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Life-support systems at modern spacecrafts are based on the reserves of different components and their partial physical and chemical regeneration. This permits cosmonauts to stay for a long time under space flight conditions (Valery Polyakov - 1 year and 4 months). At the same time, in many countries works are in progress on the creation of closed ecological life-support systems involving the use of biological objects of different phylogenetic levels (Mashinsky and Nechitailo, 1996). In the known ground-based ecological systems one to several thousands of biological species are used to support the human life functions. For instance, only Chlorella was used in the first 1-day experiment in Moscow in a closed biological system with the participation of a man, while in the two-year experiment in the Bioshere-2 complex in Arizona more than 4000 species were used (Alling and Nelson, 1993).

The primary source of potable water planned for the International Space Station will be generated from the reclamation of humidity condensate, urine, and hygiene waters. It is vital to crew health and performance that this reclaimed water be safe for human consumption, and that health risks associated with recycled water consumption be identified and quantified. Only recently has data been available on the chemical constituents in reclaimed waters generated in microgravity. Results for samples collected during Mir-21 reveal that both the reclaimed water and stored water are of potable quality, although the samples did not meet U.S. standards for total organic carbon (TOC), total phenols, and turbidity.

Liquid and gas exchange within a particulate plant-rooting medium is likely to be altered in a microgravity environment. A difference in gravitational force can result in significant offsets in control parameters developed on earth for optimum plant growth, due to the shift in hydrostatic water distribution. The experiment being developed will examine the effects of variable gravity on water distribution and gas diffusion. We are developing and testing an automated gas diffusion measurement system for use on the International Space Station (ISS). To allow comparison of μg and 1g conditions, gas diffusion cell designs were horizontally oriented to minimize gravitational effects using 1) a ‘thin rectangular profile’ cell and 2) a cylindrical cell design for flight. Electronic solenoid valves provide air and water flow control while pressure transducers measure water and substrate potential.