First Advisor
Jay Nadeau
Term of Graduation
January 2026
Date of Publication
9-1-2026
Document Type
Dissertation
Language
English
Subjects
Colwellia psychrerythraea, Digital Holographic Microscope, International Space Station, Microgravity, Motility
Physical Description
1 online resource ( pages)
Abstract
Designing for spaceflight favors the reduction of unnecessary features and cost-cutting, whether thisbe computation, hardware, or procedure. Resources are spent toward fortification and mission success over convenience. Such design goals paired with the relatively smaller budgets of academia lead us to do as much as we can in-house and use open-source as much as we can without compromising mission success. We also believe that thoroughly testing technology in extreme environments on earth is necessary for the success of a flight instrument. We focus on microscopy for life detection. I have spent my time here learning methods of hand-building microscopes to observe non-standard samples. The first paper presented describes the need for visible excitation in fluorescence microscopy when looking for common biosignatures, like chlorophyll. This was important to highlight due to the growing popularity of deep UV excitation and imaging for life detection applications. Most of my time was spent with a digital holographic microscope (DHM) design developed by our collaborators for field and flight applications. Most applications of DHM rely on a single cell occupying a significant portion the field of view to get detailed phase information. This would not lend itself well to observing a large volume of cells nor give us the ability to observe motility patterns with cells moving at more than a body length per second. As such, the second paper shows that in cases with unresolved particles, signals are dominated by scattering, thus giving amplitude, rather than phase, reconstructions a higher signal-to-noise ratio. This is especially important for detection in environmental samples with unknown composition. By this point, I could quickly build a DHM and had ample experience analyzing a range of field and lab data. This prepared me to take on the development of a flight version of the DHM when the opportunity arose. Knowing the microscope inside and out allowed me to focus purely on the instrumentation needed to operate on the International Space Station. The bulk of my graduate career was spent building and documenting the Extant Life Volumetric Imaging System (ELVIS) payload. The third paper details the hardware and lessons learned when developing a payload. The payload performed successfully: we were able to mature our Technology Readiness Level (TRL) of the DHM and obtain high science yield from the experiment. The final paper presents results from the spaceflight experiment. We wanted to investigate the behavior of motile bacteria in true microgravity. We found that the bacteria swimming on the ISS had both an average higher speed of 26 ± 13 µm/s (N=1293) with a fairly normal distribution, compared to the ground bacteria’s average speed of 21 ± 12 µm/s (N=1880) and skewed distribution toward lower speeds. Additionally, the bacterial growth was significantly slowed with the ISS doubling time at approximately 3.8 days, compared to the ground’s 55 ± 5 hr doubling time. Currently, there are no future operations planned for ELVIS, but it remains operational and ready to fly again. Future work could involve flying organisms with different motility patterns, which could use the same hardware and procedures as our operations. Because the sample chamber is completely removable, there is a built-in modularity, allowing different sample configurations, including but not limited to a flow chamber.
Rights
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Recommended Citation
Johnston, Nikki, "Developing Field and Spaceflight Microscopy" (2026). Dissertations and Theses. Paper 7198.