BIORAT: Preliminary Evaluation of Biological Life Support in Space Environment 2000-01-2384

For long time space missions, a reliable life support system including food supply, gas generation and waste management is necessary. For this purpose the MELiSSA (Micro-Ecological Life Support Alternative) concept has been conceived as a micro-organisms and higher plant based ecosystem intended as a tool for understanding the behavior of artificial ecosystems and for the development of the technology for a future biological life support systems. Based on an aquatic ecosystem, the MELiSSA loop is constituted of four microbial compartments, a higher plant compartment and the crew. The driving element is the recovery of food, water and oxygen from waste, like faeces, urine, non-edible plant material and CO2.

Several scientific experiments indicate that a higher microbial growth rate is present in reduced gravity than on earth. This growth rate in reduced gravity can be twice the value obtained on earth. As the microbial growth is one of the main factors to size the processes, it is very important to quantify these effects on the micro-organisms used in the MELiSSA loop. The BIORAT experiment is an introductory step to microgravity experiments. The BIORAT breadboard was built taking into account engineering principles needed for future development of flight hardware. The BIORAT experiment demonstrated that an engineering approach enables to control, on a long duration, a simple ecosystem reduced to gas exchanges with no accumulation in the loop. The BIORAT study focussed on two compartments of the MELiSSA loop: the photosynthetic reactor and the consumer compartment. A specific designed photobioreactor, which can be operated in reduced gravity conditions, was used. Carbon dioxide, produced by the test animal, is consumed by the algae in the photosynthetic process, resulting in a production of oxygen.

The validation of the system consisted of the characterisation of specific parameters and control variables like gas transfer and light-energy. The gas transfer coefficient was measured to quantify the aeration capacity of the photobioreactor. The gas transfer was high enough to ensure a sufficiently short response time for oxygen recovery of the consumer compartment and to absorb the CO2 with a high efficiency.

The growth and photosynthetic activity of the Spirulina at different light intensities was measured to calibrate and validate a specific designed mathematical model of the photobioreactor system. Based on the model, a control strategy was designed to control the oxygen production by acting on the light intensity. The control of the CO₂ mole fraction in the consumer compartment at steady state can be performed by acting on the pH of the photobioreactor.

The demonstration of the breadboard will be performed by using a mouse in the consumer compartment.