|Title||Characterizing photobioregenerative technology for simulataneous thermal control and air revitalization of spacecraft and surface habitats|
|Year of Publication||2019|
|Academic Department||Department of Aerospace Engineering Sciences|
|University||University of Colorado Boulder|
Algal photobioreactors have been researched as potential solutions to air revitalization in a spacecraft cabin environment by absorbing CO2 and producing O2 through photosynthesis. This photosynthesis, and consumption of produced biomass, theoretically provides a closed-loop solution for long-duration spaceflight. Addressing multiple spaceflight requirements simultaneously with algae has the potential to reduce launch mass, power and volume of future Environmental Control and Life Support (ECLS) systems. Additionally, inoculating algal culture into a water-based thermal cooling loops (flight-proven standard of active cooling found on the International Space Station (ISS)) could incorporate simultaneous air revitalization and thermal control into a common system. However, this imparts rapid, extreme thermal swings on algal cells not evolved for culture in a transient thermal environment. Therefore, the effect of dynamic thermal environments on the CO2/O2 turnover of algae was characterized to provide a first-order assessment of system feasibility. This research characterizes the effect of dynamic environments, both transient thermal environments and varying levels of CO2 concentration, on metabolic processes of the algal culture. Experiments using Antarctic algal species were included to investigate if cold-acclimated algae are more efficient than Chlorella at CO2/O2 turnover in the active cooling environment. The simultaneous heat and mass transfer coefficients of a nonporous, gas-permeable membrane were characterized, and membrane models developed for future design considerations. A photobioreactor system was designed with considerations for gravity-independence, prototyped, and tested using parameters defined by the ISS cabin environment. A failure modes and effect analysis distilled lessons learned from the previous experiments, which also informs the use of algae for bioregenerative life support. In conclusion, the resulting values from the previous characterization experiments, along with values found in literature, were used to make a first-order mass-balance comparison between current ISS ECLSS and photobioregenerative technologies. This work serves as an initial evaluation of the feasibility for using an algal photobioreactor for simultaneous air revitalization and active thermal control of a spacecraft or surface habitat.