Clarifying Objectives and Results of Equivalent System Mass Analyses for Advanced Life Support

Abstract

This paper discusses some of the analytical decisions that an investigator must make during the course of a life support system trade study.Equivalent System Mass (ESM) is often applied to evaluate trade study options in the Advanced Life Support (ALS) Program. ESM can be used to identify which of several options that meet all requirements are most likely to have lowest cost. It can also be used to identify which of the many interacting parts of a life support system have the greatest impact and sensitivity to assumptions. This paper summarizes recommendations made in the newly developed ALS ESM Guidelines Document and expands on some of the issues relating to trade studies that involve ESM. In particular, the following three points are expounded:1) The importance of objectives: Analysis objectives drive the approach to any trade study, including identification of assumptions, selection of characteristics to compare in the analysis, and the most appropriate techniques for reflecting those characteristics.2) The importance of results inferprefafion: The accuracy desired in the results depends upon the analysis objectives, whereas the realized accuracy is determined by the data quality and degree of detail in analysis methods.3) The importance of analysis documentation: Documentation of assumptions and data modifications is critical for effective peer evaluation of any trade study.ESM results are analysis-specific and should always be reported in context, rather than as solitary values. For this reason, results reporting should be done with adequate rigor to allow for verification by other researchers.

Theoretical design of a space bioprocessing system to produce recombinant proteins

“…ESM is a metric to estimate the flown mass required to implement a space technology and can help guide selection of alternative technologies 14,25,30 . The metric is a linear model to estimate mass of the system along with mass equivalences for providing volume and other infrastructure within a spacecraft (Supplementary data 1).…”

“…These calculations were highly correlated (r = 0.992), and the 2015 equivalency factors are reported in the figures to enable comparisons to prior technology proposals. Due to the variability in calculating ESM for preliminary designs, the metric is only used for selection of competing technologies when ESM estimates approach a 5-to 10-fold difference 25,33 . Figure 3a shows ESM calculations for dewatering methods.…”

“…Since carbonic anhydrase is unlikely to be the only useful product in deep space missions, the ability to produce a variety of recombinant proteins from multiple chassis organisms was a key consideration for the designs. The designs were compared using equivalent system mass (ESM) analysis 14,25 , a system complexity metric (SCM) 16 , technology readiness level (TRL) 26 , and crew-mediated steps to guide future prototype development efforts.…”

Effects of atmospheric pressure, and of the partial pressures of CO2 and N2, on the growth rates of Anabaena sp. PCC 7938: Assessment and implications for cyanobacterium cultivation on Mars

“…There, mass is affected by changes in the volumeto-surface ratio. However, the involved orders of magnitude suggest that the reduction in the mass of a photobioreactor's outer walls allowed by growing cyanobacteria under a low pressure on Mars would be negligible compared to the overall equivalent system mass 41,42 (ESM) of cyanobacterium cultivation (Ramalho et al, submitted), and a fortiori of the overall mission. Decreasing the cultivation pressure can, however, be expected to significantly improve the ESM by reducing the need to process gases from the Martian atmosphere.…”

Complexity Evaluation of an Environmental Control and Life-Support System Based on Directed and Undirected Structural Entropy Methods

“…Top-level design is the overall scheme design formed by system hierarchy and corresponding technology selection, which is crucial for the overall optimization and evaluation of ECLSS. Levri [ 16 , 17 , 18 ] discussed the metric method and calculation procedure of equivalent system mass, which is often applied to evaluate trade study options in the advanced life-support program. Around 2000, Rodriguez [ 19 ], Goudarzi [ 20 ] and others [ 21 , 22 ] established the dynamic top-level models of an advanced life-support system, including crew, crop, waste processing and resource recovery, food processing and nutrition.…”