An Analysis of Hybrid Life Support Systems for Sustainable Habitats

Abstract

The design of sustainable habitats on Earth, on other planetary surfaces, and in space, has motivated strategic planning with respect to life support (LS) system technology development and habitat design. Such planning requires LS system analyses including both high fidelity modeling and high level trade space exploration of candidate architectures. A particularly relevant trade for sustainable, long duration missions exists between the implementation of physicochemical and bioregenerative LS technologies. In the case of the food subsystem, there are distinct advantages and disadvantages to employing either prepackaged food or a biomass production system (BPS). This project investigates the trade between biologically grown food and stored food as part of the broader bioregenerative-physicochemical trade-off in environmental control and life support systems (ECLSS) for isolated and confined environments. Lunar and Mars surface habitats with varying degrees of bioregeneration for food and atmosphere revitalization are simulated using the BioSim advanced life support system simulation. An equivalent system mass (ESM) analysis is carried out, and improvements to crop lighting systems and agricultural system autonomy are considered as two possibilities for reducing infrastructure costs for biological food growth systems. The ESM analysis indicates that reducing lighting costs and increasing autonomy of the food production, processing, and preparation systems associated with the BPS will increase its feasibility and cost-effectiveness for use in long-term space flight. With no technology improvements, mission durations at which the ESM cost of a hybrid system is lower than that of a physicochemical system with similar performance will likely not be less than about 4 years for lunar surface missions and 4.8 years for Mars surface missions; however, with significant improvements to the BPS and its supporting infrastructure needs, these "crossover" times can be more than halved. The H metric is proposed for classification of fully or partially regenerative habitats. The multidisciplinary ECLSS optimization considers 14 design variables and models and evaluates integrated ECLSS's for non-crew time ESM and crew time. Ultimately the question that is posed is, what is the optimal combination of physicochemical and bioregenerative life support technologies for a given mission or mission campaign, and how can this drive strategic technology development?