Flow diagram ( left ) and breadboard design ( right ) used during the course of the development of the Astrium SUPPLY Unit. The syringes fixed at the Astrium miniaquaria were used 

Context in source publication

Context 1

... use aquatic animals for space flight experiments, the flight hardware has to scope with biological requirements and with the technical feasibility. A strong biological requirement is that the hardware has to be adapted to various developmental stages because—in some sense—animals at the different stages of development have to be considered as different organisms with respect to their demands for survival. Embryos need for a certain period of their life no food supply; they take it from their yolk. For example, Xenopus laevis embryos can be exposed to a 10 days lasting space flight at a temperature of 20 ◦ C to 21 ◦ C with a survival rate of about 80% to 85% when they are not older then 3 days after fertilization at launch (Horn 2006). According to the stage table from Nieuwkoop and Faber (1967), they have reached at that time stage 40/41 when reared at 23 ◦ C. Clean spring water and permanent air-exchange by means of an air transparent membrane such as bioFolie25 as cover of the transport aquarium are sufficient (Horn and Sebastian 1999). Similar transport conditions are sufficient for young fish Oreochromis mossambicus that were launched at stages up to 16 ( = 15 dpf at 20 ◦ C; cf. Anken et al. 1993) (Sebastian et al. 2001) or salamander embryos ( Pleurodeles waltl ) if launched at stages up to 25 ( = 4 dpf at 18 ◦ C; cf. Gallien and Durocher 1957; Horn et al. 2009). In contrast, older animals need regular food supply. Space flights with older developmental stages are needed if age related sensitivities to altered gravity are investigated. This question is closely linked to the demonstration of a critical period during development. Critical periods are typical for most sensory systems including vision (cf. Hubel and Wiesel 1970), hearing, feeling, olfaction, or gustation. During these periods of life animals are very sensitive to deprivation from envi- ronmental stimuli. The experimental demonstration of a critical period is only possible if animals at different periods of their life are exposed to sensory deprivation. For the sense of gravity that controls body, head and eye posture, weightlessness during space flight is the respective deprivation. Safety regulations require a specific number of containments; limited availability of crew time favours automated hardware. After three successful experiments with Xenopus tadpoles up to stage 45 on the space missions STS-55, STS- 84 and Soyuz-Andromède (cf. Horn 2006), flights with more developed stages were required by the scientists to find out whether the development of the vestibuloocular reflex is characterized by a critical period. This scientific goal per se required life support systems with a highly efficient control for water cleanness and steady food supply. A list of biological and technical requirements was proposed to the engineers that were considered as necessary for a successful flight (Table 1). This list prompted a concept that was called Dornier-Mini- System (Sebastian et al. 1998). An important compo- nent of the Dornier-Mini-System was the miniaquarium developed for the transport of small aquatic animals in space and used successfully several times with Xenopus tadpoles, young fish and salamander tadpoles (Horn and Sebastian 1999; Sebastian et al. 2001; Horn et al. 2009). Transformation into reliable flight hardware went on in a stepwise manner. The basic technical and biological concept was adapted to the miniaquarium technique (Horn and Sebastian 1999). An intensive interdiscipli- nary cooperation between biologists and engineers was initiated because the technical development needed careful biological tests (Franz 2003; Franz et al. 2003). A survival system (Fig. 1) developed on the basis of biological and technical requirements (cf. Table 1) worked successfully in darkness made it independent of the integration of aquatic plants. Additional studies with this breadboard were dealing with the significance of denitrifying bacteria in this system as well as with the velocity of water flow that might affect tadpoles’ activity in case of microgravity exposure. Conditions could be defined to keep Xenopus tadpoles alive for 1 month. Based on the results of these bread-board tests, the design for the Astrium SUPPLY Unit was developed (Fig. 2). From the technical point of view, an exhausted unit can be exchanged by a new one increasing life duration of the life support system. Design and development of SM and FM XNP Hardware used for the experiment XENOPUS (XNP) on the Soyuz TMA13 flight in 2008 were performed by KAYSER ITALIA, Livorno/Italy. The basic com- ponents of the flight module (FM-XNP) were the Xenopus Units (XU) and the Xenopus Container (XC) that was composed of the base plate and the cover (Fig. 3). Eight XUs could be integrated into one XC. Each XU had its own peristaltic pump; the osmotic pump was integrated within the aquarium. Tests on a Science Module (SM-XNP) led to significant improve- ments for the Flight Module (FM-XNP). The FM-XC as well as the SM-XC Mockup had an available air volume of 1.8 l or L. Calculations of the air volume needed by 24 tadpoles during a period of 14 days were done on the basis of data about oxygen consumption published by Territo and Burggren (1998). During the necessary 2-week period in the closed container, a group of 24 stage 45 tadpoles needs a total air volume of 172.14 ml, while a group of 24 stage 54 tadpoles needs 1721.40 ml. Based on the pre- EST observations and these calculations, the number of tadpoles for the EST were put to five per XU for stage- 48 and four per XU for stage-51 animals. A total number of 10 tests were performed with the SM-XNP containing eight SM-XUs with the goal to keep tadpoles alive in the system active for 15 days. Five supporting tests each with a group of 8 EADS- Astrium miniaquaria completed the pre-flight tests. The number of active tadpoles in each XU was checked once every day, starting with the day of SM-XNP activation. It became clear that some parameters were critical; others were less critical (Table 2). Handling and pre-selection of tadpoles included daily exchange of water during the last 4 days before loading of the SM XUs; for the experiment EVIAN spring water was used. The tadpoles were fed with a suspension of nettle powder; its concentration should not exceed 1 g nettle powder in 40 ml water. A so-called tadpole protector was mandatory to avoid trapping of tadpoles in corners between the osmotic pump and the narrow sides of the aquarium. Bacterial contamination was significantly re- duced if new tubes were used. Use of antibiotics can be recommended because analyses of water from XUs and nettle powder suspension after rearing of tadpoles for 3–7 days in the closed XUs revealed a reduction in the number of non-denitrifying bacteria strains. Autoclavation of food was disadvantageous as indicated by high rates of tadpole losses after living 10 days in the system. Depressurization has to be limited to a level of not more than p = 300 mb (Fig. 4). Less critical parameters are listed in Table 2. Based on the tests with SM-XNP and supporting tests with the Astrium miniaquaria, conditions for the Experiment Sequence Test (EST) were fixed ...