ECLSS Analysis for Mars Missions: Addressing Failure and Crew Time Uncertainty Using Bayesian Estimation

Mars missions, including flyby missions, require a minimum duration of approximately 500 days. Due to the 26-month launch window cycle and the limitations of interplanetary orbits, such missions offer limited flexibility for mid-course corrections or early returns to Earth. Consequently, crewed missions demand a significantly more reliable Environmental Control and Life Support System (ECLSS) than what is needed for the International Space Station (ISS) in low Earth orbit. This paper evaluates the reliability of a regenerative ECLSS using operational data from the ISS, applying two different methods: the Constant Failure Rate (CFR) model and the Bayesian estimation model. The analysis shows that, for both 600-day and 1200-day manned Mars missions with two crew members, a regenerative ECLSS is more advantageous than a storage ECLSS, in terms of mass. Additionally, the average Orbital Replacement Unit (ORU) mass calculated using the Bayesian estimation model aligns with the calculations based on the CFR model's Mean Time Between Failures (MTBF), while the 5th percentile of the ORU mass corresponds to the results obtained when the MTBF is extended by a factor of ten. For a 1200-day mission, the average crew time required for maintenance of the entire ECLSS is 907 hours, which corresponds to 45 minutes per day. The system’s availability for this mission is 0.9687. Given that a hybrid ECLSS, which integrates storage ECLSS, is being used for the Mars mission, this level of availability is deemed acceptable, provided it can effectively prevent prolonged, continuous failures.