Ecophysiological Models in Simulations of an Aquatic Habitat for Closed-Loop Life Support Research

Abstract

A limitation in closed-loop life support system research is the no-availability of small-scale experimental capacities that may help to better understand the challenges in system closure, integration, and control. Ground-based aquatic habitats are an option for small-scale research relevant to bioregenerative life support systems (BLSS), given that they can operate as self-contained systems enclosing a habitat composed of various species in a single volume of water. This paper elaborates on the modeling, design, and simulation of a recon gurable aquatic habitat for experiments in BLSS and automation. It focuses in the process of respiration: higher plants of the species Bacopa Monnieri produce O2 for snails of the genus Pomacea. The snails consume the O2 and generate CO2, which is used by the plants in combination with radiant energy to generate O2 through the process of photosynthesis. The paper expands the description of biological processes by introducing models of ecophysiological phenomena of the organisms involved. The model of the plants include a description of the rate of CO2 assimilation as a function of irradiance. The snails instead are modeled through their rate of consumption, treated as a combination of a constant and a random variable to account for changes in metabolic rates and aestivation.The latter consists in brief periods of torpor of the metabolism of the snails in which oxygen consumption is considerably reduced. Simulations and validation runs with hardware show how these phenomena may act as disturbances for the control mechanisms that aim to maintain safe concentration levels of dissolved oxygen in the habitat.