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Constant Oxygen Monitoring during 13 Days on Satellite Mission in Outer Space
PreSens OEM Components Applied for Biological Experiments in Zero Gravity
Sebastian M. Strauch, and Michael Lebert
Cell Biology Division, Department of Biology, Friedrich-Alexander University Erlangen-Nuremberg, Germany
The OMEGAHAB is a closed artificial ecosystem that was sent into orbit for 13 days on board the Russian satellite FOTON-M3 in 2007. Objective of this biological experiment was to keep fish larvae (Oreochromis mossambicus) alive in a closed system with oxygen produced by the algae Euglena gracilis. A constant decrease in oxygen concentration was monitored with the EOM-O2-mini inside the OMEGAHAB. However, enough oxygen remained to keep the fish larvae alive; 11 out of 26 larvae survived the trip to orbit and back. All control and monitoring components of the OMEGAHAB demonstrated good functionality and robustness and even endured the landing of the return capsule. Results and experiences gained in this study were used for further development of the artificial ecosystem, and in 2013 the successor OMEGAHAB B-1 was sent into orbit on board the Bion-M1 satellite.
The automated biological experiment OMEGAHAB (Oreochromis mossambicus Euglena gracilis Aquatic Habitat) was developed in cooperation by the Friedrich-Alexander University of Erlangen-Nuremberg and the University of Hohenheim. Fundamental idea of this project was to create a closed ecosystem where fish larvae spend their first days in life in orbit. Euglena should produce the oxygen needed by the cichlid larvae, while at the same time take up CO2 produced by the fish. The fish larvae as well as the algae were recorded on video for several minutes each day to analyze their movement patterns in weightlessness. After the mission the vestibular organs of the fish larvae were investigated, to determine the influence of zero gravity on tissue growth. The whole experimental set-up had to comply with guidelines concerning dimensions, weight and energy budget, and it had to be constructed so it would keep 20 - 30 fish larvae alive for 15 days. The aquarium consisted of a fish compartment and an algae compartment with a gas exchange unit. The tank had cylindrical shape and was made of polycarbonate with a customary aquarium filter made of polymer foam. A control system had to be built to monitor oxygen levels inside the closed ecosystem. In case enough oxygen was produced the photosynthetic light sources should be dimmed automatically to conserve energy. For oxygen monitoring chemical optical sensors and the EOM-O2-mini by PreSens were used. With this system oxygen measurements could be taken non-invasively through the transparent tank walls. No extra holes had to be drilled into the aquarium, which was a major advantage as it reduced mechanical stress on the components. Unlike Clark-type electrodes the chemical optical sensors do not consume oxygen, and have very good long time stability. Furthermore, the OEM component has a small footprint and the whole system is very robust, so it was ideally suited for integration in the control system of the OMEGAHAB. During the first days of the experiment the fish larvae would need no food, as they have a yolk sac which they consume. In case they developed faster a feeding system was installed to avoid the larvae starving during the experiment. A pump for water circulation, and a temperature control consisting of a cooling system, a heating foil attached to the outside wall of the tank, and three temperature sensors were also implemented. The algae were illuminated with LEDs for optimal photosynthetic yield. Furthermore, lights and video cameras were installed so the fish larvae as well as the algae could be visually monitored. Two identical OMEGAHAB modules were built: The flight module (FM) was brought to the Cosmodrome in Baikonur, Kazakhstan, where it was installed inside the FOTON-M3 satellite and sent into orbit on 14. Sept. 2007. The flight spare module (FSM) stayed on ground and was taken to Samara, Russia. All experimental processes were run in parallel on the FM in orbit and the FSM on the ground for a 13 days period.
A Biological Experiment in Weightlessness
Oxygen measurements were started as soon as the OMEGAHAB left Erlangen for transport to Kazakhstan, 7 days before the experiment was sent into orbit. The fish larvae were put into the tank on day 4 - the day the OMEGAHAB was going to be installed inside the satellite. Temperature measurements during the experiment showed ripples (data not shown) which were caused by an electronic artifact and occured each time the fans of the cooling system were turned on. Oxygen measurements, therefore, show the same irregularity, as the rippled temperature values were used for temperature compensation of the measurements. In Figure 2 the recorded oxygen values inside the FM and FSM are depicted. The starting O2 concentration in the FM was quite low with only 1 g L-1, while in the FSM values of 7 g L-1 could be recorded, during transport. The change of the fish water before and after the fish were set in the tank of the FM (day 4) caused a strong increase in oxygen concentration up to 6 g L-1. Blips in the O2 concentration curves are correlated with agitation of the modules during transport or during the climb of the rocket into orbit. After the FM reached orbit and the FSM was running according to the protocol on the ground, a constant downward trend in oxygen concentrations can be observed in both modules. Nevertheless, the OMEGAHAB was functioning correctly. Preliminary tests had already shown that O2 production cannot keep up with O2 consumption of this number of fish larvae. Oxygen concentrations of down to 1 g L-1 are not harmful to the fish larvae as long as oxygen values decrease slowly to this minimum, which was factored in when planning the experiment. The O2 consumption in both modules can be compared and is quite similar, differences may only have been caused by varying consumption of the food added by the feeding system from day 10 on, or different times at which some of the fish larvae died. Algae managed to get inside the fish compartment probably through a leaky filter system. Inside the fish compartment they had no photosynthetic illumination and also consumed oxygen, which might have contributed to oxygen decrease. A malfunction which caused the water pumps of the FSM to stop two days before the experiment was terminated resulted in a dramatic decrease in oxygen supply. There only 1 live fish larva could be retrieved, while in the flight module 11 out of 26 larvae survived. The oxygen level in the FM was sufficient for the larvae for the whole experimental period.
OMEGAHAB B-1 - The experiment in 2013
In OMEGAHAB B-1 Euglena gracilis together with the water plant Ceratophyllum should produce oxygen. This time Mexican freshwater shrimps (Hyalella azteca) were put in the aquarium together with the cichlid larvae. The CO2 produced by the animals could be used by the water plants for photosynthesis. Microorganisms inside the filter would convert fish excretions into smaller components serving as fertilizer for the plants. Some snails were put inside the tank to keep the walls of the aquarium clean from growing microorganisms, so video recordings of the animals would not be impaired. Oxygen inside the tank was again monitored non-invasively with the OEM system by PreSens. The system had already proven its suitability, many advantages and was functioning soundly during its use on the first mission. In OMEGAHAB B-1 the EOM-pH-mini system by PreSens was also applied to gather additional data about pH values inside the aquarium (Fig. 3). While OMEGAHAB had stayed in orbit for 13 days its successor was sent on a 1 month mission, from 19. April - 19. May 2013. Due to an unforeseen contamination the experiment started to fail in an early phase: a number of unexpected microorganisms with fish pathogenic properties infested the system and lead to an early demise of the larvae. Putrescence led to an overpressure inside the aquarium and to leakage, which in turn shut down the otherwise flawlessly working electronics after ten days. Analysis of the recorded data will, nevertheless, give valuable information.