C.R.O.P.^® demonstrator for human space exploration: Experiment analysis and system model development

Bioregenerative life support systems offer the advantage of simultaneously revitalizing air by fixing carbon dioxide and producing oxygen, purifying waste water, and generating human edible consumables by e.g. growing plants. The C.R.O.P.^® (Combined Regenerative Organic food Production) biofilter system, developed at the Institute of Aerospace Medicine at the German Aerospace Center, is a sustainable concept for the improvement of wastewater in combination with plant cultivation. Two demonstrators incorporating C.R.O.P.^® biofilters, a controlled growth environment, and a hydroponic growth method have been built at the European Space Agency under the Spaceship EAC initiative as an example for a bioregenerative life support system, as well as to investigate the operational concept around such a system. The design, execution and analysis of experiments in the demonstrators are presented. Experiments with Micro-Tina tomato plants (Lycopersicon esculentum Mill.) proved the functionality of the demonstrators. Environmental conditions such as temperature, humidity and photoperiod inside the growth chamber, as well as pH and electrical conductivity of the water were continuously observed and are found appropriate for plant growth. The addition of synthetic urine to the hydroponic system provides all nutrients required for tomatoes to grow through an entire lifecycle. The plants' total biomass, leaf area index and total number of tomatoes are significantly lower compared to the experiment with fertilizer as additive to the system. Another experiment where lunar regolith simulant is used as growth medium instead of rockwool germinated successfully, but plants are unable to develop flowers and fruits. In addition to the experiments, a simulation model of the C.R.O.P.^® demonstrator is developed, partly based on experimental data for the conditions of the controlled environment. In order to predict crop performance, the simulation model implements the existing crop production models Modified Energy Cascade Model. Simulation results and experimental results are compared to validate the final C.R.O.P.^® demonstrator model.