Review of Failure Modes of a Photobioreactor System Used for Long Duration Spaceflight Environmental Control and Life Support

NASA is currently planning human spaceflight missions with longer durations than ever before. Crewed missions mean environmental control and life support systems (ECLSS) must be incorporated into mission designs to meet crew metabolic requirements. Today, ECLSS technology is partly open-loop, still using some consumables and producing waste. This approach can quickly become mass or volume prohibitive, as the system scales with mission size. Closed-loop technologies, specifically photosynthetic algal photobioreactors, can offer multiple functions such as air revitalization (CO2 absorption and O2 provision) and thermal control with less launch mass and volume for long-duration flights. However, if the reliability or robustness of the system is too low, the need for spares or increased crew time nullifies the benefits of multifunctional technologies with potential to close the loop. Identifying the potential failure modes of a photobioreactor system in reduced gravity environments is the first step to assessing its overall reliability and robustness for a spacecraft and habitat. Presented failure modes either depended upon the application or are associated with culturing algae itself. Data from terrestrial algal pilot plants were used to identify potential difficulties with large scale cultures. Previously flown experiments and systems with similar operation to a photobioreactor were used to baseline the response in microgravity. The identified system failure modes, their causes, and proposed mitigation strategies are presented. As a result of this review, photobioreactor designs can continue to strive for greater reliability and robustness by being cognizant of potential failure modes, with inclusion of mitigation methods or failure tolerance.