube containing sorbent materials during testing; 3) an environmental monitoring and control system consisting of valves, a heater, and temperature, humidity, and pressure sensors; and 4) an automated gas analysis system to measure preand post-sorbent siloxane concentrations using a gas chromatograph and Valco sampling valves. The adsorptive capacity of Chemsorb 1000, an activated carbon sorbent derived from coconut shell char, for PDMS was tested in this system. The sorbent was challenged with a linear (L2, Hexamethyldisiloxane) and a cyclic (D3, Hexamethylcyclotrisiloxane) siloxane under ISS nominal conditions and adsorptive capacities were determined from breakthrough curves.
The Advanced Plant Habitat (APH) was installed on the International Space Station (ISS) in October 2017. Following a successful EVT (Experiment Verification Test) study at Kennedy Space Center (KSC), using Arabidopsis lines with varying levels of lignin, two inaugural studies were carried out on ISS in 2018 under the same experimental design, with the corresponding ground controls at KSC. The APH for this study deploys a substrate-based root module designed for plant growth in microgravity. Upon experiment initiation (such as for the EVT), the root module is primed (liquid imbibition) by flooding the root zone to initiate seed germination and to remove air from the porous tubing and particulate media. In the APH ISS inaugural study, the speed of supplying water to initially dry media was found to adversely affect the overall moisture distribution within the root module in microgravity (but not at 1g). Non-destructive estimations of Arabidopsis plant growth were carried out by monitoring changes in rosette leaf area on a daily basis. These data indicated that the original priming procedure caused patchy moisture distribution that affected plant growth and survival. An improved methodology for priming the second root module of PH-01 was devised and implemented in the second experiment. Leaf area and color estimates suggested that the modified priming scheme improved moisture distribution and plant growth. These data, when compared with the EVT study, suggest that nondestructive measurements of plant growth can aid towards optimization of plant growth conditions in microgravity.
