Defining ECLSS Robustness for Deep Space Exploration

Human exploration of deep space will require Environmental Control and Life Support Systems of increasing dependability as mission duration and distance from Earth increases. As crews travel to distant unexplored environments, designers will need heightened confidence in life support availability under increasing levels of uncertainty and risk. Variation in system performance, environmental conditions, resource consumption, waste generation, and even mission characteristics will lead to unexpected responses, increased likelihood of failures, and even design obsolescence. The cost of system failures will also rise, due to launch mass and volume constraints, time and cost of resupply, and reduced ability to abort to Earth. If not accounted for early in design, this increased risk and cost of uncertainty might preclude the economic feasibility of human deep space exploration. The choice of an ECLSS architecture will include many different combinations of technologies that fulfill the functions of atmosphere revitalization, waste removal, and the provision of food and water. The difficult question facing ECLSS designers is how to optimize for the system performance and cost effectiveness necessary for mission feasibility. How do we reduce mass, energy usage, and waste while also ensuring availability of critical life support functions? An optimal architecture must take into account many facets of system performance, such as quality, safety, reliability, and maintainability. Exploration life support systems must continue functioning under harsh conditions, for long durations, without support, and with limited resources or resupply. This review discusses sources of uncertainty in deep space ECLSS design and potential impacts on system functionality. The concept of robustness is proposed to characterize and improve ECLSS performance in off-nominal conditions and abnormal operation. The characterization of ECLSS robustness will lay the foundation for future work in identifying design features and practices for sustaining operation in the face of the uncertainty of deep space missions.