ANALYSIS OF FACTORS AFFECTING THE IMPLEMENTATION OF AN ALGAL PHOTOBIOREACTOR INTO A SPACECRAFT LIFE SUPPORT SYSTEM by Tobias Niederwieser B.S., Technical University Munich, 2013 M.S., University of Colorado, 2015 A thesis proposal submitted to the student’s graduate committee in partial fulfillment of the requirement for the degree of Doctor of Philosophy Department of Aerospace Engineering Sciences University of Colorado, Boulder Fall 2018 This thesis entitled: Analysis of Factors Affecting the Implementation of an Algal Photobioreactor into a Spacecraft Life Support System written by Tobias Niederwieser has been approved for the Department of Aerospace Engineering Sciences. David Klaus, Ph.D. Professor, Aerospace Engineering Sciences Patrick Kociolek, Ph.D. Professor, Ecology and Evolutionary Biology Date The final copy of this thesis has been examined by the signatories, and we find that both the content and the form meet acceptable presentation standards of scholarly work in the above-mentioned discipline. ii Abstract Niederwieser, Tobias (Ph.D., Aerospace Engineering Sciences) Analysis of Factors Affecting the Implementation of an Algal Photobioreactor into a Spacecraft Life Support System Thesis directed by Professor David M. Klaus Algal-based life support systems offer a promising bioregenerative technology for future human space missions by performing the functions of air revitalization, water recycling, and food production. However, despite six decades of active research, no algal-based life support systems have yet been used in a spacecraft. This dissertation analyzes key factors affecting the implementation of an algal photobioreactor into a spacecraft life support system. A comprehensive set of optimum parameters for growing Chlorella vulgaris in a spacecraft was defined to identify research gaps regarding the influence of atmospheric pressure, gravity, contaminants, and radiation as unique cabin environmental factors. From this starting point, the first known comprehensive publication featuring an international and fully historical review of algal spaceflight experiments was completed. Then, using a newly developed and validated flow- through test stand to measure algal metabolism and growth under altered gas compositions and pressures, it was demonstrated that altered total cabin pressure within spacecraft relevant ranges (8.2-14.7 psia) while maintaining normoxic iii conditions did not affect algal growth or metabolism for the conditions evaluated. Additionally, this dissertation features the first known combination of metabolic measurements with metagenomic analysis of non-axenic cultures representative of spacecraft operational environments. Promoting bacterial contamination, together with a variety of green algal taxa, provides novel insight for interpreting results across different algal metabolism studies. The effect of select typical spacecraft chemical contaminants was also assessed. Finally, a first-order feasibility analysis was conducted that established a minimum algal culture volume of 15 liters as being sufficient to support one human in terms of air and water regeneration under ideal performance conditions. This finding was then used to derive the accompanying infrastructure and support requirements that were incorporated into a conceptual design of the system. The data obtained from this work can be used to support an Equivalent System Mass (ESM) analysis or trade study for spacecraft implementation. Additionally, this thesis serves as a basis for future modelling and experimental verification work needed to increase the Technology Readiness Level (TRL) of algal life support systems that can ultimately help enable sustainable, long-duration human exploration of space. iv Acknowledgments This work was supported by a German National Academic Foundation Fellowship and the William F. Marlar Memorial Foundation. Special thanks also go to Ryan Wall, Emily Weidenfeller, and Thomas Ruck who helped me with conducting the experiments. Thanks also to Emily Matula who shared most lab equipment with me and always had the one tool or reagent that I needed in emergencies. I would like to say a special thanks to my committee members David Klaus, James Nabity, Louis Stodieck, Patrick Kociolek, and Alexander Hoehn for their support and guidance in establishing my research and for continuously asking the hard questions. I am especially thankful for the collaboration with Nolan Kane for support in the genomic analysis. I further would like to thank the support of BioServe Space Technologies for using their labs and their support in building my experimental setup. Especially thanks to Paul Koenig for supporting me when I needed a snap ring machined in 15 minutes and asking every day when I will be finished with my PhD. Thanks also to Luis Zea and Jonathan Anthony for being inspiring, motivational, and supporting officemates during that time. A big thanks goes to my parents who have always supported me and raised me to where I am today. Lastly, all of this work would not have been possible without the unlimited support of my friends, colleagues, and family that allowed me to focus on the dissertation but at the same time gave me the opportunity to escape from the research with nature, sports, culture, travel, conferences, or simply by their presence. v Contents 1 Introduction ............................................................................................................. 1 2 Background .............................................................................................................. 6 Cabin environmental effects on the growth and behavior of Chlorella vulgaris ....................................................................................................................... 8 2.1.1 Introduction.................................................................................................. 8 2.1.2 Spaceflight cabin environmental parameters ........................................... 10 2.1.3 Relevant variables and impact .................................................................. 15 2.1.4 Recommendations ...................................................................................... 32 2.1.5 Summary .................................................................................................... 37 Resultant publications and presentations ...................................................... 38 3 Problem statement ................................................................................................ 39 Synopsis of thesis objectives ............................................................................ 40 3.1.1 Objective 1 – Assess the influence of microgravity on algal growth based on past flight-experiments. ................................................................................... 40 3.1.2 Objective 2 – Development of a novel test bed for flow-through measurements of algal metabolism under altered pressure ............................... 41 3.1.3 Objective 3 – Effect of varying total pressure on population growth and metabolism of Chlorella vulgaris at constant oxygen and carbon dioxide partial pressures ................................................................................................................ 42 3.1.4 Objective 4 – Effect of altered oxygen concentration on population growth and metabolism of Chlorella vulgaris under reduced total pressure .................. 44 3.1.5 Objective 5 – Effects of chemical contaminants on the health of algal cultures ......................................................................................................... 45 3.1.6 Objective 6 – First-order feasibility assessment of using an algal photobioreactor for spacecraft life support........................................................... 46 4 Algae in microgravity ............................................................................................ 49 4.1.1 Introduction................................................................................................ 49 4.1.2 Material and methods ................................................................................ 49 4.1.3 Results ........................................................................................................ 50 4.1.4 Discussion................................................................................................... 59 4.1.5 Conclusions ................................................................................................ 62 vi Resultant publications and presentations ...................................................... 71 5 Development of an algal photobioreactor for research with altered atmospheric pressure and composition .................................................................................... 72 Materials and methods .................................................................................... 73 5.1.1 Requirements ............................................................................................. 74 5.1.2 Design ......................................................................................................... 76 5.1.3 Challenges .................................................................................................. 81 Results and discussion ..................................................................................... 83 Conclusion ........................................................................................................ 87 Resultant publications