Abstract
The MELiSSA Pilot Plant (MPP) is testing in terrestrial conditions regenerative life support technologies for human exploration in Space. One of its components is a controlled Higher Plant Chamber (HPC) accommodating hydroponic plant cultures. It consists of a 9 m3 single closed growth chamber providing adequate environmental conditions for growing plants, enabling the production of food, water and oxygen for the crew. A critical aspect for a reliable HPC performance is to achieve homogeneous air distribution. The initial experiment carried out in the MPP with lettuce as salad crop, showed uneven plant growth throughout the HPC, which was attributed to inadequate air distribution due to non-homogeneous air velocity profile along the inlet-vents. After a detailed computational fluid dynamics (CFD) analysis, the heating, ventilation, and air conditioning subsystem of the HPC was upgraded and a new experiment was carried out in optimized air flow conditions. Nine-day seedlings of lettuce cultivar “Grand Rapids” were transplanted into the HPC and harvested at the end of the growing cycle, where shoot fresh weight, dry biomass, and shoot mineral composition were analyzed. During the experiment, the environmental control system performed remarkably well based on the biometric measurements as well as the mineral composition leading to a vast homogeneous growth. Overall, the results demonstrated the beneficial effect of an adequate air distribution system in HPCs and the effectiveness of CFD-analysis to design properly the gas distribution. The obtained results are of high relevance for life support systems in space involving plants growth.
Highlights
Controlled ecological life support systems (CELSSs) or bio-regenerative life support systems (BLSSs) have been defined as systems that guarantee human life for long-term in space environments, being able to provide the necessary food sources (Guo et al, 2017)
The two tests conducted in our study reflect the need to have a proper distribution of the gas phase in a plant chamber in order to guarantee uniform plant growth throughout the overall cultivation area of the Higher Plant Chamber (HPC). Both tests shared the same methodology in terms of plant material, growth conditions and biomass analysis as described above, as well as the plant harvest scheduled at 28 days after transplanting (DAT)
This lack of homogeneity showed a different plant growth stage between the HPC modules, in particular all plants in the growth chamber were at the phenological phase of head development (Stage 4) according to Biologische Bundesanstalt, Bundessortenamt and CHemical industry (BBCH) scale for leaf vegetables (Meier, 2001), but about 70% of lettuce plants had already reached the full maturity (Code 49 of BBCH-scale)
Summary
Controlled ecological life support systems (CELSSs) or bio-regenerative life support systems (BLSSs) have been defined as systems that guarantee human life for long-term in space environments, being able to provide the necessary food sources (Guo et al, 2017). Their main objective is to provide the crew with food, oxygen and water without the need of continuous. The sizing, design, and construction of the different compartments of this Pilot Plant has been performed for a final demonstration target of providing the oxygen required for one human and 20–40% of the required food
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