Performance and Sensitivity of the Energy Cascade Models for Lettuce Production in Bioregenerative Life Support Systems

Abstract Long-duration space missions will require the use of Bioregenerative Life Support Systems (BLiSS) to ensure renewability of the crews food and oxygen. Sustainable management of these systems will require accurate predictions of biomass accumulation and gas exchanges from crop production. Four Energy Cascade (EC) models have been developed to predict biomass yield and transpiration rates of BLiSS crop production. Lettuce cultivars Waldmann’s Green and BG231-1251 were grown at a daily average temperature of 21 °C, ambient CO2, and a daily light integral of 22.03 mol m-2 d-1 to evaluate the ECs predictive abilities. All ECs overestimated lettuce biomass and underestimate transpiration with root mean square errors (RMSEs) ranging between 49.58 to 96.99 g m-2 and 0.80 to 2.30 L m-2 d-1, respectively. Global sensitivity analysis indicated that the ECs biomass predictions are insensitive to temperature changes. The ECs are additive with environmental parameters, such as light and CO2, accounting for half of any output’s sensitivity. Interactions between parameters accounted for, at most, a third of the ECs sensitivity. The ECs provide a baseline for BLiSS crop management; however, this comprehensive, retrospective analysis reveals systematic biases in predictions of lettuce crops, stemming from erroneous canopy closure methodology and lack of temperature responses. Further work on lettuce, or other crops, can use this analysis as a benchmark to improve the range, accuracy, and reliability of the ECs for sustaining BLiSS and the astronauts they support.